Z-Berry: Z-80 computer

https://sites.google.com/site/zberrysbc/home

by mmastrac • 9 years ago

90 55 9 years ago

sites.google.com

Theodores2• 9 years ago

But does it run Linux?

If not then good luck writing code to page out to that 512k of RAM. I do wonder what the 1980 computer scene would have been like if 512k was there because that was the smallest amount available, instead of the normal 16k. It was only when the PC came along that this amount of memory was available. PC programs took a while to be as concisely optimised as home computer code had to be. So maybe the scarcity of RAM was a good thing.

jacquesm8• 9 years ago

I had 256K in bankswitched 16K blocks in an 8 bit micro in 1982. Cost a small fortune and it was a bit awkward to use but it worked.

Theodores2• 9 years ago

That was USD 300 of RAM, so a small fortune.

znpy• 9 years ago

I hope you've got a good story about that.

perbu• 9 years ago

Not sure if you're being sarcastic or not. But the Z80 is a 8 bit CPU. Linux was never ported to any 8 or 16 bit architectures - for rather obvious reasons.

qubex• 9 years ago

Linux was never ported to 16- or 8-bit hardware but through the magic of Turing completeness and emulation somebody did actually manage to get an 8-bit micro-controller: http://dmitry.gr/index.php?r=05.Projects&proj=07.%20Linux%20...

(Yes, this is so convoluted, and so unusable, that it basically reinforces, rather than refutes, your point.)

pacaro• 9 years ago

Well, the ELKS[1][2] project has been working on a 16bit port on and off since the late 90s. At one point Alan Cox[3] was an active contributor.

[1] http://elks.sourceforge.net/

[2] https://github.com/jbruchon/elks

[3] https://en.wikipedia.org/wiki/Alan_Cox

cestith• 9 years ago

Since it's a Z-80 which is a primarily 8-bit microprocessor with some 16-bit features and no MMU I'm going to go with no Linux.

However, microcontrollers and game systems have been using more than 64k with it for ages now. It's all done with bank switching. https://www.retrobrewcomputers.org/doku.php?id=boards:sbc:z-... explains how Z-Berry does its bank switching.

Someone• 9 years ago

You can use the bank switching logic as a minimalistic/sort of MMU, giving each process a full memory bank and nothing else.

To get real protection of programs against other programs and of the kernel against any programs you would have to make the bank switching logic privileged, but I would think that's doable with some external logic that snoops the memory bus and only allows switching to another bank if either the current bank is bank zero or the destination bank is bank zero and the instruction pointer matches that of the kernel's entry point.

You also would have to force a switch to bank zero to preempt processes. I think the easiest approach would be a timer that, when it expires, switches to bank zero and interrupts the CPU.

With this hardware, that could give you 7 processes, max. I think you could have fun with a minimal Unixlike OS in that.

Edit: it will be a bit of a challenge to pass arguments to the kernel if the kernel can't rely on hitting trusted code when it bank-switches back to a process to, say, read a memory buffer, but that can probably be overcome by force-mapping, say, the last kB of RAM to the kernel's memory space.

nategri2• 9 years ago

Unusual, yes, but half a meg wouldn't exactly be an exotic amount of RAM for a 1980s 8-bit.

cr0sh• 9 years ago

My Tandy Color Computer 3 had 512K (standard was 128K) and an 8-bit CPU (6809). It did have something akin to a MMU though (the GIME chip) - which paged the RAM in banks of 8K.

As far as what it was used for - people mainly used it for RAM disks; it could also be used for page-flipping for the higher-res graphics modes the CoCo 3 supported.

For the OS-9 Level II operating system, it was used much more efficiently to allow for larger (or more) programs to be multi-tasked, along with other uses.

(for those unaware - OS-9 was a multi-user, multi-tasking operating system for the 6809 and other 8-bit microprocessors of the day - but mainly geared to Motorola CPUs - including later the 68k family)

vhodges2• 9 years ago

There's an OpenSource replacement called Nitros9 http://www.nitros9.org/documents.html

Also: https://github.com/nealcrook/multicomp6809/wiki

and finally: https://www.retrobrewcomputers.org/doku.php for more retro goodness.

xioxox• 9 years ago

The Amstrad PCW was also a Z80 system with 256 or 512 KB RAM accesible using bank switching. Normally it acted as a RAM disk.

dajt3• 9 years ago

Eh? Just write your own bank switching code. The whole setup is different to MMU paging. Not having looked at the specs I'm guessing you do an I/O write to something that sets the bits of the address lines above 15 to select the bank.

You could go two ways:

1. Have some amount of RAM outside the bank switching scheme so code and data living there is always available and bank switch above or below that fixed area.

2. Switch the entire 64k at a time, meaning your code and data has to be copied into the same place in each bank.

tluyben2• 9 years ago

MSX (z-80 based) unix; https://github.com/marioaugustorama/uzix-kernel

Much cooler (imho) is http://symbos.de/ though, also for z80 machines.

mysterydip• 9 years ago

I like it. Compact, supports keyboard and SD card and display. I'd like to read up more on it but the pages are a bit sparse (and I can't view the youtube videos where I am, so I'll have to check those later).

jacquesm8• 9 years ago

The obvious way to solve the 'will crash when switching banks because next instruction is from different bank' is to replicate the bank switching code to all banks.

makomk2• 9 years ago

Of course, in order to copy the bank switching code to the other banks you need to switch to them first. Which means that this copying can only be done by the ROM.

jacquesm8• 9 years ago

No, you'd do that with a little bit of PIC running in one of the other parts of RAM.

amelius• 9 years ago

Why not simply run a Z80 emulator on a raspberry pi?

nottorp• 9 years ago

Sir, you're no fun.

Too bad that you can't order one pre built. I'm not competent enough to solder that.

nategri2• 9 years ago

Why not simply make guacamole in a cement mixer?

rvense• 9 years ago

Why learn to play an instrument when you can just buy a CD?

flavio813• 9 years ago

Why drummers carry those big bass drums and cymbals when they can just use a pocket drum machine?

hoodoof3• 9 years ago

Why paint a portrait when you can paint a house?

dajt3• 9 years ago

Because for a certain type of person having your code run on a real Z80 is much cooler.

Insanity• 9 years ago

This is really cool! I've recently been playing around with z80 emulators, but it must be neat to try it on an actual device.

ddofequaldevhda• 9 years ago

http://www.sunrise-ev.com/z80.htm

geijoenr• 9 years ago

you should definitely take a look at Fuzix,

https://github.com/EtchedPixels/FUZIX

Jaruzel• 9 years ago

I would love for some one to make something like this but with 286/386 CPUs. Would be great for the retro PC crowd.

jseutter• 9 years ago

Something like this already exists: https://www.linux.com/news/here-come-x86-hacker-boards . I think these should be able to run DOS.

If you want to go full retro, x86 is relatively difficult due to the support circuitry needed. Full ISA, ram, ports, etc. PCs were fairly complex machines back in the day.

zokier• 9 years ago

I think of all the modernish Z80 computers FAP80[1] is my favorite. Of course it is also massively more complex project than this, but that complexity enables FAP80 to function as a proper standalone computer that you could actually use if you were so inclined.

[1] https://news.ycombinator.com/item?id=13438610

hoodoof3• 9 years ago

I really enjoyed reading the blog posts about the build of this. Gave me so much insight into the inner workings of those machines.

flavio813• 9 years ago

"Z-Berry is the smallest Z80 based computer ever built."

Not to be pedantic, but the Timex Sinclair 1000 of 1981 had a lower chip count than this computer.

Take a look at the board: http://oldcomputers.net/pics/ZX81-mb.jpg

And it even includes the RF modulator.

Of course, the Z-berry is a far more powerful Z80 computer.

Ready to run again all your CP/M 80 programs?

PS: What would have RULED would be to include in the Z-Berry a socket for the SID* sound chip or at the very least two POKEY* chips.

* SID: Commodore 64 sound chip. POKEY: Atari 8-bit (800/400/800XL/etc) sound chip.

colejohnson66• 9 years ago

Maybe he meant the literal smallest?

userbinator• 9 years ago

If we extend the definition of "Z80 computer" to include those which aren't using the original Zilog Z80 DIP40 CPU, e.g. SoCs, then these may be the smallest:

https://en.wikipedia.org/wiki/S1_MP3_player

https://www.bunniestudios.com/blog/?p=138

https://www.bunniestudios.com/blog/?p=139

jdmoreira• 9 years ago

Yes, but of the ICs in the Timex Sinclair 1000 is the Ferranti ULA which packs a lot of features.

hoodoof3• 9 years ago

Off the specific topic, but on topic of retro machines, but I feel that the new BBC micro:bit project should actually have been a rebuild of the actual BBC micro, but with an HDMI display/USB/network.

jamiek88• 9 years ago

That would have been awesome.

The econet system too, this time with email and web access but still the hackable LAN that was so much fun to navigate and spoof.

?&D22=100 to change my station number to the IT teachers station when he'd left for the day. Thus all logs were from his machine, seemingly.

He hated me and my mate. To the point where he had spooled all system privileged activity to actually print out (not to a text file, he wasn't the smartest even to us 14 year olds) to paper.

It was his genius plan to narrow down which room we were logging into from!

The next day we see a locksmith changing the locks to his private computer room.

He never did catch us. Someone snitched in the end. We told a friend who boasted unbeknownst to us to others and the jig was up.

Banned from computers for the rest of school.

A really cool science teacher got us involved with the weather station (it recorded data from NOAA sats to the BBC micro!!) so got the ban amended to 'no computers with network access' so we could use the computer in his lab.

Of course we then learned how to splice cables and made a reeeeeally long econet cable and had a system of lookouts.

Good times.

Thanks Mr. Bush you were a good guy who nurtured our interest. AS for you Mr. Pollard, as an adult I get why you hated us but still, if you'd have asked us to help with the network or the lab or something we could have avoided our war.

Sorry guys, big barely relevant anecdote but hopefully someone else will smile at the fun days of the BBC Micro and remember the econet hacks.

vhodges2• 9 years ago

There's this too: http://sowerbutts.com/socz80/ (100+Mhz)

_sbrk• 9 years ago

Not the smallest, not even close.

http://noplabs.com/cpm50/cpm50.html

dajt3• 9 years ago

That looks really cool. I built the cpuville kit a few years ago but its I/O decoding was borked, it didn't expose enough control signals through its extension mechanism, and its pin headers were at an odd spacing so you couldn't just plug a prototyping board onto it.

I designed a and built new I/O extender to fix all those problems but PCB design is not fun for me so I never made a PCB for it.

This one looks to have none of those problems.

VectorLock• 9 years ago

The real question is: If you could run CPM on this, what CPM software would you want to use?

flavio813• 9 years ago

Visicalc?

I recall using a PROLOG interpreter on a Kaypro II under CP/M. Worked neat.

Also i used an ALGOL-60 compiler. In fact, just a subset of ALGOL-60. So, in some ways, a limited subset of a subset of Pascal.

Z-Berry: Z-80 computer

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