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Cortex-A35 Counter-timer Physical Count register (CNTPCT_EL0) always reads zero

Tao Lu

Counter-timer Physical Count register CNTPCT_EL0 always reads zero on FVP_Base_Cortex-A35x1. 

I expect the value of this register to change over time. 

I set $CNTFRQ_EL0=35000000, and $CNTP_CTL_EL0=5.

What is the possible reasons, and how is there any configuration I need make to enable this counter? Thanks

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  • +1 Arm Employee Badge in reply to Tao Lu

    Hi Tao,

    The counter is not counting because the CNTVALUEB input to the Cortex-A35 is driven by a model which requires some programming to start supplying the clock for the counters. If you are interested the model is the MemoryMappedCounterModule.

    You can get around this by setting a parameter in the model to just start counting and the counter will count.

    Add

    -C bp.refcounter.non_arch_start_at_default=1

    to your command line for FVP_Base_Cortex-A35x1 and it will work.

    Thanks,

    Jason

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  • +1 Arm Employee Badge in reply to Tao Lu

    Hi Tao,

    The counter is not counting because the CNTVALUEB input to the Cortex-A35 is driven by a model which requires some programming to start supplying the clock for the counters. If you are interested the model is the MemoryMappedCounterModule.

    You can get around this by setting a parameter in the model to just start counting and the counter will count.

    Add

    -C bp.refcounter.non_arch_start_at_default=1

    to your command line for FVP_Base_Cortex-A35x1 and it will work.

    Thanks,

    Jason

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