Interfacing Graphical Displays - AN0047
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1. before each buffer flip This creates much extra bus traffic and since the drawing code overwrites the entire background each frame it is completely uneccesary emWin specifies a method to implement a custom frame copy operation Using the function LCD SetDevFunc itis possible to specify a function that should take care of the frame copy instead of the default emWin behavior In the example this function is implemented with an empty body to disable the frame copy 5 4 Window Manager This examples illustrates the emWin window manager In the window manager each window is responsible for drawing itself The windows do this by specifying a callback routine and listen for the WM PAINT message Multi buffering support is enabled for this example too but the buffer copy optmiziation is not implemented as the window manager relies on the buffer copy for its drawing algorithm 5 5 More emWin Examples More examples for emWin can be found in the installed files by Simplicity Studio under reptile emwin examples Most of these examples can easily be viewed by copy pasting directly into one of these example projects 2012 08 13 an0047_Rev1 01 www energymicro com Er NT32 the world s most energy friendly microcontrollers 6 Further Reading Documentation for emWin can be found in the emWin User Manual located in the reptile emwin doc folder under Simplicity Studio or on the SEGGER website http www segger com 2012 02. Direct Drive connection diagram sasak ence eee e teeta Ie eaaa aana hehe hene hene 7 9 5 Timing diagratm RGB Rue EE 8 2012 08 13 an0047_Rev1 01 www energymicro com Er nNT32 the world s most energy friendly microcontrollers List of Equations 2 1 Number of pixel cycles for 1 frame oer Een ri EEN AE neds bebe ee ER aa ENEE EENEG ERR ur SC Re 3 2 2 Total frame rate Frames Per Second ssssssssssssssssssssssssseseene hene he ne he men hen tentem nen ren tee rentrer rennen 3 2012 08 13 an0047_Rev1 01 www energymicro com ENERGY micro Energy Micro AS Sandakerveien 118 P O Box 4633 Nydalen N 0405 Oslo Norway www energymicro com
3. EBI WITH DIRECT DRIVE 2012 08 13 an0047_Rev1 01 www energymicro com 32 the world s most energy friendly microcontrollers Figure 3 4 RGB mode with Direct Drive connection diagram PIXEL DATA EBI CSx EBI AD EBI DCLK EBI VSYNC EBI HSYNC EBI DTEN EBI CSTFT Note The term RGB mode used in this context has nothing to do with color displays It refers to the type of display interface where the MCU itself is in charge of the timing signals HSYNC VSYNC DTEN DOTCLK Both pixel data and timing signals for the display has to be supplied from the MCU side If this has to be controlled by software the CPU load can be significant This is especially true for displays with a large resolution For this reason the Direct Drive feature has been developed to drive displays autonomously In this mode Direct Drive takes the role of the display controller reading the frame buffer from memory and generating the necessary timing signals to transfer the pixels to the display When using Direct Drive drawing to the display is divided into two steps In step 1 the CPU calculates the image to be displayed and writes this to a frame buffer in memory In step 2 Direct Drive uses the frame buffer to update the display Note that these steps are performed in parallel Direct Drive does not wait for the CPU to finish a frame It is continuously updating the display
4. an EFM32GG990F 1024 is used This device has 128 kB of internal RAM In this case an external memory block is required to store the frame buffer 2 2 Frame Rate To calculate the frame rate we need the pixel clock frequency the size of the display in pixels and porch intervals The size of the porch intervals in the equations below are given in pixel clock cycles Number of pixel cycles for 1 frame Ng HBP WIDTH HFP 2 1 NFRAME VBP T HEIGHT T VFP i Ni INE i Equation 2 1 p 3 gives the number of pixel clock cycles needed to update one full frame To calculate the total frame rate we then need to know the pixel clock period Total frame rate Frames Per Second FPS Fexcik NFRAME 2 2 2 3 Bus Access When both an external frame buffer RAM and display controller is connected to the EBI bus bus access can become the bottleneck of the system The pixel data first has to be written to RAM over EBI and then transferred from RAM to the display over the same bus In RGB mode it is possible to take advantage of the porch intervals to optimize this see Section 3 2 2 p 8 During these intervals no pixel data is sent to the display so this is a good time to write pixels to RAM 2 4 Flickering and Tearing Effects Flickering and tearing are visual artifacts that reduce the overall user impression of an application When drawing a frame it is common to first fill the background with a color or image and then draw text
5. buttons or other user interface elements on top If the drawing is done directly to the display there will be a small time window where only the background is visible to the user When the frame is redrawn several times per second it will look like the Ul elements are blinking or flickering 2012 08 13 an0047_Rev1 01 www energymicro com EFINJ32 the world s most energy friendly microcontrollers Tearing occurs if the display controller is in the middle of displaying a frame and then suddenly switches to the next frame The top of the display will then show the old frame while the bottom shows the new one To the user it will appear to be visible lines across the screen between the two images 2 5 Multiple Buffering Multiple buffering is a technique for avoiding flickering When multiple buffering is used with the MCU is drawing to one frame the back buffer while the display controller is showing the other the front buffer There are two schemes double or triple buffering The advantage of triple buffering is that the CPU never has to wait for the display controller to finish In the double buffering scheme when the CPU has finished drawing a frame to the back buffer it then has to wait for the display controller to switch buffers before it can start writing to the other buffer In triple buffering the CPU can just start drawing on next buffer and flag the finished buffer as pending The drawback using multiple buffering is the
6. descriptor is 1024 elements For a QVGA 320x240 display this means a total of 320 240 1024 75 descriptors are needed The destination address will depend on which EBI bank the display is mapped to and which address pin is used for D C As an example assume the display is mapped to EBI Bank 1 address 0x84000000 EBI A 0 is connected to D C and a 1 on this pin means data mode Furthermore if the address mode is 16 bit all addresses are shifted one bit to the right see the EBI Chapter 16 bit address mode in the Reference Manual for an explanation of this The DMA is in this case configured to write to address 0x84000002 2012 08 13 an0047_Rev1 01 www energymicro com EFM32 the world s most energy friendly microcontrollers The source incrementis set to the same value as the pixel size e g 2 byte for a 16 bits per pixel display The destination increment is zero because we are always writing to the same address The timing parameters for the display controller needs to be configured for the EBI bank that the controller is mapped to The software example indicate how this is done for the display on the EFM32GG DK3750 Development Kit Also see the application note ANO034 External Bus Interface 4 3 Direct Drive Direct Drive uses the RGB interface and automatically feeds the display with pixels from the frame buffer in memory Direct Drive automatically generates the control timing signals HSYNC VSYNC DTEN DOTCLK fo
7. from the frame buffer in memory The CPU is completely decoupled from Step 2 so the only limiting factor is how fast it can draw to the frame buffer in RAM After the CPU has completed a frame and written it to RAM it is free to do other tasks like calculating the next frame or even go to sleep if no more frames are needed It is possible to use either interal or external RAM for the frame buffer with Direct Drive External RAM is usually preferred however On one hand internal memory is limited and might even be to small to hold the frame buffer The second reason is that when using internal memory this memory has to be accessed often by both Direct Drive and the CPU This can cause a number of wait states on the CPU and slow down the application When driving from external memory the CPU s working memory and frame buffer is completely decoupled Note The alpha blending and masking features in Direct Drive can not be used together with emWin and are not discussed in this application note To see how they can be used refer to the scroller example for the EFM32GG DK3750 2012 08 13 an0047_Rev1 01 www energymicro com ErFnNvI32 the world s most energy friendly microcontrollers 3 2 1 Multiple Buffering Multiple buffering is easily implemented with Direct Drive The hardware can read the frame buffer from any part of the available memory So to change the visible buffer software only needs to change the value in the TFT FRAMEBASE
8. mode X v lt 2 GE i i m gt Y T ZA VISIBLE d KE AREA a 9 E a a a a gt Vf P P uf ul B alg P P gl P ul LD DAS EASES SSS Y d ul ul ul lg gl al PP ELL ALPS af 45 DOTCLK DATA HSYNC DTEN 2012 08 13 an0047_Rev1 01 www energymicro com EFM32 the world s most energy friendly microcontrollers 4 Software Configuration This chapter will explain how to set up the software to drive a display in either 8080 mode or RGB mode with Direct Drive and perform drawing with emWin In both driving modes the emWin library is set up to draw to an external memory block Then the frame is transferred to the display Either by Direct Drive in RGB mode or by DMA in 8080 mode 4 1 emWin The emWin library contains 3 configuration files that need to be modified by the application The most important file is LCDConf c In this file the following has to be configured The emWin display driver In this application note we use a linear driver which will draw directly to a memory mapped video memory A color conversion This needs to correspond with the color format that the display is expecting Internally emWin always uses a 32 bit ARGB format The video memory start address This is required by the linear driver to know where to start drawing The display size The linear driver needs to know the width and height in pixels of the di
9. register This register contains the start address of the visible frame buffer To avoid tearing this should be done during the vertical porch interval before the start of a new frame Direct Drive can trigger an interrupt routine automatically during the VSYNC phase 3 2 2 Timing and Porch Intervals The RGB interface has 4 control timing signals in addition to the data lines The VSYNC Vertical Sync signal is asserted before each frame Similarly the HSYNC Horizontal Sync signal is asserted before each line The DOTCLK Dot Clock is a continuously toggling clock The pixels are always read on the active edge of this clock The last signal DTEN Data Enable is asserted whenever the controller should receive data DTEN together with VSYNC and HSYNC controls the porch intervals DIEN is deasserted for the entire duration of these intervals When updating the display there is some time required between lines and frames where no pixels are touched These intervals are called porch intervals The Horizontal Back Porch and Horizontal Front Porch is the time before and after each ine Similarly there are intervals specified before and after each frame called Vertical Back Porch and Vertical Front Porch An integrated display controller will control these intervals itself However if the display is run in RGB mode the MCU is responsible for controlling them Direct Drive controls these intervals automatically Figure 3 5 Timing diagram RGB
10. the part of the frame buffer which is currently being displayed should not be changed If the MCU is able to update the frame buffer faster than the controller is updating the display a frame buffer update should start in the time before a new display update i e the VSYNC period In this way the display controller will always read a pixel from the new frame buffer On the other hand if the display controller can update the display faster than the EFM32 can write the frame buffer the frame buffer write should start just after the display controller begins displaying the frame In this way the display controller is always reading old data and as long as the frame buffer update finishes within 2 display updates there will be no tearing See Figure 3 2 p 6 Figure 3 2 Frame update in 8080 mode m Z el DISPLAY CONTROLLER FAST MCU SLOW MCU FRAME POS R W START L TIME The display controller will normally have an output signal to help synchronize frame buffer updates Refer to the data sheet for the display controller on how to respond to this signal 3 2 RGB Mode With Direct Drive Another common way to drive displays is the RGB mode This mode should be used if the display does not have its own frame buffer In this mode the MCU is responsible for sending pixels to the display directly Figure 3 3 Direct Drive STEP 2 CORE PIXELS Working Sleeping CONTROL
11. 11 5 1 8080 Mode With DMA EE 11 5 2 RGB Mode With Direct Drive sss mee hehe he he he hehehe he hi he he hehe nere 11 5 3 Multiple Buffering With Direct Drive asana aaa aana eaaa nana m emen heme hem nemen sentimenti nennen 11 5 4 Window Manager EE 12 5 5 More emWin Examples esae teris REENEN ieie e itai aot e iude le eile apah panagara a aje gae ie rue i 12 6 F rther E ee 13 y cuienMieme P 14 y UEM E cT 14 Teen TASI SIOM Hee EE Ee 14 A Disclaimer and Trademarks concision alame araga Kaneka cece ee Da SURGA ara ajeng aia Ka hen menthe menie mentre tent eerie treten NG a eji KS 15 ERT lim 15 A2 Trademark Information dicic eneen tt bee neuve itta t M ae EE EE 15 B Contact Information ice iii ee irt t ec piso purae rin dero ae PUR RR Re Po x RR EO SE CPP UNE EFL REUNIR NET ess 16 B 1 Energy Micro Corporate Headquarters aana aaa eaaa eaaa eee meme hehehe he nenne here nennen 16 RE Global Contacts cenie imene 16 2012 08 13 an0047_Rev1 01 www energymicro com the world s most energy friendly microcontrollers List of Figures 2 1 TAPIS DUHENI EE 4 3 1 8080 mode connection diagram saa eea eee aana eaaa eaaa aana meme meme nennen men me nenne min men rennen rennen tee ren rennes 5 3 2 Frame update in 8080 mode 2 en ied dove Leste SEENEN ES DR AR E ERNENNUNG EN ege Ee 6 B20 INC CE Gara ajaa MH Ern 6 3 4 RGB mode with
12. 8 13 an0047_Rev1 01 www energymicro com 7 Revision History 7 1 Revision 1 01 2012 08 13 Updated file paths for display driver 7 2 Revision 1 00 2012 08 01 Initial revision 2012 08 13 an0047 Rev1 01 the world s most energy friendly microcontrollers www energymicro com M32 the world s most energy friendly microcontrollers A Disclaimer and Trademarks A 1 Disclaimer Energy Micro AS intends to provide customers with the latest accurate and in depth documentation of all peripherals and modules available for system and software implementers using or intending to use the Energy Micro products Characterization data available modules and peripherals memory sizes and memory addresses refer to each specific device and Typical parameters provided can and do vary in different applications Application examples described herein are for illustrative purposes only Energy Micro reserves the right to make changes without further notice and limitation to product information specifications and descriptions herein and does not give warranties as to the accuracy or completeness of the included information Energy Micro shall have no liability for the consequences of use of the information supplied herein This document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits The products must not be used within any Life Support System without the specific written c
13. EFM 32 the world s most energy friendly microcontrollers Interfacing Graphical Displays AN0047 Application Note Introduction This application note demonstrates how to drive a graphical display with the EFM32 microcontrollers Using the QVGA TFT LCD on the EFM32GG DK3750 Development Kit the examples include how to drive the display in 8080 mode and in RGB mode using the integrated Direct Drive feature It will be shown how to set up the SEGGER emWin Graphical Library that Energy Micro provides for free to all our customers This application note includes This PDF document Source files zip e Example C code e Multiple IDE projects O ENERGY micro www energymicro com E F INv132 the world s most energy friendly microcontrollers 1 Introduction 1 1 Graphical Displays Graphical displays gives more flexibility in creating a user interface compared to segmented or character displays However they can be more complex to operate and they do require more CPU time to update than their simpler counterparts 1 2 Display Interface Display controllers can have many different interfaces towards the MCU and these can be grouped into 4 main categories In a memory mapped configuration the display controller is connected to both address and data lines of the MCU and both registers and video memory can be written to directly This is the fastest type of configuration but it also requires the most pins A
14. anager has support for touch inputs cursors and skinnable widgets It also has several PC tools available including a bitmap converter and font converter These tools produce C files which can easily be compiled into your application For more information about emWin please consult the emWin user manual It can be found in the Simplicity Studio Directory under reptile emwin doc The PC tools can be found in reptile emwin exe 2012 08 13 an0047_Rev1 01 www energymicro com EFNJ32 the world s most energy friendly microcontrollers 2 Display Considerations This section will introduce some concepts challenges and requirements which are important to be aware of when designing an application with a graphical display Later it will be shown how to deal with these topics using the EFM32 2 1 Memory and Frame Buffer The frame buffer is the memory location holding the pixel data which are currently displayed The display controller needs to read this memory every update of the display On displays without an internal frame buffer the frame buffer has to be stored in RAM It is then the MCU s responsibility to update the display from this frame buffer If the display has a small enough resolution the frame buffer can be stored in internal RAM However this can be impossible for larger displays For example a QVGA 320x240 display with 16 bits color depth requires 320 240 2 1024 150 kB of RAM for one frame Take the case where
15. controller in 8080 mode It is possible that the display on the EFM32GG DK3750 will hang when switching between the two driving modes 8080 and RGB If this happens toggle the AEM button twice to get the display working again 5 1 8080 Mode With DMA This example uses emWin to draw a frame to PSRAM and then DMA to copy the entire frame to the display controller over the 8080 interface The PSRAM block is mapped to EBI bank 2 Referring to the EFM32 Giant Gecko user manual this corresponds to the memory range 0x88000000 Ox8bffffff emWin is configured to start drawing the frame at memory location 0x88000000 This is done in the LCD X Config function found in LCDConf c Also in this function the linear 16 bit driver and an RGB565 color conversion is selected After the frame is drawn to memory it has to be transferred to the display controller The display controller is mapped to EBI bank 1 As discussed in Section 4 2 p 9 the DMA is configured to read the frame and write it to 0x84000002 The timing and control signals of both PSRAM and the SSD2119 display controller is done in the file ebi conf c 5 2 RGB Mode With Direct Drive In this example the display is driven in a RGB mode with Direct Drive emWin is configured the same way as for the 8080 example and the Direct Drive feature is initialized and enabled In this mode there is no need for software to specify when to send the frame buffer to the display Direct Dr
16. he CPU causes too much bus traffic during frame updates Once per Dot Clock only allows one bus transfer to be interleaved per dot clock The last option is porch only With this option bus accesses are only allowed during porch intervals The porch parameters has to be within the limits given by the display controller However it can also be desirable to increase these intervals to give the CPU more bus access time 4 4 External Memory Frame Buffer If using external memory for the frame buffer the timing and control signals for this memory also has to be programmed into the EBI registers The software examples show how this is configured on the EFM32GG DK3750 Development Kit For a more general description please refer to the EBI Chapter in the Reference Manual for the device 2012 08 13 an0047_Rev1 01 www energymicro com EFINTJ32 the world s most energy friendly microcontrollers 5 Software Examples These examples show how to set up emWin and drive the QVGA TFT LCD on board the EFM32GG DK3750 Development Kit The display controller is connected with both an 8080 and an RGB interface to the EFM32 EBI Also connected to the EBI bus is a 4AMB PSRAM Note that these examples contain several application specific source files which are common for all the examples They can be found in the common folder This include the emWin configuration files and ebi conf c which configures the EBI timing parameters for PSRAM and the display
17. ive autonomously handles the display updates After the initialization the CPU never has to interact with Direct Drive again 5 3 Multiple Buffering With Direct Drive When only using one frame buffer with Direct Drive both tearing and flickering can occur If the application requires animations multiple buffering should be added This example contains a modified LCDConf c file that adds the required code to use multi buffering with emWin and Direct Drive The first task is to tel emWin how many buffers to use This is done with GUI MULTIBUF Config NUM BUFFERS The second modification is to implement the LCD X SHOWBUFFER callback This callback is received every time emWin is done drawing a frame i e when the buffers should be flipped It is possible to flip the buffers immediately in this routine However by doing so the flipping is not synced with the display 2012 08 13 an0047_Rev1 01 www energymicro com E E IM 32 the world s most energy friendly microcontrollers updates so tearing will still occur A better method is to use an interrupt routine that flips the buffers on the VSYNC signal To draw with multiple buffering surround the drawing calls with GUI_LMULTIBUF_Begin and GUI_MULTIBUF_End This tells emWin when a frame is finished drawing One more optimization is done with respect to multi buffering The default behavior of emWin is to copy the entire front buffer to the back buffer
18. memory usage For triple buffering 3 complete frames has to be stored in memory Using the QVGA example from before the requirement now becomes 450 kB of RAM for storing the frame buffers Figure 2 1 p 4 shows an example of triple buffering The current visible frame buffer is frame 0 This frame is currently being read by the display controller and shown on the display The CPU is finished drawing the entire frame 1 has flagged it as pending and is currently drawing to frame 2 On the next VSYNC signal the display controller will start reading from the memory address at frame 1 Figure 2 1 Triple buffering FRAME 2 EFM32 I WRITING DRAWING FRAME 1 PENDING FRAME 0 VISIBLE READING DISPLAY VIDEO MEMORY 2012 08 13 an0047_Rev1 01 www energymicro com the world s most energy friendly microcontrollers 3 Driving a Display With the EFM32 This chapter will show how to drive a display from a EFM32 microcontroller using the External Bus Interface EBI The EBI provides access to parallel interface devices including RAM FLASH and parallel displays Devices connected to the EBI are memory mapped to the EFM32 s memory space All timing and control signals are controlled by hardware Access to the devices from software are simple read and write instructions The EBI also has an integrated Direct Drive feature This feature is made specifically designed to dri
19. nd Pacific www energymicro com americas www energymicro com emea www energymicro com asia 2012 08 13 an0047_Rev1 01 www energymicro com the world s most energy friendly microcontrollers Table of Contents Te IMTROGUCTION ee dE EEN 2 tle Graphical Displays T EE 2 1 2 Display ln EE 2 E E lee TT EE 2 2 Display Considerations e 3 2 1 Memory and Frame B ffer sajane ae inre tret deese pagan an aaa ence nr tu RII EEN AER Fee eg 3 2 2 Frame Ici pe KAEN 3 2 3 BUS ACCESS ce Ecc 3 2 4 Flickering and Tearing Effects eaaa eaaa meme emen nemen ne ne ne ne ne ne ne ne nenne 3 2 5 Multiple B ffetitit ege retine ete pago tere itx Bg canine hig Aa a Rote el Ban E a KA ma a D ime Pee Ra o cae npud E Rub cong a aaa 4 3 Driving a Display With the EEMOL 5 3 1 Intel 38080 Mode 5 3 2 RGB Mode With Direct Drive 1 ie AE insti Lene RR E REI E Ea EEEE aga ag a RARE Sen 6 4 Software Configuration ssssssssssssssssses emm mee mene mee ne ne he ee ne ee ne ee ne eene ee ne ne ne enne nnns 9 LEE LEM 9 4 2 8080 Mode With DMA EE 9 E DNR 10 4 4 External Memory Frame Butter 10 5 Software Examples eaaa aana eaaa nana e aana aaa aana aana aaa eaaa nana na aaa aaa anana eceeceeseeaeeseeseeseeseeeeeseeeeeaeeeeeaeees
20. onsent of Energy Micro A Life Support System is any product or system intended to support or sustain life and or health which if it fails can be reasonably expected to result in significant personal injury or death Energy Micro products are generally not intended for military applications Energy Micro products shall under no circumstances be used in weapons of mass destruction including but not limited to nuclear biological or chemical weapons or missiles capable of delivering such weapons A 2 Trademark Information Energy Micro EFM32 EFR logo and combinations thereof and others are the registered trademarks or trademarks of Energy Micro AS ARM CORTEX THUMB are the registered trademarks of ARM Limited Other terms and product names may be trademarks of others 2012 08 13 an0047_Rev1 01 www energymicro com the world s most energy friendly microcontrollers B Contact Information B 1 Energy Micro Corporate Headquarters Postal Address Visitor Address Technical Support Energy Micro AS Energy Micro AS support energymicro com P O Box 4633 Nydalen Sandakerveien 118 Phone 47 40 10 03 01 N 0405 Oslo N 0484 Oslo NORWAY NORWAY www energymicro com Phone 47 23 00 98 00 Fax 47 23 00 98 01 B 2 Global Contacts Visit www energymicro com for information on global distributors and representatives or contact sales energymicro com for additional information Americas Europe Middle East and Africa Asia a
21. parallel interface configuration usually has a full data width but no address bus To send commands or addresses to the controller the display often has a C D pin Command Data to select if the current value on the input is a command or register address or data This pin can also be called D l or RS A serial interface is the slowest form but it requires very few pins An SPI configuration can use 3 or 4 pins and even DC bus with only 2 pins are possible Since all pixel data has to be sent over a serial line it takes many clock cycles to update the whole display This can make for cheap configurations but are normally not suitable for animations An RGB interface is a special kind of parallel interface This interface works for displays without a frame buffer The MCU is responsible for updating the display manually by providing both pixel data and timing signals This application note is discussing two types of interfaces A parallel interface known as the Intel 8080 and the RGB interface 1 3 Graphical Library To create a useful GUI it is helpful to have a graphical library A graphical library provides the software developer with functions to draw shapes text and images and takes care of drawing operations like alpha blending and anti aliasing Energy Micro provides the emWin Graphical Library from SEGGER through Simplicity Studio for free In addition to the standard drawing operations this library also provides its own window m
22. r the display and also controls the external memory if needed to feed the display with data The timing and polarity of the control signals needs to be configured when initializing Direct Drive Please refer to the Reference Manual for a complete description of these emlib contains helper functions to ease Direct Drive configuration The function EBI_TFTInit will both configure and start Direct Drive The only parameter it takes is an initialization structure which must be filled beforehand The software examples in this application note show how this is done Some of the most important parameters of Direct Drive are summarized here Drive Mode specifies whether Direct Drive should read from internal or external memory EBI Bank specifies which EBI bank to use for memory in case drive mode is set to external Address Offset the offset relative to EBI bank base address Data Width width of pixel data can be either byte or halfword lt Interleave controls interleaving of EBI bus Dotclock Period prescaling of the dot clock Porch Intervals controls how much Direct Drive will leave the bus idle for each frame The interleave flag specifies how interleaving of the EBI bus is performed when using Direct Drive It has three possible values Unlimited allows for interleaved bus access at any time This is the fastest option uses the most of the available bus time but can cause visible jitter on the display if t
23. splay The file GUI X c configures system specific timer and delay The supplied example should fit most applications In GUIConf c the emWin library itself is initialized emWin requires some memory for internal book keeping and this is allocated here The memory it needs depends on the features used and how many GUI objects are created In general a few kB should be enough Please refer to the emWin user manual for a more detailed discussion of these files 4 1 1 PC Tools emWin also ships with a number of PC tools These tools all generate C files that can be compiled into the application These tools can be found in the Simplicity Studio folder under reptile emwin exe The bitmap converter generates C files from normal image files BMP GIF and PNG are supported The font converter can generate fonts for use with emWin The input can be any normal windows font lt The GUI Builder is a WYSIWYG tool for creating windows menus etc The binary to C converter converts arbitrary binary files into C arrays The unicode to C converter converts text files in UTF 8 format into C string arrays 4 2 8080 Mode With DMA In the 8080 mode DMA is used to transfer the frame from RAM to the display controller The scatter gatherer mode is used to allow a full frame to be transferred in one DMA cycle In this mode multiple alternate descriptors are set up to transfer parts of the frame buffer sequentially The maximum element size for one
24. ve graphical displays in the RGB mode For more information about EBI consult the Reference Manual 3 1 Intel 8080 Mode A common interface standard is the Intel 8080 mode This mode should be used if the display has an integrated display controller and frame buffer The EBI write operations from the MCU update the frame buffer of the display controller The display controller handles all the display updates from this frame buffer An advantage of this mode is that the MCU only needs to perform EBI write operations whenever the frame changes In addition to the data lines the 8080 mode uses the following control signals RE read strobe WE write strobe CS chip select and D C data command The polarity and timing of these signals can all be controlled by EBI Refer to the datasheet of the display controller on how to set up these The D C signal can be thought of like a 1 bit address line and allows software to program registers in the display controller Figure 3 1 8080 mode connection diagram PIXEL DATA EBI_CSx EBI AD D C EBI A 0 FRAME SYNC Note that not all EFM32 devices with EBI has the Direct Drive feature Please consult the EBI chapter in the Reference Manual to see if a devices supports this feature 2012 08 13 an0047_Rev1 01 www energymicro com EFINT32 the world s most energy friendly microcontrollers 3 1 1 Avoiding Tearing To avoid tearing in the 8080 mode
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