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Date   : Wed, 15 Apr 2009 20:09:40 +0100
From   : mfirth@... (Michael Firth)
Subject: ReCo6502 now available

I would agree that there must be a solution for Tube ULA replacement on the 
ARM7 co-pro, but Sprow hasn't leapt in to give details when Tube ULA 
replacements have been discussed here before.

>From Mark's e-mail it sounds like what the ULA needs to do is already well 
understood, but another source of details would be the BeebEm source code, 
as it emulates the Tube ULA.

Something like the Xilinx XC3S200AN self-programming FPGA would be more than 
large enough for the job, and they are only $16.50 (list - see 
https://webapps.nuhorizons.com/storefront/PartSearch.do;jsessionid=1E711171B231AA5836A7B405D7F28FE3?PostAction=GO&Mode=initSearch&Commodity=ALL&I6.y=0&PartNumberSearch=XC3S200AN&pSearchType=CompanyPart
) 
- it may seem a lot, but it is around the same cost as a second hand Tube 
ULA, and doesn't have a limited supply.

A secondary problem then probably becomes level translation, as the Xilinx 
part only has up to 3.3V I/Os. There are 5V capable Xilinx parts, but they 
are very old, and hence now very expensive.

Regards

Michael


----- Original Message ----- 
From: "Ian Wolstenholme" <bbcmailinglist@...>
To: <bbc-micro@...>
Sent: Wednesday, April 15, 2009 7:10 PM
Subject: Re: [BBC-Micro] ReCo6502 now available


Presumably Sprow has come up with a solution to the Tube ULA as
there isn't an original part in the ARM7 co-processor.

Best wishes,



Ian

----- Original Message -----
From: Mark Haysman [mailto:jumbos.bazzar@...]
To: bbc-micro@...
Sent: Wed, 15 Apr 2009 19:06:14 +0100
Subject: Re: [BBC-Micro] ReCo6502 now available

>> It also requires you to remove the ULA from your existing 6502 second
>> processor
>
> Has anybody tried to engineer a replacement for the Tube ULA?
>
> I was playing with an XMOS XS1-G4 development kit over Christmas. The
> XS1-G4 is a cheap 400MHz quad-core microprocessor with extremely fancy
> IO facilities that's designed for doing FPGA-like stuff. The thought
> occurred at the time that it probably wouldn't be too hard to knock up
> an XS1 coprocessor for the BBC, with the chip emulating the ULA (and any
> external CPU you like) in software...

You're not going to need anything so fancy to just do the ULA (altho the
complete caboodle with it sounds good!). A CPLD may do it, but not one of
the smaller ones. Register 1 is a 24 byte FIFO (and Reg 3 is  a 2 byte
FIFO), so that's 208 registers before you even start on the others, status
registers and control logic, altho the app notes say that R1 is only used
for 10 byte VDU command length transfer, so maybe the size of it could be
reduced without too much affect on performance. You could always place the
RAM outside the CPLD, but that then defeats the "single chip" neatness.
There are certainly chips that it will fit into with ease, it's just a case
of balancing the cost to make it worthwhile doing.

Mark.



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