sysTimestampFreq的问题?

PIII的处理器,使用Time Stamp,i8253Timer.c
config中设置
#define INCLUDE_TIMESTAMP



#define SYS_CLK_RATE 100     /*system clock rate:100 tick per 1sec*/



#ifdef INCLUDE_TIMESTAMP /* select TSC(default) or PIT2 */
#   undef  INCLUDE_TIMESTAMP_PIT2 /* include PIT2 for timestamp */
#   define INCLUDE_TIMESTAMP_TSC  /* include TSC for timestamp */
#   define PENTIUMPRO_TSC_FREQ 0 /* TSC freq, 0 for auto detect */
#endif /* INCLUDE_TIMESTAMP */
支持TSC



那sysTimestampFreq函数返回的sysTimestampFreqValue,sysTimestampFreq=399986561,但是它的意义是什么？在i8253Timer.c中只看到
sysTimestampFreqValue初始值＝0并没有其他赋值的地方了，那时候sysTimestampFreqValue被赋值399986561？




谢谢