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wrong cycle timing of instructions on ARM11
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wrong cycle timing of instructions on ARM11
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chandrakala reddy
over 7 years ago
Note: This was originally posted on 4th February 2013 at http://forums.arm.com
Hi,
Iam using RVDS3.0 for ARM11. some of the instructions are not executing in the time specified by the ARM documentation. for example, according to ARM documents, SMLAD instruction has to take 1 cycle for execution and 2 stalls if the result is immediatly used. but in real time, it is taking 2 cycles for execution. is it a bug on RVDS3.0 or am i missing any thing here. can any one please help me out.
Regards,
Chandrakala
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chandrakala reddy
over 7 years ago
Note: This was originally posted on 4th February 2013 at
http://forums.arm.com
Hi,
Thanks for the reply. there is no register dependency in the code.
Following is my code
SMLAD r0, r1, r2, r3
SMLAD r4, r5, r6, r7
SMLAD r8, r9, r10, r11
SMLAD r12, lr, r1, r6
Is there any issue with the code?
Regards,
Chandrakala
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chandrakala reddy
over 7 years ago
Note: This was originally posted on 4th February 2013 at
http://forums.arm.com
Hi,
Thanks for the reply.
How can i measure exact cycles for ARM11. Is there any way to do that. Has RVDS latest versions solved this problem. Are there any simulators to measure exact cycles.
Regards,
Chandrakala
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chandrakala reddy
over 7 years ago
Note: This was originally posted on 4th February 2013 at
http://forums.arm.com
Thank a lot for the replies. I will use hardware for profiling.
Regards,
Chandrakala
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Martin Weidmann
over 7 years ago
Note: This was originally posted on 4th February 2013 at
http://forums.arm.com
Couple of possibilities....
* You could just be measuring it incorrect - you haven't given any details of how you are doing this
* It could be a register dependency on one of the inputs
* It could be something like a cache or TLB miss.
I would have thought the second one is the most likely.
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Martin Weidmann
over 7 years ago
Note: This was originally posted on 4th February 2013 at
http://forums.arm.com
No, the later versions of RVDS didn't include any more accurate (cycle wise) models. You'd have to use real hardware to get accurate results.
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Chris Lamb
over 7 years ago
Note: This was originally posted on 4th February 2013 at
http://forums.arm.com
Hi,
Are you using the models of the ARM11 CPUs delivered as part of RVDS3.0?
If so, they are based on ARMulator models which stopped being cycle accurate
after v5. Some v6 instructions had approximate cycle counts added, but the complexity
of the pipeline meant that ARMulator could only provide a static calculation. As a result,
none of the v6 instructions in a model can be relied upon to provide a correct cycle
count.
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