Exercise 4-1. DSP Peripherals EXERCISE OBJECTIVES

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Exercise 4-1 DSP Peripherals EXERCISE OBJECTIVES Upon completion of this exercise, you will be familiar with the specialized peripherals used by DSPs.

1 Exercise 4-1 DSP Peripherals EXERCISE OBJECTIVES Upon completion of this exercise, you will be familiar with the specialized peripherals used by DSPs. DISCUSSION The peripherals found on the TMS320C50 ('C50) DSP are good examples of the types used on many existing programmable DSPs. The 'C50 used by the Lab-Volt Digital Signal Processor FACET board, has many of its on-chip peripherals communicating with devices on the circuit board. The 'C50 serial port is used to communicate with the CODEC. The 'C50 parallel port is used to communicate with the ROM memory chip, the 4 I/O INTERFACE displays, and the DIP switch. The 'C50 master clock is externally generated by the oscillator and input to the DSP. Two of the 'C50 external user interrupt lines are each connected to a push-button on the surface of the FACET circuit board. 4-7

A DSP serial port is usually divided into two sections: a receive section and a transmit section. The transmit and receive sections may be independent.

2 A DSP serial port is usually divided into two sections: a receive section and a transmit section. The transmit and receive sections may be independent. There will be a: receive data line receive frame synchronization line receive bit clock line transmit data line transmit frame synchronization line transmit bit clock line In other DSPs, independent receive and transmit data pins exist, however, the frame synchronization and bit clock lines are shared between the two sections. The 'C50 serial port operates through three memory-mapped user registers (known as DRR, DXR, and SPC). DRR (Data Receive Register) is where words received through the serial port receive data pin are stored. DRR is memory-mapped to data memory address (dma) 20h. DXR (Data transmit Register) is where words to be transmitted through the serial transmit data pin are stored. Once a word is stored in DXR the serial port transmit circuitry takes charge of transmitting the word. DXR is memory-mapped to dma 21h. SPC (Serial Port Control) is a status and mode control register for the DSP serial port. 4-8

Through the memory-mapped Serial Port Control register (SPC) the 'C50 DSP allows the programmer to specify the serial port transmit and receive characteristics.

3 Through the memory-mapped Serial Port Control register (SPC) the 'C50 DSP allows the programmer to specify the serial port transmit and receive characteristics. The bit clock line polarity, the shift direction, data word length, and whether the frame synchronization signals are bit-length or word-length are serial port characteristics that certain DSP chips may permit the programmer to configure. A DSP parallel port is usually implemented in one of two ways. The main processor data bus can be used as the parallel port or the parallel port can be made separate from the processor external bus interface. Processors separating the parallel port from the external bus interface simplify interfacing to external devices. 4-9

4 DSPs which use their data bus as a parallel port typically reserve a special section of their address space for access to off-chip devices. In some DSPs, the reserved memory addresses are accessed with specialized instructions. The 'C50 has two such parallel port instructions (IN and OUT). The 'C50 IN and OUT instructions are used to read and write a data word from and to an external I/O port. I/O port accesses are distinguished from program and data accesses by a designated strobe or handshake pin. The pin is asserted when the external read or write is performed. Clock signals are used to sequence DSP operations. A clock signal consists of a square wave at some known frequency. The highest frequency clock signal within a processor is known as the master clock. The master clock signal is typically generated externally. However, a number of DSPs now have phase-locked loops (PLL). These DSPs require only a very lowfrequency input signal to generate using the PLL the master clock signal. The master clock signal can be generated in many different ways. The choice of which way to generate the clock signal can usually be configured by the programmer. A large number of programmable DSPs provide timers. A timer is a peripheral that changes the content of a register at regular intervals in such a manner as to measure time. Some DSPs provide a timer output pin. A square wave at the timer frequency can be output from the pin providing a software-controlled oscillator to a programmer. 4-10

5 The 'C50 timer as used on the FACET circuit board outputs a square wave at a frequency of 10 MHz. The signal is input to the codec as its master clock. Recall that in exercise 2 of Unit 2, we had used the timer of the 'C50 DSP. The timer register (TIM) was read at the beginning and at the end of an algorithm. In this manner the duration of the algorithm was measured. Measuring the duration of an event is a possible timer application, however, on DSPs, timers are usually used as a source of periodic interrupts. A timer in reality consists of a: & clock source & prescaler & counter The clock source usually consists of the DSP master clock signal. A plethora of package pins exist on programmable DSPs, related to some of these pins are additional peripherals that we have not yet covered in this discussion. & External user interrupts & Bit I/O ports The TMS320C50 DSP found on the FACET circuit board uses external user interrupts. In fact, most DSPs provide this type of peripheral. An external interrupt functions exactly the same as an internal interrupt, however, in most cases, external user interrupts are given lower response priority than other interrupts. 4-11

The TMS320C50 DSP found on the FACET circuit board uses bit I/O ports (two of them, BIO# and XF), also known in certain DSPs as general-purpose I/O pins, to establish communication between the C5x

6 The TMS320C50 DSP found on the FACET circuit board uses bit I/O ports (two of them, BIO# and XF), also known in certain DSPs as general-purpose I/O pins, to establish communication between the C5x VDE and the DSP. Bit I/O ports are software controlled. In this particular application (communication between the C5x VDE and the DSP), software control of the BIO# and XF I/O ports is done with a communication program (kernel) held in off-chip ROM. The software is first run by the DSP when communication between the C5x VDE debugger program and the DSP is attempted. CODEC is the abbreviation for CODer-DECoder. It is an electronic circuit that converts analog signals into digital representations, and decodes digital signals into analog form. Though signal processing can be entirely done with digital signals, most often a conversion from analog-to-digital and back again is required. 4-12

A CODEC is usually made up of the following components: & a programmable input gain & an anti-aliasing filter & an Analog-to-Digital converter & a Digital-to-Analog converter & a post-filter As

7 A CODEC is usually made up of the following components: & a programmable input gain & an anti-aliasing filter & an Analog-to-Digital converter & a Digital-to-Analog converter & a post-filter As stated, 'C50 communication with the codec is established through the DSP receive and transmit serial interfaces. The dual serial communication can only be implemented after both the serial DSP peripherals and the codec are initialized. PROCEDURE Timer Initialization In this procedure section, you will initialize the timer of the TMS320C50 DSP. Note: Before using the C5x VDE please make certain the circuit board power source is turned ON, and that the serial connection is present between the host computer and the DIGITAL SIGNAL PROCESSOR circuit block labeled SERIAL PORT. * 1. Open the C5x VDE, and load the ex4_1.dsk program file into the DSP. * 2. Place a breakpoint at the program memory address labeled CODECINIT. Do not place the breakpoint at the CALL CODECINIT source statement. * 3. Place a second breakpoint at the program memory address labeled SERIALINIT. 4-13

8 * 4. Press the C5x VDE RUN command, this will execute the DSP initialization code preceding the CODEC initialization subroutine (CODECINIT). The timer initialization code sets the timer to generate a 10 MHz signal that is output on a DSP package pin (TOUT). Note that the TOUT package pin is part of the second AUXILIARY I/O header. * 5. Connect oscilloscope channel 1 to the TOUT pin on the AUXILIARY I/O circuit block. See HELP Unit 04 shelp5 * 6. Press the C5x VDE RUN command, this will execute the code that initializes the DSP timer to generate a 10 MHz signal. In particular it is the PRD (timer PeRioD register) and TCR (Timer Control Register) that are initialized. As previously stated these two registers control the timer for the C50 DSP. 4-14

* 7. Adjust the oscilloscope to trigger on the TOUT waveform. What is the frequency of the TOUT signal? f TOUT = MHz It is the TOUT signal that is sent to the codec.

9 * 7. Adjust the oscilloscope to trigger on the TOUT waveform. What is the frequency of the TOUT signal? f TOUT = MHz It is the TOUT signal that is sent to the codec. The 10 MHz signal is used by the CODEC as the master clock. The timer can, however, be reconfigured to generate a signal with a different frequency. * 8. Using the C5x VDE, open a View Peripheral Registers window. * 9. Edit the PRD register to 00C7h. * 10. Adjust the oscilloscope to trigger on the TOUT waveform. What is the frequency of the TOUT signal? f TOUT = khz The timer frequency is related to the PRD and TCR registers as follows: 7 ö ì 7 0& #õ7''5øìô#õ35'øìô where f TOUT T M C TDDR PRD is the frequency of the TOUT signal, is the period of the DSP master clock (this value is (1/20 MHz) = 50 ns), is the decimal value of a series of bits within the TCR register, and is the decimal value of the PRD register. 4-15

10 * 11. Using the C5x VDE, edit the PRD peripheral register back to 0001 h. Verify that the TOUT signal now has a frequency of 10 MHz. See HELP Unit 04 shelp6 * 12. Using the C5x VDE, edit the TDDR bits (found in the TCR register) to 3. What is the frequency of the TOUT signal? f TOUT = MHz * 13. Using the C5x VDE, edit the TCR peripheral register back to 0000 h. Verify that the TOUT signal now has a frequency of 10 MHz. See HELP Unit 04 shelp6 The PRD register value is related to the TOUT frequency and the TCR register as follows: 35' ö ì I 7287 #7 0& #õ7''5øìô ì * 14. Holding the TDDR bits constant at zero and using the above equation, what decimal value would the PRD register have to take on for the timer to have a frequency of 1.25 MHz? PRD = d * 15. Using the C5x VDE, edit the PRD register to 000F h (15 d). Verify if the TOUT signal has a 1.25 MHz frequency. * 16. Using the C5x VDE, return the values of the PRD and the TCR registers respectively to 0001 h and 0000 h. The timer will then have a frequency of 10 MHz, this is the required codec master clock frequency to be used in the next section. * 17. Remove the connection between the DSP circuit board and the oscilloscope. 4-16

11 DSP Serial Interface and CODEC Initialization In this procedure section, you will initialize the CODEC using the DSP serial interface. * 18. Using the C5x VDE, set a breakpoint at program memory address labeled RESET. * 19. Press the C5x VDE RUN command, this will initialize the DSP serial port and establish communication between the DSP and the CODEC. Using the SPC (Serial Port Control) register, the DSP transmit and receive serial ports have been enabled and initialized to use 16-bit words. Transmit frame synchronization has also been enabled. 4-17

The reset must occur before the control words initializing the codec sampling frequency, filter cut-off frequency and other codec

12 * 20. Using the C5x VDE, set a breakpoint at the program memory address of the instruction labeled LACC #6h,9. * 21. Press the C5x VDE RUN command, this will reset the CODEC. The reset must occur before the control words initializing the codec sampling frequency, filter cut-off frequency and other codec characteristics can be transmitted from the DSP to the codec. * 22. Using the C5x VDE, set a breakpoint at the program memory address labeled RETURN. * 23. Press the C5x VDE RUN command, the DSP will then transmit the codec control words (TA, TB, RA, RB, and AIC_CTR). 4-18

It is these words that set the CODEC sampling and cut-off frequencies, and other characteristics. The Voltmeter Program In this procedure section, you will operate the voltmeter program. * 24.

13 It is these words that set the CODEC sampling and cut-off frequencies, and other characteristics. The Voltmeter Program In this procedure section, you will operate the voltmeter program. * 24. Connect the OUTPUT of the DC SOURCE to the ANALOG INPUT of the CODEC circuit block and to a voltmeter (as shown in the figure). * 25. Execute the RUN command, found on the C5x VDE Toolbar. This starts the voltmeter program. Note that the I/O interface displays a value. This is the voltage reading of the signal sent from the DC SOURCE OUTPUT. * 26. Change the voltage level of the DC signal by turning the DC SOURCE potentiometer. The signal sent to the codec is sampled and transmitted via the serial port to the DSP. The DSP then converts the value into its proportional voltage value (the program can only read values between V and 2.99 V) and outputs it to the I/O INTERFACE via the parallel I/O ports. * 27. Note that the value read off of the voltmeter and the value read by the DSP do not always correspond. This is due to imprecisions within the CODEC during voltage signal sampling. 4-19

14 What type of communication is used between the CODEC and the DSP on the Digital Signal Processor circuit board? a. parallel ports b. bit I/O ports c. serial ports d. none of the above How are words transmitted by the DSP to the I/O INTERFACE displays? a. serial ports b. parallel ports c. bit I/O ports d. interrupts * 28. Remove the connection between the DC SOURCE circuit block and the voltmeter. CONCLUSION & A DSP provides many peripherals, which are specialized for signal processing applications. & A DSP serial port is usually divided into two sections: a receive section and a transmit section. & A large number of programmable DSPs provide timers. A timer is a peripheral that changes the content of a register at regular intervals in such a manner as to measure time. & CODEC is the abbreviation for coder-decoder. It is an electronic circuit that converts analog signals into digital representations, and decodes digital signals into analog form. REVIEW QUESTIONS 1. Which of the following is not a DSP peripheral? a. parallel port b. serial port c. central arithmetic logic unit d. bit I/O port 4-20

15 2. Which of the following choices is used by a serial port interface? a. A bit clock line. b. A data line. c. A frame synchronization line. d. All of the above. 3. Which of the following is used in many DSPs as a parallel port? a. the timer output pin b. clock generator c. main processor data bus d. external user interrupt lines 4. The timer found in most DSPs, may be used as which of the following? a. a sine wave generator b. a source of periodic interrupts c. a voltmeter d. a register for storing the accumulator 5. Which of the following serial port characteristics may some DSPs permit the programmer to configure? a. data word length b. bit clock line polarity c. bit clock shift direction d. bit- or word-length frame synchronization signals. 4-21

Exercise 2-3. Addressing EXERCISE OBJECTIVES

Exercise 2-3. Addressing EXERCISE OBJECTIVES Exercise 2-3 Addressing EXERCISE OBJECTIVES Upon completion of this exercise, you will understand the function that of address generation unit within a DSP and the specialized addressing modes that it