Re: Two PCI device with the same Dev. ID & Vendor. ID

["Thomas J. Merritt" <tjm@cgt.com>]

|<><><><><> Original message from Andrew Ircha  <><><><><>
|Young-Su Kwon wrote:
|> Information that I have found :
|> 1. In PCI 2.2 spec., there is "subsystem ID" but that is not for
|> the cards from the same manufacturer.

Subsystem ID is for the case when the PCI chip is designed and manufactured
by a different company than designs and manufactures the PCI card.  The
PCI subsystem ID identifies the PCI card manufacturer.  For your case this
sounds like it should be the same for both cards.

|> 2. Although "subsystem ID" is supported in PCI 2.2 spec., the
|> Windows device driver does not have "subsystem ID".
|> 3. This problem is the same for the case when two grahics cards
|> that are the same model from one manufacturer are installed.
|> 4. I remember that two PCI voodoo cards
|> (Old model of graphics card from Voodoo) can be installed
|> to boost up the system performance. How can it be possible?
|
|The subsystem vendor ID should have your company's number, which is
|assigned by PCI-SIG. The subsystem device ID is your choice. So I think
|point 1 is incorrect.
|
|The Windows driver usually reads the vendor id, device id, subsystem
|vendor id, subystem device id and revision to install the correct
|drivers - so I think point 2 is incorrect most of the time. Do you mean
|that you can't see the "subsystem ID" in the device manager?

I beleive that Windows NT will only call the device driver once to
probe the device/devices.  If you want your NT driver to support more
than one device it is necessary to iteratively claim each device that
you support.  If you don't claim all of the devices, then you will only
get the first device and the remaining devices will be disabled.

|I don't know how you can plug two graphics cards into one workstation
|and expect them both to work. If that were the case, why would people go
|to the trouble of making twinhead graphics cards?

It all depends upon the device driver.  Many graphics cards have device
drivers that support multiple similar or identical boards.  

TJ Merritt
tjm@codegen.com
1-415-834-9111