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Implement a real delay() that at least approximates a usec delay.

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This commit is contained in:
briggs 1994-12-03 14:03:23 +00:00
parent c169980753
commit f04205a867
1 changed files with 40 additions and 5 deletions
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45
sys/arch/mac68k/mac68k/clock.c
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@ -1,4 +1,4 @@
/* $NetBSD: clock.c,v 1.10 1994/10/26 08:46:55 cgd Exp $ */
/* $NetBSD: clock.c,v 1.11 1994/12/03 14:03:23 briggs Exp $ */
/*
* Copyright (c) 1988 University of Utah.
@ -361,10 +361,45 @@ void resettodr(void)
printf("WARNING: cannot set battery-backed clock.\n");
}
/*
* The Macintosh timers decrement once every 1.2766 microseconds.
* MGFH2, p. 180
*/
#define CLK_RATE 12766
/*
* delay(usec)
* Delay usec microseconds. This is inaccurate because it
* assumes that it takes no time to actually execute. We should
* try to compensate for this sometime because access to the via
* is hardly cheap.
*
* Paranoia can be removed whenever... ;-)
*/
void
delay(n)
int n;
delay(int usec)
{
n *= 1000;
while (n--);
int ticks, paranoia=0x10000000;
int t, timerh, timerl;
if (usec <= 0) usec = 1;
ticks = usec / CLK_RATE;
ticks = ticks * 10000;
while (ticks) {
t = min (ticks, 65535);
timerh = (t & 0xff00) >> 8;
timerl = (t & 0xff);
via_reg(VIA1, vT2C) = timerl;
via_reg(VIA1, vT2CH) = timerh;
while (!(via_reg(VIA1, vIFR) & V1IF_T2) && paranoia)
paranoia--;
ticks -= t;
}
if (!paranoia) printf("paranoia in delay()!!!\n");
}