src/arch/i386/include/gpxe/rdtsc_timer.h

   1 #ifndef _GPXE_RDTSC_TIMER_H
   2 #define _GPXE_RDTSC_TIMER_H
   3
   4 /** @file
   5  *
   6  * RDTSC timer
   7  *
   8  */
   9
  10 FILE_LICENCE ( GPL2_OR_LATER );
  11
  12 #ifdef TIMER_RDTSC
  13 #define TIMER_PREFIX_rdtsc
  14 #else
  15 #define TIMER_PREFIX_rdtsc __rdtsc_
  16 #endif
  17
  18 /**
  19  * RDTSC values can easily overflow an unsigned long.  We discard the
  20  * low-order bits in order to obtain sensibly-scaled values.
  21  */
  22 #define TSC_SHIFT 8
  23
  24 /**
  25  * Get current system time in ticks
  26  *
  27  * @ret ticks           Current time, in ticks
  28  */
  29 static inline __always_inline unsigned long
  30 TIMER_INLINE ( rdtsc, currticks ) ( void ) {
  31         unsigned long ticks;
  32
  33         __asm__ __volatile__ ( "rdtsc\n\t"
  34                                "shrdl %1, %%edx, %%eax\n\t"
  35                                : "=a" ( ticks ) : "i" ( TSC_SHIFT ) : "edx" );
  36         return ticks;
  37 }
  38
  39 #endif /* _GPXE_RDTSC_TIMER_H */