On most
machines of 486 or better, the loop topped out at somewhere
around a 500khz sample rate. This is entirely bus speed limited - some
P4s do worse than some 486s.
The P4 comment implies that *all* PC's have this upper limit
(enforced in hardware? or, emulated in software??)
I can't say with any certainty that *all* PC's are so limited, however I tried
my code on several P1, P2, P3 and P4 machines with a fairly consistant
upper limit of somewhere around 500khz ... Certainly any ISA pports would
have this limit, however I observed similar results with the on-mainboard
pports of the later machines. I would guess that since these appear in the
ISA address space, the chipset is providing ISA timing.
I have not tried it on a PCI pport - the software is DOS based, so there is
no PCI driver, although one should be able to have the BIOS set it up - I
*think* I have a PCI pport card around here somewhere...
I'm pretty sure it's not a software thing, as this code runs under plain old
DOS and contains nothing to artifically limit the port speed.
Sorry, thats I all I can give you - my observations. I do not have official
specs for non-ISA pports. I'll see if I can find a PCI card and test it.
Regards,
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools:
www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html
