Z80 was the CPU of the ZX Spectrum. Oh the memories... https://en.wikipedia.org/wiki/ZX_Spectrum
Also the many unbranded MP3/"MP4" players that very widespread in the mid to late 2000s: https://en.wikipedia.org/wiki/S1_MP3_player
Zilog Z80 CPU – Modern, free and open source silicon clone
51–60 of 75 posts
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#52Wow. Just looked it up; the Z80 is now _50 years old_.
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#53So, um... you're saying I should not have dumped my life's savings into ordering Z80 chips as part of the "last time buy"? :-(
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#54I 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.
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/
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#55Earlier quoted context omitted.
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.
But look here, it's even doing a switch-case over the opcode, which is very typical for a software CPU emulator: https://github.com/rejunity/z80-open-silicon/blob/974c7711b2... Instruction decoding on a real Z80 CPU doesn't work at all like that :) A non-emulator-approach would probably use the reverse engineered Z80 netlist from visual6502.org to base the design on, no idea if this is even doable with modern chip de…
So what? A re-implementation of a CPU doesn't require the netlist to be equal. That would mean just moving to a new process node or tooling suddenly means your new brand new CPU is "software emulating" the old one just because it might do somethings slightly differently. A frankly ridiculous proposition.
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#56Earlier quoted context omitted.
But look here, it's even doing a switch-case over the opcode, which is very typical for a software CPU emulator: https://github.com/rejunity/z80-open-silicon/blob/974c7711b2... Instruction decoding on a real Z80 CPU doesn't work at all like that :) A non-emulator-approach would probably use the reverse engineered Z80 netlist from visual6502.org to base the design on, no idea if this is even doable with modern chip de…
So what? A re-implementation of a CPU doesn't require the netlist to be equal. That would mean just moving to a new process node or tooling suddenly means your new brand new CPU is "software emulating" the old one just because it might do somethings slightly differently. A frankly ridiculous proposition.
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Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#57Z80 was the CPU of the ZX Spectrum. Oh the memories... https://en.wikipedia.org/wiki/ZX_Spectrum
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.
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#58Does anyone know what clock speeds we might be able to expect from this?
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…
IIRC this is what the people making swap-in accelerators for 6502 chess computers are doing
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#59Earlier quoted context omitted.
> 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…
Aren't ti-83 calculators still sold today using z80?
Any Z80 based (not eZ80) TI calculators on the market today have the Z80 core built into an ASIC instead of a discrete chip, meaning that they wouldn’t be impacted by parts availability.
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#60Earlier quoted context omitted.
> 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'…
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.
Once made a tape-loading like pattern, and tried to get it as stable (not moving up or down on screen) as possible.
Managed to produce a program where with key presses, you could change delay in the loop in +/- 1 clockcycle increments. Mind you: fastest Z80 opcodes take 4 cycles.
How then? Well, there's also opcodes that take 5 cycles. Or 6. Or 7. And 8=2*4, 9=4+5, etc. Program just automated the insertion/removal of those in the inner loop. Of course I had to pick instructions that didn't mess with some Z80 registers.
Great fun (& educational) figuring out stuff like that. Fun times...