Real Time DSP and the Motorola 56300 DSP

Real Time DSP and the Motorola 56300 DSP Chip R. C. Maher ECEN 4002/5002 DSP Laboratory Spring 2002

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 ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 2

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 ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 3

Unit Sample Response • The response of an LTI system to a unit sample is very useful. Note that: Sifting Linearity Convolution ECEN 4002 Spring 2002 Time Invariance Real Time DSP R. C. Maher 4

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? ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 5

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 ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 6

Sampling Effects: Frequency Domain Xc(j ) - N S > 2 N Fourier Transform of continuous function N Fourier Transform of sampled function XS(j ) -2 S - N S < 2 N (aliasing) S 2 S XS(j ) -2 S - S ECEN 4002 Spring 2002 N Real Time DSP S 2 S R. C. Maher 7

The Motorola 5630 x Programming model Introduction to instruction set Assembler directives ECEN 4002 Spring 2002 Real Time DSP R. C. Maher

ALU 5630 x ALU ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 9

ALU Registers X 0 Y 0 X 1 Y 1 A 2 A 1 A 0 B 2 B 1 B 0 ECEN 4002 Spring 2002 Real Time DSP General-Purpose: • 24 bits • Move to/from other registers • Move to/from memory • ALU/Mult operands Accumulators: • 56 bits [ 8 : 24 ] • Move to/from other registers • Move to/from memory • ALU/Mult results R. C. Maher 10

5630 x Addressing Unit ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 11

AGU Registers Index Registers Modulo Registers Offset Registers R 0 M 0 N 0 R 1 M 1 N 1 R 2 M 2 N 2 R 3 M 3 N 3 R 4 M 4 N 4 R 5 M 5 N 5 R 6 M 6 N 6 R 7 M 7 N 7 ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 12

Addressing Examples move x: (R 4), X 0 move x: (R 0)+, X 1 move x: (R 4)-, X 1 move x: -(R 0), X 1 move x: (R 4)+N 4, X 0 move x: (R 0)-N 0, X 1 move x: (R 4+N 4), X 0 ECEN 4002 Spring 2002 ; Register Indirect ; w/ postincrement by 1 ; w/ postdecrement by 1 ; w/ predecrement by 1 ; w/ postincrement by N ; w/ postdecrement by N ; w/ indexed offset by N (no update) Real Time DSP R. C. Maher 13

Program Layout • Instruction format: lab 1 Label field mac Operation field x 0, y 0, a Operand field x: (r 0)+, x 0 X move field y: (r 4)+, y 0 Y move field • Some assembler directives: ORG EQU INCLUDE DS DC ; (comment) ECEN 4002 Spring 2002 Real Time DSP R. C. Maher ; comment Comment field END 14

Memory Organization • 56303 – Program: – X Data: – Y Data: $0 - $0 FFF (4 k words) $0 - $07 FF (2 k words) • 56307 – Program: – X Data: – Y Data: ECEN 4002 Spring 2002 $0 - $3 FFF (16 k words) $0 - $5 FFF (24 k words) Real Time DSP R. C. Maher 15

Real Time Signal Processing ECEN 4002 Spring 2002 Real Time DSP R. C. Maher

“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 ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 17

DSP System DSP receives an interrupt as each sample arrives Clock A/D Converter Clock DSP Data Microprocessor Data High speed serial data ECEN 4002 Spring 2002 D/A Converter DSP receives an interrupt when D/A ready for sample Real Time DSP R. C. Maher 18

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? ? ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 19

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. ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 20

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. ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 21

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: asm 56300 –a –b –g –l file. asm – Check for errors, and re-edit as necessary ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 22

Edit | Assemble | Load | Test (cont. ) • Download. cld module to the EVM – Run the Domain Technologies Debugger EVM 30 XW – “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) ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 23

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: r 6 is used as a stack pointer ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 24

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 ECEN 4002 Spring 2002 Real Time DSP R. C. Maher 25