Hi,
Whilst looking at the mc146818 code in vmd I noticed something that initially
struck
me as a pasto as the same code is present in the rtc_update_regb() function.
However
it led me to look at how other emulators handle the updating of registers.
Based on
that here's a diff to only reschedule the periodic interrupt after updating
register A
if something changed in register A.
When updating register A we were checking in register B if the
PIE bit was set in order to decide if rtc_reschedule_per needed
to be called. if that bit was changed then the timer rate would
already have been adjusted by rtc_update_regb so the call from
rtc_update_rega is not needed. This now matches what qemu and
other emulators are doing too.
This has been running fine for a few days in a number of VMs.
OK?
Index: mc146818.c
===================================================================
RCS file: /cvs/src/usr.sbin/vmd/mc146818.c,v
retrieving revision 1.18
diff -u -p -r1.18 mc146818.c
--- mc146818.c 12 Jul 2018 10:15:44 -0000 1.18
+++ mc146818.c 26 May 2019 12:13:32 -0000
@@ -216,7 +216,7 @@ rtc_update_rega(uint32_t data)
__func__);
rtc.regs[MC_REGA] = data;
- if (rtc.regs[MC_REGB] & MC_REGB_PIE)
+ if ((rtc.regs[MC_REGA] ^ data) & 0x0f)
rtc_reschedule_per();
}
--
jasper
