Turnbull China Bikeride/Turnbull China Bikeride - Disc 2.iso/BARNET/ARMLINUX/MAIL/9805/000140_owner-linux-arm…r.rutgers.edu _Sat May 23 19:47:20 1998.msg

Internet Message Format | 1998-06-02 | 4KB

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From: Theo Markettos <[e-mail]>
Subject: Re: PowerROMmed cards
Reply-To: [e-mail]
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Date:     Sat, 23 May 1998 15:17:30 +0100
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On Fri, 22 May 1998 22:54:01 +0100 (BST), [e-mail] said:

> Theo Markettos writes:
> > > I think that it may be possible to detect the card by the location of
> > > the  FAS216 (or NCR53C9x) chip.  I personally think that the drivers
> > > should not load/initialise if they can't detect the SCSI chip where
> > > they believe it should be.  This would then get around these problems.
> >
> > That sounds _very_ dodgy.  Firstly, IIRC some cards used a 5380
> > (A3000-style  8 bit ones spring to mind).  Secondly, if I had to design a
> > podule with a ROM, page latch and SCSI chip in 4K of address space, there
> > are a few obvious ways to do it, which might be used on more than one
> > card, which would make telling the difference difficult.  Also, hardware
> > probing may well be dangerous - you may be accessing read sensitive
> > hardware, which could do nasty things (like generate an interrupt or FIQ)
> > that you're not expecting.
>
> Hang on - what I said was 'should not load'.  In other words, you're trying
> to  put a driver in that might not be correct for the card.  If you don't
> check that the SCSI chip is there, then you'll read/write it anyway later
> to initialise  it and perform the SCSI bus scan.

I see - so you mean that once you've worked out what card it is and
therefore what the memory map is, you then check to see whether the chip is
where you think it is, and if it's not then you don't initialise the driver.
That makes sense - it's something that might be handy for all podules, SCSI
or not.  If there's, say, a bad connection with the podule bus, you might be
able to read the ROM without problems, then find that you couldn't access the
driver chip.  If this was in the middle of some critical data transfer the
driver might hang waiting for a ready signal that never came because the chip
wasn't being read and rubbish was returned instead.

Apologies if this already happens for most drivers - I'm speaking as a RISC
OS and hardware person with a users knowledge of Unix, not a Unix hacker.

Cheers,
Theo

--
Theo Markettos          Home:   [e-mail]
Liphook                 Work:   [e-mail]
Hampshire
UK                      Web site, including Acorn backup software
                        http://www.marketto.demon.co.uk/

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