Does anyone have a document describing what the PC/PCI aka SBLink signals actually are? I know what they're called - SERIRQ, PCI Sideband Grant, and PCI Sideband Request.

In other words, if one were trying to synthesize those signals from other PCI, ISA, and/or LPC bus signals, one would need to know exactly what the expansion card is expecting and how to interface that with the chipset.

• SERIRQ looks suspiciously like the LPC bus SERIRQ, but is it actually the same?
• The Grant / Request lines must be DMA grant / request, but they can't just be one of the normal PCI GNT/REQ pairs, since a PCI card already has access to those. It also can't be the LPC DMA method, since the DMA channel number is encoded onto the 4 LPC data lines. I would guess it's the ISA DMA lines serialized somehow, but the signal name doesn't say that.
• Are these signals synchronized with the PCI clock? That would make sense, especially if the PCI clock is synchronized as a multiple of the ISA clock (4x ISA).