1. Moving Arrays -- 1
Completion of ideas needed for a general and complete program
Final concepts needed for Final Review for Final – Loop efficiency

2. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Tackled today
Declaring and initializing arrays off the stack – Review and a little bit of new
Useful for background DMA tasks
Useful for minimizing total memory used in non-general program
Declaring arrays and variables on the stack – Review and a little bit of new
Re-entrant code and thread safe
Demonstrating memory to memory DMA
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

3. Declaring fixed arrays in memory – not on the stack
short foo_startarray[40];
short far_finalarray[40];
void HalfWaveRectifyASM( ) {
// Take the signal from foo_startarray[ ] and rectify the signal
// Half wave rectify – if > 0 keep the same; if < 0 make zero
// Full wave rectify – if > 0 keep the same; if < 0 then abs value
// Rectify startarray[ ] and place result in finalarray[ ]
for (int count = 0; count < 40; count++) {
if (foo_startarray[count] < 0) far_finalarray[count] = 0;
else far_finalarray[count] = foo_startarray[count]; }
The program code is the same – but the data part is not
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

4. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Attempt 1
.section data1
Tells linker to place this stuff in memory map location data1
.align 4 We know processor works best when we start things on a boundary between groups of 4 bytes
[N * 2] We need N short ints
We know the processor works with address working in byes
Therefore need N * 2 bytes
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

5. We said “wrong approach” look at memory
20 bytes (16 bits) for
N short value in C++ = N * 2 bytes
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

6. Said “Correct approach NOT what I expected”
ASM Array with space for N long ints .var arrayASM[N];
ASM Array with space for N short ints var arrayASM[N / 2];
ASM Array with space for N chars var arrayASM[N / 4];
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

7. Better answer is “Look at the assembler manual”
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

8. Improving what we did before
Big warning – external array initialization occurs on “reload” and NOT on “restart” – Understanding why this is true and why it is a problem will solve many issues when programming
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

9. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

10. When DMA might be useful -- Video manipulation
Program
Wait for picture 1 to come in – video-in
Process picture 1 – lots of mathematics perhaps
Wait for picture 1 to be transmitted – video out
Spending a lot of time waiting rather than doing
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

11. When DMA might be useful -- Double Buffering
Program
Wait for picture 2 memory to fill – video-in
Picture 3 comes into memory – background DMA Process picture 2 – place into picture 0 location
Picture 4 comes into memory – background DMA Process picture 3 – place into picture 1 location Transmit picture 0 – background DMA
Picture 0 comes into memory – background DMA Process picture 4 – place into picture 2 location Transmit picture 1– background DMA
Picture 1 comes into memory – background DMA Process picture 0 – place into picture 3 location Transmit picture 2 – background DMA
Picture 2 comes into memory – background DMA Process picture 1 – place into picture 4 location Transmit picture 3– background DMA
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

12. We are only going to look at a simple DMA task
Normal code
P0  address of start_array[0];
P1  address of final_array[0]; R0  max-value needed to transfer
R1  How many values already transferred
R1 = 0;
LOOP: CC = R0 <= R1 IF CC JUMP DONE:
R2 = [P0++]; VERY BIG PIPELINE [P1++] = R2; LATENCY ISSUES JUMP LOOP; MANY INTERNAL PROCESSOR STALLS
DONE: WHILE WAIT FOR R2 TO BE Do something else READ, STORED and then TRANSMITTED
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

13. We are only going to look at a simple DMA task
DMA_source_address_register  address of start_array[0];
DMA_destination_address_register  address of final_array[0]; DMA_max_count_register  max-value needed to transfer
DMA_count_register  How many values already transferred
R1 = 0;
LOOP: CC = R0 <= R1 IF CC JUMP DONE: DMA_enable = true
R2 = [P0++]; DMA transfer happen in background [P1++] = R2; Miminized pipeline issues JUMP LOOP;
DONE: Do something else Do something else
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

14. Write some test so we know how to proceed -- Test 1
Internal memory test – arrays on stack
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

15. Write some test so we know how to proceed -- Test 2
External memory test – arrays in external SDRAM
SDRAM -- MANY MEGS AVAILABLE
Addresses hard-coded
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

16. Write some test so we know how to proceed -- Test 3
Most probable way to use DMA – Store in SLOW external memory Move to process in FAST internal memory, put back into external
SDRAM
Addresses hard-coded
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

17. Some results Code details later
Debug Mode
Release Mode
L1  L1
8748
625
L1  L1 DMA
6579
6477
SDRAM  SDRAM
39132
28200
SDRAM  SDRAM DMA
12175
12090
SDRAM  L1 DMA
5265
4836
SDRAM  L1 DMA L1  SDRAM DMA
9792
9276
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

18. Memory to memory move Debug Code
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

19. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Review for final
A) What happened here?
B) What happened here?
C) What happened here?
D) Why did this happen?
E) What happened here?
F) Determine loop efficiency in terms of instructions in terms of cycles / read_write op
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

20. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Answer questions A B C D E
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

21. Review for final -- Worksheet
F) Determine loop efficiency in terms of cycles / read_write op
internal memory -> internal memory
size was ?
Useful reads ?
Useful writes ?
Cycles as measured ?
cycles / useful mem op
Why not an exact number? Instructions in loop?
Total # of reads / write ? / loop
? read / writes – around ? cycles
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

22. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Review for final
F) Determine loop efficiency in terms of cycles / read_write op
internal memory -> internal memory
size was 300
Useful reads 300
Useful writes
Cycles as measured
8748 / 600 = 14.58
Why not an exact number? Instructions in loop? 19
Total # of reads / write 9 / loop
2700 read / writes – around 3 cycles
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

23. Review for final -- Worksheet
F) Determine loop efficiency in terms of cycles / read_write op
SDRAM -> SDRAM
size was ?
Useful reads ?
Useful writes ?
Cycles as measured ?
cycles / useful mem op
Why not an exact number? Instructions in loop?
Total # of reads / write ? / loop
? read / writes – around ? cycles
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

24. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Review for final
F) Determine loop efficiency in terms of cycles / read_write op
SDRAM external -> SDRAM memory
Useful reads / writes 300 each
Cycles as measured
39132 / 600 = 65.22
Why not an exact number? Instructions in loop? 19
Total # of reads / write 9 / loop
7 * 300 read / writes internal
2 * 300 read / writes external
Time r/w external = – 2100*3
33000 / 600 = 5.5 cycles
Factor of 2 slower
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

25. Memory to memory move Release Mode
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

26. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Review for final
A) What happened here?
B) What happened here?
C) What happened here?
D) Why did this happen inside loop?
E) What happened here?
F) Determine loop efficiency in terms of instructions in terms of cycles / read_write op
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

27. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Answer questions A B C D E
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

28. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
F) Determine loop efficiency in terms of cycles / read_write op
internal memory -> internal memory
size was 300
Useful reads 300
Useful writes
Cycles as measured
625 / 600 = 1.05
Why not an exact number? Instructions in loop? 4
WE WOULD EXPECT 1200 cycles!!!!
Where did the difference go?
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

29. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Worksheet
F) Determine loop efficiency in terms of cycles / read_write op
SDRAM -> internal memory
size was ?
Useful reads ?
Useful writes ?
Cycles ? as measured
? / ? = ?
SDRAM access ? cycles
L1 memory cycle
Would make sense to process in
L1 memory?
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

30. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
F) Determine loop efficiency in terms of cycles / read_write op
SDRAM -> internal memory
size was 300
Useful reads 300
Useful writes
Cycles as measured
28200 / 600 = 47
SDRAM access 47 cycles
L1 memory cycle
Would make sense to process in
L1 memory – so move
SDRAM to L1 to process
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

31. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Worksheet
F) Determine loop efficiency in terms of cycles / read_write op
SDRAM -> internal memory
size was ?
Useful reads ?
Useful writes ?
Cycles ? as measured of those are L1 writes
Leaving ?
? / ? = ?
SDRAM read before ? cycles
SDRAM read now ? cycles
L1 -> L ? cycle
Would make sense to process in
L1 memory – so move
SDRAM to L1 to process
Loads of overhead in SDRAM to SDRAM
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

32. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
F) Determine loop efficiency in terms of cycles / read_write op
SDRAM -> internal memory
size was 300
Useful reads 300
Useful writes
Cycles as measured of those are L1 writes
Leaving 4500
4500 / 300 = 15
SDRAM read before cycles
SDRAM read now cycles
L1 -> L cycle
Would make sense to process in
L1 memory – so move
SDRAM to L1 to process
Loads of overhead in SDRAM to SDRAM
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

33. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
F) Determine loop efficiency in terms of cycles / read_write op
SDRAM -> internal memory
size was 300
Useful reads 300
Useful writes
Cycles as measured of those are L1 writes
Leaving 4500
4500 / 300 = 15
SDRAM read before cycles
SDRAM read now cycles
L1 -> L cycle
Would make sense to process in
L1 memory – so move
SDRAM to L1 to process
Loads of overhead in SDRAM to SDRAM
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

34. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Tackled today
Review of handling external arrays from assembly code
Arrays declared in another file
Arrays declared in this file NEW
Needed for arrays used by ISRs
Arrays declared on the stack
Pointers passed as parameters to a subroutine
Can’t use arrays on the stack when used by ISR
DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019

35. DMA , Copyright M. Smith, ECE, University of Calgary, Canada
Information taken from Analog Devices On-line Manuals with permission
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DMA , Copyright M. Smith, ECE, University of Calgary, Canada
1/1/2019