Date   : Thu, 06 Mar 2008 19:05:04 +1100
From   : msmcdoug@... (Mark McDougall)
Subject: FPGA BBC - yah!

Mike Tomlinson wrote:

> I find it quite remarkable that you were able to get a FPGA design
> running without having the real machine to hand to refer to.  Well done
> :)

Thanks! To be honest, a real machine isn't terribly useful - the schematics, 
advanced user guides, ROM disassemblies and a debug build of MESS are much 
more useful for prying into the innards and debugging your implementation.

I've done more than a handful of FPGA implementations of 8/16-bit 
arcade/micro platforms and I've never once used the real hardware to assist 
in the development - it's all been documentation, schematics and emulators.

Of course, ultimately I *also* like having the real hardware!

Slightly OT but (IMHO) quite interesting - I had a Juno First arcade board 
with faulty a video RAM chip which suffered from partially corrupt graphics 
but was otherwise working. The PCB has a sea of 4116 DRAM chips - soldered 
into the board - and I had no easy way of determining which was at fault.

I had the idea of modifying the MAME driver to simulate a faulty RAM chip! I 
tried each bit until the pattern I saw on the screen matched that in MAME. I 
then identified the chip from the schematics on the PCB, and unsoldered it 
and replaced it - I was right!!! :O

Regards,

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