Date   : Fri, 19 Sep 2008 06:45:00 +1000
From   : msmcdoug@... (Mark McDougall)
Subject: BBC Micro on an FPGA?

michael.firth@... wrote:

> Have you got any more information on what hardware is needed for the
> 'PACE' project, and where it is available from?

<http://pacedev.net/forums/showthread.php?t=3>

> Your sites seem to have a lot of information about the software /
> firmware side of the project, but don't have much on what hardware is
> needed to use it - e.g. what format the CVBS interface would take.

Currently the composite output is designed for an ADV724, so it's strictly 
RGB out with composite video timing inside the FPGA.

A problem I'd like to solve is getting 50Hz composite video displayed on 
modern VGA monitors. 60Hz is easy using scan doubling, but 50Hz is not so 
straight-forward. On a lot of platforms, the video timing is central to the 
whole system timing, so the refresh rate isn't something that is easily changed.

The idea of PACE is to be as target-independent as possible. There's a *lot* 
of FPGA dev boards out there - both Xilinx and Altera - so I'm trying to 
make it as accessible as possible. However, it *will* require some minimal 
porting effort (and possibly some hardware add-ons) to get it running on a 
new platform.

> As we've a lot of old Xilinx evaluation boards lying around at work, I'd
> hope that there would be something I could push into service.

The current designs utilise internal RAM to varying extents atm - it's 
something I'm trying to move away from where possible.  It should be 
possible to run the BBC micro on a relatively modest FPGA/dev board by 
moving the system roms into flash or external SRAM, for example.

> Have you done any investigation on creating a 'Tube' system in an FPGA? -
> presumably if you can emulate one 6502 then doing two should be easy if
> the FPGA resources are there.

I'm not overly familiar with the BBC but the Tube is something I've been 
interested in - it would be almost trivial in an FPGA! But not having any 
software or experience in using it, I wouldn't be able to do much in the way 
of testing etc so I haven't attempted to implement anything yet...

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"