Reading Cortex-A9 CNTFRQ register using ARM Compiler 5 inline assembly

Thank you for your detailed reply.

I have 2 followups , by your permission:

1. I read below that cortex-a9 is armv7-a architecture. so why it lacks this register?

https://developer.arm.com/Processors/Cortex-A9

2. Do you know which register I need in order to get the cpu frequency in case cntfrq doesn't exists? (baremetal app)

Thanks again

Thank you for your detailed reply.

I have 2 followups , by your permission:

1. I read below that cortex-a9 is armv7-a architecture. so why it lacks this register?

https://developer.arm.com/Processors/Cortex-A9

2. Do you know which register I need in order to get the cpu frequency in case cntfrq doesn't exists? (baremetal app)

Thanks again

bsp_user said:

1. I read below that cortex-a9 is armv7-a architecture. so why it lacks this register?

Armv7-A supports a number of optional extensions (e.g. Virtualisation, Generic Timer, Large Physical Addresses...).  Not all Armv7-A processors will support all of the extensions.

You can check a processor's TRM to see which extensions are implemented, and the information is also reported via feature registers in the processor.

Thank you for your help.     Do you have any Idea how I can read the frequency in another way (since this register doesn't exists)

I think Ronan answered on the other thread.  But one comment, for processors that support the Generic Timer, CNTFRQ reports the frequency of the timers - not of the core.  The timer frequency is fixed and typically slower than the core's frequency (which might be subject to DVFS).