Guys ('n Gals, too! Any out there ?)

Could you point me to a quick tute or sample code for accurately measuring the
frequency of the ISA-BUS in MHz (using the frame buffer of an old VGA) ? Assume the
processor speed is known or determined in advance.

TIA very much, happy Easter to those who celebrate it.

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Cz.
Posted on 2004-04-09 07:59:08 by Czerno
Well my guess is to go and look for a timing diagram on the ISA bus, and do a byte-by-byte write into the VRAM on ISA device. From the timing diagram you can get how many clk cycles it takes for the ISA bus to complete one write cycle and then take the amount of bytes written per second and multiply it by that value and you'll get the bus speed in Hz. This will probably not give you an accurate value but it may be close enough.
Posted on 2004-04-09 19:48:10 by x86asm
x86asm wrote : "... and do a byte-by-byte write into the VRAM on ISA device. ..."

Yes, but, which kind of memory writes ? I want to avoid dealing with unpredictable delays caused by wait-states, caching and the like. My routine should reliably estimate the ISA bus speed without knowing any chpset specifics !

Shouldn't I try timing a long REP MOVSW into the video buffer ? I guess I'll have to experiment anyway... And thank you for your comment!
Posted on 2004-04-13 05:05:40 by Czerno