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TIMER: Avoid clocks with changing tick rates as the primary calibrated timer

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Some simulators have clocks that have dynamically programmable tick
rates. Such a clock is only a reliable candidate to be the calibrated
clock if it uses a single tick rate rather than changing the tick rate
on the fly.  Generally most systems like this, under normal conditions
don't change their tick rates unless they're running something that is
examining the behavior of the clock system (like a diagnostic).  Under
these conditions this clock is removed from the potential selection as
"the" calibrated clock that all others are relative to and if necessary,
an internal calibrated clock is selected.
This commit is contained in:
Mark Pizzolato
2020-02-23 00:31:45 -08:00
parent 1725ed20db
commit 26fa91a335
1 changed files with 14 additions and 3 deletions
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17
sim_timer.c
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@@ -943,9 +943,9 @@ if (rtc->hz != ticksper) { /* changing tick rate? */
(rtc->last_hz != ticksper) &&
(ticksper != 0))
rtc->currd = (int32)(sim_timer_inst_per_sec () / ticksper);
_rtcn_configure_calibrated_clock (tmr);
rtc->last_hz = rtc->hz;
rtc->hz = ticksper;
_rtcn_configure_calibrated_clock (tmr);
if (ticksper != 0) {
RTC *crtc = &rtcs[sim_calb_tmr];
@@ -2451,6 +2451,16 @@ return SCPE_OK;
clock with an appropriate tick rate, an internal clock is run that meets
this requirement, OR when asynch clocks are enabled, the internal clock
is always run.
Some simulators have clocks that have dynamically programmable tick
rates. Such a clock is only a reliable candidate to be the calibrated
clock if it uses a single tick rate rather than changing the tick rate
on the fly. Generally most systems like this, under normal conditions
don't change their tick rates unless they're running something that is
examining the behavior of the clock system (like a diagnostic). Under
these conditions this clock is removed from the potential selection as
"the" calibrated clock all others are relative to and if necessary, an
internal calibrated clock is selected.
*/
static void _rtcn_configure_calibrated_clock (int32 newtmr)
{
@@ -2463,7 +2473,8 @@ for (tmr=0; tmr<SIM_NTIMERS; tmr++) {
rtc = &rtcs[tmr];
if ((rtc->hz) &&
(rtc->hz <= (uint32)sim_os_tick_hz) &&
(rtc->clock_unit))
(rtc->clock_unit) &&
((rtc->last_hz == 0) || (rtc->last_hz == rtc->hz)))
break;
}
if (tmr == SIM_NTIMERS) { /* None found? */
@@ -2499,7 +2510,7 @@ if (tmr == SIM_NTIMERS) { /* None found? */
SIM_INTERNAL_UNIT.action = &sim_timer_clock_tick_svc;
SIM_INTERNAL_UNIT.flags = UNIT_IDLE;
sim_register_internal_device (&sim_int_timer_dev); /* Register Internal timer device */
sim_rtcn_init_unit (&SIM_INTERNAL_UNIT, (int32)((CLK_INIT*CLK_TPS)/sim_int_clk_tps), SIM_INTERNAL_CLK);
sim_rtcn_init_unit_ticks (&SIM_INTERNAL_UNIT, (int32)((CLK_INIT*CLK_TPS)/sim_int_clk_tps), SIM_INTERNAL_CLK, sim_int_clk_tps);
SIM_INTERNAL_UNIT.action (&SIM_INTERNAL_UNIT); /* Force tick to activate timer */
}
return;