Date: Wed, 3 Jan 1996 15:48:07 +0100 (MET) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: phk@critter.tfs.com (Poul-Henning Kamp) Cc: jkh@time.cdrom.com, hasty@rah.star-gate.com, freebsd-hackers@FreeBSD.ORG Subject: Re: FreeDetect & Plug n Play Message-ID: <199601031448.PAA22549@labinfo.iet.unipi.it> In-Reply-To: <1142.820668770@critter.tfs.com> from "Poul-Henning Kamp" at Jan 3, 96 12:32:31 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. 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. 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. 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. Luigi ==================================================================== Luigi Rizzo Dip. di Ingegneria dell'Informazione email: luigi@iet.unipi.it Universita' di Pisa tel: +39-50-568533 via Diotisalvi 2, 56126 PISA (Italy) fax: +39-50-568522 http://www.iet.unipi.it/~luigi/ ====================================================================
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