Date: Wed, 3 Jan 1996 12:43:59 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Cc: phk@critter.tfs.com, jkh@time.cdrom.com, hasty@rah.star-gate.com, freebsd-hackers@FreeBSD.ORG Subject: Re: FreeDetect & Plug n Play Message-ID: <199601031944.MAA15328@phaeton.artisoft.com> In-Reply-To: <199601031448.PAA22549@labinfo.iet.unipi.it> from "Luigi Rizzo" at Jan 3, 96 03:48:07 pm
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> > There actually is a P&P for ISA, where the motherboard completely disables > > all but one slot, so you know what you found where. > > I must first say that I don't know exactly how PnP works on ISA, > but I believe that in the standard there are no dedicated lines on > the ISA bus so that one can disable a single slot. There are two mechanisms. Some ISA implementations implement PNP controls for all slots. This means you can disable the slots per the normal PNP mechanism and do the probing. For ISA systems without this feature (almost all of them, in other words), you disable the PNP cards and probe the fixed location cards. The card/slot disabling is done by writing to one of the "unused" LPT port addresses (quoted because IBM and several other "enhanced" LPT port cards actually used the addresses and so are "incompatible" with PNP). Then you abbreviated binary search enable the PNP cards, query them, and establish mapping templates for DRQ, IRQ, and address range(s). After you have all the templates, you do a topological sort to make them not collide, and go back and establish mappings. If you have non-PNP ISA cards at fixed locations, you make fake single zone mappings for them and include them in the sort (making them dead areas unavailable to the real PNP cards). > To come back to Poul's mail: in general, it should not be the > motherboard which disables the slot, it is the software that disables > PnP cards. Of course *some* motherboards might do what Poul says, > but this is not generally applicable. On the other end, PnP compliant > devices should work on all motherboards. Poul's right: they do. Consider a PNP PCMCIA device. The bridge chipset that establishes the ISA mapping for the device (there are six basic bridge chipsets) is the same thing (effectively) as a mappable PNP device directly connected. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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