On 16 Jun 2014, at 08:28, Michael Tuexen <tue...@freebsd.org> wrote:
> your patch for accessing the value is correct. However, the initialisation
> code also
> needs to be adopted to the platform. So in addition to your patch, you also
> need:
Thanks!
> Is there an easy test to see if the code actually works as expected and not
> that it just
> allows the system to boot?
Yes. :-)
#include <sys/types.h>
#include <stdio.h>
static __inline uint64_t
get_cyclecount(void)
{
uint32_t ccnt;
uint64_t tsc;
/* Read CCNT. */
__asm __volatile("mrc p15, 0, %0, c15, c12, 1": "=r" (ccnt));
tsc = (uint64_t)ccnt;
return (tsc);
}
#define N 100000
int
main(int argc, char *argv[])
{
int i;
uint64_t ccnt[N];
for (i = 0; i < N; i++)
ccnt[i] = get_cyclecount();
for (i = 1; i < N; i++)
printf("%6d %016llX %16llu\n", i, ccnt[i], ccnt[i] - ccnt[i -
1]);
return (0);
}
Should print a whole lotta numbers, incrementing, unless you hit the wraparound.
> Regarding the 32-bit limitation: Do we want to increment the register only
> every
> 64 clock cycle?
Definitely not! The value is in the low bits; wrap is of little consequence.
M
--
Mark R V Murray
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