Date   : Wed, 15 Dec 2004 22:55:21 +0100
From   : John Kortink <kortink@...>
Subject: Re: Debugging ADFS and IDE drives

On Wed, 15 Dec 2004 21:17:54 +0000 (GMT), Sprow wrote:

>In article <041215005502@...>,
>   Jonathan Graham Harston <jgh@...> wrote:
>> > Message-ID: <041213145502@...>
>>  
>> Yes! YES! *YES!* <fx: pulls clenched fist down, lifting knee slightly>
>>  
>> It works!
>
>Sounds like it's all down hill from here now.
>
>[...]
>
>Worth checking your 1MHz bus terminators, I don't buy the ground bounce
idea
>as there's acres of low impedance copper on the back of the board, but I
>like Pete's idea of trying some other magic patterns
> eg. &FF/&FE
> so what does &FF/&7F do?
> what about a few sectors of alternating &AA/&55

IMHO it's useless trying that, since it cannot have
any significance. Never try to rationalise chaotic
behaviour, it's a waste of time.

>The 1MHz bus is so slow my money would be dodgy drive!

Possible but extremely rare. What I do know is *all* IDE
drives adhere to :

- setup parameters
- issue command
- wait for DRQ
- do exactly 256 reads or writes
- DRQ guaranteed low

It's just so basic. If it doesn't do that right, no machine,
be it PC or BBC, will be able to use such a drive. Like I
said earlier, trivially easy test : hang it off a PC and try
the magic patterns that bring it down on the beeb.

All I've ever found 'different' in IDE drives is

a) Drives not updating CHS post-access
b) Drives not reacting to generic init sequence when
   very specific delays between commands are observed
c) Presence/absence of LBA mode

Never in data transfer. Like I said, it's so basic. It should
simply work.


John Kortink

-- 

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