DSP for under £50
Ron Taylor G4GXO
www.cumbriadesigns.co.uk
Signals to numbers –
and back again
Microprocessor
Analogue
Analogue to Digital
Converter
Digital
Analogue
Digital to Analogue
Converter
Analogue to Digital Conversion
+ve
Voltage
0V
-ve
Sampling
points
Analogue to Digital Conversion
Amplitude of each sample above or below
mid range is converted into a signed binary number
+ve
Number
range
0
-ve
00010100
01110100
01110110 11100100
(sign bit sets –ve or +ve value)
Each number sent serially from CODEC to processor
Signals to numbers –
and back again
Microprocessor
Analogue
Analogue to Digital
Converter
Digital
Analogue
Digital to Analogue
Converter
The search for a suitable DSP
development system
• Low cost hardware
• 16bits or more
• Windows based supported development
software (which should also be low cost or
better still free!)
• Capable of running a DSP IF scheme
Juha Niinikoski, OH2NLT
“Cheap DSP”
dsPIC30F processor
Juha Niinikoski, OH2NLT
George Heron, N2APB
“SDR Cube Transceiver”
Direct Conversion Transceiver using a dsPIC33F processor
A solution…
• DSP only card with plenty of I/O for controls etc.
• Microchip dsPIC33FJ64GP306 at 40MIPS (70MIPs with dsPIC33E)*
(64 pin PTQF – not too difficult to solder)
• Texas TLV320AIC23B stereo CODEC
(28 pin SOP – easy to solder)
• MPLAB IDE and the free version of the C30 compiler
• Nominal 12V operation
• I/O on 0.1” headers, optional pull up resistors, no analogue signal
conditioning.
*To be tested
The Eden dsP Module
Eden dsP Module
CODEC Config and control
L
R
Stereo Audio
in/out
Out
L
R
TLV320AIC23
CODEC
In
+12V
SPI
I/F
PSU
(Regs)
dsPIC33FJ64
AC97
Codec I/F
I/O Ports
LEDs
(2)
Audio data transfer
I2C
Bus for
I2C Devices
RS232
Ext Comms
Serial Interfaces
Indicators
Controls (logic/switches etc)
Eden dsP Module
Eden dsP Module
Eden dsP Module
Eden dsP Module
+12V PSU
Programmer
USB
Connection
Eden dsP
MPLAB Development Software
Programmer (MPLAB)
Example programs
Program is stored in the
dsPIC33F flash memory
Add the free C30 Compiler to edit the example
Programs or start writing your own!
Eden dsP Module
Once programmed, the Eden dsP will run the software whenever
it is power up – until it is overwritten with a new program.
+12V
Eden dsP
Host equipment
Receiver/Transceiver
AF Filter
Spectrum display etc., etc.
The Eden dsP may be
programmed whilst installed
in its host equipment.
What next?”
Digital Filters
Two most common types
IIR
“Infinite Impulse Response”
input
x
output
a
b
y
FIR
“Finite Impulse Response”
input
FIR
Coeff
Table
output
Digital Filters
IIR - Infinite Impulse Response Filter
–
–
–
–
•
•
•
•
Feedback system, similar to analogue Op Amp Filter
Simple to code
Little memory used
input
a
x
Very fast execution
Roll off not spectacular
Phase varies with frequency
Potential for instability
Useful for general non critical filtering
e.g, microphone filters etc
b
output
y
Digital Filters
Common
filter program
FIR - Finite Impulse Response Filter
–
–
–
–
–
–
Based upon a delay line
input
Most commonly used filter type
Convolution process (multiply, add “MAC”)
Employs a table of constants to define filter
Capable of phenomenal performance
Fixed phase shift and delay
• Memory and processor usage high
FIR
output
Coeff
Table
Filter “Kernel”
Sets filter parameters
The FIR Filter
3 step “production line” process,
similar to a conveyor belt in a
factory… or a sushi bar?
The FIR Filter
1.
Load new sample into a delay line, shifting all current samples
along one position.
The FIR Filter
1.
2.
Load new sample into a delay line, shifting all current samples
along one position.
Multiply each value on the delay line with a filter constant.
!
axb=c
The FIR Filter
1.
2.
3.
Load new sample into a delay line, shifting all current samples
along one position.
Multiply each value on the delay line with a filter constant.
Add all of the multiplication results together to
make the output sample.
FIR Filter
Step 1. Values move along
delay line with each
new sample
Input
Delay Line (filter taps)
Tap 1
a
x
Tap 7
b
x
c
x
d
e
x
x
f
x
g
x
Sum
Step 2. Multiplication
of each tap value by
by a kernel constants
(a, b, c, etc)
Step 3. Accumulate
(running sum of multiplications)
Output
One sample in, one sample out
Last
Value
Discarded
(overwritten)
FIR Code
Written in assembler for fast (efficient) execution
;*********************************************************************************************
;
; FIR Filter
;
; Universal FIR Filter code
;
;*********************************************************************************************
Load input sample
mov AF_in, w0
; Get input and load into w0
mov
mov
mov
mov
mov
dec
#_fir_delay,w8
w8, XMODSRT
_fir_delay_end, w8
w8, XMODEND
_fir_n, w1
w1, w1
;
;
;
;
;
;
Load delay line start address into w8
XMODSRT = start address of delay line
Load delay line end address
XMODEND = end address of delay line
Load number of taps (N) into w1
Decrement w1 = M (N-1)
mov
mov
mov
mov
_fir_delay_ptr, w8
w0, [w8++]
w8, _fir_delay_ptr
_fir_coef_end, w10
;
;
;
;
Load delay line pointer into w8
Move new sample into position pointed to by w8
Update delay line pointer
tap vector end to w10
clr A, [w8]+=2, w5, [w10]-+2, w6
repeat w1
; Clear MAC Accumulator A, load w5 with sample pointed to by w8 and w6
; with that at w10, post increment and decrement pointers
; Repeat MAC instruction w1 times = Number of taps - 1
mac w5*w6, A, [w8]+=2, w5, [w10]-=2, w6
sac.r a,w0
mov w0, _AF_out
Prepare delay line
Set up addresses
For delay line and
Kernel table
Multiply and add each record
Output result
; Round off result
; Copy output word to filter output
;*********************************************************************************************
FIR Filter Kernel
// FIR Filter Kernel
//
// Ron Taylor Cumbria Designs 2012
//
// Filter Kernel 1 N=201 Fs=8000 F1=500
#define
N 201
const int fir_4_data[N]={
0x0000, 0x0000, 0x0000, 0x0000, 0x0000,
0x0002, 0x0001, 0xFFFF, 0xFFFD, 0xFFFC,
0x0000, 0xFFFE, 0xFFFE, 0x0001, 0x0006,
0xFFEB, 0xFFE0, 0xFFDF, 0xFFE9, 0xFFFB,
0x0000, 0x0006, 0x0016, 0x0028, 0x002D,
0xFF9C, 0xFFDD, 0x0030, 0x0075, 0x0093,
0x0000, 0x0026, 0x002A, 0xFFF5, 0xFF8C,
0x0153, 0x01E8, 0x01E8, 0x014B, 0x004D,
0x0000, 0xFFB3, 0xFEE8, 0xFE12, 0xFDD1,
0x0588, 0x0205, 0xFD15, 0xF845, 0xF54E,
0x0CCD, 0x0ADD, 0x05B5, 0xFF09, 0xF902,
0x0588, 0x06C6, 0x05CB, 0x0363, 0x00AE,
0x0000, 0xFFBC, 0xFF2A, 0xFEB6, 0xFEBA,
0x0153, 0x0068, 0xFF83, 0xFEF0, 0xFED1,
0x0000, 0xFFDF, 0xFFDF, 0x0008, 0x0048,
0xFF9C, 0xFF81, 0xFF90, 0xFFBD, 0xFFF2,
0x0000, 0x0005, 0x0010, 0x0019, 0x0018,
0xFFEB, 0xFFFA, 0x0007, 0x000F, 0x0010,
0x0000, 0x0001, 0x0001, 0x0000, 0xFFFE,
0x0002, 0x0002, 0x0001, 0x0001, 0x0000,
0x0000,
};
F2=900
0x0000,
0xFFFD,
0x000C,
0x000D,
0x001B,
0x0080,
0xFF16,
0xFF51,
0xFEA9,
0xF576,
0xF576,
0xFEA9,
0xFF51,
0xFF16,
0x0080,
0x001B,
0x000D,
0x000C,
0xFFFD,
0x0000,
// Set number
// Tap data
0x0000, 0x0001,
0xFFFE, 0x0000,
0x0010, 0x000F,
0x0018, 0x0019,
0xFFF2, 0xFFBD,
0x0048, 0x0008,
0xFED1, 0xFEF0,
0xFEBA, 0xFEB6,
0x00AE, 0x0363,
0xF902, 0xFF09,
0xF54E, 0xF845,
0xFDD1, 0xFE12,
0x004D, 0x014B,
0xFF8C, 0xFFF5,
0x0093, 0x0075,
0x002D, 0x0028,
0xFFFB, 0xFFE9,
0x0006, 0x0001,
0xFFFC, 0xFFFD,
0x0000, 0x0000,
of taps
0x0001,
0x0001,
0x0007,
0x0010,
0xFF90,
0xFFDF,
0xFF83,
0xFF2A,
0x05CB,
0x05B5,
0xFD15,
0xFEE8,
0x01E8,
0x002A,
0x0030,
0x0016,
0xFFDF,
0xFFFE,
0xFFFF,
0x0000,
0x0002,
0x0001,
0xFFFA,
0x0005,
0xFF81,
0xFFDF,
0x0068,
0xFFBC,
0x06C6,
0x0ADD,
0x0205,
0xFFB3,
0x01E8,
0x0026,
0xFFDD,
0x0006,
0xFFE0,
0xFFFE,
0x0001,
0x0000,
FIR Designer
A free FIR design program from those really nice people at;
www.cumbriadesigns.co.uk
Demonstration
Designing a high performance audio CW Filter
•
•
•
•
FIR Filter
300Hz Bandwidth centred on 700Hz
Design and test filter in “FIR Designer”
Demonstrate filter using an FT817
– AF input from headphone socket
– External LM380 AF power amplifier
; Filter Kernel
0x0000, 0x0000,
0x0000, 0x0000,
0xFFFF, 0x0000,
0xFFF9, 0xFFFA,
0xFFFC, 0xFFFC,
0x0000, 0x000C,
0xFFE2, 0xFFF6,
0x0000, 0x0008,
0x004D, 0x0073,
0x0000, 0x003C,
0x0047, 0x001F,
0x0185, 0x0157,
0x00A0, 0x00A3,
0x0000, 0xFE5A,
0x053A, 0x01D1,
0x099A, 0x082A,
0x053A, 0x06C9,
0x0000, 0x0129,
0x00A0, 0x0040,
0x0185, 0x013D,
0x0047, 0x0043,
0x0000, 0xFFBA,
0x004D, 0x0017,
0x0000, 0xFFF9,
0xFFE2, 0xFFD7,
0x0000, 0xFFF8,
0xFFFC, 0xFFFE,
0xFFF9, 0xFFFB,
0xFFFF, 0xFFFF,
0x0000, 0x0000,
0x0000,
N=301 Fs=8000 F1=550 F2=850
0x0000, 0x0000, 0x0000, 0x0000,
0x0000, 0x0000, 0x0000, 0x0000,
0x0001, 0x0002, 0x0003, 0x0003,
0xFFFC, 0x0001, 0x0005, 0x0008,
0xFFFE, 0x0000, 0x0000, 0xFFFE,
0x0017, 0x001D, 0x001A, 0x000D,
0x000D, 0x001E, 0x0024, 0x001F,
0x0009, 0xFFFE, 0xFFE8, 0xFFCF,
0x0078, 0x0056, 0x0016, 0xFFCA,
0x0059, 0x0053, 0x0034, 0x0010,
0xFFCC, 0xFF67, 0xFF19, 0xFF0B,
0x00BA, 0xFFE0, 0xFF10, 0xFE92,
0x0060, 0x0011, 0xFFF7, 0x0038,
0xFCC2, 0xFBE1, 0xFC42, 0xFE0B,
0xFD7C, 0xF98F, 0xF758, 0xF7AC,
0x0451, 0xFF43, 0xFA94, 0xF7AC,
0x0637, 0x03F2, 0x00E0, 0xFE0B,
0x0194, 0x0158, 0x00C4, 0x0038,
0xFF9E, 0xFEF4, 0xFE8B, 0xFE92,
0x009F, 0xFFE7, 0xFF52, 0xFF0B,
0x0024, 0x0006, 0xFFFD, 0x0010,
0xFF84, 0xFF72, 0xFF8C, 0xFFCA,
0xFFE5, 0xFFC6, 0xFFC1, 0xFFCF,
0xFFF9, 0x0002, 0x0011, 0x001F,
0xFFD9, 0xFFE6, 0xFFFA, 0x000D,
0xFFF5, 0xFFF7, 0xFFFB, 0xFFFE,
0x0002, 0x0006, 0x0008, 0x0008,
0xFFFD, 0x0000, 0x0003, 0x0003,
0x0000, 0x0000, 0x0000, 0x0000,
0x0000, 0x0000, 0x0000, 0x0000,
0x0000,
0x0000,
0x0003,
0x0008,
0xFFFB,
0xFFFA,
0x0011,
0xFFC1,
0xFF8C,
0xFFFD,
0xFF52,
0xFE8B,
0x00C4,
0x00E0,
0xFA94,
0xF758,
0xFC42,
0xFFF7,
0xFF10,
0xFF19,
0x0034,
0x0016,
0xFFE8,
0x0024,
0x001A,
0x0000,
0x0005,
0x0003,
0x0000,
0x0000,
0x0000,
0x0000,
0x0000,
0x0006,
0xFFF7,
0xFFE6,
0x0002,
0xFFC6,
0xFF72,
0x0006,
0xFFE7,
0xFEF4,
0x0158,
0x03F2,
0xFF43,
0xF98F,
0xFBE1,
0x0011,
0xFFE0,
0xFF67,
0x0053,
0x0056,
0xFFFE,
0x001E,
0x001D,
0x0000,
0x0001,
0x0002,
0x0000,
0x0000,
0x0000,
0x0000,
0xFFFD,
0x0002,
0xFFF5,
0xFFD9,
0xFFF9,
0xFFE5,
0xFF84,
0x0024,
0x009F,
0xFF9E,
0x0194,
0x0637,
0x0451,
0xFD7C,
0xFCC2,
0x0060,
0x00BA,
0xFFCC,
0x0059,
0x0078,
0x0009,
0x000D,
0x0017,
0xFFFE,
0xFFFC,
0x0001,
0x0000,
0x0000,
0x0000,
0xFFFF,
0xFFFB,
0xFFFE,
0xFFF8,
0xFFD7,
0xFFF9,
0x0017,
0xFFBA,
0x0043,
0x013D,
0x0040,
0x0129,
0x06C9,
0x082A,
0x01D1,
0xFE5A,
0x00A3,
0x0157,
0x001F,
0x003C,
0x0073,
0x0008,
0xFFF6,
0x000C,
0xFFFC,
0xFFFA,
0x0000,
0x0000,
0x0000,
Information header added and data
formatted for use with C program
// FIR Filter Kernel
//
// Ron Taylor Cumbria Designs 2012
//
// Filter Kernel N=301 Fs=8000 F1=550 F2=850
#define
N 301
const int fir_coeff[N]={
0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000,
0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000,
0xFFFF, 0x0000, 0x0001, 0x0002, 0x0003, 0x0003,
0xFFF9, 0xFFFA, 0xFFFC, 0x0001, 0x0005, 0x0008,
0xFFFC, 0xFFFC, 0xFFFE, 0x0000, 0x0000, 0xFFFE,
0x0000, 0x000C, 0x0017, 0x001D, 0x001A, 0x000D,
0xFFE2, 0xFFF6, 0x000D, 0x001E, 0x0024, 0x001F,
0x0000, 0x0008, 0x0009, 0xFFFE, 0xFFE8, 0xFFCF,
0x004D, 0x0073, 0x0078, 0x0056, 0x0016, 0xFFCA,
0x0000, 0x003C, 0x0059, 0x0053, 0x0034, 0x0010,
0x0047, 0x001F, 0xFFCC, 0xFF67, 0xFF19, 0xFF0B,
0x0185, 0x0157, 0x00BA, 0xFFE0, 0xFF10, 0xFE92,
0x00A0, 0x00A3, 0x0060, 0x0011, 0xFFF7, 0x0038,
0x0000, 0xFE5A, 0xFCC2, 0xFBE1, 0xFC42, 0xFE0B,
0x053A, 0x01D1, 0xFD7C, 0xF98F, 0xF758, 0xF7AC,
0x099A, 0x082A, 0x0451, 0xFF43, 0xFA94, 0xF7AC,
0x053A, 0x06C9, 0x0637, 0x03F2, 0x00E0, 0xFE0B,
0x0000, 0x0129, 0x0194, 0x0158, 0x00C4, 0x0038,
0x00A0, 0x0040, 0xFF9E, 0xFEF4, 0xFE8B, 0xFE92,
0x0185, 0x013D, 0x009F, 0xFFE7, 0xFF52, 0xFF0B,
0x0047, 0x0043, 0x0024, 0x0006, 0xFFFD, 0x0010,
0x0000, 0xFFBA, 0xFF84, 0xFF72, 0xFF8C, 0xFFCA,
0x004D, 0x0017, 0xFFE5, 0xFFC6, 0xFFC1, 0xFFCF,
0x0000, 0xFFF9, 0xFFF9, 0x0002, 0x0011, 0x001F,
0xFFE2, 0xFFD7, 0xFFD9, 0xFFE6, 0xFFFA, 0x000D,
0x0000, 0xFFF8, 0xFFF5, 0xFFF7, 0xFFFB, 0xFFFE,
0xFFFC, 0xFFFE, 0x0002, 0x0006, 0x0008, 0x0008,
0xFFF9, 0xFFFB, 0xFFFD, 0x0000, 0x0003, 0x0003,
0xFFFF, 0xFFFF, 0x0000, 0x0000, 0x0000, 0x0000,
0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000,
0x0000,
};
0x0000,
0x0000,
0x0003,
0x0008,
0xFFFB,
0xFFFA,
0x0011,
0xFFC1,
0xFF8C,
0xFFFD,
0xFF52,
0xFE8B,
0x00C4,
0x00E0,
0xFA94,
0xF758,
0xFC42,
0xFFF7,
0xFF10,
0xFF19,
0x0034,
0x0016,
0xFFE8,
0x0024,
0x001A,
0x0000,
0x0005,
0x0003,
0x0000,
0x0000,
// Set number of taps
// Tap data
0x0000, 0x0000, 0x0000,
0x0000, 0x0000, 0xFFFF,
0x0000, 0xFFFD, 0xFFFB,
0x0006, 0x0002, 0xFFFE,
0xFFF7, 0xFFF5, 0xFFF8,
0xFFE6, 0xFFD9, 0xFFD7,
0x0002, 0xFFF9, 0xFFF9,
0xFFC6, 0xFFE5, 0x0017,
0xFF72, 0xFF84, 0xFFBA,
0x0006, 0x0024, 0x0043,
0xFFE7, 0x009F, 0x013D,
0xFEF4, 0xFF9E, 0x0040,
0x0158, 0x0194, 0x0129,
0x03F2, 0x0637, 0x06C9,
0xFF43, 0x0451, 0x082A,
0xF98F, 0xFD7C, 0x01D1,
0xFBE1, 0xFCC2, 0xFE5A,
0x0011, 0x0060, 0x00A3,
0xFFE0, 0x00BA, 0x0157,
0xFF67, 0xFFCC, 0x001F,
0x0053, 0x0059, 0x003C,
0x0056, 0x0078, 0x0073,
0xFFFE, 0x0009, 0x0008,
0x001E, 0x000D, 0xFFF6,
0x001D, 0x0017, 0x000C,
0x0000, 0xFFFE, 0xFFFC,
0x0001, 0xFFFC, 0xFFFA,
0x0002, 0x0001, 0x0000,
0x0000, 0x0000, 0x0000,
0x0000, 0x0000, 0x0000,
Demonstration
Headphone Socket
AF Amplifier
DSP Module
AF In
Speaker
AF Out
Demonstration
Headphone Socket
Signal path control
AF Amplifier
Speaker
AF Out
AF In
Eden dsP card
DSP in Radio
DSP in Radio
Two general architectures;
Direct Conversion
DSP IF System
DSP Receiver Architecture
Direct Conversion Receiver
Filter Bank
AF Out
DDS
Demod
Digital phase shifter
PC or DSP Unit
High IP3 switching Mixers
FST3125 etc
AF Amplifier
Speaker
DSP Receiver Architecture
DSP IF
Dual Conversion, VLF 2nd IF
Crystal Filter
2nd Mixer
6kHz IF Amplifier
Preselector
2nd IF
15kHz
15kHz
IF Out
1st IF
20MHz
VFO
Carrier
oscillator
15kHz IF In
AF Amplifier
DSP Module
(2nd IF)
AF Out
Speaker
DSP Receiver Architecture
Multirate DSP IF
48kHz Sampling Rate
9.6Hz Sampling Rate
AF I Channel
3kHz
Decimator
15kHz IF
input to
mixers
DSP Module
Phase shifting filters
5
Sin
15kHz IF In
15kHz quad CIO
Cos
Gain
control
5
3kHz Decimator
AF Q Channel
AGC
Demod
Auto-notch
De-noiser
AF Out
;******************************************************************************************
;
; I and Q Mixers
;
;
;******************************************************************************************
mixers:
; I mixer
mov
mov
mul.ss
mov
; Q mixer
mov
mov
mul.ss
mov
return
_I_mix_in, w1
_I_carrier,w0
w0, w1, w2
w3, _I_mix_out
;
;
;
;
Get input signal and place in w1
Get carrier and place in w0
Signed 16bit x 16bit multiply, 32 bit result in w2 and w3
Save most significant word to mixer output
_Q_mix_in, w1
_Q_carrier,w0
w0, w1, w2
w3, _Q_mix_out
;
;
;
;
Get input signal and place in w1
Get carrier and place in w0
Signed 16bit x 16bit multiply, 32 bit result in w2 and w3
Save most significant word to mixer output
DSP IF Demo
48kHz Sampling Rate
9.6Hz Sampling Rate
AF I Channel
3kHz
Decimator
15kHz IF
input to
mixers
DSP Module
Phase shifting filters
5
Sin
15kHz IF In
15kHz quad CIO
Cos
Gain
control
5
3kHz Decimator
AF Q Channel
AGC
Demod
Auto-notch
De-noiser
AF Out
Getting Started in DSP
•
•
•
•
•
“Eden dsP” Card, about £50 to build
Software MPLAB, C30, FIR Designer, demo programs - all free!
PIC programmer (PICkit 3 etc)
Modest PC for programming
Literature
– Digital Signal Processing, Steven Smith
– Digital Signal Processing Technology (ARRL), Doug Smith
– ARRL/RSGB Handbooks
– Beginners Guide to C, Greg Perry
– The C Programming Language, Brian Kernigham and Dennis
Ritchie