Zilog Z80 CPU – Modern, free and open source silicon clone

https://github.com/rejunity/z80-open-silicon

by jnord • 2 years ago

362 71 2 years ago

Renaud• 2 years ago

What Tiny Tapeout is doing is amazing. Who would have thought that makers and students could have their own chip design made real for so little money?

The tools look amazing as well. You'll won't design the next Intel CPU on that 130nm process but to think that the Z80 will fit on 0.064 mm2 is just amazing.

It's great that there will still be an alternative to the official chip now that it won't be manufactured any more.

Now I want that gorgeous mauve ceramic package with a gold-plated cover over the chip...

https://twitter.com/l_vanek/status/1783557817133039738/photo...

https://tinytapeout.com/

chx• 2 years ago

To save a click

160 x 100 um tile + ASIC + demonstration board: The standard price is $300 plus shipping.
However, Efabless is sponsoring a special early bird offer of $150 (plus shipping), limited to one order per person.
Each extra tile is $50, and extra analog pins start from $40 per pin.

Unless I am badly mistaken 160 x 100 um is .16 x .1 mm which means the tile is 0.016 mm2 meaning a 0.064 mm2 die takes four slots?

mk_stjames• 2 years ago

Yes it is taking up a 2x2 tile on the tinytapeout.

https://app.tinytapeout.com/projects/668

rowanG0773• 2 years ago

I could not find the pin capabilities. Is it possible to build an sdram controller or even drive ddr?

ashleyn• 2 years ago

130nm process puts them at roughly Pentium III era. Not bad!

rvense• 2 years ago

That's wild. A Pentium III would still be useful in a pinch. How big was a P3 die, though?

skywal_l• 2 years ago

Actually more of a Pentium IV.

    Pentium III: 250 nm to 130 nm [0]
    Pentium VI: 180 nm to 65 nm [1]

Which is indeed amazing.

[0] https://en.wikipedia.org/wiki/Pentium_III

[1] https://en.wikipedia.org/wiki/Pentium_4

belter• 2 years ago

Z80 was the CPU of the ZX Spectrum. Oh the memories...

https://en.wikipedia.org/wiki/ZX_Spectrum

mattl• 2 years ago

So many good machines: the Amstrad CPC range, a whole slew of Sega consoles, the early MSX stuff and of course the Tatung Einstein. 3 inch disk machines of the world unite!

rwmj• 2 years ago

Not to mention the world of CP/M business machines which was surprisingly large in the UK well into the late 80s, again thanks to Amstrad: https://en.wikipedia.org/wiki/Amstrad_PCW

flohofwoe7• 2 years ago

All 8-bit computers manufactured in East Germany too (via the reverse enginered Z80 clone U880). For instance the KC85/2..4:

https://floooh.github.io/virtualkc/p010_kc85.html

An "Adrian's Digital Basement" episode about the KC85/3:

https://www.youtube.com/watch?v=At9UNYFHuaE

mchannon• 2 years ago

You forgot about Donkey Kong (and Junior, and 3, and Mario Bros.)

Punch-Out!!

But most noteworthy is Galaga: Ran on 3, count 'em, 3, Z80's.

yincrash• 2 years ago

My mobile computer of choice in school, the TI-83 series calculators.

userbinator3• 2 years ago

Also the many unbranded MP3/"MP4" players that very widespread in the mid to late 2000s: https://en.wikipedia.org/wiki/S1_MP3_player

ztetranz• 2 years ago

And of course the TRS-80 and clones such as the Dick Smith System-80 that we had in Australia and New Zealand. Lots of good memories programing with EDTASM. I only had a cassette drive so if my code went wrong I usually had to hit reset and reload EDTASM and my code again from tape.

Andrex• 2 years ago

I thought it was used for the Game Boy, but apparently while there are many similarities they're basically incompatible[0].

0. https://forums.nesdev.org/viewtopic.php?t=18335

LeFantome• 2 years ago

It was also the CPU in my first computer--the Coleco ADAM: https://en.wikipedia.org/wiki/Coleco_Adam

I still have my copy of Programming the Z80 that I got as a kid: https://en.wikipedia.org/wiki/Programming_the_Z80

Retr0id2• 2 years ago

Does anyone know what clock speeds we might be able to expect from this?

drmpeg• 2 years ago

This page says 50 MHz.

https://github.com/rejunity/z80-open-silicon/blob/main/docs/...

tyingq• 2 years ago

Interesting. Saw this on the Wishbone Z80 project notes:

"Guy Hutchison (see TV80 project) has synthesized an early version of the core in a 130nm TSMC process. He determined the design to contain about 20k gates and run at about 240 Mhz. While the speed is somewhat less than "target", optimizations of the logic should increase this somewhat."

Guy Hutchison's TV80 is also mentioned on this project's page.

swetland• 2 years ago

That's the expected clock rate for the TT07 run... but Tiny Tapeout designs only have 8 in, 8 out, and 8 bidirectional IOs (plus a reset and clock input) available, so they're using a multiplexing strategy where the Z80 clock runs at 1/4 of the base clock rate and alternates between control signals, A0-A7, control signals, and A8-A15 on the OUT pins:

https://github.com/rejunity/z80-open-silicon/blob/68438f0019...

So you'd get an effective 12.5MHz Z80 clock and need a bit of external logic to demultiplex the full IO interface. Still not too shabby!

The goal (per the project README) appears to be to prototype with TT07 and then look into taping out standalone with ChipIgnite in QFN44 and DIP40 packages (which would be able to have the full traditional Z80 bus interface and run at the full clock rate).

Dwedit2• 2 years ago

If you were designing a new compatible processor for older systems, the limiting factor would be the memory bus. A cache would be necessary to get high speeds.

The cache would need to know about all bank-switching performed by the system, and understand how the memory banks are mapped into the memory space.

Could have:

* Plain read-only memory (you cache this)

* Plain RAM not shared with other devices (you cache this)

* Memory-mapped IO (you don't cache this)

* RAM shared with other devices where the other device does not write there, such as video memory (write-through cache, full read cache)

* RAM shared with other devices where the other device can write there (don't cache this)

Retr0id2• 2 years ago

IIRC this is what the people making swap-in accelerators for 6502 chess computers are doing

robxorb• 2 years ago

For those wondering, the 6502 and various derivatives are still being manufactured, by one of its original creators [0] - so I'd guess an equivalent development in the world of the Z80's nemesis is unlikely anytime soon.

[0] https://www.westerndesigncenter.com/wdc/chips.php

ksherlock• 2 years ago

65*C*02, which might fail if your 6502 code depends on illegal opcodes or incidental memory access or BCD math cycle timing or BCD math flags or perhaps decimal mode being set in an interrupt routine.

grumpyprole• 2 years ago

The 65C02 came out in 1983, so I think we've had plenty of time to document and workaround these issues!

zczc• 2 years ago

And eZ80 (binary compatible, but not pin-compatible with Z80) is still being manufactured by Zilog.

monocasa• 2 years ago

Interestingly the classic z80 was end of lifed just two weeks ago.

https://hackaday.com/2024/04/19/end-of-life-for-z80-cpu-and-...

Fatnino3• 2 years ago

What will the ti-83/4 calculator use now?

RetroTechie2• 2 years ago

It would be interesting to know Zilog's sale volumes for discrete Z80s (say, over the past decade). What uses they were purchased for, and DIP/PLCC/flatpack ratios.

There must be millions floating out there. But with distributors like Mouser or Farnell gone, for anyone looking to buy some, it's eBay & co which tends to be a crapshoot.

lelanthran• 2 years ago

It would be interesting to know Zilog's sale volumes for discrete Z80s (say, over the past decade).

Not the past decade, but two decades ago (2005) the z80 was still popular. At work, I was working on a product based on, IIRC, a Rabbit Semiconductor product, which was a module with on-chip ethernet. It was a Z80 running at 40Mhz.

Personally, I also had a little siemens organiser thing, that also was z80 based (not sure of the actual specs). I recall trying to write programs for it and failing (may not have been open; no way to reprogram or download new code to it, maybe).

[EDIT: The organiser was a siemens IC35]

sitkack• 2 years ago

The PDIP version is being discontinued, but the eZ80 is still being manufactured.

https://arstechnica.com/gadgets/2024/04/after-48-years-zilog...

https://en.wikipedia.org/wiki/Zilog_eZ80

http://www.zilog.com/docs/um0077.pdf

https://www.zilog.com/docs/ez80acclaim/ps0153.pdf

polpo• 2 years ago

It could happen at any time to the 65C02. The Z80 was only EOLed a few weeks ago because they couldn’t get wafers from their fab any more. Any chip on an old process is at risk of this.

Koshkin• 2 years ago

I couldn’t help but notice that the circuit layout looks like a uniform gate array rather something resembling a custom layout you usually see in die photos.

flohofwoe7• 2 years ago

Because it's a Verilog implementation which is much closer to a software CPU emulator than the real thing (e.g. it has nothing to do with the original Z80 "transistor layout").

For instance here's the LD A,(DE) "instruction payload":

https://github.com/rejunity/z80-open-silicon/blob/974c7711b2...

And here's the same machine cycle in my software emulator:

https://github.com/floooh/chips/blob/bd1ecff58337574bb46eba5...

Both set the address bus to the content of the DE register (and at the same time the MREQ|RD pins need to be set somewhere to indicate a memory read to the outside world, in my emulator this happens in the _mread macro), and in the next clock cycle load the data bus into the A register.

What's interesting though is that the Verilog implementation doesn't seem to update the internal WZ register with DE+1, which makes me wonder if undocumented behaviour is correctly implemented, but maybe updating WZ is handled elsewhere (there are references to the WZ register in other places).

In the end, if it looks and feels like a Z80 from the outside (e.g. the right pins are active at the right time) the internal implementation doesn't matter.

rowanG0773• 2 years ago

Just because this is done in verilog doesn't make it emulation. It's probably just machine placed and routed. Almost everything is these days in digital design.

Vogtinator• 2 years ago

It only looks like that if you treat it as a C-like programming language, which it is not. Unless specified otherwise, all the statements are "executed" in parallel by the synthesized logic. There is no emulation.

tcbawo• 2 years ago

I had heard about Z80’s 4-bit ALU (2x for 8-bit math). Is this considered a major bottleneck? Were there later extensions that added higher bit integer math? I’m curious whether an open source version of the chip will enable new features and variants.

flohofwoe7• 2 years ago

Is this considered a major bottleneck?

No, because an ALU instructions with a register as source is already running as fast as possible (at 4 clock cycles, which is the duration of an opcode fetch 'machine cycle'). Or from a different perspective: an 8-bit ALU wouldn't have made math instructions faster, but would have cost twice as many transistors.

The 4-bit ALU is just an internal implementation detail that isn't visible to the outside (except maybe through the existence of the half-carry flag which indicated a carry from the lower into the higher nibble).

And if you want a CPU replacement that plugs directly into old home computers, the CPU needs to have the original instruction timing, otherwise software that depends on 'cycle counting' won't work (probably less of an issue on the ZX Spectrum though because the Speccy didn't have a programmable video hardware like for instance the Amstrad CPC).

The eZ80 is a modernised and more efficient design, with (among other things) a wider ALU: https://en.wikipedia.org/wiki/Zilog_eZ80. Not an option for keeping old home computers alive though, for this you'd want an exact Z80 clone with the original timings and undocumented behaviour.

becurious2• 2 years ago

Cycle counting was key on the Spectrum - for obvious things like the tape load routines but also for advanced techniques like the ‘Rainbow processor’ - updating the attribute bytes (those responsible for the infamous color clash) as each scan line progressed you could get different colors on each scan line.

userbinator3• 2 years ago

The Netburst P4s also used a half-wide (16-bit) ALU running at 2x the clock frequency (actually by clocking on both edges, like DDR RAM), which meant ALU operations with a carry/borrow between the two halves took an extra cycle: https://www.realworldtech.com/isscc-2001/7/

phendrenad2• 2 years ago

I wonder if this will ever be priced competitively with the massive number of used or NOS Z80 chips out in the wild.

ein0p• 2 years ago

eBay says a Chinese Z80 clone is less than $4 with free shipping. This isn’t even going to be competitive with lower end FPGAs. It’s more of a fun “why not” type of project.

londons_explore• 2 years ago

How do those clones work? Are they asics, or microcontrollers/fpga's which do emulation?

kumarski• 2 years ago

Looks dope.

(I was on early efabless.com team) open source EDA.

userbinator3• 2 years ago

I wonder how compatible it is with the original Z80, which had many undocumented instructions as well as the infamous "trap gates" (look at the "Oral History Panel on the Founding of the Company and the Development of the Z80 Microprocessor" documented linked on that page) that might've had an effect on certain obscure instruction sequences and designed to identify the difference between it and clones.

rsynnott• 2 years ago

Wow. Just looked it up; the Z80 is now _50 years old_.

mindcrime• 2 years ago

So, um... you're saying I should not have dumped my life's savings into ordering Z80 chips as part of the "last time buy"? :-(

MisterTea• 2 years ago

I think the real joy of these old 8-bit CPU's is the simplicity and how a single person can wire up a computer by hand.

In uni we built an 8088 board in microprocessor class and it was the best class I ever took; it demystified drivers and hardware for me. I attempted a redesign using KiCAD which added an IO expansion port and better layout with an LCD port for a 2x16 character LCD. I had a prototype made by Futurlec but made a massive mistake in footprint assignment that required an interposer. Furthest I got was soldering in the 8284 and the IC sockets then got distracted by life and its sitting in a box still.

Microcontrollers are great, everything in one package but there's something enormously satisfying about being able to design and build a computer by hand. FPGAs sort of bring this back but the tooling is byzantine dog shit.

avnd• 2 years ago

The open source tooling isn’t perfect but it’s growing fast! I work in this space and recommend checking out the OpenROAD[1] project, which has full synthesis and pnr for select FPGAs.

[1] https://theopenroadproject.org/

Zilog Z80 CPU – Modern, free and open source silicon clone

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