Z280 to Z80 adapter revisit | MSX Resource Center (Pagina 8/9)

Master (154)

26-01-2019, 18:13

Quote:

Then someone of good will could consider eZ80 CPU.

The eZ80 may not be (well, it is not) suitable for a MSX. Most ports under 0x00FF are used already. With the amount of logic needed to circumvent that you will need an FPGA. Then you can do much better with the FPGA alone.

Van Giangiacomo Zaffini 2

Champion (287)

26-01-2019, 20:36

@Edevaldo: didn't knew It. Thank You. I will look into that.

Van zett

Hero (608)

26-01-2019, 20:46

i think the fastes way to do this is to copy the hc90 way. its all worked out in a working system

Van Edevaldo

Master (154)

27-01-2019, 03:33

What is HC90?

There are many ways to architect a high performance MSX.
Someone interested in the Z280/Z380 should have it in a local bus, with RAM and ROM connected directly to it. Then you need a bridge to the standard MSX bus where slots and legacy peripheral would reside running at regular speeds.

PCs are kind of remarkable in that sense. The original PC was very rich in peripherals, timers, DMA, interrupt controllers... Arguably the most sophisticated 8-bit computer. When the PC-AT was designed it already isolated the processor/memory from those ISA peripherals so the CPU could accelerate and maintain compatibility. 16-Bit ISA was created including 16-Bit DMA and more interrupts. If CGA had a color palette... I digress.

If the goal is ultimate performance, you need to go for an FPGA implementation. Again, assuming performance is the main goal, the approach will be very similar. The CPU may have caches tightly connected and running at high clocks. Memory and other high bandwidth peripherals need will be in a crossbar switch running probably at 1/2 CPU speed. And everything that does not require the ultimate speed will be in a "low" speed crossbar switch. Where eventually you will have a bridge to the legacy MSX bus to be able to provide slots. Some form of hierarchical architecture like this is needed because you cannot run the entire thing at the same speed without reducing the speed itself.

Van lintweaker

Champion (464)

27-01-2019, 08:44

With HC90 he probably means the Victor HC-90 which as both a Z80 and a Z180.
I already have the Z180 running, not the speed(up) I am aiming for.

Van zett

Hero (608)

27-01-2019, 09:09

Yeah sorry the victor hc90. i got one and it runs fast on the z180(HD64180). it uses a special set of roms for it. it got all extra options to make z80 software and msx code work.

Van erpirao

Paragon (1315)

31-01-2019, 21:49

hello, any news of the adapter z80-z280?
Thank you

Van erpirao

Paragon (1315)

31-01-2019, 21:53

lintweaker wrote:

I've been playing with the Z180 and Z280 for a while now. It is difficult to get it running optimally (limited number of needed extra wait states vs highest possible frequency).

For now I am focussing on using an FPGA to build a 'enhanced' Z80 (*) or maybe later a Z80 with MSX engine like capabilities. I am basing it on the 'T80' Z80 FPGA core as used in e.g. 1ChipMSX, socz80 etc.
The KdL sources form a very nice base to work with.

The FPGA stuff has a steep learning curve (for me at least) but eventually I'll get there

(*) yes, I know. With the FPGA I can build a complete MSX but that is not my goal

Have you thought about the cores nextz80 & y80e?

Van lintweaker

Champion (464)

01-02-2019, 10:27

erpirao wrote:

Have you thought about the cores nextz80 & y80e?

Thanks for the links. I am currently testing with T80(a) as used in a few projects (e.g. OCM).
With that I also settled on using VHDL, the cores you mentioned use Verilog.

Van lintweaker

Champion (464)

01-02-2019, 10:30

erpirao wrote:

hello, any news of the adapter z80-z280?
Thank you

No, sorry. No updates on that currently. I'll probably revisit the Z280 once a have a real parallel keyboard for my MSX clone. Now my keyboard becomes unusable when the speed is too fast or too slow.