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Real Time DSP and the Motorola 56300 DSP Chip

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  1. Real Time DSPand theMotorola 56300 DSP Chip R.C. Maher ECEN4002/5002 DSP Laboratory Spring 2003

  2. Introduction: DSP Review • Sampled signal is represented as a sequence of numbers: x[n] • Unit sample [n] : …0,0,0,1,0,0,0, … • Can write: “Sifting” property Real Time DSP R. C. Maher

  3. Linearity, Time Invariance • Linear systems: additivity and scaling • Time-Invariant systems: delay (shift) of input sequence simply causes the same delay (shift) of output sequence Real Time DSP R. C. Maher

  4. Unit Sample Response • The response of an LTI system to a unit sample is very useful. Note that: Sifting Linearity Convolution Time Invariance Real Time DSP R. C. Maher

  5. Unit Sample Response (cont.) • NOTE: we can find the response of an LTI system to any input if we know h[n] • What if input is a complex exponential? Real Time DSP R. C. Maher

  6. Frequency Response • Frequency response is the discrete-time Fourier transform of the unit sample response: • This is a periodic function with period 2 • 2 corresponds to the sample rate, fs , of the sampled-data system Real Time DSP R. C. Maher

  7. Xc(j)  -N N XS(j)  -2S -S -N N S 2S Sampling Effects: Frequency Domain Fourier Transform of continuous function Fourier Transform of sampled function S > 2 N S < 2 N (aliasing) XS(j)  -2S -S S 2S Real Time DSP R. C. Maher

  8. The Motorola 5630x Programming model Introduction to instruction set Assembler directives

  9. ALU 5630x ALU Real Time DSP R. C. Maher

  10. ALU Registers X0 X1 Y0 Y1 • General-Purpose: • 24 bits • Move to/from other registers • Move to/from memory • ALU/Mult operands • Accumulators: • 56 bits [ 8 : 24 : 24 ] • Move to/from other registers • Move to/from memory • ALU/Mult results A2 A1 A0 B2 B1 B0 Real Time DSP R. C. Maher

  11. 5630x Addressing Unit Real Time DSP R. C. Maher

  12. R4 R0 R1 M1 R2 M3 M2 R3 M0 M4 R5 M5 R6 M6 R7 M7 N2 N7 N6 N0 N1 N4 N3 N5 AGU Registers Index Registers Modulo Registers Offset Registers Real Time DSP R. C. Maher

  13. Addressing Examples move x:(R4),X0 ; Register Indirect move x:(R0)+,X1 ; w/ postincrement by 1 move x:(R4)-,X1 ; w/ postdecrement by 1 move x:-(R0),X1 ; w/ predecrement by 1 move x:(R4)+N4,X0 ; w/ postincrement by N move x:(R0)-N0,X1 ; w/ postdecrement by N move x:(R4+N4),X0 ; w/ indexed offset by N (no update) Real Time DSP R. C. Maher

  14. Program Layout • Instruction format: lab1 mac x0,y0,a x:(r0)+,x0 y:(r4)+,y0 ; comment • Some assembler directives: ORG EQU INCLUDE END DS DC ; (comment) Label field Operation field Operand field X move field Y move field Comment field Real Time DSP R. C. Maher

  15. Memory Organization • 56303 • Program: $0 - $0FFF (4k words) • X Data: $0 - $07FF (2k words) • Y Data: $0 - $07FF (2k words) • 56307 • Program: $0 - $3FFF (16k words) • X Data: $0 - $5FFF (24k words) • Y Data: $0 - $5FFF (24k words) Real Time DSP R. C. Maher

  16. Real Time Signal Processing

  17. “Real Time” means: • Input/output streams are sustained – no gaps or dropped data • Processing must occur within the sample period 1/fs (at least on average) • Fixed delay through the system (the latency) usually must be minimized • Availability of data drives the system Real Time DSP R. C. Maher

  18. DSP Microprocessor A/D Converter D/A Converter DSP System DSP receives an interrupt as each sample arrives Clock Clock Data Data High speed serial data DSP receives an interrupt when D/A ready for sample Real Time DSP R. C. Maher

  19. DSP Software Development • Write software • Assemble and link • Download to EVM • Run! …but how to determine if it works or not?? …and what if program doesn’t work?? Real Time DSP R. C. Maher

  20. Testing and Debugging • Can be a complicated process because: • Write and assemble code on PC, but then download and run on EVM: indirect observation is required. • Algorithm and implementation errors are often subtle and ellusive numerical details. • Real Time programs can’t be run in “slow motion,” so identifying bugs requires creative methods. Real Time DSP R. C. Maher

  21. Testing and Debugging (cont.) • Suggestions: • Develop and test your code incrementally. Make only small changes code changes before testing again. In other words, never be more than one change away from a working program. • Test code segments in isolation using the debugger or the software simulator. • Learn to use your eyes and ears to find bugs. Real Time DSP R. C. Maher

  22. Edit | Assemble | Load | Test • Edit source code file • Use simple text editor (DOS Edit, Notepad, etc.) • Plain text, not case sensitive • USE LOTS OF COMMENTS!! • Use modular code design and organization • Assemble • Execute: asm56300 –a –b –g –l file.asm • Check for errors, and re-edit as necessary Real Time DSP R. C. Maher

  23. Edit | Assemble | Load | Test (cont.) • Download .cld module to the EVM • Run the Domain Technologies Debugger EVM30XW • “File | Load…” and browse to the .cld file • Test the module • Start the code (green button on Debugger) • Observe input/output signals • When in doubt, stop and download known good code (e.g, pass.cld) Real Time DSP R. C. Maher

  24. The Pass.asm Program • Initializes codec (stereo) • Handles codec data interrupts • Main program loop polls for data ready, then puts left sample in A and right sample in B • Uses some X and Y memory • Note: r6 is used as a stack pointer Real Time DSP R. C. Maher

  25. Lab Assignment #1 • Due at START of class in one week • Topics: • Use EVM and software tools • Observe sampling and reconstruction • Program #1: gain multiplier • Program #2: word length and quantization • Program #3: aliasing Real Time DSP R. C. Maher