Simple Real-Time Sonar with the DSP56824
Contents
1. Calculate distance to the target Results to host Communicat to hostthe polar coordinats of Display the Routine fargetidistance mm and angle dgr results in Display Rouire graphical manner J O Stepper Control Routine J Command a two step rotation ofthe motor STOP Figure 2 General Sonar Operations Flow Figure 2 emphasizes the most important routines developed for the sonar system as well as their relative position in time during the operation of the sonar One of the most important characteristics of the sonar general data flow evident in the illustration is the parallelism of routine execution between the host side and the DSP side Items denoted in Figure 2 as a and B are stable states of the data flow When the execution on the DSP reaches the state it waits asynchronously for an external event in order to go further that is the host computer signal is ready to receive results from the DSP After receiving the signal the DSP executes a series of routines ultimately reaching the distance calculation loop which corresponds to a 1 8 degree horizontal scan two 0 9 degree step rotations of the stepper motor from a total of 180 degrees the sonar angular detection range In the same manner when the execution on the host side reaches the P state the computer sends a wait for data command to the DSP and loops indefinitely until one of the following conditions occur the2. amp 0x01 Application gt ProcessMessages return inportb 0x3f8 20 Simple Real Time Sonar with the DSP56824 A MOTOROLA Graphical User Interface Implementation After the synchronization between host computer and DSP is established a set of detection results is automatically sent to PC The results are then processed by the graphical user interface on the host for display and at the same time the DSP starts a new detection iteration for the next angular step 1 8 degrees A new synchronization phase will begin after the host displays the current results and the DSP finishes its detection iteration 4 2 Graphical User Interface Implementation The sonar GUI was designed to run under Windows 9x NT platforms on a recommended graphical resolution of 800 x 600 pixels Users control the general sonar behavior start stop and exit using the corresponding buttons provided by the interface Sonar activity and detection results are displayed in real time using three modes 1 Graphical display window depicts the detected targets at relative coordinates corresponding to their real position to the sonar transducers This is the most intuitive mode similar to classical radar and sonar scopes 2 Numerical mode displays the exact polar coordinates of the currently displayed target in two separate boxes one for the target range in millimeters and one for the angular position in degrees 3 Prog
3. move loopa3 jsr decw bgt move move rts leftcount go_left 2 x0 rotate_right_x0 rightcount over 100 leftcount over 2 XO rotate_left_x0 leftcount over 100 rightcount m01 save_m save_r0 r0 3 m01 x0 Loopc2 rotate_left loopc2 loopa2 save_m m01 r0 save_r0 m01 save_m save_r0 r0 3 m01 x0 Loopc2 rotate_right loopc2 loopa3 save_m m01 r0 save_r0 Command the motor to rotate two steps 7 to the left until leftcount 7 reaches to zero then to the right in j the same manner Test if leftcount is zero If rightcount is zero 7 rotate 2 steps to the right 7 and decrement rightcount 7 If rightcount reaches zero 7 initialize leftcount to 100 If lettcount isn t zero 7 rotate 2 steps to the left 7 and decrement leftcount 7 If leftcount reaches zero 7 initialize rightcount to 100 Rotate the motor to the left with a 7 number of steps specified in X0 This routine calls rotate_left to 7 rotate the motor one step left Save the M01 register into memory Load RO with a value stored into Initialize M01 with the length of 7 stepper command circular buffer Rotate left with one step until 7 the value of loopc2 reaches zero Restore M01 and save RO into memory Rotates the motor to the right 7 The number of steps for rotating jj are s
4. DSP sends results through the serial link or the user stops the sonar operation from the graphical user interface Detailed descriptions of the routines depicted in Figure 2 are provided in Section 3 and in Section 4 of this application note 4 Simple Real Time Sonar with the DSP56824 A MOTOROLA Transducer Interface Circuits 2 2 Transducer Interface Circuits Two ultrasound transducers one for acoustic emission and the other for echo reception and the corresponding signal conditioning circuits represent the analogue component of the sonar We used a 400SR 400ST pair of capacitive transducers because of their good acoustic characteristics 40 kHz ultrasound transducers frequency tolerance of 1 kHz good directivity and small size To accommodate the small emitting transducer impedance and to increase the signal gain an operational amplifier based interface logic was implemented as presented in Figure 3 400 SR 400 ST 15 15 Figure 3 Emitter and Receiver Transducer Circuits This scheme obtains a theoretical voltage gain of 20 for the emitted signal Filtering capacitors were provided to eliminate the noise on the circuit power lines From the DSP Evaluation Module s GPIO Port the 40 kHz generated rectangular signal is amplified and filtered through the emitting transducer interface circuits resulting in a sine wave of the same frequency as the input of the transducer For the echo signal reception and condition
5. after page 0 Initialize BCR for zero wait states Configure PLL feedback divider 3 6864 MHz 19 70 0416 MHz Enable PLL using oscillator clock PLLE 1 PS1 1 VCS0 1 Neo Ne Ne Ne Ne Ne Ne Ne Ne Ne e Configure GPIO pins Enable GPIO interrupts Enable all level of interrupts The routine which programs SPI on port C to communicate with host computer is given below When the SPI is configured as a master the software selects one of the eight different bit rates for the clock The routine also configures the MAX3100 UART universal asynchronous receiver transmitter used as RS 232 interface 10 Simple Real Time Sonar with the DSP56824 O MOTOROLA Code Listing 5 Serial Int Serial_Program Emitted Wave Generation erface Configuration Routine bfset pc7 pcd max3100 CS high bfset pc7 pcddr make pc7 output bfset 0070 pcc enable spi 1 on port c 4 6 move 0111 spcrl configure spil control register divide by 32 70MHZ 32 2 1875MHZ idles 0 push pull drivers interrupts disables master mode cpl 0 and cph 0 spi disable bfset 0040 spcrl enable SPI1 configure max3100 move 00e4 y0 fifo off rm 1 move 0001 y1 115 2k length 8 no parity 1 stop bit disable ir mode bfclr pc7 pcd cs low move y0 al get data jsr Write transfer data to max3100 move yl al get data jsxr Write transfer data to max3100 bfset pc7 pc
6. areas self guided devices car parking systems etc A simple sonar system can also serve as a very versatile and intuitive support for teaching and experimenting with digital signal processing algorithms and their implementation on DSPs O MOTOROLA Conclusions 23 6 References 1 DSP56800 16 Bit DSP Family Manual order number DSP56800FM D 2 DSP56824 16 Bit DSP User s Manual order number DSP56824UM D 3 DSP56824 Evaluation Module Hardware Reference Manual order number DSP56824EVMUM D 4 Motorola DSP Assembler Reference Manual Motorola Inc 1996 5 3D Tracking Sonars with High Accuracy of Range Measurements for Autonomous Mobile Robot Navigation A M Sabatini EUSIPCO 96 European Signal Processing Conference Trieste Italy 1996 6 Wideband Inverse Filtering to Improve Active Sonar Detection in Background Reverberation P Delachartre et al EUSIPCO 96 European Signal Processing Conference Trieste Italy 1996 7 RADAR Signal Extraction Using Correlation F Lancon et al EUSIPCO 96 European Signal Processing Conference Trieste Italy 1996 24 Simple Real Time Sonar with the DSP56824 A MOTOROLA
7. parameter is the so called detection resolution the uncertainty of distance calculation For the proposed sonar implementation the detection resolution is given by V e Sound 3 148 mm Eqn 6 F sampling Again practical evaluations of this parameter issued higher results for the same reasons explained above Further improvements of the sonar system will start by reducing the noise in the system as much as possible Transducer interface circuits will be better designed the amplification schemes optimized especially on the receiver side with special care on maximizing the Signal to Noise Ratio SNR Optimization of the sonar specific algorithms implementation on the DSP is another potential performance enhancement of the system We intend to develop and test a sonar detection algorithm based on the cross correlation of digital signals For increasing sonar s detection range a more powerful ultrasound transducer pair can be used along with higher gain amplifier circuits as well as a CODEC with higher sampling rate and conversion resolution A straightforward application of the proposed sonar system is an autonomously self guided mini robot able to move from a predefined start point towards a destination avoiding possible obstacles encountered on its route Other possible applications include intelligent devices like autonomous vacuum cleaners object searchers operating in difficult environments gas poisoned or no visibility
8. program parameters and variables are defined in this section peripheral and core DSP registers used by the sonar program temporary values sonar functional parameters constants and so on O MOTOROLA Sonar Implementation on the DSP56824 7 Program de results a mv Code Listing 2 fines define ipr define ber define perl define pero define pba define pbddr define pbint define pcd define pcddr define pec define spcerl define spsrl define spdrl nd to Ffb FEO F 3 FEZ fec feb fea fef fee fed feo fed fed xxx MMMM KM KM KM MM x UW UI UI IH DMM HMM DH Fy Fh FH FH Fh Fm Fh Fh Fh FH FH FH Fh perform software loops define go x S0 define loopel xsS1 define loopc2 x 2 define save_r0 TESS define save_m x S4 define leftcount F255 define rightcount x S6 define angle XES define distance rx 987 Program equates SPIF equ 0080 dummy equ 0000 pc7 equ 0080 WRITEUP equ 0080 READ equ 0000 PLL_DIV equ 19 dim equ 2048 dim_mot_buf equ 4 no_detection equ 0 noise_level equ 6 av_points equ 20 no_wave equ 40 General Program Defines Interrupt priority Bus control regis PLL control PLL control Port B data Port data Port In Port da Port da Port spi 1 con spi 1 sta regis regis direc ta regis ta direc B B Cc G Cc F L r F E L A r T F r register ter re
9. step right rotation of the stepper motor the next sequence on the GPIO lines 14 15 needs to be 00 The motor command data structure implements a circular buffer which will be scanned upwards or downwards depending on the rotation type needed The command is shown in the Code Listing 3 Code Listing 3 Stepper Motor Command Data Structure org x 1000 this circular buffer retains the command words for the motor buffer m dim_mot_buf pas de 0000 de 8000 de c000 de 4000 endbuf Further on the DSP stack initialization along with the PLL GPIO and interrupts setup is made AA mororoLa Sonar Implementation on the DSP56824 9 org receive buffer buffer m_buf ds endbuf org jmp org jsr org Start move move move bfset x 2000 m dim dim p 0000 Start p 0014 Irga_ISR p 0100 40 sp 0000 bcr PLL_DIV 1 lt lt 5 pcer0 4208 pcrl Delay to meet the pll lock setup time move do nop nop delayl move do nop nop delay2 move move bfset bfclr move move move move move move move Slfff 1lc lc delayl Slff 1c lc delay2 SFO00 pbddr 8000 ipr 0100 sr 0200 sr dim m01 Hl n pas save_r0 100 x0 x0 leftcount 0 x0 x0 rightcount Code Listing 4 Main Program Initialization Sequence start of program Port B GPIO Interrupt Starting location of this program Ne Ne Ne e Set stack pointer to first location
10. A new Start Conversion command will be issued after the read store operation completed successfully onto the interrupt handler subroutine Although the converter is capable of 12 bits resolution the data read routines use only the 9 most significant bits of the conversion result to perform an initial noise filtering of the received signal Code Listing 7 Read 2048 Echo Signal Samples Read_ADC move 50101 pbint Configure GPIO pin 0 to generate 7 interrupt on falling edge detection move m_buf RO move dim lc do lc read_sample jsr reads nop nop read_sample nop move 50000 pbint GPIO pins masked to prevent other 7 interrupts rts reads bfclr S1000 pbd Reset GPIO pin 12 nop Use two NOPs to obtain nop 7 the required shape bfset 1000 pbd move F0 go read1 Test the go variable to be altered 7 by the interrupt handler bftsth 1 go Jog read1 rts Irga_ISR Interrupt handler routine read a 7 conversion result from ADS and movep pba x0 j store the 9 MSB into the buffer ror x0 ror x0 ror x0 bfclr SFEOO x0 move x0 x RO move 255 g0 fti 3 4 Target Polar Coordinates Calculation At this point the sonar program on the DSP has a received data buffer ready for the specialized algorithms of extracting the target s polar coordinates First the digital signal stored in the buffer is low pass filtered to eliminate the noise as much as possible The Moving_Average routine de
11. Freescale Semiconductor Simple Real time Sonar with the DSP56824 Application Note by Mihai V Micea Lucian Muntean and Daniel Brosteanu AN2086 D Rev 0 06 2001 LO lt 7 freescale semiconductor How to Reach Us Home Page www freescale com E mail support freescale com USA Europe or Locations Not Listed Freescale Semiconductor Technical Information Center CH370 1300 N Alma School Road Chandler Arizona 85224 1 800 521 6274 or 1 480 768 2130 support freescale com Europe Middle East and Africa Freescale Halbleiter Deutschland GmbH Technical Information Center Schatzbogen 7 81829 Muenchen Germany 44 1296 380 456 English 46 8 52200080 English 49 89 92103 559 German 33 1 69 35 48 48 French support freescale com Japan Freescale Semiconductor Japan Ltd Headquarters ARCO Tower 15F 1 8 1 Shimo Meguro Meguro ku Tokyo 153 0064 Japan 0120 191014 or 81 3 5437 9125 support japan freescale com Asia Pacific Freescale Semiconductor Hong Kong Ltd Technical Information Center 2 Dai King Street Tai Po Industrial Estate Tai Po N T Hong Kong 800 2666 8080 support asia freescale com For Literature Requests Only Freescale Semiconductor Literature Distribution Center P O Box 5405 Denver Colorado 80217 1 800 441 2447 or 303 675 2140 Fax 303 675 2150 LDCForFreescaleSemiconductor hibbertgroup com Information in this document is provided solely to enable
12. OLA Introduction 1 t i E 1 ue propagation qn A ae m where V 340 is the propagation speed of acoustic waves in air and t is the total propagation delay of acoustic waves propagation s Transducers are used to receive acoustic energy When they are designed to receive equally in all directions they are called omni directional Transducers can be constructed with minimal directionality in which case they have a range of angles known as beamwidth from which to receive energy While receiving the narrow beamwidth allows the transducer to reject interfering noise because the ambient noise comes from all directions This is represented mathematically by a logarithmic term called the directivity index DI The criterion for detection requires that the amount of power collected by the receiver to exceed the noise level by a certain threshold The ratio of signal to noise in logarithmic form is the SNR The minimum SNR for detection is called the detection threshold DT Therefore detection generally occurs meaning more than 50 of the time whenever SNR gt DT The transmission loss noted here as TL represents the signal loss from source to receiver The transmission loss term includes all the effects of the energy spreading out attenuation and other various effects As a result the SNR at the sonar receiver can be written explicitly for a passive system which has a one way transmission as shown in Equation 2 SN
13. Roassive SL DI TL NL Eqn 2 where SL is the source level of emitted acoustic energy DI directivity index of the receiver TL transmission loss NL noise level For an active system there is an additional term called target strength TS which describes the reflection of energy from the target The target strength acts as a source level after reflection and therefore includes any directional effects of reflection The target strength is a function of the target size surface material shape and orientation in the same way that radar cross section varies Equation 3 also shows that there is a two way transmission loss for the active system SNRactive SL 2TL TS NL DI Eqn 3 Although these terms look similar in active and passive systems the values for each term will generally be quite different 2 Simple Real Time Sonar with the DSP56824 A MOTOROLA General System Architecture 2 Proposed Sonar System Description This section introduces the proposed sonar implementation using the DSP56824 processor Also presented is a general block diagram of the system the hardware and functional description of its components and the specialized DSP algorithms 2 1 General System Architecture The application presented uses the DSP65824 to implementation an active sonar system Figure illus trates the general system architecture of our example Emitted wave Emitter receiver platform Target Received wa
14. SPI1 bfset Fpc7 pcd cs high move al b0 Save lower byte of status in b0 bftsth S0080 b1 Check Transmit empty bit R bee Again2 If R 0 then rx have not a new 7 Character rts 3 6 Transducer Platform Rotation The final procedure of the sonar main program specifies the rotation of the transducer platform with a 1 8 degree step to the left or to the right In general the sonar sensors platform is designed to perform consecutive 180 degrees rotations to the left and to the right This is implemented with software by using two general parameters rightcount and leftcount At startup leftcount is set to 100 while in rightcount we have 0 As a result the transducer platform will begin rotating toward the left with a 1 8 degree step For each step performed the corresponding variable in our case leftcount is decremented When leftcount reaches the 0 value the sonar rotating platform finished its complete 180 degrees left turn and rightcount is set to 100 A consecutive 180 degrees right turn is then initiated O MOTOROLA Sonar Implementation on the DSP56824 17 Code Listing 13 Transducer Platform Rotation Command Routines rotate_motor tstw jgt move jsr decw jgt move jmp go_left move jsr decw jgt move over rts rotate_left_x0 move move memory move move loopa2 jsr decw bgt move move rts rotate_right_x0 move move move
15. a situation where personal injury or death may occur Should Buyer purchase or use Freescale Semiconductor products for any such unintended or unauthorized application Buyer shall indemnify and hold Freescale Semiconductor and its officers employees subsidiaries affiliates and distributors harmless against all claims costs damages and expenses and reasonable attorney fees arising out of directly or indirectly any claim of personal injury or death associated with such unintended or unauthorized use even if such claim alleges that Freescale Semiconductor was negligent regarding the design or manufacture of the part Abstract and Contents The focus of this paper is on the techniques of analysis and implementation of a simple real time SONAR system with a DSP56824 based board connected to a host computer SONAR system s general architecture and its principles of functioning are further presented Specific digital signal processing algorithms developed for the ultrasound frequencies are described in detail along with their implementation using the DSP56824 processor Finally a particular application developed with the proposed SONAR system is presented as a case study Some prospects and future work related to this subject are also mentioned as conclusion 1 Introd ction cecco oietens ease e E R bed nee eee nde E RA A E 1 1 1 General Description of a Sonar System 2 0 2 eee tenes 1 2 Proposed Sonar System Description
16. al program parameters rightcount and leftcount to calculate in degrees the actual angular position of the transducer platform The two rotation parameters rightcount and leftcount are altered by the stepper motor control routine For example if the transducer platform is currently turning leftward leftcount contains the number of rotation steps to be done until the complete rotation to the left will be performed totalling 180 degrees while rightcount variable is forced to 0 value This stepper motor routine will be described Section 3 6 The Calc_Position routine returns the calculated angle in degrees to the Y1 register Code Listing 10 Angle Coordinate Calculation Procedure Calc_Position move leftcount x0 cmp 0 x0 jgt _multiply move 100 x0 sub rightcount x0 _multiply move 9 y0 Calculate the angle in degrees mpy x0 y0 a 7 multiplying with 9 and dividing with 5 asr a 7 9 5 1 8 1 8 degrees represent the angl move 5 x0 7 of 2 motor steps jsr divide move yl angle Store the result into angle rts 14 Simple Real Time Sonar with the DSP56824 W MOTOROLA Transmission of Results to the Host 3 5 Transmission of Results to the Host A complete set of target coordinates is now available and stored into the distance and angle variables on the DSP The next step is to transmit these results to the host computer to be used for the real tim
17. ance calculation The implementation of data communication routines between DSP and the host computer are also presented Section 4 Sonar Implementation on the Host describes the sonar implementation on the host side the data link routines with the DSP and the graphical user interface developed under the Windows platform Finally Section 5 Conclusions presents a synthesis of the work along with practical results performance estimations of the sonar system and investigates additional applications for simple sonar systems 1 1 General Description of a Sonar System The basic sonar system estimates the distance to a target by calculating the overall propagation time of a specially selected audio or ultrasound wave between the sonar and target In an active sonar system the wave propagates from the transmitter to the target and back to the receiver analogous to pulse echo radar and passive sonar systems in which the target is the source of the energy that propagates to the receiver In an active sonar system the source of the acoustic wave is part of the sonar system The electrical energy from the transmitter must be converted into acoustic energy by a transducer In a passive sonar system the source is the target itself Knowing the propagation speed of the acoustic waves in the particular environment where the sonar operates say in air the estimated target distance from the sonar is determined using Equation 1 O MOTOR
18. ation received signal filtering detection of the emitted pattern in the received data buffer and target distance calculation as well as the data communication routines for both the host side and the transducer interface the analog to digital converter and the stepper motor control routines The host computer provides the graphical user interface of the sonar The user starts and stops the sonar operation and the GUI displays the detected targets in a graphical intuitive manner simulating the real life radar and sonar scopes AA MOTOROLA Proposed Sonar System Description 3 When activated the proposed sonar system performs the steps illustrated in the general data flow shown in Figure 2 Host PC Side DSP Side START START SPI Port initialization serial interface Interrupts configuration PC standard ke hittaization Routine GPIO Port B configuration initialization g3 40 periods ofa rectangular shape signal at 40k Hz Waitfor Dab z send he sample values to transducer interface through GPIO port for results H Configure ADC for inputsignal sampling and Echo Receiving convertion at 108 kSps Samples Second Routine Read 2048 samples from ADC intoreceived dat buffer Digital Filer Routine Y Digital Low pass Filter 20 c ce ficient Moving Average Filter Calculate maximum value of cata in buffer Distance Calculation Treshold he resultto avoid display in Routine abserce ofa target
19. ation of waves between a target and the detector Sonar however differs fundamentally from radar and electro optics because the energy is transferred by acoustic waves Digital signal processing techniques increase the versatility of modern sonar systems resulting in a wider range of detection better precision data storage and post processing capabilities as compared to previous analog sonar systems Digital filtering algorithms can be applied to the received data thus improving the target detection capabilities in noisy environments Therefore using digital signal processors DSPs to enhance sonar performance is advantageous This application note presents a simple real time sonar implementation using the DSP65824 Section 1 1 General Description of a Sonar System explains a typic sonar system along with its principles of operation Section 2 Proposed Sonar System Description introduces the suggested sonar implementation using the DSP56824 Also presented is a general block diagram of the system the hardware and functional description of its components and the specialized DSP algorithms The focus of Section 3 Sonar Implementation on the DSP56824 provides details of the sonar specific algorithms on the DSP56824 processor This section also discusses the routines developed for generating the emitted wave samples echo signal reception and pre processing noise filtering emitted pattern recognition and target dist
20. d cs high configuration max3100 done res 3 2 Sonar uses a rectangular signal as source wave The required signal parameters are 40 kHz frequency to be compatible with the emitting transducer and 40 periods to ensure enough signal energy for range maximization Emitted Wave Generation Routine Gen_Signal uses GPIO pin 13 for transmitting the source signal to the transducer interface circuits The variable no_wave stores the total number of signal periods that is 40 periods Code Listing 6 Source Signal Generation Routine Gen_Signal do no_wave semnal bfclr 52000 pbd reset the bit 13 pin 13 low move 430 a0 delay to obtain the 40kHz wave rep a0 nop bfset 2000 pbd set the bit 13 pin 13 high move 430 a0 rep a0 nop nop semnal nop rts 3 3 Echo Signal Sampling and Storing After the emitted wave is generated and sent to the corresponding transducer the sonar enters the echo signal reception and sampling procedure Here the ADS is commanded for 2048 consecutive conversion cycles by asserting the GPIO pin 12 the Start Conversion line within the reads routine as shown in Code Listing 7 O MOTOROLA Sonar Implementation on the DSP56824 11 A valid conversion result is acknowledged by the ADS through its Status line connected to the DSP s GPIO pin 0 When it is activated an interrupt occurs and a 9 bit data is read from the converter and stored into the buffer
21. e Next the DSP commands the analog to digital converter to fill a 2048 word buffer with samples from the received echo signal This is accomplished by the Read_ADC procedure Actual calculation of the distance to a target is performed on the data buffer written during the Read_ADC step First the received signal is filtered using a Moving Average type of low pass digital filter Next we look for the maximum value on the buffer Its relative position will then be represented in millimeters and stored into the distance variable The Calc_Position results in the angular coordinate of the target the angle parameter At this point the DSP has a complete set of results to be sent to the host computer through the serial data link It starts the synchronization procedure Gen_Sincro which waits for the host to acknowledge it is ready to receive the results and at the same time ensures a correct data transaction on the serial interface After the correct synchronization step the two target coordinates distance and angle are sent to the host computer for display Finally the stepper motor is commanded for a 1 8 degree rotation of the transducer platform and the main sonar program loops back to the next target detection iteration Extensive implementation details of all the above routines will be given in the following sub sections 3 1 Program Definition and Initialization Phase All the general
22. e if a new character can be j sent r A r 4 F r cs low Upper byte of write sequence Write to max3100 Data Write to max3100 cs high Dummy read read SPSR1 to clear SPIF 7 so SPI can write Output data is in al If SPIF 1 then data is transferred If SPIF 0 then rx is not finished cs low d Command to Read from max3100 Send command to SPI1 Save upper byte of status in bl Command to Read from max3100 Send command to SPI1 7 cs high Save lower byte of status in b0 Check Transmit empty bit If T 0 then tx is not finished Dummy read Output data to spil If SPIF 1 then data is transferred If SPIF 0 then rx is not finished Input data is in al Read a byte from host computer Before this it is necessary to 7 check if a byte is available and then 7 to send a command to max3100 Check to see if there is a new character to read r f O MOTOROLA Transducer Platform Rotation bfclr pc7 pcd cs low move READ al Command to Read from max3100 jsr Read Send command to SPI1 move READ al Command to Read from max3100 jsr Read Send command to SPI1 bfset pc7 pcd cs high rts Check_Read Again2 bfclr Hpc7 pcd cs low move READ al Command to Read from max3100 jsr Read Send command to SPI1 move al bl Save upper byte of status in bl move READ al Command to Read from max3100 jsr Read Send command to
23. e sonar display procedures The DSP initiates the synchronization procedure which waits for the host to acknowledge that it is ready to receive the results and at the same time ensures a correct data transaction on the serial interface The synchronization routine has twin roles to ensure that the correct data transfers on the serial link and more importantly to synchronize the data flow between the host and the DSP and P execution states depicted in Figure 2 on page 4 Code Listing 11 presents the synchronization routine Gen_Sincro Basically it waits for the host computer to reach its own synchronization phase doing a blocking read on the serial port SPD until the host sends a data byte The routine acknowledges with a 0X55 response byte and waits for the next host serial write This time the DSP responds with a different value OX AA Both steps are repeated five times The host computer performs serial communication error checking using the two values sent during the synchronization procedure Code Listing 11 Synchronization Procedure on the DSP Gen_Sincro do 5 sincro Define the five times iteration jsr Read_Char Read a byte from host computer move 555 x0 jsr SendChar_x0 Write 55 to host jsr Read_Char Read a byte from host move SAA x0 jsr SendChar_x0 Write SAA to host nop nop sincro nop rts After the synchronization phase is completed successfully the transmission
24. gister 1 ter 0 ter tion register terrupt register ter tion register control register trol register tus register spi 1 data register Variables used in program to retain temporary values port G pit 7 read command P receive buffer dim SPIO Interrupt complete flag dummy value to write write upper instruction byte LL Feedback Multiplier nsion the dimension buffer words no object is aximum noise m the number of Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne of command motor constant used to indicate that detected level coefficients for moving average fil 7 Eh 7 emitted signal lter number of periods for the In the next sequence of code we define a circular buffer for the stepper motor command In order to perform a 0 9 degrees one step rotation the stepper we used needs a two bit input code explained in Table 1 Table 1 Stepper Motor Command Sequence GPIO Pin Numbers 14 15 One Step Left Rotation One Step Right Rotation Simple Real Time Sonar with the DSP56824 gt MOTOROLA Program Definition and Initialization Phase Depending on the current configuration of the two command lines GPIO Pin 14 and 15 the next step rotation will be commanded by following the corresponding direction shown in Table 1 see also Figure 5 on page 6 For example if the current command lines configuration is 01 and we need to perform a one
25. ing we implemented a similar signal amplification this time with a theoretical voltage gain of 40 and impedance regulation circuit Consecutively the resulted output signal needs to be converted from analog to digital in order to be sent to the DSP for further processing Because of the relatively high frequency of the ultrasound signal 40 kHz the DSP56824EVM on board audio codec MC 145483 13 bit linear single channel is not appropriate for our sonar application Instead we developed a Burr Brown sampling ADS774 based analog to digital scheme able to work at 108 kSps kilo Samples per second The ADS774 is controlled by the DSP through two dedicated GPIO lines one for starting the conversion cycles on the ADS and the other for pooling the conversion status to detect an end of conversion that acknowledges available data from ADS shown in Figure 4 From the total of 12 bits output of the converter the DSP uses the 9 most significant bits as a supplementary noise reduction measure AA MOTOROLA Proposed Sonar System Description 5 _ ADSII4 GND Figure 4 Analog Digital Converter Circuit 2 3 Stepper Motor Control Both transducers assembled on a small platform are driven by the stepper motor see Figure 1 on page 3 The motor is controlled by the DSP through 2 dedicated GPIO lines interfaced by the control circuit illustrated in Figure 5 MOTOR STEPPER GND Wee 15v 7404 Figure 5 Stepper Motor Con
26. n range is a parameter of sound velocity application independent variable and of the data buffer length and echo sampling rate the two application dependent variables L Loutt Vsound Eqn 4 max 2 sampling D where Lhuff 2048 words is the received data buffer length used Fsampling 108 kHZ represents the sampling frequency used for echo receiving Vsound 340 m sec is the velocity of acoustic waves in air at normal temperature As a result the theoretical maximum detection range of the implemented sonar is D max 3223 7 mm Eqn 5 The value in Equation 5 resulting from Equation 4 is a theoretical one because we ignored the energy loss of acoustic waves during their propagation in the air from source to the target and backwards and also because of the reflection loss on the target These parameters are dependent on local air pressure and temperature as well as the size surface and shape of a particular target see discussion in Section 1 1 The acoustic noise present in the environment as well as the inducted electrical noise at the reception side were also ignored Our practical results demonstrate the importance of the parameters ignored in the equations above At the maximum theoretical limit of the distance about 3 2 m and using a large surface 1000 x 500 mm rectangle the system was able to detect the target but the results were highly unstable at the limit of error threshold The second main sonar
27. nar In the following paragraphs we get into further implementation details for the two components mentioned above 4 1 Serial Data Link Implementation Command and data communication with the DSP is implemented on the host side through the PC standard serial interface RS232 configured at its maximum bit rate 115200 bps bits per second with 8 data bits one stop bit and no parity 8N1 The selected bit rate is high enough for the proper sonar functioning in real time because the necessary data throughput between the host computer and DSP has medium values When the sonar program is started on the host computer it preforms the serial port initialization The corresponding routine initSerialInterface is shown in Code Listing 14 O MOTOROLA Sonar Implementation on the Host 19 Code Listing 14 Host Serial Port Initialization Routine void initSerialInterface void outporthb 0x3fb 0x80 set the serial speed to 115200 bps outportb 0x3f8 1 outportb 0x3 9 0 outporthb 0x3fb 3 set the serial mode to 8N1 Now the host computer is ready to receive consecutive sets of detection results from the DSP for further display To get a single set of results that is consisting of a pair of two byte words one for the calculated distance of a target in millimeters and one for the current orientation angle of the sonar transducer platform in degrees the main program activates the serial transaction sy
28. nchronization routine sincro The synchronization routines both on the host and on the DSP have twin roles to ensure correct data transfers on the serial link and more important to synchronize the data flow between the host and the DSP and P execution states depicted in Figure 2 on page 4 Code Listing 15 Synchronization Routine on the Host Computer int sincro int k for k 0 k lt 10 k Application gt ProcessMessages prevent complete lock of other Windows applications writeByte Oxff send a synchronization byte and check correct sequence when receiving from DSP if readByte 0x55 k 2 0x55 return 0 return 1 Code Listing 15 presents the synchronization routine sincro on the host Basically it sends ten consecutive synchronization data bytes to the DSP and waits for a response byte from peer after each one sent The routine also checks the received bytes to correspond to the predefined sequence of 0x55 OxAA Serial communication is completed by the byte read and write pair of routines called also from the synchronization procedure Code Listing 16 describes the two routines Code Listing 16 Byte Read and Write Pair of Routines void writeByte unsigned char b while inportb 0x3fd amp 0x20 Application gt ProcessMessages outportb 0x3 8 b unsigned char readByte while inportb 0x3fd
29. o store it into the distance variable Furthermore to avoid considering fake targets when the sonar receives only noise the resulted maximum value is compared to a predefined threshold the noise_level variable If it is below the threshold the result is considered noise and ignored variable distance is written with the no_detection predefined value O MOTOROLA Sonar Implementation on the DSP56824 13 Code Listing 9 Maximum Value and Its Buffer Index Calculation Seek_MAX move 0 yO move m_buf RO move 2020 1lc do lc _search Search entire buffer for the maximum move x RO x0 7 value of a sample and store cmp x0 y0 7 it along with its index position jge _is_ge move x0 y0 move m_buf x0 move RO yl sub x0 yl _is_ge nop nop nop _search nop move noise_level x0 Compare the obtained value with cmp x0 y0 7 the noise_level gt _is_greater If the maximum level found is lower 7 then we consider no object detected move no_detection distance rts _is_greater move 170 x0 Calculate the distance in mpy x0 yl a 7 millimeters by multiplying with asr a 7 170 sound speed 2 and dividing 7 with 108 codec samplingrate move 108 x0 jsr divide move yl distance Store the result in distance rts The second target polar coordinates parameter to be calculated is the angle The Calc_Position routine described in Code Listing 10 uses two gener
30. of the actual sonar detection results follows Code Listing 12 describes the basic serial data communication routines used by the DSP O MOTOROLA Sonar Implementation on the DSP56824 15 Out_yl Code Listing 12 Serial Data Communication Routines jsr move jsr JS move lsrr jsr rts SendChar_x0 Write Txbyte jsr bfclr move JSE move jsr bfset rts move move bftsth bec rts Check_Write Againl Read Rxbyte biel move jsr move move jsr bfset move bftsth bec rts move move bftsth bec move res Read_Char 16 jsr elr Read_Char yl1 x0 SendChar_x0 Read_Char 8 x0 yl x0 x0 SendChar_x0 Check_Write pc7 pcd WRITEUP al Write x0 al Write pc7 pcd spsrl1 a0 al spdrl SPIF spsrl Txbyte pc7 pcd FREAD al Read al bl FREAD al Read pc7 pcd al b0 S0040 b1 Againl spsrl1 a0 al spdrl SPIF spsrl Rxbyte spdrl1 al Check_Read a Simple Real Time Sonar with the DSP56824 Send a word 2 bytes from DSP to host 7 computer using the SendChar_x0 7 routine to send a byte Wait a byte from host Send the least significant byte Wait a byte from host Right shift the word with 8 bits Send the most significant byte A routine used to send the LSB of XO 7 to host computer First check to see if MAX3100 will 7 accept a new byte and if yes send 2 7 bytes command data byte Check to se
31. ress bar display presents the distance to the currently displayed target in an intuitive manner by showing a scale of the sonar minimum and maximum detection range Figure 6 presents a screen capture of the sonar graphical user interface during a real time example O MOTOROLA Sonar Implementation on the Host 21 fi SONAR SOund Navigation And Ranging Figure 6 Sonar Graphical User Interface 5 Conclusions A simple real time sonar implementation with the DSP56824 is presented in this paper We described the general characteristics of a sonar system emphasizing the advantages of introducing a specialized DSP as the core of the system Additionally we provided details of the general architecture of the proposed sonar system and the hardware components The implementation of the sonar specific digital signal processing algorithms on the DSP56824 is extensively explained in the Section 3 along with the serial communication routines developed for data transactions with a host computer A classical sonar scope like graphical user interface was also designed on the PC for visualizing the results as intuitively as possible The proposed sonar system was tested using targets of different sizes shapes and surfaces Theoretical performance characteristics are based on two main parameters 22 Simple Real Time Sonar with the DSP56824 MA MOTOROLA Graphical User Interface Implementation First the maximum sonar detectio
32. scribed in the Code Listing 8 implements a Moving Average type of low pass digital filter with 20 coefficients 12 Simple Real Time Sonar with the DSP56824 A MOTOROLA Target Polar Coordinates Calculation Code Listing 8 Moving Average Digital Filter Implementation Moving_Average move move move do move move move m2 move sub abs move move add dec jne move JS move nop nop ml rts divide asl bielr rep div move add asr rts m_buf RO 255 y0 dim lc remi RO R1 0 a av_points x0 x R1 y0 b b b1 b0 0 b1 b a x0 m2 av_points x0 divide yl x RO a 0001 sr 16 x0 a a0 yl x0 a a Scan entire buffer Store the sum of av_points number 7 of samples into A ae i Values in the buffer read from the ADS converter are Bipolar Offset Binary coded with 9 bits As result we need to subtract the 255 value to comply the internal integer coding scheme Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Divide the sum with the number of points to obtain the average This value is stored back in the current position Divide A with X0 and return the 7 Quotient in Y1 and the remainder 7 in A using a repetitive division method The filtered data buffered is then processed to find the maximum value and its index in the buffer The sonar program will interpret this information to extract the target distance in millimeters and t
33. system and software implementers to use Freescale Semiconductor products There are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits or integrated circuits based on the information in this document Freescale Semiconductor reserves the right to make changes without further notice to any products herein Freescale Semiconductor makes no warranty representation or guarantee regarding the suitability of its products for any particular purpose nor does Freescale Semiconductor assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability including without limitation consequential or incidental damages Typical parameters which may be provided in Freescale Semiconductor data sheets and or specifications can and do vary in different applications and actual performance may vary over time All operating parameters including Typicals must be validated for each customer application by customer s technical experts Freescale Semiconductor does not convey any license under its patent rights nor the rights of others Freescale Semiconductor products are not designed intended or authorized for use as components in systems intended for surgical implant into the body or other applications intended to support or sustain life or for any other application in which the failure of the Freescale Semiconductor product could create
34. tored in X0 The next two routines rotate the motor one step left right using 2 GPIO pins rotate_left movep andc other ones move decrement RO or movep 18 phd y0 S3fff y0 x r0 x0 y0 x0 x0 pbd Simple Real Time Sonar with the DSP56824 Read a command word from the circular buffer and send it to GPIO Mask needed bits to preserve the Read a motor command word and Set reset bits 14 and 15 Output the result to GPIO O MOTOROLA Serial Data Link Implementation jsr delay Wait to ensure the correct motor 7 functioning rts rotate_right movep pbd yO andc 3fff y0 move x r0 x0 Read a motor command word and decrement RO or y0 x0 movep x0 pba jsxr delay rts delay This routine assures the proper motor setup 7 time It is used after sending the command 7 two bits to the motor driver move 350 Lloopcl Initialize a counter loopal move 250 x0 rep x0 nop decw loopcl Use a software counter bgt loopal rts After executing the rotation procedures the main sonar program loops back to generate another source signal to the transducer the beginning of another target detection sequence 4 Sonar Implementation on the Host As mentioned in the Section 2 the host computer performs two basic tasks e establishes a serial data link with the DSP for command and result transactions e provides an intuitive and interactive graphical user interface for the so
35. trol Circuit The stepper motor rotates the transducers platform with a total angle of 180 degrees left and right with a two step resolution one step corresponds to 0 9 degrees More details on commanding the stepper are provided in Section 3 6 Simple Real Time Sonar with the DSP56824 AA MOTOROLA Program Definition and Initialization Phase 3 Sonar Implementation on the DSP56824 As shown in previous sections all the sonar specific algorithms are implemented on the DSP56824 The main program on the DSP follows the general steps presented in Figure 2 on page 4 Code Listing 1 presents the main program sequence of sonar implementation First the general data structures used by the main program and the subsequent routines are defined and the DSP initialization is made In the Section 3 1 we describe this initial phase of the program The main program incorporates into an infinite loop all the routines developed for the target detection distance calculation and communicates the results to the host Code Listing 1 Sonar main program on DSP Defines_and_Init here are the general data structures defines and the Sonar initialization main jsxr Gen_Signal jsr Read_ADC JSE Moving_Average jsr Seek_MAX jsr Calc_Position jsr Gen_Sincro move angle yl jsr Out_yl move distance yl jsr Out_yl jsr rotate_motor jmp main Generation of the emitted signal is the first step performed by the sonar program the Gen_Signal routin
36. ununun naaa 3 2 1 General System Archit ct re 2s 424509 2a0s ca ee kaiaa OEE sees E eer eee rote Gee 3 2 2 Transducer Interface Circuits 2 yes esuddes cable toys eedaeee cesueeoueyeereewes 5 2 3 Stepper Motor ContOleesrscssncerere treer et nE EIERNE E ORERE ERNER NTE 6 3 Sonar Implementation on the DSP56824 00 00 7 3 1 Definition and Initialization Phase 0 cece eee ee eee eee 7 32 Emitted Wave Generation Ganndaee Seek eee ee Se ner 11 3 3 Echo Signal Sampling and Storing 1 20 0 0 eee eee ene ee 11 3 4 Target Polar Coordinates Calculation 0 0 c eee cee eee 12 3 5 Transmission of Results to the Host 0 0 cece eee een eee 15 3 6 Transducer Platform Rotation 0 cece cece eee ene 17 4 Sonar Implementation on the Host 0 0 0 cee cece 19 4 1 Serial Data Link Implementation 2 2264 d44eee do0g eres asad eeendoudshesudes 19 4 2 Graphical User Interface Implementation 0 0 e eee eee eee 21 5 GONCIUSIONS eee pe a a a E E E a G 22 6 References uuuuusuuersuurreurrrerrrunerrrerrrrrrrerrrrrernne 24 M MoTOROLA Abstract and Contents i Simple Real Time Sonar with the DSP56824 A MOTOROLA 1 Introduction SONAR SOund NAvigation and Ranging systems like RADAR and electro optical systems have a large field of applications in robotics navigation and target detection The common principle of functioning is based on the propag
37. ve Step motor DSP system Host computer Figure 1 Sonar System Architecture The primary feature of this active sonar system is that both the acoustic wave source and the receptor are assembled together on a rotating platform The two transducers were selected as a pair of ultrasonic emitter and receiver with similar electro acoustic properties They define the sonar working frequency for the acoustic signals as fggnar 40 KHZ The emitter receiver platform is driven by a stepper motor controlled from the DSP board The electronic amplifier and driver circuits for the ultrasound transducers as well as the analog to digital conversion logic for properly receiving of the incoming echo signal are additional features of this system They can be assembled on a separate circuit board or on the rotating platform in close proximity to the transducers The first option is preferred because it reduces the total weight of the platform thus requiring a stepper motor with relatively low parameters for example size power consumption and weight We used the DSP56824 based Evaluation Module EVM as the core unit of the sonar system It is directly connected to the transducer interface logic through Port B configured as the General Purpose I O port GPIO It is also connected to the host computer using the standard PC serial interface The DSP performs all the sonar specific data processing operations for example emitted wave samples gener
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