Mail Archives: djgpp-workers/1999/05/18/08:01:42
Somebody reported enough details on c.o.m.d., so I looked into this. It
seems like Windows waits until the next timer tick before its virtualized
timer device begins to behave according to the new mode. The code below
simply waits until then before returning to the caller, the first time
uclock is called. This seems to eliminate the problem of negative
results during the first 55msec, at least on my Windows 95 machine.
Does anybody see any danger in waiting like this, on the first call
only? If not, I will check this in.
*** src/libc/pc_hw/timer/uclock.c~0 Mon May 17 09:34:50 1999
--- src/libc/pc_hw/timer/uclock.c Mon May 17 09:47:20 1999
***************
*** 1,9 ****
--- 1,11 ----
/* Copyright (C) 1996 DJ Delorie, see COPYING.DJ for details */
/* Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details */
#include <time.h>
+ #include <errno.h>
#include <pc.h>
#include <libc/farptrgs.h>
#include <go32.h>
+ #include <dpmi.h>
#include <libc/bss.h>
static int uclock_bss = -1;
*************** uclock(void)
*** 26,31 ****
--- 28,35 ----
if (uclock_bss != __bss_count)
{
+ int e = errno;
+
/* switch the timer to mode 2 (rate generator) */
/* rather than mode 3 (square wave), which doesn't count linearly. */
*************** uclock(void)
*** 36,41 ****
--- 40,60 ----
base = 0;
last_tics = 0;
uclock_bss = __bss_count;
+
+ /* It seems like Windows 9X virtualization of the timer device
+ delays the actual execution of the above command until the
+ next timer tick. Or maybe it only consults the actual device
+ once per tick. In any case, the values returned during the
+ first 55 msec after the timer was reprogrammed still look as
+ if the timer worked in mode 3. So we simply wait for one clock
+ tick when we run on Windows. */
+ _farsetsel(_dos_ds);
+ otics = _farnspeekl(0x46c);
+ do {
+ errno = 0;
+ __dpmi_yield(); /* will set errno to ENOSYS on plain DOS */
+ } while (errno == 0 && _farnspeekl(0x46c) == otics);
+ errno = e;
}
/* Make sure the numbers we get are consistent */
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