RE: Subsystem Vendor and Device IDs

["Peter N. Glaskowsky" <png@woof.net>]

> Another suggestion is I2C ROMs.  I don't like this solution because every
> PCI device would need one.  With 3 PCI chips in the system, I would have
3
> fairly useless chips taking up space.  It would be really nice for this
> implementation if we could have 1 serial ROM that all 3 PCI devices would
> share.

It could be SPI ROMs, easier (and cheaper because SPI is free, while I2C
has a license fee, I think) to deal with than I2C ROMs. Or a Dallas
Semiconductor DS2502, which has a one-wire interface. (Or a special version
of their DS2401, which is normally a serial number device, but you could
probably get them programmed with the subsystem vendor & device ID info
instead.) Some of these SROMs are around $0.25 each, which is a reasonable
price to pay in exchange for proper Win95 compatibility.

But if the devices are on separate expansion card, you can't get them to
read from a common SROM, and if they're all on the motherboard, you don't
need them to. Program the BIOS to initialize the subsystem stuff if you
need to (you might not, since it's there for expansion cards anyway), and
make sure the devices don't reset their subsystem fields in response to a
software reset or allow those fields to be changed by a config write. If
you've put in this special mechanism to load the subsystem data at powerup,
then that should be the last time the data need to be changed.

..                    png



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