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From:	RayeR <glaux AT centrum DOT cz>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: timing problems using uclock()
Date:	Sun, 30 Mar 2008 08:36:22 -0700 (PDT)
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I have also found some weird behavior of uclock()
I made udelay() function based on some other function using clock()
I use it for I2C and SPI communication under pure DOS. I don't know
what
exactly goes wrong but when using udelay() it sometimes trashes
communication
with SMBus host and it gets locked. If I replace say udelay(1000) by
delay(1) it doesn't
never happed. I tried udelay in a loops and measure run time but it
seems to be OK.
Maybe there's some random jitter. Any Idea how to make a precise
timer?

//***************** wait for delay us
***************************************
void udelay(DWord usec)                // based on precise 1us timer
uclock(), usable for 10us resolution
{                                      // works under DOS/Win9X/NT but
not Win3.x
  volatile uclock_t cl_time;
  volatile uclock_t start_time=uclock();
  if (usec==0)                         // pokud je prodleva nulova
    return;                            // tak hned skonci
  cl_time=(usec*UCLOCKS_PER_SEC)/977000;
  while (1)                            // cekaci smycka
    {
    clock_t elapsed=uclock()-start_time;
    if (elapsed>=cl_time)              // pokud citac dosel k cilove
hodnote
      break;                           // tak skonci
    __dpmi_yield();                    // vzdej se zbytku slice time
ve prospech jinych procsu
    }
}

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