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PDP10: Ignore 0 value writes to the timer interval register

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This avoids a divide by zero which is never right, but it is unclear
what the real hardware did.  It wouldn't be useful in any case.

As discussed in #486
This commit is contained in:
Mark Pizzolato 2017-11-14 18:47:05 -08:00
parent 107f620f4c
commit 3eadc405d0
1 changed files with 5 additions and 1 deletions
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6
PDP10/pdp10_tim.c
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@ -297,7 +297,7 @@ int32 old_clk_tps = clk_tps;
/*
* The value provided is in hardware clicks. For a frequency of 4.1
* MHz, that means that dividing by 4096 (shifting 12 to the right) we get
* the aproximate value in millisenconds. If any of rhe rightmost bits is
* the aproximate value in milliseconds. If any of the rightmost bits is
* one, we add one unit (4096 ticks ). Reference:
* AA-H391A-TK_DECsystem-10_DECSYSTEM-20_Processor_Reference_Jun1982.pdf
* (page 4-37)
@ -305,6 +305,10 @@ int32 old_clk_tps = clk_tps;
tim_new_period = new_interval & ~TIM_HWRE_MASK;
if (new_interval & TIM_HWRE_MASK) tim_new_period += 010000;
if (tim_new_period == 0) {
sim_debug (DEB_TPS, &tim_dev, "update_interval() - ignoring 0 value interval\n");
return FALSE;
}
/* clk_tps is the new number of clocks ticks per second */
clk_tps = (int32) ceil(((double)TIM_HW_FREQ /(double)tim_new_period) - 0.5);
if (clk_tps != old_clk_tps)