Date   : Thu, 08 Jan 2004 22:17:31 +0000 (GMT)
From   : Sprow <info@...>
Subject: Re: IDE Interface for BBC

Hi,
I keep thinking about this too, but at my last decision point I decided I'd
go for either compact flash or MMC with a bit of hardware assistance for an
SPI bus (simply because my camera takes MMC/SD cards). Compared with the
size of the average beeb program even a 256MB flash card is HUGE, costing
about £50 last time I looked. There are other reasons (see later).

Anyway, on to catching up...

In article <040106025502@...>,
   Jonathan Graham Harston <jgh@...> wrote:
> 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?

>          A3=low/high                       A0=low/high
>   FCx0  Data low byte              FCx0   Data low byte
>   FCx1  Error                      FCx1   Data high byte

Might be nice to have the transition from FCx0 -> FCx1 to autoincrement when
you read or write from FCx0.
Or hows about reading a whole 256 bytes and presenting it at FDxx? That's
probably a bit too much hardware effort - remember you're unlikely to get
more than about 25kbytes/s over the 1MHz bus if you're doing everything 8
bit and in PIO mode.

> 2: How useful would it be to be able to remove the hard drive from the BBC
> and plug it into an Arc and access it natively with RISC OS ADFS?  RISC OS
> supports ADFS/47 entries/old map, which is the ADFS used on 8bit Acorns. 

I'm pretty sure support for old map /fixed/ discs was removed from FileCore
sometime around RISC OS 3.1, referenced by knowing someone who tried reading
a SCSI I (SASI) drive on an Archimedes having removed it from a Master.

I'd suggest FAT format makes more sense.

Ripping the SCSI code out of beeb ADFS and using IDE instead is attractive
though.

[snip]

> Also, if there is no demand for drive interchangability, I can access the
> cylinder/head/sector in a different order. In fact, judging by the fact 
> that RISC OS<3.60
> falls over with drives larger than 500MB, I suspect that's exactly what
> RISC OS ADFS actually does.

The change from silly cylinder/head/sector addressing to LBA was the key, as
well as fixing a number of silly bugs in ADFS and FileCore, and busting
through the restrictions of several API's which had &20000000 as end of list
terminators. Please please please use LBA.
You could use drives bigger than 500MB, you just had to have a partition on
it.

In article <ykv$toHtDz+$Ewhy@...>,
   Mike Tomlinson <mike@...> wrote:
> Hard drives are large enough nowadays that the loss of half the capacity
> isn't a problem.  This simple 8-bit IDE interface for the Sinclair
> Spectrum does it like this (with one chip) - this may give you some
> ideas:  http://members.tripod.com/~piters/simpif.htm

The problem now is that harddrives are too big, and in order to coax BIOS'
they falsely claim they're 4G drives. The beeb will need to have a load of
interrogation code to work out their real size, or just give up and assume
it's a 4G drive.

In article <v5$oqYIriN$$Ewr9@...>,
   Mike Tomlinson <mike@...> wrote:
> Do you buffer the 1MHz bus (with a LS245 or similar)?

I hope so, as well as having the appropriate pass through connectors and
optional termination resistors.

> It'd be great to be able to stick one of those 2.5" laptop drives inside
> a Beeb and have an all-in-one unit.  Power would be no problem; it could
> be tapped off one of the power feeds and 2.5" drives only use 5v.

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)

Also, you'd need to support two IDC cable densities as laptop drives use
finer wire and smaller connectors.

In article <1073561853.17506.17.camel@...>,
   Jules Richardson <julesrichardsonuk@...> wrote:
> It's been a long time since I've looked at the IDE interface - isn't the
> a command (or maybe a physical attribute of the interface) to put the
> drive into 8-bit mode in order to maintain compatibility with the
> earliest IDE host interfaces? 

I don't think that's mandatory any more (or if it is, I've certainly seen
drives which don't bother).

In article <20040108132402.6B7B524EDF9@...>,
   Colin f <colin@...> wrote:
> If and when anyone does get an IDE interface working on the Beeb, and
> doesn't find they need multi-gigabytes of storage, I've found Compact Flash
> cards are great for use as IDE drives in old computers.
> CF has an ATA compatible mode, so you just need to buy an IDE to CF
> interface cable, which cost about a tenner last time I bought one.

Bingo - gets my vote!
Sprow.