From: joef@extro.ucc.su.OZ.AU () Subject: Re: AMD Cyrix chips etc. Date: Sun, 2 Aug 1992 00:03:03 GMT
apm233m@vaxc.cc.monash.edu.au writes:
>> .... When you
>> are asking the AMD chip to do a FPU instruction you can get delays of up
>> to _5_ milliseconds before the chip returns an error so that the Software
>> FPU emulation can kick in. This [unfortunatly] means that AMD chips go at
>> about the speed of a 8mhz XT .....
>> ........
>> ---
>> Disclaimer: My machine is a 386/33 - with an AMD chip w/o FPU. ....
>I don't understand. Are you saying that this is a problem just with 40MHz
>parts or just with 33MHz parts... or both?
I did make that a bit confusing, didn't I. :-\ Anyway it's on all the
AMD 386 series chips [as far as I know]
>My machine has a 33MHZ AMD 386 cpu and an OPTI chipset. I have written an
>80387 emulator which works with djgpp and I have done quite a bit of work in
>trying to get reasonable speed. Whenever I have checked the details of timings,
>I find that I can account for most of the cycles taken to emulate any function.
>The user-program-level performance of my emulator is: less than 100 microsec
>for basic arithmetic, less than one millisec for any other function.
>Maybe the timing problem you have found is due to the support chipset? Or
>perhaps the BIOS has not been told that an 80387 is not installed?
I'm not a CPU guru, and I'm just relaying what I saw in the *hardware
groups a few months back. As far as I recollect the CPU just halts for some
reason.
Joe