🚀 go-pugleaf

In article <1805.102.uupcb@ssr.com>, dick.zeitlin%acc1bbs@ssr.com (Dick Zeitlin) writes:
> JY> .                           The time should be accurate to at
>   > .least 10 ms but the clock() function in C and the other time
>   > .functions I've looked at are only accurate to 55 ms (because
>   > .it's updated 18.2 ticks/sec).
> 
> Read the timer-0 (or maybe it's timer-1) register at Port 0x40, which is
> used to generate that 18.2/sec tick.  That register is incremented at
> approx. 1.2 mHz.  It's a 16 bit register, and should provide sufficient
> resolution for your needs. <~>


DON'T just go ahead and read it.  You need to make sure what you get is
the actual time data.  This can be done with a simple latch instruction
to the timer chip (outp(0x43, 0)).  THEN you get the data from I/O 40H
in two bytes (LSB first, MSB 2nd).  Remember to give the poor chip some
time to recover between I/O to the same addr to support those designs
that don't automatically add wait states to slow down I/O operations.

The accuracy of the timer is 1/1193180 seconds and it should be used
with the DOS timer count that's in the BIOS data-area.

Aki.
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