Date   : Thu, 16 Apr 2009 08:50:16 +0100
From   : info@... (Sprow)
Subject: ReCo6502 now available

In article <y2a8wm257qi.fsf@...>,
   Adam Sampson <ats@...> wrote:
> Has anybody tried to engineer a replacement for the Tube ULA?

In article <0D97808EBFD44F9FB6490C2E4FF24183@...>,
   Mark Haysman <jumbos.bazzar@...> wrote:
> 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

In article <DCAA45EC13FB485187F0F97070CB3338.MAI@...>,
   Ian Wolstenholme <bbcmailinglist@...> wrote:
> Presumably Sprow has come up with a solution to the Tube ULA as
> there isn't an original part in the ARM7 co-processor.

In article <49E62F2F.8050206@...>,
   Phill Harvey-Smith <afra@...> wrote:
> The real pain with CPLDs is that it seems as the number of logic blocks 
> goes up so does the number of pins, making accessing a CPLD with enough 
> registers harder as it means a large pincount

You've all already mentioned the main points
 * CPLDs don't have enough register bits versus going to 200+ pin packages
 * FPGAs have plenty of bits (or block RAM) but few have 5V tolerance

The FPGA on the ARM coprocessor is a register compatible clone of the Tube
ULA, though it doesn't currently emulate the DMA grant and request lines: I
couldn't see them being used on any of the coprocessor service guide
schematics anyway.

Its registers are detailed in the last couple of pages of the ARM copro user
guide. They happen to be wired up on word boundaries rather than byte
boundaries for minor-ARM-related reasons by offsetting the address lines,
its base address can be read with OS_Memory 9.

It would be technically possible to pop the FPGA and configuration PROM onto
a 40 pin DIL carrier board, I'd stab at ~?35 to make them which suggests
John's idea of just swapping the chip out of an existing board (since you
can't use two at once anyway!) makes best sense,
Sprow.