AM2634: CPU Cycle counter

Dominik Wuest

Part Number: AM2634

I want to check the runtime of some calculations on the AM2634 using the Launchpad development board. For that I'm using the FreeRTOS empty example and the Cycle Counter API from the SDK.

Now I have the following problem. When I measure a known time, for example before and after xTaskDelayUntil, the cycle counter is much lower than expected.
Converted I get a clock frequency of around 8 MHz. The CPUCLK should be 400 MHz and that of the SYSCLK 200 MHz.

This is probably a thinking error. Can someone give me a hint?

Thanks.

over 3 years ago

0 Dominik Wuest over 3 years ago

Prodigy 180 points

I think the reasons are WFI or WFE instructions. The CPU core goes into a power-down mode because there is no work to do. I am right?

0 Aakash Kedia over 3 years ago in reply to Dominik Wuest

TI__Mastermind 26145 points

Hi Dominik,

Are you using CycleCounterP_* APIs to calculate the clock cycles and then getting the clock frequency ?

Best Regards,
Aakash

0 Dominik Wuest over 3 years ago in reply to Aakash Kedia

Prodigy 180 points

Hi Aakash, yes exactly. I'm using the CycleCounterP_* API. I think this is not accurate if a task is delayed.

0 Aakash Kedia over 3 years ago in reply to Dominik Wuest

TI__Mastermind 26145 points

Hi Dominik,

Let me come back to you on this. As far as I know the CycleCounter are not the CPU cycles so it should not stop even when the CPU is in WFI.

Best Regards,
Aakash

0 Dominik Wuest over 3 years ago in reply to Aakash Kedia

Prodigy 180 points

Hi Aakash

The API uses the CP15_CYCLE_COUNT Register. Isn't this the CPU Counter?

+1 Aakash Kedia over 3 years ago in reply to Dominik Wuest

TI__Mastermind 26145 points

Hi Dominik,

My bad.. These are definitely the CPU cycles, so when the CPU is in WFI, the cycles do not add up for the delay. I suggest you to use TimerP_* APIs for the time calculation.

Best Regards,
Aakash

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AM2634: CPU Cycle counter