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

Hi,

Because of how Fast Models partition work your application could complete without the A35 updating the CNTPCT_EL0 register from 0. Try to extend the run of your application from the CNTPCT_EL0 initialization to you reading its value to check that it is still zero even on longer application executions.

Another option if the above does not work is to lower the 'quantum' of the simulation. This quantum value loosely represents the number of instructions run before checking other peripherals in the system and could be affecting the CNTPCT_EL0 register population. Add the switch '--quantum 10' after the FVP_Base_Cortex-A35x1 executable on the terminal/command line to lower the quantum value to 10 (it defaults to 10000).

Thanks,
-Zach

Hi,

Because of how Fast Models partition work your application could complete without the A35 updating the CNTPCT_EL0 register from 0. Try to extend the run of your application from the CNTPCT_EL0 initialization to you reading its value to check that it is still zero even on longer application executions.

Another option if the above does not work is to lower the 'quantum' of the simulation. This quantum value loosely represents the number of instructions run before checking other peripherals in the system and could be affecting the CNTPCT_EL0 register population. Add the switch '--quantum 10' after the FVP_Base_Cortex-A35x1 executable on the terminal/command line to lower the quantum value to 10 (it defaults to 10000).

Thanks,
-Zach

Hello Zach,

Thank you very much for your help. But the problem is still there. This is what I have done exactly. Could you please take a quick look to see is my CNTPCT_EL0 initialization enough? I observe the value in DS-5 debugger. 

On one terminal:

/usr/local/DS-5_v5.29.1/bin/FVP_Base_Cortex-A35x1 -a /usr/local/DS-5_v5.29.1/examples/Bare-metal_examples_Armv8/startup_Cortex-A35x1_AC6/startup_Cortex-A35x1_AC6.axf -C bp.secure_memory=false --quantum 10 -S
terminal_0: Listening for serial connection on port 5000
terminal_1: Listening for serial connection on port 5001
terminal_2: Listening for serial connection on port 5002
terminal_3: Listening for serial connection on port 5003

Info: FVP_Base_Cortex_A35x1: CADI Debug Server started for ARM Models...

On the other terminal:

$ /usr/local/DS-5_v5.29.1/bin/debugger --cdb-entry "ARM FVP::Base_A35x1::Bare Metal Debug::Bare Metal Debug::Debug Cortex-A35" --image "/usr/local/DS-5_v5.29.1/examples/Bare-metal_examples_Armv8/startup_Cortex-A35x1_AC6/startup_Cortex-A35x1_AC6.axf"
Connected to stopped target ARM_Cortex-A35
>set $CNTP_CTL_EL0=1
>set $CNTFRQ_EL0=35000000
>p/x $CNTP_CTL_EL0
$1 = 0x5
>p/x $CNTFRQ_EL0
$2 = 0x2160EC0
>where
#0 [start64]
>p/x $CNTPCT_EL0
$3 = 0x0
>n 20
Execution stopped in EL3h mode at EL3:0x0000000080000050
In startup.S
EL3:0x0000000080000050 103,0 msr HCR_EL2, x2
>p/x $CNTPCT_EL0
$4 = 0x0
>n 20
Execution stopped in EL3h mode at EL3:0x00000000800000A0
EL3:0x00000000800000A0 196,0 isb
>p/x $CNTPCT_EL0
$5 = 0x0
>n 20
Execution stopped in EL1h mode at EL1N:0x00000000800000F0
EL1N:0x00000000800000F0 LDR x0,[pc,#360] ; [0x80000258] = 0x80007240
>p/x $CNTPCT_EL0
$6 = 0x0
>n 20
Execution stopped in EL1h mode at EL1N:0x0000000080000118
EL1N:0x0000000080000118 MSR MAIR_EL1,x1
>p/x $CNTPCT_EL0
$7 = 0x0
>n 20
Execution stopped in EL1h mode at EL1N:0x0000000080000140
EL1N:0x0000000080000140 LDR x22,[pc,#312] ; [0x80000278] = 0x800AA000
>p/x $CNTPCT_EL0
$8 = 0x0
>n 20
Execution stopped in EL1h mode at EL1N:0x0000000080000168
EL1N:0x0000000080000168 SUB x3,x5,#1
>p/x $CNTPCT_EL0
$9 = 0x0
>n 20
Execution stopped in EL1h mode at EL1N:0x0000000080000190
EL1N:0x0000000080000190 ADD x1,x1,#0x200,LSL #12
>p/x $CNTPCT_EL0
$10 = 0x0
>n 20
Execution stopped in EL1h mode at EL1N:0x00000000800001B8
EL1N:0x00000000800001B8 BL {pc}+0x178 ; 0x80000330
>p/x $CNTPCT_EL0
$11 = 0x0
>n 20
Execution stopped in EL1h mode at EL1N:0x00000000800001E0
EL1N:0x00000000800001E0 AND x4,x4,#0xffffffffffe00000
>p/x $CNTPCT_EL0
$12 = 0x0

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

Jason,

It's validated. You saved my week. Thank you so much. 

Tao