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68 Katy – 68000 Linux on a Solderless Breadboard

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Re: 68 Katy – 68000 Linux on a Solderless Breadboard

#11

Post by vt240 »

josteink wrote: post #3

That is seriously good work and an amazing DIY project! I remember when I was a kid, trying to just get a pre-made Linux-image boot on my Amiga. I had a 68020 CPU, but due to no MMU and no FPU (neither being "normal" accessories at the time) I just couldn't get the thing to boot at all. Later, when I acquired a 68030 CPU, I at least had the MMU covered, but I was still a kid and didn't have a budget for a FPU. So I s…

Your post just brought back a flood of memories for me about the frustration I went through as a kid trying to port free software to 68k BSD. I started out running MachTen [1] which ran under System 7 on the Mac. There was something odd about the way it did dynamic linking, I can’t remember now, but it just turned any port into a nightmare. I don’t know why it took me so long to figure out there was a mac68k NetBSD, which had a much better/compatible toolchain for building stuff. I don’t remember ever trying to get linux going on 68k, but I can sympathize.

[1] https://www.tenon.com/products/machten/23-info.shtml

Re: 68 Katy – 68000 Linux on a Solderless Breadboard

#14

Post by pantalaimon »

zurn wrote: post #2

To clarify the article's text, uClinux is not (just) a distribution, but a version of the kernel that rus on MMU-less hardware. The full Linux kernel does have m68k support, but it needs a 68020 or better CPU. This gets you real memory protection, VM etc.

Wasn't uClinux merged into mainline a long time ago?

Re: 68 Katy – 68000 Linux on a Solderless Breadboard

#16

Post by userbinator »

chubot wrote: post #7

This is amazing! It's pretty surprising to me how little there is on the board. It looks comprehensible. I wonder if you could do this with a modern CPU and RAM. What would it look like?

A lot of newer CPUs aren't available in DIP packaging which means they won't be usable with a breadboard; the M68k is one of the more unusual ones in that it's available in a 64-pin DIP, the longest common DIP package. E.g. all the x86 processors moved to square packages starting with the 80186/80188, only the 8086/8088 were in DIP.

DIP packages are problematic for high-speed operation since the leads to the pins near the ends are longer than the ones in the middle, creating signal skew; hence the move to square/BGA packages.

That being said, there are microcontrollers with a relatively powerful ARM core and in DIP, but they usually have internal memory and use the pins for peripherals, not as a full memory data/address bus.

Re: 68 Katy – 68000 Linux on a Solderless Breadboard

#17

Post by unwind »

lovelearning wrote: post #10

"...hung at calibrating display loop. Aha, I needed a timer interrupt...." He must be a true genius, to be able to infer the second from the first.

I actually had to go back and check, and it seems you're correctly quoting his mis-quoting of the startup log.

It's "delay loop", which at least gives some clue that it has to do with timing. I'm sure the OP at least knows this, but just had a typo in his blog post.

Re: 68 Katy – 68000 Linux on a Solderless Breadboard

#18

Post by Zardoz84 »

josteink wrote: post #3

That is seriously good work and an amazing DIY project! I remember when I was a kid, trying to just get a pre-made Linux-image boot on my Amiga. I had a 68020 CPU, but due to no MMU and no FPU (neither being "normal" accessories at the time) I just couldn't get the thing to boot at all. Later, when I acquired a 68030 CPU, I at least had the MMU covered, but I was still a kid and didn't have a budget for a FPU. So I s…

68008 it's a 68000 with a 8 bit external data bus and limited address bus. It's like the 8088 of the 68000 family. It was used on the Sinclair QL. If a Linux can run on a 68008, can run on any 680X0, that includes old Macs, QL, Amigas, Ataris (not the 8 bit family), etc...

Re: 68 Katy – 68000 Linux on a Solderless Breadboard

#19

Post by Theodores »

I built a 68008 breadboard 'computer' as a student with 6522 VIA, an EPROM of 'code', some RAM and some LED lights to show if anyone was home. It took a lot of work to get that far. And that was a long time ago. The benefits of the 68008 were the same - minimal pins to wire up, more chance of it actually working.

Anyway I am impressed that someone can get a distro working on 68008, getting to the start line of that project is a big deal, going the extra miles - very impressive!

Re: 68 Katy – 68000 Linux on a Solderless Breadboard

#20

Post by Narishma »

userbinator wrote: post #16
chubot wrote: post #7

This is amazing! It's pretty surprising to me how little there is on the board. It looks comprehensible. I wonder if you could do this with a modern CPU and RAM. What would it look like?

A lot of newer CPUs aren't available in DIP packaging which means they won't be usable with a breadboard; the M68k is one of the more unusual ones in that it's available in a 64-pin DIP, the longest common DIP package. E.g. all the x86 processors moved to square packages starting with the 80186/80188, only the 8086/8088 were in DIP. DIP packages are problematic for high-speed operation since the leads to the pins nea…

A lot? Make that pretty much all. The only things you still find in DIP format are very low-end micro-controllers.
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