Lab 4- Introduction to C-based Embedded Design Using Code Composer Studio, and the TI 6713 DSK

Transcription

1 DSP Programming Lab 4 for TI 6713 DSP Eval Board Lab 4- Introduction to C-based Embedded Design Using Code Composer Studio, and the TI 6713 DSK This lab takes a detour from model based design in order to develop more comfort in working with CCS and to become more familiar with real-time DSP programming in C. The lab will also further emphasize the Board Support Library functions that come with the DSK as well as the utility of the TI 6713 s DSP/BIOS feature that allows periodic thread scheduling to perform real-time multitasking. Hardware Requirements: TI 6713 DSK PC Software Requirements: Texas Instruments Products - Code Composer Studio 3.1 (available with the TI 6713 DSK) Installation: 1. Ensure that all of the software products are installed. They should be. Hardware Setup 1. Connect the TI 6713 eval board to the PC using the USB cable. 2. Connect power to the board. 3. Don t press any buttons on the board. PART 1: UNDERSTANDING FUNCTIONAL AUDIO REAL-TIME PROCESSING In this section you will survey a blank-slate project that passes audio and performs other processes in an efficient manner. 1. From My Computer in an Explorer Window, find the folder for CCS entitled CCStudio_v3.1. In the path C:\CCStudio_v3.1\examples\dsk6713\bsl\, (the bsl stands for board support library) copy the project folder, dsk_app. Go back to the C:\CCStudio_v3.1\ folder and open the My Projects folder, then paste the project folder here. 2. Start CCS, in the top menu bar click on Project Open, then open the project entitled dsk_app that you just pasted into C:\CCStudio_v3.1\ My Projects. 3. In the select tree to the left of the viewing window, expand the dsk_app.pjt(debug) tree, then expand the Source folder and double click on the dsk_app.c file. This is the main c- code file where most of the dsp work is done. 4. Read all the comments at the beginning of the file to acquaint yourself with how real-time audio might be handled in actual production code. For the rest of this lab you need to be able to understand some basics about the chip, hardware architecture, and code structure of this example, including some of the key header and.cmd files and their purpose. You should be able to answer the following questions: ( in addition to this code you should probably refer to the CCS help file or the help file that came with the DSK referenced in Lab 1)

2 a. How is audio data handled by the CODEC and transferred to and from the CODEC? Where is this in the code? b. Describe the function of the DSP/BIOS. What is its role in this particular example? (For more info, click on help in the menu bar up top and go to tutorials, then read the information on the DSP/BIOS) c. What is a periodic thread? How is related or used by the DSP/BIOS? What is it used for in this code? d. What is the McBSP and how is it used in this example? What is the purpose of using two sets of serial ports, McBSP0 and McBSP1? (for more info, read help files) e. What is EDMA and how is it used in this example? Explain Linked EDMA transfers. (for more info, read help files) f. Explain the PING/PONG buffer operation and its benefit in real-time audio processing. What is the advantage of two sets of buffers? 5. In addition to answering these questions, make sure you run through the code in dsk_app.c to gain a basic understanding of what is going on, as you are going to modify this existing code to implement a simple DSP process in the next section. You may want to refer to the help file under Software/Examples associated with this example for even more detailed information. 6. Make sure you are connected to the target. Go to Debug Connect to connect if you are not. Press F7 to build the project to an.out file. To load the.out file onto the DSP, choose File Load Program and when the window opens, look in the Debug folder for the dsk_app.out, choose this file to load onto the 6713 DSP. You can now run the example by pressing F5. 7. While the program is running you can see LED 1 and 2 rapidly blinking. What does the blink rate signify? Find the lines of code in dsk_app.c that specify this blinking. 8. Try pressing the DIP switches that enable the DSP/BIOS multi-tasking functions, the LED blink and the dummy load. Where are these functions located in the code? 9. Notice the names and type of functions that actually access the LEDs and DIP switches on the board, these functions are in the BSL (Board Support Library) that we have used in earlier labs. 10. Stop the DSP by pressing Shift F5. PART 2: DESIGN OF A SIMPLE FILTER IN CCS USING C In this part of the lab, you will implement a simple IIR filter in the existing framework of the dsk_app example. 1. By this point you should be well acquainted with the code in the dsk_app example. With this knowledge you need to first find the function that processes the data in the current buffer sample by sample. Right now this will be a simple loop with a line of code that declares the output sample equal to the input sample and then increments both. 2. To test that you ve found the right place in the code, first play audio through the board (you should still have it built and loaded from step 6 of Part 1), then add a simple gain (just multiply the input samples by 5 or something). Next, rebuild, reload, and re-run the code on the DSP to verify that it is indeed louder this time. 3. The equations below describe the transfer function of a simple resonant Bi-quad IIR digital filter. In this section you will design this filter with fixed parameters, but in section 4 you will make these parameters user adjustable using the DSP/BIOS. The parameters you need to specify are the Gain (G), the center frequency in Hz ( ), and the Q. Everything else in the equations below is calculated from these three parameters. f o

3 2 Transfer Function: b0 b2 z G a1z + a 2 z (1) G = gain (2) 2 b o = (1 R ) / 2 (3) b2 = b o (4) a1 = 2R cos( θ ) (5) 2 a 2 = R (6) R = 1 BW / 2 (7) BW ( bandwidth) = ωo / Q (8) 2R cos( ωo ) cos( θ ) = 2 1+ R (9) 2π * f o ω o = f (10) s The equations for bo and b2 put zeros at D.C. and Nyquist and act as a gain normalization, so that if the Q changes or the center frequency sweeps the resonance peak is always at 0 db. 4. To design this filter you will need to create several new global variables in the code: Gain, Q, center frequency, a buffer (memory) for the input, and a buffer for the output. The other variables (filter coefficients, etc) can be declared locally in the process function. Make sure to include <math.h> at the top of the code. 5. Design this filter with a Q of 3, a center frequency of 2000 Hz, and a gain of Make sure you save the modified code, then rebuild, re-load, and run the new code with your filter design. 7. In order to verify that your filter is working correctly you should be able to use some the debugging and watch tools that were covered in the tutorial from Lab Halt the DSP by pressing shift F5. PART 3: CHANGING FILTER PARAMETERS USING THE DSP/BIOS In this part of the lab you will make several of the filter parameters user-adjustable with the DIP switches on the 6713 DSK. Although there are many ways to do this, this section will guide you through performing this real-time parameter interface using the periodic thread options available because of the DSP/BIOS on the TI Take some time to review periodic thread functions and how they are used by the DSP/BIOS. The last paragraph of the comments at the top of the dsk_app.c is very important for this section, make sure you understand it. The configuration file called dsk_app.cdb is located in the select tree in the DSP/BIOS Config folder. 2. We have mentioned two periodic thread functions earlier (Section 2 step 8) that are declared at the bottom of the code, blinkled() and load(). The first blinks LED #0 every 500ms if DIP switch #0 is pressed, and the second executes a process dummy load every 10 ms if DIP switch #1 is pressed. 3. To see where and how these are handled by the DSP/BIOS, double click on the dsk_app.cdb file (from step 1) to open the DSP/BIOS configuration file for this example. This is a graphical interface that lets you manage all the DSP/BIOS settings. 4. The.cdb file should appear as select tree. Expand the scheduling tab, then expand the PRD Period Function Manager tab. Click on the PRD_blinkLED function. You should now see something similar to Fig. 2.

4 Figure 1 5. Survey the properties that are now displayed in the right hand side of the window. You can edit these properties by right-clicking on the function in the select tree, and by choosing properties. You should now see something similar to Fig. 3. Figure 2

5 6. Notice you can create a comment about what the function does or change the period of the function, etc. The function that the DSP/BIOS is going to schedule is declared in the function: box. Notice the _ before the name of the function, this is used because we are scheduling a C function. Always put the underscore before a C function when scheduling in the DSP/BIOS configuration file. blinkled is an actual C-function declared at the bottom of the code. The DSP/BIOS now knows to look for it and run it every 500 ms (Each tick corresponds to 1 ms in real-time). 7. Experiment with two things: First try changing the blink rate from 500 to 1000 ms or 200 ms. Second, go into the actual function in the C-file and change which LED will blink. Change it from #0 to #3. 8. So far you ve created a simple filter with fixed parameters (Q,,and G), and learned how to schedule functions with the DSP/BIOS. These filter parameters should be global variables in your code. Now you are going to create new functions scheduled by the DSP/BIOS that change any two of these parameters in real-time. Follow the steps below to do this. a. You will want to use the DIP switches and the LEDs, so comment out all the places in the C-file that make use of these. This should include the LED toggling of the Ping-Pong buffers, the LED blinking of the blinkled function, the DIP switch function in the blinkled function, and the DIP switch function of the dummy load function. b. Create two new functions at the bottom of the code near the other periodic threads. They do not need to return a value, as they will be working on global variables. You could for example create one for gain and one for center frequency. c. You have four DIP switches available to use for interface. You could use two for each function, where one switch increments the parameter value and the other decrements it. For example DIP switch #0 might increment the gain by 0.1 every time it is pressed and DIP switch #1 might decrement the gain by 0.1 every time it is pressed. d. To have some visual feedback, assign each LED switch to toggle on and off when a corresponding DIP switch is pressed. For example when you press switch #0 to increment the gain, have LED #0 blink on and off. e. Be sure to put upper and lower bounds on all of your parameter values. You do not for example want to be able to decrement the center frequency above the Nyquist frequency or below 0 Hz. The easiest way to do this is to use the modulo operator % to create a cyclical parameter adjustment scheme. f. Next, you want to schedule these two new functions using the DSP/BIOS periodic threading abilities. Open the.cdb configuration file again, and follow the tree to the PRD periodic function manager. Right-click on the PRD main tree and click on insert PRD as seen in Fig. 4 (on the following page). g. Click on new PRD function to change the name using the same name of the function that you used in the C-code, with PRD_ before it. h. Repeat f and g for your other function. i. Right click on either function and adjust the properties. Write a comment about what the function does, enter the threading period (in ms), and enter the actual function name. Remember to put the underscore _ before the function name to specify a C function. 9. You should now have code that does real-time multi-tasking processing audio and simultaneously scheduling the software interrupts that allow you to adjust the audio processing parameters. Re-build, and pending no build errors, re-load, and run the code to check and see if it works as planned. As always, if you have problems use the multitude of debugging tools available to you in CCS. f o

6 Figure 3