Re: [rtl] How to convert RDTSC tics to microseconds

[Tomasz Motylewski]

On Wed, 22 Sep 1999 [EMAIL PROTECTED] wrote:

> Is there any way to determine the CPU clock frequency so that I can divided
> timestamps from the RDTSC by frequency and get microseconds ?

I use the following code:


#define RDTSC2(h,l)   __asm__ volatile ("rdtsc" : "=a"(l) , "=d"(h))
#define RDTSC1(l)     __asm__ volatile ("rdtsc" : "=a"(l))


unsigned long scaler_ns;

int rt_time_ns_calibrate()  {
        union {
                unsigned long long ll;
                struct {unsigned long l,h; } st;
        } t1,t2;
        long long ns;
        RTIME tu1, tu2;
        long flags;

        rtl_no_interrupts(flags);
        RDTSC2(t1.st.h,t1.st.l);
        tu1=rt_get_time();

        while(rt_get_time() < tu1 + (CALIBR_FOR_us*RT_TICKS_PER_SEC)/1000000);

        RDTSC2(t2.st.h,t2.st.l);
        tu2=rt_get_time();
        rtl_restore_interrupts(flags);
        ns=(tu2-tu1)*1000000000LL/RT_TICKS_PER_SEC;
        scaler_ns=((t2.ll-t1.ll)<<16)/ns;
        return 0;
}

#define ns2clocks(t_ns) ((unsigned long)(((unsigned long long)t_ns*scaler_ns)>>16))


The I use in init_module :

        rt_time_ns_calibrate(); /*calibrate ns resolution timer (Pentium only)*/
        printk("scaler_ns=%d, this is %d kHz, %d\n",scaler_ns,(long)(((long
                long)scaler_ns*1000000)>>16), ns2clocks(1000000));



--
Tomek

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