Date   : Sun, 24 Jul 2005 17:46:40 +0100
From   : Philip Pemberton <philpem@...>
Subject: Re: ARM copros, speech cartridges, real time clocks, etc

In message <1122206439.10259.37.camel@...>
          Jules Richardson <julesrichardsonuk@...> wrote:

> I seem to recall the need for the 6502 was partly due to speed
> limitations at the ISA bus, and partly due to the overhead in processing
> on the PC itself. 
> 
> The second bit would unlikely be a problem these days. Not sure about
> the former as I don't know what USB throughput is like compared to the
> ISA bus.

About twice as fast IIRC.
PCI is much faster - 33MHz main clock (IIRC - might be 66MHz), with
burst-transfer modes and other nice little things to make bus transfers oh so
much faster :)

Simple way: FPGA + PIC + serial EEPROM. Blow the microcode (fuse map) for the
FPGA into the SEEPROM, then rig the PIC to upload said microcode at boot
time. By the time the BIOS does a PCI scan, the card should be up and
running.
If you feel pedantic, you could use a CPLD instead. That would eliminate the
PIC and the E2PROM, and would also be active at boot time. The only problem
you might have is lack of I/O lines and (maybe) difficulty of upgrading the
microcode.

> Oh, I have heard a rumour that Econet for the VAX machines was done by
> attaching a BBC micro to the VAX, and the VAX would talk to the BBC
> (presumably over the 1MHz bus) and let the BBC do the interfacing to the
> rest of the network. 

Eww! Talk about over engineering...

> With a bit of ROM code on the bbc side it could give the PC Econet
> ability, or allow fast transfers of data from the PC's disk to the BBC,
> or let you use the BBC's floppy drives from the PC to do archiving etc.

Floppy controller - Microchip USB PIC + 8271 (or 1771). What's so hard about
that? Or go the PCI->CPLD->ISA->8271/1771 route if you're hellbent on PCI.

Later.
-- 
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem@...                        | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.me.uk/          | 48xCD, ARCINv6c IDE, SCSI
... Error - [A]bort, [R]etry, [F]ake like it's working...