Date   : Sat, 12 Jun 2004 16:28:33 +0200
From   : John Kortink <kortink@...>
Subject: Re: Solid state storage for the beeb

On Sat, 12 Jun 2004 13:11:01 +0100, Sprow <info@...> wrote:

>[...]
>
>What would be really great would be a 1770 emulation layer

I don't doubt that'll happen. My primary concern is with running
games, so I started with a bog standard 8271 FS. It wasn't much
work doing the emulation layer for that, only a couple of days
work. The 1770 won't be any different.

>, then with support to spot the DOS partition table, and my DOSFS.
>This way it could also be used for transferring lumps of data from
>the PC (well, via my digital camera and a USB cable actually) in
>edition to every floppy disc I ever had.
>
>I must say I'd be a little surprised if you can get 64kB/s over what is
>effectively a synchronous serial link, the 24bBC RAM disc musters about
>20kB/s using the 1MHz bus with a really tight loop - if the beeb is
running
>about 0.5MIPS then you'd have to be slurping one byte every 8
instructions.

Yes, but the interface optimization I mentioned entails
conversion of the serial link to a parallel one (by using
a CPLD between beeb and MMC). This will I/O bits to/from
the card at, say, 8 MHz (20 MHz is the maximum for current
MM cards, but this will hardly be necessary in this case).
I can probably make do with one port access per byte, which
would take the transfer speed even higher (the MM card should
be able to keep up easily).

>Perhaps a few words about the hardware John? Maybe *it's* doing all the
hard
>work and the beeb just polls a location or sits on the NMI line doing
page
>long bursts?

Just polled I/O. The DFS doesn't go into NMI. The read/write
command is emulated directly.


John Kortink