1. *
07/16/96
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Stereo Sound repositioning Details of hardware FIFO buffers Hardware FIFO in “C”
M. R. Smith, Electrical and Computer Engineering University of Calgary, Alberta, Canada ucalgary.ca *

2. To be tackled today Concept of Lab. 2 -- Software FIFO stack*
07/16/96
Concept of Lab Software FIFO stack
Software Circular Buffers -- 2 approaches
FIFO stacks allowing the modeling of audio channels associated with sound positioning through delays
Details of Lab Hardware FIFO stack
Same code except for variants of new routine
Compare software and hardware circular buffers
Developing new code in Assembly code
Delay line as FIR, FIR coeffs in dm or pm space
Hardware circular buffer in assembly code
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

3. Labs. 2 and 3 -- delay line -- Concept*
07/16/96
DELAY1
No delay between left/right ear sound arrivals -- then sound perceived in centre of head
Delay in right ear sound arrival will shift sound to left as “sound” seems to get to left ear first
O DELAY
DELAY2
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

4. DAG generator architecture*
07/16/96
Animation from SHARCNavigator from Web
Also see DSP workshop book and exercises
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

5. Audio channel delay modeled using software circular buffers*
Audio channel delay modeled using software circular buffers
07/16/96
void SoftCircularBuffer_LeftDelay(int delay, int *channel_one) {
int count;
static float left_delayline[MAXDELAY] = {0};
static float *left_pt_out = &left_delayline[0]; (Points to most delayed sample)
static float *overflow_pt = &left_delayline[MAXDELAY];
float *left_pt_in = left_pt_out + delay; // CAREFULL point offset size
if (left_pt_in >= overflow_pt) left_pt_in - MAXDELAY;
// Insert new value into the back of the FIFO delay line
*left_pt_in = (float) *channel_one;
// Grab delayed value from the front of the FIFO delay line
*channel_one = (int) *left_pt_out;
// Update the FIFO delay line using pointer arithmetic for circ. Buff
left_pt_out++;
if (left_pt_out >= overflow_pt) left_pt_out = left_pt_out - MAXDELAY;
} // SPEED OF CODE -- INDEPENDENT OF DELAY SIZE
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

6. Principle of Hardware Circular Buffers*
07/16/96
AFTER APPLYING MAGIC
void SoftCircularBuffer_LeftDelay(int delay, int *channel_one) {
int count;
static float left_delayline[MAXDELAY] = {0};
static float *left_pt_out = &left_delayline[0]; (Points to most delayed sample)
static float *overflow_pt = &left_delayline[MAXDELAY];
float *left_pt_in = left_pt_out + delay; // CAREFULL point offset size
if (left_pt_in >= overflow_pt) left_pt_in - MAXDELAY;
// Insert new value into the back of the FIFO delay line
*left_pt_in = (float) *channel_one;
// Grab delayed value from the front of the FIFO delay line
*channel_one = (int) *left_pt_out;
// Update the FIFO delay line using pointer arithmetic for circ. Buff
left_pt_out++; MAGIC OCCURS AND POINTER POSITION OKAY
if (left_pt_out >= overflow_pt) left_pt_out = left_pt_out - MAXDELAY;
} // SPEED OF CODE -- INDEPENDENT OF DELAY SIZE
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

7. Approach Set up B4, I4, L4 and M4 for circular buffers and use them
Problems
Working in a multi-tasking environment
Working with “C/C++” interrupt environment
Working with normal “C”
Everybody using the same set of registers
ADVANTAGE THIS LECTURE
We know more than the compiler does
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

8. MySetUp( ) ADIsound soundemo; MySetUp( ); -- Sets up circular buffer
while (ReadSource(&left_in) ) {
-- Use circular buffer
ProcessSound(left_in, &left_out) ;
WriteSource(left_out); }
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

9. MySetUp( ) – Non-21XXX processor
float * start_of_FIFOarray = GARBAGE;
int length_of_FIFOarray = GARBAGE;
float *current_FIFO_oldest_pointer = GARBAGE;
float left_channel[MAXLENGTH];
MySetUp( ) {
SaveMyEars(left_channel, MAXLENGTH) – Make 0 length_of_FIFOarray = MAXLENGTH start_of_FIFOarray = left_channel;
current_FIFO_oldest_pointer = left_channel;
“C” convention – means &left_channel[0];
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

10. Modeling Audio Channel Delays using Mass Memory Moves*
07/16/96
Modeling Audio Channel Delays using Mass Memory Moves
#define MAXDELAY 0x80
void MemoryMove_LeftDelay(int delay, int *channel_one) {
int count;
static float left_delayline[MAXDELAY] = {0};
// Insert new value into the back of the FIFO delay line
left_delayline[0 + delay] = (float) *channel_one;
// Grab delayed value from the front of the FIFO delay line
*channel_one = (int) left_delayline[0];
// Update the FIFO delay line using inefficient memory moves
for (count = 0; count < delay; count++)
left_delayline[count] = left_delayline[count + 1]; }
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

11. Principle of Hardware Circular Buffers*
07/16/96
float * start_of_FIFOarray; int length_of_FIFOarray; float *current_FIFO_oldest_pointer;
AFTER APPLYING MAGIC -- MySetUp() #pragma – Please use circular buffers – there is an actual “C” extension I forget the exact syntax -- SHARC and Blackfin similar
void SoftCircularBuffer_LeftDelay(int delay, int *channel_one) {
int count;
int temp;
temp = *current_FIFP_oldest_pointer; // Get oldest value
*current_FIFO_oldest_pointer = *channel_one; // Replace with newest value
*channel_one = temp;
current_FIFO_oldest_pointer++; // Letting hardware buffer work
// Equivalent would happen in FIR – except working in a loop
} // SPEED OF CODE -- INDEPENDENT OF DELAY SIZE
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

12. What “Compiler” actually has to do*
07/16/96
void SoftCircularBuffer_LeftDelay(int delay, int *channel_one) {
int count;
int temp;
Save the following registers to the stack I3, L3, B3 (and perhaps M3) THEN DO
B3 = start_of_FIFO_array; L3 = length_of_FIFO_array I3 = current_FIFO_oldest_pointer;
Now use I3, B3 and L3 for hardware operations
temp = *current_FIFP_oldest_pointer; // Get oldest value
*current_FIFO_oldest_pointer = *channel_one; // Replace with newest value *channel_one = temp;
current_FIFO_oldest_pointer++;
current_FIFO_oldest_pointer = I3 -- remember the pointer
Recover the following registers from the stack I3, L3, B3 (and perhaps M3)
// Equivalent would happen in FIR – except working in a loop
} // so save / recovery of registers is not as big an over-head
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

13. New Knowledge 68K, Blackfin
Live with the overhead (previous slides)
AMD 29K – 128 registers – set some aside specially for special purposes – untouchable by compiler
Alternate sets of registers
Intel i960 – 15 sets of alternate general registers
SHARC – 2 sets of data and DAG registers that are selectable in banks
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

14. MySetUp( ) –21XXX processor
float * start_of_FIFOarray = GARBAGE; // Use alternate
int length_of_FIFOarray = GARBAGE;
float *current_FIFO_oldest_pointer = GARBAGE;
float left_channel[MAXLENGTH];
MySetUp( ) {
SaveMyEars(left_channel, MAXLENGTH) – Make 0
DeactivateInterrupts( );
SwitchToMyAlternateRegisters( ); length_of_FIFOarray = MAXLENGTH Alternate L2 start_of_FIFOarray = left_channel; Alternate B2
current_FIFO_oldest_pointer = left_channel; -- Alternate I2
Could do L3, B3 and I3 for right channel, but other techniques possible
SwitchToOriginalRegisters( )
ReactivateInterrupts( );
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

15. Hardware Circular Buffers – Pseudo Code*
07/16/96
AFTER APPLYING MAGIC -- MySetUp()
All necessary information in “Alternate Registers
void HardCircularBuffer_LeftDelay_ASM(int delay, int *channel_one) {
int temp;
DeactivateInterrupts( );
SwitchToMyAlternateRegisters( );
temp = *current_FIFP_oldest_pointer; // Get oldest value
*current_FIFO_oldest_pointer = *channel_one; // Replace with newest value
*channel_one = temp;
current_FIFO_oldest_pointer++; // Letting hardware buffer work
SwitchToOriginalRegisters( )
ReactivateInterrupts( );
// Equivalent would happen in FIR – except working in a loop
} // SPEED OF CODE -- INDEPENDENT OF DELAY SIZE
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith -- *

16. Issues -- 1
Can’t just switch to alternate register bank and back to original
Multi-tasking environment – may already be in alternate bank – e.g. interrupted an assembly program already using the alternate register bank
Solution – save and recover PROCESSOR CONFIGURATION
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

17. Issues -- 2
Can’t just switch to alternate register bank and back to original
We need R0 (return), R4 (INPAR1) etc unchanged
Another interrupt may come along and want to use stack to store values during ISR
Solution – be selective on what registers you use
Solution – Deactivate interrupts – and know the amount of time that system can’t respond.
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

18. MODE1 register Memory mapped system register – typical today
#include "def21061.h"
#include "clanguage_21XXXregister_defines.i“
bit set MODE1 BitPattern; nop
bit clr MODE1 BitPattern; nop
PROBLEM – Can’t use the alternate registers for 1 cycle – possible race condition
SOLUTION – NOP after changing – guarentees no problem
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

19. MySetUp( ) –21XXX processor
float * start_of_FIFOarray = GARBAGE; // Use alternate
int length_of_FIFOarray = GARBAGE;
float *current_FIFO_oldest_pointer = GARBAGE;
float left_channel[MAXLENGTH];
MySetUp( ) {
SaveMyEars(left_channel, MAXLENGTH) – Make 0
SetUpAlternateRegisters_ASM( ); }
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

20. MySetUp( ) –21XXX processor
.extern _left_channel[MAXLENGTH];
ALL NECESSARY DEFINES
_SetUpAlternateRegisters_ASM( ) {
DeactivateInterrupts( ); Might already be de-activated
SwitchToMyAlternateRegisters( ); -- Might already be in alternate bank // length_of_FIFOarray = MAXLENGTH
LEFT_LENGTH_Alt_L2 = MAXLENGTH;
// start_of_FIFOarray = _left_channel;
LEFT_BASE_Alt_B2 = _left_channel; // Has side effect
// current_FIFO_oldest_pointer = left_channel;
LEFT_OLD_pt_Alt_I2 = _left_channel; // Overcomes side effect
SwitchToMyOriginalRegisters( ); -- Might not want to switch back
ReactivateInterrupts( ); Might not want to be activated
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

21. MODE1 register Details – Appendix on E-14 of MANUAL
Bit 2 – SRCU – alternate register select for computation units?
Bit 3 – SRD1H – DAG1 alternate register select (7-4) – DON’T TOUCH – “C” issue
Bit 4 – SRD1L – DAG1 alternate register select (3-0)
Bit 5 – SRD2H – DAG2 alternate register select (15-12)
Bit 6 – SRD2L – DAG2 alternate register select (11-8)
Bit 7 – SRRFH – Register file alternate select for R15-R8
Bit 10 – SRRFL – Register file alternate select for R7-R0
Bit 12 – IRPTEN – Global interrupt enable
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

22. Useful Macros -- Define
Going to be doing this stuff often
Define assembly language macros
#define TOAlternateRegisters() bit set MODE1 SRRFL; nop
#define FROMAlternateRegisters() bit clr MODE1 SRRFL; nop
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

23. MySetUp( ) –21XXX processor
#define DeactivateInterrupts( ) ?????????
#define SwitchToMyAlternateRegisters( ) ?????????
_SetUpAlternateRegisters_ASM( ) {
R0 = MODE1; // In this case, we know R0 is not being destroyed
DeactivateInterrupts( ); // Might already be deactivate
SwitchToMyAlternateRegisters( ); // length_of_FIFOarray = MAXLENGTH LEFT_LENGTH_Alt_L2 = MAXLENGTH;
// start_of_FIFOarray = _left_channel;
LEFT_BASE_Alt_B2 = _left_channel; // Has side effect
// current_FIFO_oldest_pointer = left_channel;
LEFT_OLD_pt_Alt_I2 = _left_channel; // Overcomes side effect
PROBLEM – HOW TO GET BACK TO ORIGINAL R0 WITHOUT UNINTENTIONALLY CAUSING A PROBLEM?
SwitchToMyOriginalRegisters( ); -- Might not want to switch back
ReactivateInterrupts( ); Might not want to be activated
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

24. Solution 1 – valid here _SetUpAlternateRegisters_ASM( ) {
#define DeactivateInterrupts( ) ?????????
#define SwitchToMyAlternateDAGRegisters( ) ?????????
_SetUpAlternateRegisters_ASM( ) {
R0 = MODE1; // In this case, we know R0 is not being destroyed
DeactivateInterrupts( ); // Might already be deactivate
SwitchToMyAlternateDAG1LRegisters( ); // length_of_FIFOarray = MAXLENGTH LEFT_LENGTH_Alt_L2 = MAXLENGTH;
// start_of_FIFOarray = _left_channel;
LEFT_BASE_Alt_B2 = _left_channel; // Has side effect
// current_FIFO_oldest_pointer = left_channel;
LEFT_OLD_pt_Alt_I2 = _left_channel; // Overcomes side effect
NO PROBLEM – HOW TO GET BACK TO ORIGINAL R0 WITHOUT UNINTENTIONALLY CAUSING A PROBLEM?
MODE1 = R0; // SwitchToMyOriginalRegisters( ); -- Might not want to switch back
// ReactivateInterrupts( ); Might not want to be activated
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

25. Solution 2 – valid elsewhere
#define DeactivateInterrupts( ) ?????????
#define SwitchToMyAlternateRegisters( ) ?????????
_SetUpAlternateRegisters_ASM( ) {
R0 = MODE1; // In this case, we know R0 is not being destroyed
SAVE R0 TO THE STACK USING I6, I7 – which we know are not to be used
DeactivateInterrupts( ); // Might already be deactivate
SwitchToMyAlternateRegisters( ); // length_of_FIFOarray = MAXLENGTH LEFT_LENGTH_Alt_L2 = MAXLENGTH;
// start_of_FIFOarray = _left_channel;
LEFT_BASE_Alt_B2 = _left_channel; // Has side effect
// current_FIFO_oldest_pointer = left_channel;
LEFT_OLD_pt_Alt_I2 = _left_channel; // Overcomes side effect
NO PROBLEM – HOW TO GET BACK TO ORIGINAL R0 WITHOUT UNINTENTIONALLY CAUSING A PROBLEM?
RECOVER R0 FROM THE STACK
MODE1 = R0; // SwitchToMyOriginalRegisters( ); -- Might not want to switch back
// ReactivateInterrupts( ); Might not want to be activated
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --

26. Lab. 3
Implement hardware circular buffers – replace the software circular buffers code from Lab. 2
Demonstrate moving sound source using
LOCAL_AUDIOSOURCE
WARNING – LOCAL_AUDIO_SOURCE is ALREADY using hardware circular buffers (I0 and I1)
CODEC_AUDIOSOURCE
Complete Lab. 2 / Lab. 3 joint report discussing timing issues / advantages / disadvantages of the various approaches. Provide documented code
Demo the working versions of the code either during Lab.3 or Lab. 4
Joint report due at the start of the Friday lecture for your Lab. 4, which is a week extension over being due within a week of your lab. Late penalties will be applied.
1/17/2019
ENCM Hardware FIFO buffers -- Details of Lab. 3 Copyright M. Smith --