Motorola 68060 FPGA replacement module (idea)

[mikej]

There is quite a bit of work going on understanding the basic architecture of the 68K

http://www.visual6502.org/images/pages/Motorola_68000.html

The micro and nano microcode instructions roms are being read out.
If this works, a table based FPGA will be much smaller and more accurate than the current code - and can be tweaked easier.
A lot of the cloaning complexity of the 68K is a fall out from the way it was efficiently implemented due to die area limitations at the time.
/MikeJ

[mikej]

Orignal problem: The FPGA Arcade has some 68020 hybrid. But the number of logic cells in the XC3S1600 is finite so any more fancy CPU has to be elsewhere. Now the solution mikej has accomplished is a daughterboard with a 68060 CPU.

The design aim with Replay is to make a fairly generic main board which has high quality common IO (audio/video etc) and cheap daughterboards for specific stuff - for example a JAMMA interface for arcade cabs. Daughterboards can be simple 2 layer PCBs and the placement and pinout specs are available from me. I also have some prototype daughterboards with 5v level converters on and a patch array where I have wired up some processors for testing. The 68060 board is pretty simple, it would be easy to make one with an FPGA on it instead for CPU development. As a said earlier I started development of a Virtex6 module which plugged into the 68060 socket, but it's much simpler just to make a different daughterboard and wire a bunch of wires to the inter-board connector. Then you can decide what you want to do with them at the other end.


Jim : "Has anyone worked with the MCC-216 "

Several of us have a real problem with this guy - he was on this forum for a while. He is using GPL code and not releasing the source, which is naughty. We will release the code for the Replay system as soon as we start shipping a stable core.
/MikeJ

[mikej]

For those saying that Altera is the better fpga for this task, what exactly makes it better, and what are you comparing it to on the Xilinx side?

Altera and Xilinx devices made on the same process are roughly the same in terms of delay and logic size. The IP available, hardmacs and IO capabilities do differentiate them for some applications. For what we are doing here there is not much in it, it's down to logic area per $.
Even in the Spartan3 I believe I can get the software CPU to 100MHz+.

/MikeJ

[mikej]

I've had a bit more of a think about this... Would it make sense to design a RISC CPU for the FPGA with the same condition codes/flags as the 68k (where instructions would set the flags as expected), but limit all the exotic addressing modes to the load/store instructions?

A simple MMU could be added to mark memory block, to assist a JIT... That way we could have an FPGA CPU that could execute code really fast, allow for easy mapping of 68k instructions to the native instructions and move the 68k->native decoding to a software JIT

This is quite a neat trick, I've been looking into it for my own 68K core.
The Replay PS2 keyboard/mouse controller uses a picoblaze softcore as it is smaller than the logic used otherwise - and you can to a lot more.

http://www.roman-jones.com/PB8051Microcontroller.htm
Here they are using it as a 8031...
/MikeJ

[mikej]

Ummm... I don't see that they are even remotely rare.  I found 15 different sources with varying amounts located in Malaysia, Taiwan, and mainland China.

As long as the part works, I would not care if they were knock-offs... but they would definitely have to pass a test rig setup and function well beyond the 50MHz rating.  I was told that these are all genuine parts, with the one supplier a bit desperate to unload all of them.  By the way, the going rate for all of the suppliers I found is about $50 per CPU.  I am not sure how that compares to the normal pricing.  I just so happened to ask one of my part suppliers in China for the latest micro pricing, and the 68060 appeared on the list.  I was kind of shocked to see that, so then I sent an inquiry to a bunch of chip wholesalers about the 68060.  There are a lot of them out their folks!

Jim, they may be the batch I rejected and sent back to them
The going rate appears to be about 45-55 USD.
Once you factor in test cost and yield we may be looking at double that.

I'll be back in Shenzhen around Easter and I'm on a sourcing mission....
/Mike

[mikej]

I've got a couple of contacts, more are always welcome... I got one of my guys there to do a bit of digging. There are people who recycle (buy used kit in bulk) and sell 68Ks and other interesting parts. We have failed to get any of the correct mask yet, but I live in hope.

I'll actually be in Taiwan in April and Malaysia in the summer.

They are finishing off the boards now, waiting for the packaging to be printed and delivered.

Slight feature creep on the core, because I have completely rewritten all the SPI protocol, I am now having to rewrite the floppy and hard disk interfaces. Almost done.

I am still quite chuffed with the ability to upload and verify ROM files to internally/external memory now, specified in a .ini file which is quite nice.
[ROMLOAD]
name = mike\kick.rom
addr = 0xE00000
size = 0x4000

etc

/Mike