Date: Wed, 03 Jan 1996 16:25:40 +0100 From: Poul-Henning Kamp <phk@critter.tfs.com> To: Luigi Rizzo <luigi@labinfo.iet.unipi.it> Cc: jkh@time.cdrom.com, hasty@rah.star-gate.com, freebsd-hackers@freebsd.org Subject: Re: FreeDetect & Plug n Play Message-ID: <1547.820682740@critter.tfs.com> In-Reply-To: Your message of "Wed, 03 Jan 1996 15:48:07 %2B0100." <199601031448.PAA22549@labinfo.iet.unipi.it>
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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. I think the idea is you gate the RD,WR,IORD,IOWR strobes on the mother board, on a per slot basis. > I have recently come across a data sheet for a TI 16550 (UART) > clone with PnP support, and from the data sheet it seems that the > selection of specific devices is done in software by running a > protocol on a few I/O ports. yes, that's how it works. > Basically (details may be incorrect), ISA PnP devices all listen > for writes on a couple of ports (one is the printer status, so that > nobody should write there). There the CPU issues commands that are > understood by PnP devices. Using some binary-search technique one > can disable all but one device, identify it, set its I/O address > and other stuff, and then continue with the next devices. Yes, for PnP ISA devices, the slot-disabling was for handling old-fashioned non-PnP devices in PnP isa-slots. > 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. Yes, we are in agreement, it's two different mechanisms, to handle two different problems. -- Poul-Henning Kamp | phk@FreeBSD.ORG FreeBSD Core-team. http://www.freebsd.org/~phk | phk@login.dknet.dk Private mailbox. whois: [PHK] | phk@ref.tfs.com TRW Financial Systems, Inc. Future will arrive by its own means, progress not so.
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