Hi Aravind,

On Tue, Aug 16, 2016 at 4:33 AM, machiry aravind machiry_msidc@hotmail.com wrote:

Hi all,

I want to measure clock frequency in secure world. I am using the function: read_cntfrq (https://github.com/OP-TEE/ optee_os/blob/master/core/arch/arm/include/arm32.h#L529) to get it.

On Hikey, The value I get is: 1.2MHz,

Right. It is set by ARM Trusted Firmware, here: https://github.com/linaro-swg/arm-trusted-firmware/blob/hikey_gendrv/plat/hi...

is it scaled down or this is the actual frequency?

Looks like it is the actual frequency. I wrote a small test in non-secure world to check this. I'm reading CNTVCT_EL0 because CNTPCT_EL0 is not accessible to user space (access is disabled by the Linux kernel). But it's the same thing essentially.

#include <inttypes.h> #include <stdio.h> #include <time.h> #include <unistd.h>

uint32_t read_cntfrq() { uint32_t val;

asm volatile("mrs %0, cntfrq_el0" : "=r" (val)); return val; }

uint64_t read_cntvct() { uint64_t val; asm volatile("mrs %0, cntvct_el0" : "=r" (val)); return val; }

double ts_to_sec(struct timespec *ts) { return (ts->tv_sec + ((double)ts->tv_nsec)/1000000000); }

double ts_diff(struct timespec *ta, struct timespec *tb) { return ts_to_sec(tb) - ts_to_sec(ta); }

int main(int argc, char *argv[]) { uint64_t a,b; struct timespec ta, tb;

printf("cntfrq=%d\n", read_cntfrq()); a = read_cntvct(); clock_gettime(CLOCK_MONOTONIC, &ta); printf("ctnvct=%ld\n", a); *sleep(20);* b = read_cntvct(); clock_gettime(CLOCK_MONOTONIC, &tb); printf("cntvct=%ld\ndelta=%ld (%g/sec)\n", b, b-a, ((double)(b-a))/ts_diff(&ta, &tb)); return 0; }

root@HiKey:/ cntfrq cntfrq=1200000 ctnvct=67224235 cntvct=91224367 *delta=24000132* (1.2e+06/sec) root@HiKey:/

Now I'm wondering if the conter frequency is exactly 1.2 MHz, or if it's a multiple of the main CPU clock which is slightly less than 1.2 GHz (which is likely IMO):

NOTICE: Booting Trusted Firmware NOTICE: BL1: v1.1(release):9d3b0ec NOTICE: BL1: Built : 16:57:57, Aug 12 2016 *NOTICE: syspll frequency:1190494208Hz*

(this ARM-TF commit sets the syspll frequency to 1.19 GHz: https://github.com/linaro-swg/arm-trusted-firmware/commit/f88eff3cb154). You may have to make more precise measurements.

HTH, -- Jerome

Thank You,

Aravind

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