Real Time DSPand the
Motorola 56300 DSP Chip
R.C. Maher
ECEN4002/5002 DSP Laboratory
Spring 2002
ECEN4002 Spring 2002 Real Time DSP R. C. Maher 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
k
knkxnx ][][][
ECEN4002 Spring 2002 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
][][][][ 2121 nxTnxTnxnxT
][][ nxTanxaT
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Unit Sample Response
• The response of an LTI system to a unit sample is very useful. Note that:
k
k
k
knhkx
knTkx
knkxT
nxTny
][][
][][
][][
][][
Sifting
Linearity
Time Invariance
Convolution
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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?
jnj
m
mjnj
m
mnj
eHe
emhe
emhny
][
][][ )(
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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
n
njj enheH ][
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Sampling Effects: Frequency DomainXc(j)
N-N
XS(j)
N-N S-S 2S-2S
S-S 2S-2S
XS(j)
S > 2 N
S < 2 N (aliasing)
Fourier Transform of continuous function
Fourier Transform of sampled function
The Motorola 5630x
Programming model
Introduction to instruction set
Assembler directives
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ALU
5630x ALU
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ALU Registers
Y0X0
A1 A0A2
Y1X1
B1 B0B2
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
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5630x Addressing Unit
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AGU Registers
R0 N0M0
R1 N1M1
R2 N2M2
R3 N3M3
R4 N4M4
R5 N5M5
R6 N6M6
R7 N7M7
Index Registers Modulo Registers Offset Registers
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Addressing Examples
move x:(R4),X0 ; Register Indirect
move x:(R0)+,X1 ; w/ postincrement by 1
move x:(R4)-,X1 ; w/ postdecrementby 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)
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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
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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 Signal Processing
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“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
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DSP System
A/D Converter
D/A Converter
DSP
Microprocessor
Clock
Data
Clock
Data
High speed serial data
DSP receives an interrupt as each sample arrives
DSP receives an interrupt when D/A
ready for sample
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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??
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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.
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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.
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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
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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)
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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
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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