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Minimize clock inaccuracies during system boot

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The initial estimate for instructions per millisec (instpermses) was
much too low for modern CPUs, and was also only updated every 5
seconds.  Combined, these were causing the clock to be erratic during
the first 5-15 seconds of system boot.

This was easily noticed by running the MIPS benchmark program right
after a system boot, where instead of delaying 5 seconds, it might
only delay 2 seconds, and then would report a bogus MIPS rating.
Waiting a minute and running it again would give an accurate rating.

Adjusting the instpermsec initial value from 2000 to 40000 and
IPMSTIME time from 5000 ms to 1000 ms (every second vs 5 seconds)
fixes the problem.
This commit is contained in:
Jim Wilcoxson
2020-04-18 03:11:56 +00:00
parent cd2b4516e5
commit 4a1bfefa4a
2 changed files with 10 additions and 6 deletions
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8
emdev.h
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@@ -1530,15 +1530,15 @@ int devcp (int class, int func, int device) {
else if (cpuid >= 15) /* newer machines: 250 ticks/second */
clkpic = -1250;
TRACE(T_INST, "Clock PIC %d requested, set to %d\n", getcrs16s(A), clkpic);
SETCLKPOLL;
ticks = -1;
SETCLKPOLL;
} else if (func == 07) {
TRACE(T_INST, "Clock control register set to '%o\n", getcrs16(A));
if (getcrs16(A) & 020)
clkrate = 102.4;
else
clkrate = 3.2;
TRACE(T_INST, "Clock control register set to '%o\n", getcrs16(A));
ticks = -1;
SETCLKPOLL;
@@ -1586,7 +1586,7 @@ int devcp (int class, int func, int device) {
targetticks = elapsedms/(-clkpic*clkrate/1000);
#if 0
if (abs(ticks-targetticks) > 5)
printf("\nClock: target=%d, ticks=%d, offset=%d\n", targetticks, ticks, ticks-targetticks);
printf("\nClock: target=%d, ticks=%d, offset=%d, ipms=%d, poll=%d\n", targetticks, ticks, ticks-targetticks, gv.instpermsec, devpoll[device]);
#endif
/* if the clock gets way out of whack (eg, because of a host
@@ -1629,7 +1629,7 @@ int devcp (int class, int func, int device) {
XXX: this code should probably be done whether or not the
clock is running */
#define IPMTIME 5000
#define IPMTIME 1000
if ((gv.instcount < previnstcount) || (gv.instcount-previnstcount > gv.instpermsec*IPMTIME)) {
if (gv.instcount-previnstcount > gv.instpermsec*IPMTIME) {