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Introduction To Embedded Systems Development

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1. t being supplied power by the microcontroller This can save a lot of energy but a few core peripherals are turned on when the LPC starts among these GPIO and Tim0 and Timl But this means that Tim2 and Tim3 start off and if you need them you ll have to turn them on Additionally if you don t need Tim0 or Tim1 you can turn them off to save some power Power control is considered a system feature and is controlled by register LPC_SC gt PCONP Each bit in that register is assigned to a peripheral with a 0 meaning unpowered and a 1 meaning that the peripheral is powered 22 BITON LPC_SC gt PCONP 22 Turn on Tim2 BITOFF LPC_SC gt PCONP 2 Turn off Timi You can find the full table of peripheral to bit mappings on pages 63 and 64 of the manual It s probably a good idea to note that you can get some very weird results if you try to work with a peripheral that s off The whole situation has undefined results but in practice writes to registers in unpowered peripherals don t do anything and reads always return 0 4 2 2 Choosing a Peripheral Clock Likewise choosing a peripheral clock is a system function and the settings for all the peripherals are on LPC_SC gt PCLKSELO and LPC_SC gt PCLKSEL1 SETBITS LPC_SC gt PCLKSELO 4 2 0b10 Set Timi to use pclk2 SETBITS LPC_SC gt PCLKSEL1 14 2 0b00 Set Tim3 to use pclkg You can find the bit assignments and settings for the peripheral clock selection on pages
2. 8 Add Calibration Routines and Basic IO In order to actively use the theramin you ll have to set up a calibration routine The amount of light on the photo sensors and therefore the voltage coming into your ADCs can vary wildly depending on the brightness of the room the relative position of your sensors and LEDs and a number of other environmental factors So in order to actually play your theramin you ll have to set up a routine to tell your LPC what range of inputs it should expect in the current environment This means you ll have to set up a routine where you tell the LPC to record the maximum and minimum voltages for each hand and scale the output frequency and amplitude accordingly 9 Bonus Play something recognizable with your newly created instrument 40 6 DAC A The DAC is the analog counterpart to GPIO s digital output Your LPC has one output line and 6 1 Working Theory 6 2 Usage To set up the DAC one has to connect a particular peripheral clock to the DAC and connect the DAC output to the corrent pin LPC_SC gt PCLKSELO 1 lt lt 22 Set pclk to 1 LPC_PINCON gt PINSEL1 1 lt lt 21 Set H 18 to AOUT To use the DAC one has to write to the DAC converter register SETBITS LPC_DAC gt DACR 6 10 1035 Set DAC to 1035 7 DMA Finish the intro Often when building embedded devices you ll have to deal with large amounts of incoming and outgoing data Be it reading thousands of s
3. 31 N LED Photoresistor LED Photoresistor No Hand Nearby Hand No Reflected Light Light Reflected Figure 15 Hand Sensor Our version will work of a slightly different principle we ll use light to sense the distance between the hand and our sensor We ll place an LED below a photo resistor so that when there s no hand or other obstacle the light from the LED will just shine onto the insensitive read of the photoresistor But when we place our hands above the sensor the light from the LED will reflect back onto the sensitive portion of the photoresistor and give us something we can sense The farther away the hand is the less light will be reflected back so this setup will give us an approximate measure of distance We can use those measurements to modulate the output of our DAC which will be plugged into a speaker giving us a simple optical theramin to play with 5 7 1 Background 5 7 1 1 Voltage Dividers Voltage Dividers are an essential part of the circuitry for our theramin and in order to understand how it all works you must understand how these components work Figure 16 Voltage Divider Schematic A standard voltage diver circuit is made with two resistors placed in series the voltage at V y is the weighted average of the voltages at V and V__ Ri R1 R2 Yes A A A E S HHHH H Potentiometers Vaiv V Vos 32 Figure 17 Potentiometer Divider Schematic Potentiometers are a special type
4. 56 and 57 of the manual t 4 2 3 Setting the Prescale Counter Once you ve made sure your chosen timer is on and is using the peripheral clock you want you can move onto setting the prescale counter and actually using it to perform timing related tasks The prescale counter is basically a 32 bit factor register inside a clock divider You can set it using the LPC_TIMx gt PC register LPC_TIM3 gt PC 14 Divide the incoming clock by 15 All of this can be found on page 495 of the manual 4 2 4 Reset and Enable Before the timer counter can actually start incrementing there are two flags within the Timer Control Register TCR The enable flag when set to one disables the timer counter s ability to increment BITON LPC_TIM2 gt TCR 0 Disable the timer counter BITOFF LPC_TIM2 gt TCR 0 Enable the timer counter The reset flag when set to one forces the timer counter s value to zero 18The choice of bits to select each clock is somewhat odd so do look at the manual 23 BITON LPC_TIMO gt TCR 0 Disable the timer counter The couter s value is stuck wherever we stopped it BITON LPC_TIMO gt TCR 1 Reset the timer counter to zero The counter s value is zero BITOFF LPC_TIMO gt TCR 0 Enable the timer counter The counter s value is still zero since the reset bit is still on BITOFF LPC_TIMO gt TCR 1 Disable the reset flag The counter s value will now start incrementi
5. A quick warning this manual is very large and you should not print it unless it s absolutely necessary 1 1 2 The LPC1769 Schematic The schematic available here describes how the pins on the development boards correspond to the pins mentioned in the manual You ll need to cross reference this schematic with Chapter 8 of the manual every time you need to figure out the physical location of any one particular pin 1 13 The LPC176X Data Sheet The data sheet available here is the last reference document you should keep handy It contains a lot of information about the limitations of the LPC the tolerances of various features and the full set of features the LPC has Thttp www nxp com documents user_manual UM10360 pdf 2http www cs umd edu class fall2012 cmsc498a manuals lpexpresso_lpc1769_ schematic pdf 3http www nxp com documents data_sheet LPC1769 68_67_66_65_64_63 pdf 2 GPIO 2 1 Prequisites Read the following tutorials to get you up to speed with the electronics e How to read a schematic e How to use a breadboard e Understanding LEDs e Using Pull Up Resistors All these tutorials are Arduino centric but you can extrapolate to what you need to do for your LPC 2 2 What is GPIO We ll start with the most basic peripheral on the LPC General Purpose Input Output GPIO is what lets your microcontroller be something more than a weak auxiliary processor With it you can interact with the environment connecting
6. Reh Ee oe nye ei Seb a Se Geek WO pea Connecting to Timers e ee a oh eRe EA Ba a i E 50 Burst Modesa ea Ae a ee ee EH ee a a a iO IVA densa ety E 54 Project Optical Theramin 26 4 6 i udici ee a ee ee 6 DAC 6 1 Working Theory Lea Sk ee ae a eA Ee PR eG Ye ae Ge ded a a 6 27 Usager nel hak Bagh he eee A A A ote Se Gee ead at BR NN By By don dad Mook ah gt 7 DMA Til GPDMA im thesbP 20m 22 bbe oe Be Soe ee eee eG tee a See x 2 DMA swith the ADO 4 uma taa E oe ee ee ee a ee Be eS DMA wath the DAC eiri cc a ote Bede gs AAA ER Gee DED EEEE Bh eB Be 7 4 DMA and Power Control Tio Projects Sound Recorder iia a e EE TO SULBBested Steps a A E EE AA AAA Ge Ge Bae RA E A BS ely Microphone Gitcuit ie sau p esis do he Kee a ERA e O ee ee ple de et eB dee 8 Appendix 8 1 Development Environment Setup 2 a 32 Standard Macros fe aire A AR ee AP BL A a a Me ke te e Deed 28 28 28 30 31 31 31 31 41 41 41 42 43 43 43 44 44 44 44 1 Introduction This book will teach you embedded system design and development using the LPC1769 an ARM Cortex microcontroller When compared to normal CPU the LPC is a simple device with only one processor core and a miniscule amount of memory yet it still manages to be useful In fact this simplicity makes it a wonderful learning tool allowing us to forgo kernel and driver interfaces and work at the lowest level possible without becoming too complicated to di
7. So if Fin and Fout are respectively the input and output frequencies then wey Fout Input Signal LILI UU LU LU LU Le Factor 0 Output LIL UU LU LU LL LL LL Le Counter Factor 1 Output LJ LJ LI LI LU Ww US LI LJ 1 Counter ANA Factor 4 Output WL T Li S Ee Counter DEREYE RF OO2 2 AOOEBAOOAB AOA Boa 2 Bi Figure 6 Clock Divider Timing Example 3 2 Phase Locked Loops Initial Target Frequency Approximation Input Signal Phase Frequency Current Controlled Oscillator Output Signal HF Error Term y Comparator CCO y Multiplicative Scaling Divider 2 Approximation Clock Divider Factor 1 M Divider Figure 7 PLLO Block Diagram PLLs are clock multipliers where a clock divider will divide the frequency of an incoming signal a PLL will multiply it A PLL is a complex self correcting feedback loop but in order to use it all one needs to know is that Fin x 2x M 1 Fout where M is the value in the M Divider s factor register 1 To see how the PLL works one must first understand that it is a feedback loop it starts with an approximation of the final output signal and refines it till it s an exact multiple of the input signal Within the PLL is a Current Controlled Oscillator CCO that will generate the final output signal it starts oscillating at some frequency that s close but not quite what we want The output of the CCO is divided
8. a current flowing from the output to the 1 5 volt source Because of Ohm s law the voltage at the output will increase if the resistor is large the voltage will increase very quickly until it hits the limit of 3 volts imposed by the Op Amp s power source Alternatively if the resistor is very small it 1l take a lot of current to increase the voltage a small amount to the point that the power source simply can t supply more current If that happens the voltage at the output will hover at whatever value the current available can sustain Op Amp modulate their output voltage with a simple algorithm If their two inputs are held at the same voltage the Op Amp will keep the output stable If Vi gt Vin then the Op Amp will raise the voltage at its output and if Vin lt Vin then the Op Amp will lower the voltage This property can be exploited to create a number of useful circuits Figure 19 Op Amp Voltage Follower Schematic 34 5 7 1 2 1 Op Amp Voltage Follower An Op Amp voltage follower has a simple function basically it makes sure that the output voltage is always equal to the input voltage To understand how this is useful we ve got to first understand how loads can change the voltages at a point Divider Divider With Load Voltage Follower with Load Figure 20 Load Voltage Schematic In figure 20 we ve set up two voltage dividers using the same Ry and 2 but the second divider has an extra load resistor applied
9. also setup Note that it is not always simple to restart the current program run r will work for some programs and sometimes using jump j to jump to the entry point of the current image found with info files works However none of these completely reset the chip the only command that will is the load command however that will flash the entire image to the chip again which may take a while for projects with large compiled binaries Also note that some circuits particularly when interfacing with other chips that have their own state may require completely unplugging the circuit between program runs If using makefiles these are directly accessible as make 1st etc run in the root directory of the desired project If you are using a build system based around IDE project files such as Eclipse or Visual Studio the targets should be accessible from a menu 8 1 3 Typical Workflows These sections detail how to do many common tasks They are written under the assumption that a Makefile build system is being used but the calls to make can all be substituted with the appropriate action in any other chosen build system 8 1 3 1 Start a new project by forking First go here and fork a new project In your terminal git submodule add http github com yourname newprojectname git add gitmodules git commit m Added a submodule for NewProjectName git submodule update cd NewProjectName YOUR_EDITOR CMakeLists txt Edit CMakeL
10. by both the Scaling Divider and the M Divider to get an approximation for the incoming signal Fou 2x M lt 1 signal is divided twice before it becomes the approximation If we re lucky enough that Fappror Fin we can substitute and solve to show that Fout 2 x M 1 x Fin meaning that we ve successfully multiplied the frequency of our input signal If Fapprox is the frequency of the approximated signal we know that Fapprox because the output 15The equation accounts for the extra scaling divider that is in the LPC s PLLO A standard PLL doesn t have this extra divider with the CCO being connected directly to the M Divider and therefore has the equation Fin x M 1 Fout 14 But if Foppror Fin then how does the PLL make Foapprox Fin Start Error Correction Input LI LF U Lr Case 1 CCO MUVUUVUVVUVUVUUL No Error No Correction Approximation LI LI LIF LI iw Input FUP LU UW UW Ww Case 2 CCO ANUVUUVVUUVUUVVUUY Too Fast Slow Down CCO Approximation TU U U LULU LUIS Input U LU LU LP Ww Case 3 CCO fUUUUUUUUUUU Too Slow Speed Up CCO Approximation LS VJ WS LIS Figure 8 PLL Error Correction This is done by the Phase Frequency Comparator which can figure out if the approximation is running at a higher or lower frequency than the input or if the approximation and the input have a different phase The difference between the approximation and the input constitute an error term Figure 8 shows the ways th
11. for that particular interrupt and know that the Interrupt Controller will automatically call another handler to care of the other interrupts Interrupt chaining lets you keep your code small and modular while still being able to handle many quickly incoming events By only disabling the flag for the particular event you ve handled you are guaranteed to have your interrupt handler called again so that it can handle a different event 2 4 3 1 Setting Up an Interrupt Handler Setting up a GPIO interrupt starts with telling the Interrupt Controller or NVIC that you want certain pins to trigger interrupts In the struct LPC_GPIOINT you ll find the registers IDOIntEnR and I00IntEnF which define which pins on GPIO Port 0 generate interrupts on a rising and falling edge Next the specific interrupt handler must be enabled All the GPIO interrupts are handled by External Interrupt 3 so we ll use a macro to tell the NVIC that it s allowed to call that specific handler Enable Rising Edge Interrupt on PO 9 LPC_GPIOINT gt IO00IntEnR 1 lt lt 9 Enable Falling Edge Interrupt on PO 9 LPC_GPIOINT gt I00IntEnF 1 lt lt 9 Turn on External Interrupt 3 NVIC_EnableIRQ EINT3_IRQn In order for the interrupt to do anything the handler has to be defined The interrupt handlers are found in cr_startup_lpc176x c in each of your project s source directories defined as weak aliases to the default interrupt handler Becaus
12. in order to let us use the LPC with our own choice of editors for coding and a standard gdb session to debug instead of having to deal with a clumsy hard to use proprietary IDE To install start by cloning the repository from github while in whatever directory you wish to work out of git clone https github com rohit507 UMD LPC1769 Build git This will have git retrieve the latest version of the build system from github We ve also created a few submodules separate repositories storing single projects that let you manage them with git at the project level instead of having to makes changes to the entire workspace whenever you wish to change a project To initialize these run the following Get submodules cd GNU LPC Core git submodule init git submodule update Next we need to run the setup script and set a few internal variables so CMake will know where it should look for the arm none eabi toolchain and proprietary tools Here the DLPCXPRESSO_DIR variable should be set to the root directory under which all of the necessary files can be found this should contain the lpcxpresso binary 0 49 Run setup script cd _setup cmake DLPCXPRESSO_DIR lt LPCXpresso Root Dir gt During setup our script copied over the CMSIS library this is a library that provides some very basic LPC functionality but we still need to unzip it On Linux or OS X Extract CMSIS library zip came unzip CMSISv2p00_LPC17xx zip d C
13. ns Figure 27 High Frequency DAC Sine Wave Oscilliscope Trace To fix this you can build an RC filter this circuit will smooth out the wave by forcing it to pour energy into the capacitor and slowing the change in voltage The exact workings of the filter are outside the scope of this book but suffice to say that it when connected will transform the raw DAC output in figure into the signal seen in figure 28 where the signal in yellow is the DAC after it s connected and the signal in pink is the voltage at Vemooth Noise Filter Off Figure 28 High Frequency RC Filter Oscilliscope Trace 6 Build Amplifier 38 Figure 29 Speaker Amplifier Circuit We can use the amplifier to change the volume of the final sound and the amount of current the Op Amp will supply If you connect up the oscilloscope now before adding the speaker and have your DAC output a sine wave you should be able to modulate output to any gain between 1 and infinity effectively turning the amp from a voltage follower to a voltage comparator and anywhere in between Sample traces are shown in figures 30 and 31 with Vsmootn in pink Ve in green and Vspeaker in blue Noise Filter Off Figure 30 Speaker Amplifier with Small Gain Noise Filter Off Figure 31 Speaker Amplifier Acting As Comparator 7 Connect Speaker Circuit 39 Figure 32 Speaker Circuit Connect up your speaker to the other circuit components and play some sound
14. send out periodic events make very precise measurements simply make the time available for your applications among other things This means you can start using temporal information in your program without having to use unwieldy spin loops and other ill advised hacks There are four timers within the LPC Tim0 Tim1 Tim2 and Tim3 All are identical but can have options set independently and can be used without interfering with each other 4 2 Speed Settings pclk1 o E e e Timer Counter pclk4 Clock Divider Toggle perke Prescale Counter Reset Disable LPC_TIMx gt PC Peripheral Clock Selector PCLKSELX Timer Control Register Figure 10 Timer Counter Block Diagram All timers are built around an internal Timer Counter TC which is a 32 bit register that is incremented periodically The rate of change is derived from the current speed of the CPU clock which peripheral clock you ve connected up and what the prescale counter is set to There s nothing more to it than that the prescale counter is a clock divider like so many others and the Timer counter is a 32 bit register and as long as nothing else intervenes it s count from 0x00000000 to OxFFFFFFFF overflow and do it all over again 4 2 1 Powering Devices Before we can get to choosing the peripheral clock and setting the prescale register we need to actually tun on the timer On reset most of the LPC s peripherals are off and aren
15. to an output Consider the output case where we have a buffer of data we wish to write out to the DAC at specifically timed intervals The DAC has a programmable countdown timer which can ask the DMA controller for a new piece of data after an interval When the DAC timer finishes and a DMA request is sent the DMA controller will write a word into the DAC output register and trigger an automatic outut update At this point the DAC will reset the timer and start counting down to another update and the DMA controller will ready the next byte of data for the DAC In this way you can fill a buffer with sound data and write it out at the same rate it was recorded Missing figure For the input case we can look at the ADC Like the DAC the ADC has a timer which can trigger a conversion and then assert a DMA request when it s done Here when the ADC timer counts down it ll immidiately start a conversion and reset itself When the conversion finishes the DMA controller will read the ADC input register and store returned data in the predefined output buffer Missing figure For SSP and other serial communications peripherals the DMA controller can read or write data as fast as it can sequentially storing or sending large chunks of data The final case is a peripheral to peripheral transfer which can be useful to forward data from one communica tions protocol to another without manual intervention o haven t really used p
16. to it V will be the same value as before but because of the existence of the additional load resistor V2 will be a different higher voltage If instead of connecting the load resistor directly to your divider you connected the divider to the voltage follower s input and the load resistor to the output as with the third setup the voltages at Vi V3 and V4 will all be equal Here the Op Amp is compensating for the change in voltage the load would otherwise cause What is happening is that when Vin gt Vin the Op Amp will increase the voltage at the output and that will being directly connected increase the voltage at Vin When the opposite is true and Vin lt Vin the Op Amp will decrease the voltage at output and Vin Both of those actions will correct the imbalance and make Vin Vin and therefore Vin Vout The Op Amp will automatically sense changes in the load and compensate so that the output is always equal to the input Figure 21 Op Amp Voltage Comparator Schematic 5 7 1 2 2 Op Amp Voltage Comparator This is very similar to the Voltage Follower but where the voltage follower has a feedback loop this circuit has no connection at all This means that when Vin gt Vin the output voltage will keep on going up till it hits the maximum voltage the Op Amp can sustain in our case usually 3v Likewise when Vin lt Vin the voltage will go down until it hits the lower limit namely Ov So the output is l
17. to p transfers Add detail in the meantime read pages 607 615 of the manual 7 1 GPDMA in the LPC The DMA controller in the LPC is called the General Purpose DMA GPDMA controller Mostly to reflect the fact that it can work Missing figure 7 2 DMA with the ADC ADC DMA Instructions go here In the meantime read the DMA and ADC sections of the manual 7 3 DMA with the DAC DAC DMA Instructions go here In the meantime read the DMA and DAC sections of the manual 43 7 4 DMA and Power Control 7 5 Project Sound Recorder This project will have you using the LPC to record sound store it on an SD Card and play it back on demand You ll have to use DMA to gather audio samples at precise frequencies and use external storage to make up for the miniscule amount of onboard storage the LPC has 7 6 Suggested Steps 1 Get DMA and the DAC working to output standard waveforms sine waves sawtooth functions triangle waves test using the oscilloscope and speaker circuit from the theramin project N Use the signal generator or your DAC output to test reading data in with ADC and DMA w we Make sure you can send and retrieve data with SPI and your SD Cards A Naisi Build the Microphone circuit make sure you get sensible output on both the oscilliscope and when you read data into your LPC al wa Add some IO LEDs and connect all the parts together so you can record at least 30 seconds of au
18. you need to understand Clock Dividers and Phase Locked Loops 3 1 Clock Dividers Factor Register Input Signal Output Signal gt Edge Detector Test Toggle gt A a Spee A i Increment gt Counter Register Figure 5 Clock Divider Block Diagram Clock Dividers are an integral part of any complex clocking system They allow you to turn a single precisely timed clock signal into another running an integer multiple slower As shown in Figure 5 internally they have two registers a counter register and a factor register The counter register simply counts all the edges in the input signal And the factor register stores the amount by which the input signal is slowed down and is usually user modifiable During operation there is an edge detector which will trigger two events whenever it sees a rising or falling edge on the input signal 1 It will test if the value in the factor register is equal to the value of the counter register 2 It will increment the counter register Then if the equality test was successful it will perform two more actions 3 Reset the counter register to 0 4 Toggle the state of the output signal switching low to high and vice versa 13 If the number in the factor register is N then the period of the input signal will be multiplied by N 1 and the frequency will be divided by the same amount as shown in Figure 6
19. 6 in the manual 17See the appendix for all the macros used herein 18 if GETBIT LPC_SC gt PLLOSTAT 25 If PLLO is connected BITOFF LPC_SC gt PLLOCON 1 Write disconnect flag PLLO_feed_sequence Commit changes 2 Disable PLLO with a feed sequence BITOFF LPC_SC gt PLLOCON 0 Write disable flag PLLO_feed_sequence Commit changes 3 If you do not plan to use the PLL set the CPU clock divider to your final value otherwise set it to 1 Change CPU Divider LPC_SC gt CCLKSEL lt CPU Clock Divider Value gt 4 Write to the Clock Source Selection Control register to change the clock source if needed Change sysclk source LPC_SC gt CLKSRCSEL lt Clock Identifier Bits gt 5 If you are not using the PLL you are done otherwise continue 6 Write values to the N Divider and M Divider and use a feed sequence to enable them The dividers can only be updated when PLLO is disabled Write divider values SETBITS LPC_SC gt PLLOCFG 0 14 lt M Divider Value gt SETBITS LPC_SC gt PLLOCFG 23 16 lt N Divider Value gt PLLO_feed_sequence Commit Changes 7 Enable PLLO with one feed sequence BITON LPC_SC gt PLLOCON 0 Set Enable Flag PLLO_feed_sequence Commit Changes 8 Set the CPU Clock Divider to its final value It is critical to do this before connecting PLLO LPC_SC gt CCLKSEL lt CPU Clock Divider Value gt Change Clock Divider 9 Wait for PLLO to ac
20. Introduction To Embedded Systems Development Rohit Ramesh Contents 1 Introduction 1 1 2 1 2 2 2 3 2 4 2 5 Resources yh ays ae ees Bh ced ar aes a bb bb OG dol Bad do Bob GPIO GPIO Outputs 222 AA A See at eh ede ha e e GPIO Diputa 2 A a ce A E E AAA ee he eh et ea Bh Ss Project Bit Banging a secare SL EVR VS wee ee ee a RO ee 3 Clocking 3 1 3 2 3 3 3 4 3 5 3 6 3 7 4 1 4 2 4 3 4 4 4 5 Glock Dividers Lit ms O A ds Da de LAA a den de o O a Phase Locked Lo0ps 200 24 E A ee a le ari Calculating Glock Speed OS rari dd A RRA AA We Se RA re FI ES Working Backwards seaca 44 4 6 0 a4 FARE a Se yee a ae eed Making The Changes 4 40 66 A SS Yb ee ee ae Ba A Peripheral Glocks lt to ae ae Bok a EA ae e OMe a ere Sher FLA BES Project Precisi n Timings 42 6648 2 AOS OS EE IA a Oe ld Timers Basic Description unico 4 6 404 4 4 pended be ob ha he es aaa Speed Settings 4 4 2 Ui te Ge aa ee ee ee AR eee Se a ee ee Match Regist rs lt s ayy accede op ara O ee A oS Ge Ba Eee aed WA See te Capture Registers soria eae oe dye ged db bb hae a ee eee EER de bb Project Serial Light Communications 0 0 00000000000 0004 ew a 2 A BD 13 13 14 15 16 17 20 20 5 ADC pl Theory of Operation a1 ais s e B ede ea A Ba a ol EE diz Basic Usage td A at i hates te Gad aa Be A eee nc ty ae te eels ds A oS wh Did Interrupts reia eevee Gist a ain ee ee BAA
21. MSISv2p00_LPC17xx On Windows Now from within the CMSIS directory we ll use CMake to generate a build system On Linux or OS X Build CMSIS cd CMSISv2p00_LPC17xx cmake G Unix Makefiles make On Windows Now we can build our skeleton project which is the bare template all your projects will be build from On Linux or OS X Build CMSIS cd Skeleton cmake G Unix Makefiles make On Windows At this point all your installation steps are done and we can go over basic usage and workflow 8 1 2 Available Targets The default build target builds a axf file with debug settings The following targets are provided lst Generate a Ist file which includes an overview of all the sections and symbols in your output along with a complete disassembly 200n Linux or OSX it should look like usr local 1pcxpresso_5 1 2_2065 1pcxpresso On Windows it should look like TODO Insert actual path here hex and bin Generate alternate formats of the normal axf output which may be useful if you want to use other tools boot Boot the LPC Link board This is required before flashing or debugging the microcontroller using the LPC Link board flash Write the currently built output to the microcontroller The microcontroller immediately starts running after the flash is complete flash halt The same as flash but the microcontroller is left in a stopped state gdb Launch a gdb session Complete debug information is
22. PB1_BASE 0x40080000UL define LPC_DAC_BASE LPC_APB1_BASE 0x0C000 define LPC_DAC LPC_DAC_TypeDef LPC_DAC_BASE The DAC is an APB1 peripheral and so LPC_DAC_BASE is the start of the memory mapped to DAC registers LPC_DAC_Typedef is a struct that s set up so that when it s aligned to that base address each of the struct s fields will align with a particular register in the DAC memory space This whole setup means that you can write to the DAC Control Registers without using a raw memory location LPC_DAC gt DACCTRL stuff If you look back at the code we wrote for LED manipulation and refactor it you ll get something much easier to work with LPC_GPIOO gt FIODIR 1 lt lt 9 Set PO 9 to write LPC_GPIOO gt FIOPIN 1 lt lt 9 Turn LED on LPC_GPIOO gt FIOPIN amp 1 lt lt 9 Turn LED off Having a layer of macros like this also makes it easier to port your code to another platform since you ll have to only change the macro definitions rather than all the pieces of code which use some registers 2 3 4 More Registers If you look closely there s 4 GPIO ports each controlling up to 32 pins and each of those blocks has 5 registers Strictly speaking you only need the FIODIR set pin direction and FIOPIN set or read pin state registers to control each pin but there are three others which allow you to perform operations much faster FIOSET and FIOCLR are the two fast output con
23. a read a bitwise logic operation and a write To make the same change using the fast registers requires only a write operation the rest of the stuff is done in hardware which is much faster FIOMASK is in effect a filter for FIOPIN FIOSET and FIOCLR If a bit in FIOMASK is a 1 then none of those registers can cause any change in that pin s state This means that you can change a subset of the bits very quickly without having to perform a masking operation every time By default all of FIOMASK s bits are set to 0 meaning that the other control registers can operate over all bits 2 4 GPIO Input Reading a pin uses the same registers we ve already used once a pin s mode is set to input in FIODIR the corresponding bit in FIOPIN holds the currently read value In addition to simply reading the registers to figure out the voltage on a pin we ve also got access to interrupts which will notify your program when the state of a pin changes while allowing you to do something else in the meantime 2 4 1 Basics Reading the current state of a pin in the middle of your code is simple we take the same two registers as before FIODIR and FIOPIN and use them slightly differently LPC_GPIOO gt FIODIR amp 1 lt lt 9 Set PO 9 to Input PinState LPC_GPIDO gt FIOPIN gt gt 9 1 Get PO 9 State Here a zero in a particular position in FIODIR means the pin is used for input and the relevant bit in FIOPIN contains its
24. amples per second from the ADC as you record sound reading megabytes per second external memory or sending large chunks of data over Ethernet quickly The simplest way to deal with these large data streams is using the CPU Loop or timer based mechanisms can move large amounts of data back and forth but at the cost of using CPU time to perform routine memcopy style tasks Occasionally it s simply not passible to handle data at full speed or satisfy IO timing requirements using the CPU and other methods are needed This is where Direct Memory Access DMA comes in DMA is a special deeply integrated peripheral that can perform memory manipulation tasks independent of the CPU This means that it s possible to perform routine data gathering tasks faster than the CPU could without wasting CPU time and with a level of timing precision that the CPU can t match Missing figure The most basic use of DMA is a memory to memory transfer which will copy data from one block of memory to another This is analogous to a standard memcpy operation albeit without blocking One can also choose to have an interrupt thrown when the copy is completed in order to avoid race conditions The next two uses for the DMA controller are memory to peripheral tranfers and peripheral to memory transfers These data transfers are deeply integrated with the revelant peripherals and can be used to automatically gather data from an input or automatically send data
25. as possible 3 Set the peripheral clock Here we use the undivided clock for the ADC but as long as the final clock constraints are considered you can choose any peripheral clock Choose undivided peripheral clock for ADC LPC_SC gt PCLKSELO amp 3 lt lt 24 LPC_SC gt PCLKSELO 1 lt lt 24 4 Set the ADC clock divider The ADC control register LPC_ADC gt ADCR controls a number of functions but for the moment we ll use it to choose the setting for the ADC clock divider This is controlled by bits 8 through 16 of the control register and can be set as follows SETBITS LPC_ADC gt ADCR 8 8 0 Set clock divider to let the clock pass unchanged 5 Put the pins you ll be using into ADC mode SETBITS LPC_PINCON gt PINSEL1 14 2 0b01 Connect ADO O to its pin 6 Pull the ADC out of power down mode The ADC also has its own internal power switch so that you can change settings while conserving power that the conversion circuitry will use BITON LPC_ADC gt ADCR 21 Turn on ADC internal power The simplest method of actually getting data is synchronous collection of values from the ADC You tell the ADC to go collect some data wait for it to tell you it s done and then read out the value When trying to synchronously access one of the eight ADC lines do the following 1 Select the ADC line you re going to read The first eight bits in LPC_ADC gt ADCR control which input lines are active an
26. can launch LPCXpresso and use it if you would like It is recommended to launch it at least once and go through the software activation step no payment necessary you are just verifying your email again as this upgrades the proprietary tools to handle a larger file size 8 1 1 2 Git You also need to install the Git version control system Git is a similar tool to SVN or CVS and allows you to store your code s history and synchronize development with other programmers We use git to manage our build system 8 1 1 3 CMake Next install the CMake build system make sure you install the very latest version a number of distros do now have the proper binaries in their repositories and you might have to build it yourself CMake is a meta build system Instead of the standard UNIX make which directly compiles source code into the desired output format CMake instead generates one of many different types of build systems which are then used to perform the actual compilation This is useful for allowing different developers to use their preferred development environment POSIX Visual Studio Eclipse etc In our example we will use CMake to generate Makefiles 8 1 1 4 MinGW If you re on windows you should also install MinGW MinGW or Minimalist GNU for Windows is a package containing all of the usual GNU tools and GNU binutils specifically targeted to compile windows binaries 8 1 1 5 UMD LPC Build The UMD LPC Build system was created
27. clk This is the output of the CPU PLL Selector and can be set to either sysclk or p110c1k cc1k This is your final system clock and is pllclk divided by the CPU Clock Divider this can be at most 120 MHz If you let D The value in the CPU Clock Divider s Factor Register then Foi1cik Fecik D 1 3 4 Working Backwards If we want to change our LPC s clock speed we must answer the following questions e Which oscillator should be connected to sysclk e Should we use the PLL and if so what should the N Divider and M Divider be set to e What should the CPU Clock Divider be set to We also must keep in mind the following restrictions e The CPU factor register on supports values between 0 and 255 e The N Divider s factor register only supports values between 1 and 32 e The M Divider s factor register only supports values between 6 and 512 and a number of extra values seen on page 38 in the manual e If we re using PLLO it must output a signal between 275MHz and 550MHz e The final clock speed cannot be more than 120MHz In order to figure out all of the above we should work backwards from our target cclk frequency Fecix First we should check if we can forgo the PLL entirely For every oscillator check if Fecix lt PFoscillator If it is check if Foscillator is an integer less than 256 If that too is true then we can do the following Fecik 8 1 Set sysc1k to connect to that oscillator 2 Bypass PLLO conn
28. current state Writes to FIOPIN FIOCLR or FIOSET don t affect input pins and making changes to the value of an input pin is basically a no op Button Pull Down Resistor 100 kQ Figure 1 A pull down resistor allows for more predictable connections between logic gates and inputs With the resistor when the button is released the ground will pull the voltage back down to Ov Without the resistor a sufficiently isolated pin might stay at 3v even after the button is released giving an incorrect reading Additionally having a large resistor is important since it will only draw a small amount of current when the button is pressed A small resistor might draw enough to stress the power supply and keep other portions of your device from functioning Once you have this set up you can connect up a switch with a pull down resistor to the input pin and be able to read the state of your button in software 2 4 2 Bouncing So if you want to toggle an LED whenever you press a button you might do something like the following int state prevstate while 1 Get state of PO 9 state LPC_GPIOO gt FIOPIN gt gt 9 1 If there s a change from O to 1 if prevstate amp amp state Toggle PO 8 LPC_GPIOO gt FIOPIN 0 T lt lt 3 prevstate state When you try that you ll notice some odd behavior not only will the LED change when you press the button but it will occasionally also change when you rel
29. d forth across the back of LEDs 3 Use interrupts to detect the state of a button connected to GPIO and switch between two patterns when it is pressed 4 Use fast switching to make the LEDs glow at different brightnesses while displaying some pattern and having some interrupt based button interaction 5 Bonus Chain up two more shift registers and use 8 RGB LEDs to display 3 distinct patterns one in each color channel 14 13The 2N2222A and PN2222A are functionally equivalent transistors with different packages so feel free to use either 14The shift register data sheet has a diagram showing how to chain them for more storage 12 3 Clocking FSE ee ee RS Clocks in the LPC all derive from one of three oscillators Main Oscillator This is the usual clock source for the LPC and runs at 12MHz Internal RC Oscillator This is driven by an internal RC circuit at 4MHz and is the clock the LPC uses when it s reset Usually software will later switch to the Main Oscillator Real Time Clock RTC Oscillator This is a 32 768 KHz Oscillator that powers the real time clock Because of the precisely chosen frequency the clock can increment a 32 bit counter on every tick and overflow once a second Each of these clocks can be used as a cpu clock or with the help of a Phase Locked Loop PLL generate a much faster CPU clock up to the LPC s limit of 120MHz Before we can get into how to set the LPC s clock there are two components
30. d when collecting data synchronously you can only have one on at a time LPC_ADC gt ADCR amp OxFF Clear first 8 lines BITON LPC_ADC gt ADCR 0 Choose line O 2 Start the conversion There are 3 bits in the ADC control register which let you choose the collection mode for the moment we ll focus on the first two Setting bits 24 to 26 in the ADCR to 0 tells the ADC that you want no conversion done and setting them to 1 tell the ADC to start a conversion immediately 29 SETBITS LPC_ADC gt ADCR 24 3 1 Start the single conversion 3 Spin on the done flag For single conversions you can look at the General Data Register which will store the results of the very last conversion Because a conversion takes 65 of the ADC s clock cycles where it ll spend time slowly increasing the precision of the value it recovers you have to wait for it to finish So you spin on the done flag in the final bit of the data register which will turn to 1 when the conversion is finally finished while LPC_ADC gt ADGDR 1 lt lt 31 0 4 Read and parse the output value And now you can find your converted value in the same register in bits 5 through 12 value GETBITS LPC_ADC gt ADGDR 5 12 5 3 Interrupts If you want to sample asynchronously using interrupts you can allow your other code to run during the relatively long sampling process The setup for interrupt based ADC use has a few extra steps 1 Enabli
31. dio 7 7 Microphone Circuit 7 7 1 Floating Ground Figure 33 Floating Ground e Test by making sure the voltage on the 1 5v node is correct 44 We re using the Op Amp to create a voltage source at Vcc 2 since we need a center point for our final signal to go above and below This center point also needs to be able to sustain a significant current draw for our other components which is why we use an Op Amp If we simply used a voltage divider the resistance of the divider itself would keep the other components from drawing the current they need you could try making the resistors small but then the current traveling through the divider itself would be problematic 7 7 2 Microphone Assembly C1 Coarse Mic Out MIC1 Figure 34 Mic Assembly e The electrolytic capacitors the big cylindrical ones are polarized the negative side has a stripe on it e Make sure that when you connect the oscilloscope to this ground to 1 5v probe to Coarse Out you see a sound signal in the millivolt range e Electret Mics also have a polarity the negative pad on the bottom has a little bronze dash etched onto the PCB next to it It s the only asymmetry on the bottom of the mic These microphones are basically air pressure sensitive transistors and with the 2k resistor it acts like a transistor amplifier with the input replaced by air pressure The capacitor and the 10 resistor together form a high pass filter what this does is
32. e error term can be combined with the current state of CCO to create a refined approximation This continual process of error checking and correction means the PLL becomes locked to the input signal and outputs a precisely frequency multiplied version thereof 3 3 Calculating Clock Speed cclk Main Oscillator osc_clk gt Real Time Clock Oscillator rtc_clk sysclk pllclk CPU Clock gt pclk1 Divider Internal RC Oscillator irc_osc E PELO __ Main PLL p Peripheral gt pclk2 N Divider PLLO Clock Dividers penes fy pclk8 System Clock Select A F i CPU Clock Divider Setting CLKSRCSEL 1 0 CCLKCFG 7 0 Main PLL Settings CPU PLL Select PLLO PLLOCON Figure 9 Cpu Clock Generation Diagram Calculating the current clock speed is a matter of following each of the intermediate steps between the three core oscillators and the final cclk signal that actually clocks the LPC s CPU sysclk This can be connected to any of the core oscillators on the LPC so its frequency can be 12MHz if connected to osc_clk 4MHz if connected to irc_osc or 32 7 KHz if connected to irc_osc p110c1k This is the output of PLLO and its frequency must be between 275 MHz and 550MHz If you let 15 N The value in the PLLO N Divider s factor register M The value in the PLLO internal clock divider s factor register then 2x M 1 x Foysclk N 1 Fr110c1k pli
33. e 8 ADC channels each of which can read in a single value at a time 5 1 Theory of Operation 5 2 Basic Usage The initial setup of the ADC consists of the following steps 1 Power the device Here we set the bit in LPC_SC gt PCONP for the ADC to turn the power on This is essentially the same as for the Timers and most other peripherals LPC_SC gt PCONP 1 lt lt 12 Manual page 56 57 2 Calculate the necessary clock the ADC can only run at 13MHz and choose a peripheral clock and ADC clock divider setting The ADC like most other components is connected to your choice of peripheral clock and then run through its own divider The ADC is also limited to a 13 MHZ clock so you must choose values for its internal clock divider and peripheral clock such that Prclko 13MH N 1 lt Z The easiest way to do this is to simply set your central clock to the 12MHz main oscillator and the various other dividers to pass that through unchanged LPC_SC gt CLKSRCSEL 1 Select main clock source LPC_SC gt PLLOCON 0 Bypass PLLO use clock source directly Feed the PLL register so the PLLOCON value goes into effect LPC_SC gt PLLOFEED OxAA set to OxAA LPC_SC gt PLLOFEED 0x55 set to 0x55 Set clock divider to 0 1 1 LPC_SC gt CCLKCFG 0 28 But you can also use settings that will let your LPC run faster and get more out the main processor while allowing the ADC to run as fast
34. e circuit is assembled connect the oscilloscope probe to the ADC input and wave your hand above the sensor to get something like figure 2 Connect the hand sensors to your LPC and check if you can receive ADC values with GDB or semi hosting 3 Get DAC to output sin waves verify with oscilloscope Once you connect your DAC output to the oscilloscope you should see something like figure 24 Noise Filter Off ins Figure 24 DAC Sine Wave Oscilliscope Trace 4 Build Voltage Reference Figure 25 Voltage Reference Circuit Since your DAC is limited to values between 0 and 3 volts we can t amplify the output around Ov so we re constructing a reference voltage for the amplifier First we use a voltage divider to get a point at 1 5v and then a voltage follower so that we can attach loads to that point and have it stay stable Once you ve constructed this section of the circuit use the oscilloscope or multimeter to check that the voltage at V ef is 1 5 5 Build RC Filter 37 DAC R4 220 i Figure 26 RC Filter Schematic The RC filter is a component we use to smooth out the jagged edges of the DAC output At high frequencies the output of your DAC will look like figure 27 with an obvious step from one output voltage value to another When you play this sound you ll be able to hear the high frequency shifts as a seperate tone from the sine wave you re otherwise playing Noise Filter Off l
35. e they re weakly defined defining a new function with the same name will make that the handler for the interrupt Turn on the LED when the button is pressed void EINT3_IRQHandler If the rising edge interrupt was triggered if LPC_GPIOINT gt I00IntStatR gt gt 9 amp 1 Turn on PO 8 LPC_GPI00 gt FIOPIN 1 lt lt 8 I If the falling edge interrupt was triggered if LPC_GPIOINT gt I00IntStatF gt gt 9 amp 1 Turn off PO 8 LPC_GPIOO gt FIOPIN amp 1 lt lt 8 Clear the Interrupt on PO 9 LPC_GPIOINT gt I00IntClr 1 lt lt 9 All the GPIO Interrupts share the same interrupt handler so it has to check which pins actually triggered the interrupt You can do this with the GPIO Interrupt Status Registers I00IntStatR will have bits set when the relevant pin was triggered by a rising edge and I00IntStatF does the same for a falling edge 1ONVIC Nested Vector Interrupt Controller 11These registers are for pins on GPIO Port 0 There are similar registers with 102 instead for pins on GPIO Port 2 The other GPIO ports don t have support for interrupts and don t have interrupt registers 10 Once you ve done the relevant action you can clear a particular pin s interrupt flag by writing a 1 to the bit in I00IntClr This means you only have to handle one pin at a time and as long as you clear that pin s interrupt flag the handler will be called again to take care of the next t
36. ease the button Sometimes it ll miss button presses completely and not change the LED s state Figure 2 What button presses actually look like This happens because buttons aren t perfect and instead of getting smooth transitions from connected to disconnected the transitions are disjointed and shaky this phenomenon is known as bouncing Because the GPIO pins can only read if something is low or high these jitters result in a number of very fast transitions before the voltage stabilizes Your LPC will see some of these transitions as a separate button presses and toggle the LED accordingly Most of the time the bouncing will happen between reads of the pin state but sometimes a read will happen in the middle of the bouncing and cause anomalous output Removing the errors caused by bouncing can be done with hardware or software In hardware using a capacitor or a Schmitt Trigger can sometimes solve the problem In software one can check if the input has been stable for a while before acting upon an event There are also many other ways to deal with bouncing that can be more complex but also more reliable 2 4 3 Interrupts There s another way to get input from GPIO pins this time without having to stop and poll the state of your button waiting for something to happen With the correct settings the processor can wait for an event in the background while letting your code run in the meantime When an event occurs the pr
37. ecting sysclk directly to pllclk 3 And set the CPU Clock Divider to Fesgillater 1 16 If we couldn t forgo the PLL then we need to figure out the PLL settings we ll use If we re using PLLO we know Fpiicix is less than 275MHz and 550MHz and that for some integer D between 0 and 255 Forcier D 1 x Fock The PLL consumes less power when it runs at a lower frequency so we should choose the smallest D that will fit within the bounds Now we know we ve got to set the CPU Clock Divider to D but we still have to figure out which oscillator to use and what to set the N and M dividers to We want this to be true 2x M 1 Xx Fsysclk N 1 Foiicik We can solve and substitute to get N 1 ee 2x F oscillator M 1 Fp1lcik So for each oscillator we can find the best approximation for the right hand side possible using a valid N and M Namely with N between 1 and 32 and M between 6 and 512 or another value given on page 38 of the manual We can then choose which combination of oscillator N and M will give us the least error Namely if we let R 2x F oscillator Foricik The error for any combination of oscillator N and M N 2 R Once we have the settings that ll minimize the timing error we can do the following then 1 Set sysclk to the proper oscillator 2 Set the N Divider and M Divider to N and M respectively 3 Connect PLLO to pl1c1k 4 And set the CPU Clock Divider to D 3 5 Ma
38. ether PLLO is on and lets you choose between connecting pllclk directly to sysclk or to PLLO See manual page 37 LPC_SC gt PLLOCFG The PLLO Configuration register this is where you set the factor registers for the N Divider and M Divider See manual page 37 LPC_SC gt PLLOFEED The PLLO Feed register you write afeed sequence to this register in quick succession in order to validate changes you ve made to the other PLLO registers and actually apply them to the PLL See manual page 40 3 5 2 Feed Sequence The PLL registers together form an update commit system where every change of PLL settings requires a feed sequence in order to actually be applied This exists so that random memory accesses won t change the settings on this device and if you want to break your LPC you ve got to actually work to do it A feed sequence consists of writing OXAA and 0x55 to PLLOFEED one after the other with no other memory operations on any of the other system control registers in between void PLLO_feed_sequence LPC_SC gt PLLOFEED OxAA LPC_SC gt PLLOFEED 0x55 3 5 3 Update Algorithm When you have chosen your settings there s a well specified algorithm t which explains what changes you have to make and in what order It is very important that you don t combine steps and make sure that you get no interrupts during this process 1 Check if PLLO is already connected if it is disable it with one feed sequence 16See page 4
39. filter out the DC element of the air pressure and any components too low in frequency to hear 45 7 7 3 Filters C1 C2 1 pF Coarse Mic Out R1 R2 10 kQ 10 kQ Figure 35 Filter Stage e Test by connecting the oscilliscope to this portion of the circuit ground to 1 5v and probe to Fine Mic Out and making sure you see a signal in the millivolt range This is two low pass filters in series which will significantly reduce the amplitude of high frequency noise 7 7 4 Offset Voltage e Test the voltage at the Offset Voltage point and make sure that it moves up and down when you fiddle with the potentiometer 10k0 Offset Voltage Figure 36 Offset Voltage The output from the microphone and the filter aren t perfectly centered on the 1 5v value so this offset voltage lets you tweak the final centering of the signal to fix that In the final output this pot will move the signal up and down on the oscilloscope 46 7 7 5 Amplifier o gt 10 nF Offset Voltage Figure 37 Microphone Amplifier e Make sure the output changes scale with the new potentiometer and moves up and down with the offset potentiometer and that you can get output signals that have a 3v amplitude Here we use an Op Amp amplifier to scale the microphone s signal to levels which our LPC can read 47 8 Appendix 8 1 Development Environment Setup Executables destined for a microcontroller are somewhat different than executable
40. hieve lock Let Fsysclk llref N 1 Fp If 100kHz lt Fpitref lt 20MHz wait for the PLL to lock 19 while GETBIT LPC_SC gt PLLOSTAT 26 Spin on Lock Flag If Fotiref lt 100kHz wait for 200 Fpliref seconds int i count lt Number of cycles with current clock speed gt while i lt count Wait sensible amount of time If 20MHz lt Fpliref wait for 200ps int i count lt Number of cycles with current clock speed gt while i lt count Wait sensible amount of time 10 Connect PLLO with a feed sequence BITON LPC_SC gt PLLOCON 1 Set PLLO Connect Flag PLLO_feed_sequence Commit Changes 3 6 Peripheral Clocks Many peripherals are timed using the Peripheral Clock Dividers There are four clocks pc1k1 pc1k2 pc1k4 and pc1k8 which are clocks derived from cc1k and are 1 2 4 and 8 times as slow as cclk Namely they are implemented with clock dividers with fixed factor registers of 0 1 3 and 7 You can see how to connect them to various paripherals on pages 56 and 57 of the manual 3 7 Project Precision Timing Many aspects of your LPC require very precise clocking Things like the USB subsystem the Analog to Digital Converter ADC and Direct Memory Access DMA all perform operations that are timed using your internal CPU clock The accuracy of those features and more depends on how accurate your clock speed is We are going to experiment with changing the clock speed to generate o
41. iding these interfaces from you This gives you the ability to work with them directly without having to deal with the virtual device abstraction a modern OS would impose When we try to read or write to a normal chunk of memory the address and instruction are sent to the memory controller The memory controller then either retrieves data from memory and places it into a register or takes data from a register and writes it to somewhere in the memory However there are a number of privileged address and when you try to read from or write to these a different pathway is taken Here when the memory controller gets the instruction it notices the address is special and instead of going to the memory module it ll forward the request to a register that s located in the relevant peripheral These registers all have different functions each of which is detailed in the manual along with the register s memory address The really important thing to notice is that you re not dealing with a normal piece of memory and these memory mapped registers can act very differently Unlike static memory where you can read or write pretty much anywhere there are a number of these memory mapped registers which you can only read from Trying to write to any of these will trap your system in a hard fault Neither can you rely on the assumption that reads are nondestructive There are some registers which are connected to FIFOs and other structures and reading fro
42. imited to 0 and 3v and its state will tell whether Ving gt Vin or not comparing the two input values 35 R2 Reference Figure 22 Op Amp Voltage Amplifier Schematic 5 7 1 2 3 Op Amp Voltage Amplifier The amplifier is based off the same principle but instead of a direct connection it uses a voltage divider The voltage divider formula tells us that the voltage at Vin Vout Vref r Vref Thanks to it s nature as a feedback loop the Op Amp will change Vout so that Vin Vin If we assume that Vref 0v then we can solve the equation for Vout and see the following holds R R2 Vout Vint Ro So Vout is a straightforward multiple of V and the amount by which it is multiplied a R2 is the gain of the amplifier You can do the same thing for other values of V y to see that it s esentially the midpoint around which you re multiplying So if Vin Vref 2v then Vout Vref gain 2v 5 7 2 Materials e 2x LED use the bright blue ones on the strip e 2 x Photoresistor e 2 x 2 kOhm Resistor e 1 x22 Ohm Resistor e 2x 10 kOhm Resistor e 1x Speaker e 1x1 Microfarad Capacitor e 1 x Potentiometer Higher Resistance is better e 2x TLV2461 Op Amp 5 7 3 Steps 1 Build 2 Hand Sensors test with oscilloscope Figure 23 Hand Sensor Circuit 36 These are voltage dividers which will use the changing resistance of the photoresistor to change the voltage at the ADC input Once th
43. ists tzt and change the project name cmake G Unix Makfiles make 8 1 3 2 Start a new project by copying In your terminal cp R Skeleton NewProjectName cd NewProjectName YOUR_EDITOR CMakeLists txt Edit CMakeLists tzt and change the project name cmake G Unix Makfiles make 51 8 1 3 3 Work on an existing project In your terminal Open source files in editor and make save changes make 8 1 3 4 Enabling semihosting for a project Open a project s CMakeLists txt file and uncomment the following line set SEMIHOSTING_ENABLED True Then just rebuild the project and semihosting messages will be viewable in gdb 8 1 3 5 Adding compiler options All compiler options are configured in Platform LPC1769_project_default cmake To add compiler options to a single project you can use CMake s add_definitions command in that project s CMakeLists txt In your CMakeLists txt add_definitions Wall Werror 02 Add more compiler flags here 8 1 3 6 Add a source file to a project When adding source files to a project remember to open that projects CMakeLists txt and add the file to the SOURCES variable In your CMakeLists txt set SOURCES src cr_startup_lpc176x c src project c Add more source files here 8 1 3 7 Flash a program In your terminal Plug in the LPC1769 make make boot make flash 8 1 3 8 Debug a program In your terminal Plug in the LPC1769 make make bo
44. king The Changes Now that we know how to choose the various clocking settings we ll use we need to learn how to apply them This involves making absolutely sure that you perform certain operations in a certain order checking and double checking the state of the system and operations that serve only to prove to the LPC you re paying attention Clocking can be a dangerous subsystem to play around in if we input badly chosen settings we could render our microcontrollers useless This is why the LPC s clocking subsystem requires people to jump through hoops to change anything 17 3 5 1 Registers Before we dive into the algorithm to change the settings we should step through the various registers we ll be using and look at their functions LPC_SC gt CLKSRCSEL The Clock Source selection register this is what will connect a particular oscillator to sysclk Look at page 34 of the manual for more details on how to operate it LPC_SC gt CCLKCFG The CPU Clock Divider s factor register this controls the divider placed right before CCLK See manual page 54 LPC_SC gt PLLOSTAT The PLLO Status register this read only register makes the currently applied PLLO settings visible to you It has the connection status of PLLO the N Divider and M Divider factor registers and a status bit which tells you if the PLL is synced yet with its input signal See manual page 39 LPC_SC gt PLLOCON The PLLO Control register this register controls wh
45. m them is the same as popping from that queue and the next time you read from the same address you ll get a different value Even the usual guarantee that a write operation is idempotent is lost There are registers where a write operation will trigger some change in the peripheral making the LPC turn an LED on or send out a signal 2 3 2 Blinking Lights So let s start with something simple Blinking Lights Connect up an LED to pin PO 9 and ground making sure to place the proper current limiting resistor in series with it To actually turn on the LED you have to first tell the LPC that the pin is to be used for output and then set the state to be on If you look in the manual you ll see that PO 9 s direction is controlled by the 9th bit in a register located at 0x2009C000 and that setting it to 1 makes it an output pin uint32_t 0x2009C000 1 lt lt 9 Set PO 9 to output Then there s another register at 0x2009C014 which controls the state of the pin so we can turn turn the light on and off by manipulating its 9th bit uint32_t 0x2009C014 1 lt lt 9 Turn On uint32_t 0x2009C014 amp 1 lt lt 9 Turn Off So now you should be able to make the light blink or by varying the amount of time on and off let it glow with varying levels of brightness 2 3 3 An Easier Way Of course writing out the memory address every time you wish to change a register isn t easy or readable You could
46. means different libraries can be compatible with each other and your code This toolchain comes with a number of tools as The GNU assembler which takes the assembly our compiler outputs and gives us ARM compatible machine code gcc The GNU compiler collection which will take our C code and turn it into assembly gdb The GNU debugger you can use this to view your program as it s executing and see what its internal state is 1d The GNU linker which takes compiled object code and can correlate all the symbols and link it into a single executable There s also a number of less important tools from Gnu Binutils that we ll be using all targeted to arm none eabi 8 1 1 Install Steps 8 1 1 1 LPCXpresso In order to save building these tools ourselves and to get the tools which will allow us to flash the LPC through the proprietary LPC Link board we ll have to download and install LPCXpresso a set of tools and Eclipse based IDE for working with the LPC To download the tools visit the LPCXpresso Website and register an account Once you have confirmed your email you will be able to visit the download page There download the latest version of LPCXpresso 5 19The ARM EABI Standard http infocenter arm com help topic com arm doc ihi0042e 1H10042E_aapcs pdf 48 for your operating system and follow the provided installation instructions Take note of the installation directory we ll use it later At this point you
47. ng since the reset flag is gone Once you re done with setting those value properly you can watch your timer counter increment Current_Timer_Val LPC_TIM3 gt TC 4 3 Match Registers Match Register Match Control Register 7 lt gt Reset Disable lt gt Disable Interrupt gt Timer Control Register Reset Figure 11 Match Register Block Diagram Within each timer are four match registers 32 bit registers which can store a specific match value When the timer counter and match register are equal certain events can be triggered Choosing the match value is just a matter of setting the match register LPC_TIMx gt MRx LPC_TIMO gt MR3 LPC_TIM2 gt MR1 uint32_t 4000 Set match register 3 on timer 0 uint32_t 453 Set match register 1 on timer 2 4 3 1 Match Settings There are three events a match can trigger a reset of the timer counter disabling the timer counter and sending an interrupt The disable and reset events work by modifying the timer control register and using its features to control the timer counter 24 The match register s disable event sets the disable flag in the TCR to 1 requiring you to manually toggle it back On the other hand the reset event simply toggles the flag in the TCR setting the timer counter to 0 but allowing it to continue incrementing To actually change which events are triggered on match requires manipulating the regis
48. ng the ADC interrupt in the NVIC NVIC_EnableIRQ ADC_IRQn 2 Setting the correct bits in the ADC Interrupt Enable register BITON LPC_ADC gt ADINTEN 0 3 Setting up the interrupt handler that will retrieve your value Reading from the GDR will turn off the interrupt flag so you don t have to do it manually void ADC_IRQHandler void other stuff Equivalent to above analog_val LPC_ADC gt ADGDR gt gt 4 OxOfff other stuff Then you can start a conversion the same way as before 30 SETBITS LPC_ADC gt ADCR 24 3 1 Start the single conversion 65 ADC clock cycles after you do the interrupt will be thrown and you can retrieve the value 5 4 Connecting to Timers 5 5 Burst Mode 5 6 DMA 5 7 Project Optical Theramin Missing figure A Theramin is a Russian musical instrument invented in 1919 and is one of the few instruments played without ever being touched There are two large antennas on a theramin which can detect the approximate position of a musician s hands and uses that to modulate the sound it produces One hand is used to control the pitch and the other is used to control the volume In a standard theramin the detection works by using its antennas and the hands of the artist as opposing plates in a capacitor By moving their hands around the artist can change the capacitance and the instrument can use that change to generate different sounds
49. ocessor will stop your currently running code run code to respond to the event and restart the execution of your main program This mode of communication is known as Interrupt Driven I O These interrupts can be very complex and so we re only going to touch on a small subset of their capabilities here For GPIO specifically an interrupt can be triggered when the CPU detects a rising or falling edge on an input pin Once the edge is detected the Interrupt Controller performs a context switch In this case saving any of the current registers to the stack and starting the executing of the interrupt handler Once the interrupt handler is done the processor will restore the previously saved registers and continue executing the original code The Interrupt Controller uses an internal flag to determine whether or not to perform a context switch and this flag is not automatically turned off once it has been set This means that if you don t manually disable the flag the interrupt handler will execute repeatedly until the flag is disabled 8Image taken from http en wikipedia org wiki File Bouncy_ Switch png 9A rising edge is the pin s value changing from a 0 to a 1 and a falling edge is the value changing from a 1 to a 0 This might not seem useful but consider a case where you ve got a number of interrupts coming in simultaneously Because the flag isn t automatically disabled you can handle one incoming interrupt disable the flag
50. of voltage divider which you can adjust on the fly A potentiometer is essentially a long resistor where you can move V up and down along it As such R1 R2 is always going to be constant and the voltage at Vp depends on the position of the potentiometer s dial The actual value can go all the way from Vi to V_ since you can lower either R1 or R2 down to 0 5 7 1 1 1 Photoresistors 5 7 1 1 2 RC Filters e Signals having frequency components e DAC producing impure signals because of the difference between transition time and rest time e Need to remove the high frequency components so that we only preserve the frequency we want to output Figure 18 Op Amp Schematic 5 7 1 2 Op Amps Operational Amplifiers Op Amps are some of the most powerful standard circuit components They are circuits that run an extremely simple algorithm that can be leveraged in very powerful ways The Op Amps can either push or pull current through their output and thanks to Ohm s law V JR this means that they can control the voltage at their output as well In figure 18 the Op Amp is connected through a resistor to a voltage source Depending in the state of its inputs it can choose to do one of three things First among these is to prevent the flow of current either in or out in this case there will be no current flowing cross the resistor and the voltage at Vout will be 1 5v Next it could push current outwards meaning there ll be
51. ot make gdb 52 In GDB b main load Make changes to the program make load c For more information on how use GDB refer to a simple tutorial or the full user manual 53 8 2 Standard Macros E BitMacros h ifndef BITMACROS_H_ define BITMACROS_H_ Some macros to speed bit twiddling define BITVALUE var 1 lt lt var define BITON var bit var 1 lt lt bit define BITOFF var bit var amp 1 lt lt bit define BITTOG var bit var 1 lt lt bit MASK 3 4 0278 define MASK start len 0 lt lt len lt lt start define INVMASK start len MASK start len OR with things to set all 1s define ORMASK start len val MASK start len amp val lt lt start AND with things to set all Os define ANDMASK start len val INVMASK start len val lt lt start Shift a set of bits over and mask it to that length same as or mask with slightly different ordering define SHIFTMASK val start len ORMASK start len val SETBITS does two write passes first pushing all the 1s from val and then all the Os This should keep from re setting any bits that are already or writing 1 to any unset bits define SETBITS var start len val do var ORMASK start len val var amp ANDMASK start len val while 0 define GETBIT var start var amp 1 lt lt start gt gt start define GETBITS var start len va
52. r amp MASK start len gt gt start define LOWBYTE var char var amp OxFF define HIGHBYTE var char ushort_t var gt gt 8 OxFF endif BITMACROS_H_ 54
53. replace it with a preprocessor macro but writing those macros would be painful and tedious Until you notice that the memory locations for these registers are structured with registers performing related tasks placed close together In fact the addresses are chosen so that they can easily map to structs Finding the base address of a particular block of registers and defining a suitable structure will give you easy to use pointers to all the registers in that block There already exists a library that defines these structs and calculates the proper base addresses CMSIS is a library written by engineers at ARM and it sets up all these memory addresses as human readable macros for you To see how it works let s look at the setup for the DAC Digital to Analog Converter 4See manual page 107 5CMSIS Cortex Microcontroller Software Interface Standard The DAC is a device which can take a digital value and turns it into an analog output it s controlled with only 3 registers the functions of which we ll look at in a later chapter In LPC17xx h you ll find a long list of struct definitions and a series of raw memory addresses The addresses point to the chunks of memory assigned to each peripheral and the structs show the layout of each of those chunks of memory isa Digital to Analog Converter DAC typedef struct __IO uint32_t DACR _ IO uint32 t DACCTRL _ 10 uint16_t DACCNTVAL LPC_DAC_TypeDef define LPC_A
54. riggered pin 2 5 Project Bit Banging Bit banging is the process of implementing a serhttp www cs umd edu rohit UESDbook pdfial communi cation protocol using software instead of dedicated hardware In this case we re going to be sending data to a shift register using 3 GPIO pins to control 8 LEDs 2 5 1 Shift Registers To control many LEDs with few outputs you need to implement a serial communications protocol a way of sending data one bit at a time to another entity In this case we are going to be sending the data to a CD4094B which has an interface based around 3 input lines the clock the data line and the strobe input Clock LT ET ET vs yv fs yv y yv Jj v Jj Data vu TS CU T E e Strobe J Data Bit 0 1 1 0 1 0 0 1 x Shift Register 0x00 0x01 0x03 0x06 0x0D 0x1A 0x34 0x69 0x69 Output Value 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x69 Figure 3 Shift Register Timing Diagram The CD4094B has in effect two registers inside of it a shift register and an output register The shift register is used to load in data one bit at a time so whenever the clock signal moves from low to high it ll do two things 1 It will shift the data it contains one bit to the right 2 Now that the lowest bit is empty it ll read the value on the data line and store it in that least significant bit So this way through 8 clock cycles you can load one byte onto the shift register starting with the highest first The outpu
55. s you intend to simply run Where a normal executable will be loaded by an OS we need to make files that can be flashed bit for bit onto the microcontroller s memory and run To greatly simplify an OS takes an executable file loads it into memory looks for a pointer to first instruction to execute in the executable s metadata and starts a process with the program counter set to that location We have no OS to offload a lot of this work to we must build files that can be moved directly onto the LPC s memory and run on a bare machine Our executables will have the loaders and initializers that an OS would normally provide in addition to our actual programs In effect creating a minimal OS that exists only to load our app and get out of the way These loaders are provided by our toolchain and allow us to concentrate on the main application To do this we will be using a toolchain building applications for arm none eabi which means arm The CPU architecture we re building our applications for this determines the instructions and registers we have available among other things none This is the operating system we re building for in this case we re building applications that run on the bare metal with no intervening OS eabi The Embedded Application Binary Interface this defines the conventions for data types file formats stack usage register usage and function parameter passing Having a standard specification for this 1
56. t register is what is actually connected to the external pins and determine whether each output pin is held low or high This register waits till it sees a rising edge on the strobe input and when it does it ll copy over the values currently in the shift register With this you can load in a byte of data with the clock and data lines and once you ve finished write it all at once to the output with the strobe line 2 5 2 Materials Other than your LPC you ll need the following 12 Thinking of them as memory registers is an imperfect abstraction While it ll serve for anything we need to do there are much more detailed explanations on the CD4094B Data Sheet and on Wikipedia 11 e 1 x CD4094B 8 Bit Shift Register e 8x LEDs e 8x 2N2222A NPN Transistor 13 The shift register in this circuit can channel only 10mA of current and if you connected it directly to the LEDs you d get a glow that s barely visible The transistors act as simple current amplifiers so that you can have brighter LEDs 2 5 3 Steps 1 Wire up the following circuit Q5 2N2222 Q7 2N2222 Q8 2N2222 Vdd Enable Q5 Q6 Q7 CD4094B 8 bit Tri State Shift Register Strobe Data Clock Qi Q2 Q2 2N2222 Q3 2N2222 Q4 2N2222 E Figure 4 Shift Register Circuit 2 Implement the serial protocol needed to write to shift registers and display a pattern where one LED turns on at a time moving back an
57. ter at LPC_TIMx gt MCR All the flags for all the timer registers are mapped to various bits in the Match Control Register MCR This mapping can be found on page 496 on the manual BITON LPC_TIMO gt MCR 10 Reset on match for match register 3 in timer 0 BOTON LPC_TIM2 gt MCR 5 Disable on match for match register 3 in timer 2 4 3 2 Match Interrupts Like a GPIO interrupt there are multiple triggers which all trigger an interrupt on the same channet of the match registers can trigger interrupts and so can other components of each timer w o To tell these interrupts apart you can use each timer s Interrupt Register IR When a component of the timer triggers the interrupt a flag in the IR is flipped and you can use that to determine what s already going on 4 3 3 External Match Registers 4 4 Capture Registers Capture Control Register J Enable Enable TIMERx IRQ CAPn x Pin Figure 12 Capture Register Block Diagram 25 4 5 Project Serial Light Communications 4 5 1 Background Missing figure 4 5 2 Materials e 1x LED use the bright blue ones on the strip e 1 x Photoresistor e 1 x Potentiometer e 1 x 2kOhm Resistor e 1 x TLV2461 Op Amp 4 5 3 Steps LED Figure 13 LED Output Circuit 26 ms AR R1 2 KQ Figure 14 Light Recieve Circuit 27 5 ADC The ADC is the analog counterpart to the GPIO s input mode There ar
58. trol registers Writing a 1 to a bit in FIOSET will enable the corresponding pin and writing to FIOCLR will disable the pin SAPB stands for Applied Peripheral Bus there are two in the LPC and some peripherals are connected to each The fast in their moniker refers to the fact that using them takes fewer operations than using FIOPIN LPC_GPI00 gt FIOSET LPC_GPI00 gt FIOCLR 1 lt lt 9 Turn LED Un 1 lt lt 9 Turn LED Off FIOSET is a good example of how the usual guarantees of memory structure are lost when working with memory mapped data Writing a 1 to FIOSET will set the corresponding bit in FIOPIN to 1 while writing a 0 will do nothing In effect FIOSET is an alias for FIOPIN However reading from FIOSET is a completely different action it will return the value from the output state register a register which stores the current output value for all the pins regardless of whether they are current being used as such Writes to FIOCLR can be similarly thought of as an alias in this case from FIOPIN amp to FIOCLR But reading from FIOCLR is undefined there is simply nothing that operation can look at when pointed at FIOCLR This idea of memory mapped registers being aliases for more complex commands hints at why these registers are called the fast output control registers Trying to change the value of a single pin with FIOPIN requires at least 3 operations operations
59. up other devices and turning your microcontroller into something useful GPIO has two fundamental operating modes input and output Input lets you read the voltage on a pin to see whether it s held low Ov or high 3v and deal with that information programmatically Output lets you set the voltage on a pin again either high or low Every pin on the LPC can be used as a GPIO pin and can be independently set to act as an input or output In this chapter we will show how to complete 2 tasks reading the state of a button and making an LED blink Using what you learn from that you ll be able to start building more complex devices and even implementing simple communications protocols 2 3 GPIO Output GPIO output is a versatile and powerful tool especially given that it takes little effort to use and control it Once you ve chosen a pin the process to use it is straightforward e tell the LPC that the pin should be used as an output e tell the LPC whether the pin should be held low or high The interesting part is how exactly you can give the LPC instructions and what it does in order to carry them out 2 3 1 Memory Mapped Registers In order to talk to the GPIO controller or any other peripheral we have we have to use memory mapped registers In most computers these low level interfaces are hidden by the kernel and often only higher level interfaces are available to developers The LPC however doesn t have a kernel or drivers h
60. utput signals at various frequencies 3 7 1 Steps 1 Write a script in any laguage you want that will calculate clock settings for you It should given a target clock speed give you everything needed to write the clock setup code clk calc target 120MHz Base Oscillator Use PLL N Divider M Divider CPU Clock Divider Target Freq Output Freq 20 Error clk calc target 200MHz Cannot Compute Target Clock Too High 2 Write a program that repeatedly toggles a GPIO pin so that you get a square wave 3 Use make 1st and the ARM Cortex M3 Manual to find the number of clock cycles between every toggle 4 Change the frequency of your output square wave without changing the loop at all use only different clocking settings 3 7 2 Questions As you progress through the exercise answer the followign questions 1 What is the lowest CPU clock speed you can achieve with this setup 2 How many clock cycles does your loop take between GPIO toggles 3 What are the options needed to get the maximum speed 120MHz 4 What is the frequency of your output signal when the CPU clock is 200Hz 120MHz 5 What clock frequency do you need to get an output signal at 1kHz 21 4 Timers 4 1 Basic Description Timers are peripherals within the LPC that are mainly internal they use the CPU clock to keep track of time and make that ability available to the user in a number of ways Timers can
61. ve headfirst into We ll exploit the simplicity to teach you about how processors are structured how to deal with many common protocols and tools and even how some fundamental parts of an operating system work The LPC itself has a number of modules which encapsulate various features of the processor We ll be working our way through those modules explaining why you would use them how they work and how to use them With each module we learn about we ll present exercises and projects that will help you cement that knowledge and give you a practical examples of how these devices can be used While we ll often be working with electronics no initial knowledge is required and we ll give you the resources to learn what you need to know as you go along 1 1 Resources This textbook will mainly work to help you build a conceptual framework around these topics there are other resources that will give you the fine detail 1 1 1 The LPC 17XX User Manual The User Manual available here will be the main document this textbook builds on It contains detailed information on all of the available features of the LPC and how you can use them Though this textbook is meant to give you all of the background that the manual lacks it is in no way a substitute There will be a lot we cannot actually go over and to get the most out of this course after every chapter you read in this textbook you should read the corresponding chapters in the manual

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