minix/lib/libc/arch/arm/read_tsc.c

   1 #include <sys/types.h>
   2 #include <minix/minlib.h>
   3
   4 void
   5 read_tsc(u32_t *hi, u32_t *lo)
   6 {
   7 /* Read Clock Cycle Counter (CCNT). Intel calls it Time Stamp Counter (TSC) */
   8         u32_t ccnt;
   9
  10         /* Get value from the Performance Monitors Cycle Counter Register.
  11          * See ARM Architecture Reference Manual B5.1.113.
  12          */
  13         asm volatile ("MRC p15, 0, %0, c9, c13, 0\t\n" : "=r" (ccnt) : : "%0");
  14
  15         /* The ARMv7-A clock cycle counter is only 32-bits, but read_tsc is
  16          * expected to return a 64-bit value. hi is therefore always 0.
  17          */
  18         *hi = 0;
  19         *lo = ccnt;
  20 }
  21