Date   : Sat, 10 Jan 2004 11:46:19 +0000 (GMT)
From   : Sprow <info@...>
Subject: Re: IDE Interface for BBC

In article <040110060610@...>,
   Jonathan Graham Harston <jgh@...> wrote:

[snip]

> > > I'm building a prototype IDE interface for the BBC. I think if I'm 
> > > careful I can get it down to a two-chip solution.
> > 
> > Presumably this doesn't include the 1MHz bus address decode and nPGFD 
> > clean up?
>  
> Yes it does. 3/4 of a quad NOR to clean nPGFC. 2 halves of a twin 2->4
> decoders to decode the address. 1/4 of a quad NOR to convert R/nW to nRD.

So how do you slow the beeb down if the drive asserts IORDY while it spins
up or seeks (which can take longer than 1us)?

[snip]

> > Eek! Please look at the current requirements from 5V, especially the 
> > surge
> > required to spin the drive up. Remember: unlike floppies, the harddisc is
> > always spinning (well, unless someone adds power down code)
>  
> Looking at the drives I have here, the requirements are:
>   5v:  275mA   350mA   500mA
>   12v: 250mA   280mA   290mA
>  
> The BBC's auxilary power socket is rated at:
>   5v: 1250mA    [Master 900mA]
>  12v: 1250mA    [Master 1A]

But no indication of the spin up requirements?

[snip]

> > > I'd prefer to stick with Acorn format and make it as compatible as
> > > possible with the Acorn Winchesters and ADFS.  It can then be prepped
> > > with SuperForm.  Using a PC format would require a new FS ROM to be
> > > written,
> > 
> > Done.
> > http://www.sprow.co.uk/bbc/dosfs.htm
>  
> Sprow, when I get the card working and get some PCBs fabricated, would you
> like one so you can add hard drive support to your DOSFS?

Slicing out the FAT12 support, adding FAT16 support, adding a HDD driver,
amongst other things could be interesting. Only got about 200 bytes free in
the ROM!
Will JGH be supplying a ROM which implements some get/put sector API via an
OSWord (thus allowing other FS' to use the interface without having to mess
around writing IDE drivers)?

>  
> > Excellent point. It would be *definitely* worthwhile popping 8k of SRAM 
> > on the IDE interface?
>  
> I was thinking of making the FS software see if there was any extended RAM
> available, on a byte-wide card such as Sprow's or a page-wide card in
> &FD00 and have the option of using that, rather than put a RAM card on the
> IDE card. 

Fair enough. My experience with being permanently short of RAM in writing
DOSFS and wanting to cache the entire FAT would suggest any RAM would help
massively. I could have raised PAGE and kept more of the FAT, my point being
that the free space map is likely to be much bigger for a HDD and hence to
keep PAGE as low as possible just sticking a cheapo 6264 on the interface
might be worth while - especially if the intention is to make a PCB longterm
as you can use SMD and put it on the back.

In article <27uO6EDsM9$$EwoH@...>,
   Mike Tomlinson <mike@...> wrote:
> Perhaps it could also search for usable sideways RAM?

Again, that would be better than none at all, but as the FS is in sideways
ROM the paging effort would make it slower than a 1MHz affair,
Sprow.