Extended cpu carts

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Door PingPong

Prophet (4093)

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20-02-2010, 14:32

can anyone think about the possibility of making a extended cpu cart with this design ?
- fpga-based z80 with a bank of 256Kb clocked as fast possible
- interface with the on-board cpu like advram
- ability for the old z80 to access in a memory mapped way the bank of 256Kb managed by the speedy z80 on the cart. (like advram does with vdp and z80).

the two cpu's should work in parallel.

A similar hw could be a fast coprocessor to the main cpu.
saving the knowledge of most msx z80 gurus

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Van Leo

Paragon (1236)

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20-02-2010, 15:14

i have been thinking to the same ande came to these 2 conclusions:
- it is hardly justificable and many people may tell it is useless , but i think it is fun as a hw project, at least.
- fpga is the most expensive way to do Z80 or other cpu , what about using regular Z80 4MHz just
for protyping , just to see how it would work for data transfers .

a Z180 is good for that ?
IDT7007 is a 32kx8 dual port sram

Van PingPong

Prophet (4093)

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20-02-2010, 15:23


a Z180 is good for that ?

IMHO a normal 4mhz z80 is too slow. maybe some other z80 alike processor but i do not know the availability at present.
i think the clock speed should never be less than 33Mhz, however

Van Leo

Paragon (1236)

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20-02-2010, 15:29

the fastest and more available is eZ80 running at 50MHz with one instruction per cycle.
But i was talking more like to make a slow prototype to understand the best way to communicate.

Van Pac

Scribe (6956)

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20-02-2010, 15:36

Here versions of Z80 compatibles CPU's:

homepage3.nifty.com/z80/

You can find a detailed description of each one of them, sorry in Japanese (use Google):)

Van Leo

Paragon (1236)

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20-02-2010, 18:12

wikipedia in also quite complete on Z80.
i have been using the whisbone high performance Z80 on speedy fpga ( virtex2 ppro V2P50 -7 )
i achieved 60MHz on it with 8kb ram.
the point is not really speedy z80 but speedy ram because most regular sram may not be working
at 33MHZ , it requires 30ns access time , and in practice ~25ns.
what about having more than 1 extra cpu ? Z80 quadricore ?
i have never seen Z380 card from padial but i guess it is a bit like this , anyone use it ?
if it was not that expensive i would have bought one by now ... 210 euros ... but i guess it uses hard to find parts as well.
Zilog misleaded a lot of developpers with their Z380 and then eZ80 , not really the same path of evolution .
...
for your cart, you see what price ?
30/50/70 euros ?

Van PingPong

Prophet (4093)

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20-02-2010, 19:46

i think max 50-60 euros. otherwise...... and what about the hw needed to sync accesses between the two on the cartridge ram? because of lack of busxxx controls i think the ram should be buffered so when the original z80 tries to read a ram location the buffered part returns data, without disturbing/stopping the fast z80.... but how costly is a similar hw?

Van st1mpy

Paladin (900)

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20-02-2010, 21:07

I would like the cpu in the cart to be something quite powerful. Z80 compatibility would be nice for some applications but I would mostly like to have something with a lot more computing power (speed and calculation wise. So 16/32 bit CPU, can handle floats etc natively with xxMHz and large addressable memory.)

Van Leo

Paragon (1236)

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20-02-2010, 22:48

what about a simplified Z80 binary compatible ( no interrupt support for instance )
i see 15 eurs for pcb and 50 euros for FPGA module.
eZ80 is 5 to 7 euros.
i think sync interface can be done with dual port SRAM, it is expensive but extra hw alos costs.

not sure fpga gives good figures ,
i have just re_synth the fz80.v core , it tops at 28Mhz, not really high perf eventough it is 4x turboR. (tested on spartan 3E 100 target )

so eZ80 is ten tmes cheaper and twice faster than fpga .

Van st1mpy

Paladin (900)

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21-02-2010, 09:03

what about starting this design by modifying the Super Gameboy cartridge? There are plenty of them on ebay (nintendo probably made more units of these than there are msx users)
its cheap (you could pick one up for $5), cheaper than buying an used gameboy.
You get a lot of parts we want (z80, music and video processor, memory)
can run gameboy code (although the video output might be an issue)

Van Leo

Paragon (1236)

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21-02-2010, 13:01

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