>>With a help of Ed (DXForth creator) the problem is recognized; Ed wrote:
>>
>>#v+
>> 4DOS (or something associated with it) is setting PIT timer 0
>> from mode 3 to
>> mode 2 - which in turn is causing MS in DX-Forth to run slow.
>>#v-
> Nice find, didn't really expect that. Any hints in the sources as to
> why they are fiddling with the timer?
my own sources say
; \sources\tomlib\mikro.asm 17.mai.87 tom
;
; routinen fuer precise zeitmessung auf PC/AT (quelle && idee BYTE 1'87 S.157)
; precision ca. +- 2 musec
IIRC:
timer mode 3
for (;;) {
count down ffff..0, set output high and trigger interrupt
count down ffff..0, set output low
}
as each output high corresponds to one timer interrupt,
you see the values 0..ffff *twice* per timer interrupt;
so this mode is useless if you want have better then 50 msec
resolution for events possibly longer then 25 msec
timer mode 2
for (;;) {
count down ffff..0, trigger interrupt
}
can be used across a timer interrupt, with 0.86 micro second resolution
unfortunatrely, IBM in their infinite wisdom initialized the original
PC/AT timer in mode 3, for whatever reason
Tom
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