GNUOrder gnuorder@tampabay.rr.com writes:
Is this the new mini micro ATX board with the C3 CPU and the VIA chipset? What kind of support does that have for an LCD screen? I was looking at the VIA site and I couldn't find out if the chipset had any digital video output. One other general question, is it possible to piggyback several devices onto a PCI slot or could you add some decoding to accomplish that?
The proper way of making a PCI riser card with multiple slots is to use a card with a PCI bridge on it. Such as this:
http://www.carypowder.com.tw/product/32bit_pci3202.htm
This card only presents one PCI load to the motherboard and the PCI bridge can then handle the 3 PCI slots on the riser card. As long as the motherboard can provide enough power to the PCI cards this is a perfectly legal design according to the PCI specs. This is probably what you want to do.
The el-cheapo way of putting more than one PCI card on a riser requires a lot of knowledge about the specific motherboard you are using. First of all, there are electrical limits (total capacitance, total loads and whatnot) that normally limits a board to about 5 PCI slots. So, with a board like this it should to be possible to just extend the wires to two slots with a passive riser card and still stay within the electrical limitations. Second, each PCI slot has a pin called IDSEL that is used for accesses to the PCI configuration space (pci_read_config_word and friends in the Linux kernel). Each slot has a unique pin, so the riser card has to "create" two IDSEL signals from somewhere. One way is to use a card such as this:
http://www.carypowder.com.tw/product/32bit_pci300-32.htm
I'm not 100% sure of how this card works, but a reasonable guess is that the extra wires are used to connect the IDSEL signal (and maybe power since there are so many wires) from other PCI slots, so I don't think this will work on the VIA card.
Now, normally the IDSEL pins are actually connected to the address bus, so for example IDSEL of PCI slot one is connected to AD12, IDSEL of PCI slot 2 to AD13 and so on. So if you know what you are doing (i.e. know the layout of the motherboard so that you can make sure there won't be any conflicts) you could just use two free pins of the address bus to create two new IDSEL signals.
So, it is possible to make a cheap passive riser card, but I doubt that it's worth the effort unless you are talking hundreds of riser cards.
/Christer (now I just wonder why I like to explain these kind of things in the middle of the night)