Messages in this thread | | | Date | Fri, 27 Nov 1998 10:59:41 +0100 | From | Harald Koenig <> | Subject | Re: The history of the Linux OS |
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On Nov 26, Brandon S. Allbery KF8NH wrote:
> In message <Pine.LNX.4.05.9811252223010.11212-100000@tahallah.demon.co.uk>, > Ale > x Buell writes: > +----- > | On Wed, 25 Nov 1998, Brandon S. Allbery KF8NH wrote: > | > Linuxers, marred only by small issues such as (IIRC) ATI and S3 video > | > cards vs. COM4. And it's right smack in the middle of the list of > | > | Ah yeah, the infamous COM4 bug with S3 chipsets. Seems some fuckwit used > | the usual COM4 I/O port as one of its I/O registers. Ahh, that particular > | chipset designer should have been taken out and made to use Microsoft > | products in eternity (with a Windows 95 Beta!). > +--->8 > > Not exactly. > > The ATI and S3 chipsets started out as enhancements of IBM's 8514/A video > card. But the 8514/A was designed for Microchannel, which addresses the > entire I/O space. So the 8514/A used several registers with addresses > 0xX2e8, for several values of X. > > The ISA bus only has 10 I/O address lines, so I/O addresses above 0x03FF > effectively wrap around. The 8514/A ports ended up aliased to 0x02e8....
nope! the ISA bus has _16_ I/O address lines. but there are some (broken!) serial cards around which only decode 10 address bits and thus cause address aliases/ghosts and collisions...
> Arguably the bad design decision was to base an ISA card on the 8514/A. It > couldn't be IBM's decision because (a) there was no wraparound on > Microchannel and (b) Microchannel is perfectly capable of sharing IRQs, so > COM4 could be on IRQ3 as originally documented without conflicting with COM2 > (and (c) they never intended 8514/A for use on ISA systems).
it _is_ IBM who made this broken decission! check the schematics in IBM PC/XT technical handbook for their serial card (`async. communication adapt.'): they're using a single 74LS30 (8port NAND) to decode AEN and A3...A9 adresses -- A10 to A15 aren't touched at all:(
Harald -- All SCSI disks will from now on ___ _____ be required to send an email notice 0--,| /OOOOOOO\ 24 hours prior to complete hardware failure! <_/ / /OOOOOOOOOOO\ \ \/OOOOOOOOOOOOOOO\ \ OOOOOOOOOOOOOOOOO|// Harald Koenig, \/\/\/\/\/\/\/\/\/ Inst.f.Theoret.Astrophysik // / \\ \ koenig@tat.physik.uni-tuebingen.de ^^^^^ ^^^^^
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