RISC-V based retrocomputer?

[Andrew Lynch]

Hi

I've been wondering about this idea I have and get some feedback as to whether this is feasible

My idea is to build a retrocomputer much like the other Z80, 6809, etc. style 8-bit microcomputers but use one of these RISC-V dev boards as the CPU instead.

https://www.aliexpress.us/item/3256804164096177.html

The RISC-V module would require software to interface to the rest of the main board memory and IO through a bus (TBD).  The other difference from would be to use a 72-pin DRAM SIMM and have the RISC-V drive it directly for system memory.

I am thinking the target OS would be NetBSD or FreeBSD since those are already frequently ported to new architectures and can run well in smaller memory space.

Although I am not 100% sure the RISC-V can handle it as I think BSD requires and MMU

[Douglas Miller]

I'm not sure everyone would agree that this is a "retro computer", but I see that Linux does have a "riscv" architecture so there does appear to be a "Unix-like" OS available for it. I'm not sure if anyone is producing a RISC-V GNU distro, though. Otherwise you'll need to build all the utilities yourself.

[horus falcon]

Hi, Andrew,

Hmm... the idea is an intriguing one.  I should think one of the RISC-V Linux distros might also be a good fit.

Ubuntu and Debian are among the list of OS choices at:  https://wiki.riscv.org/display/HOME/Operating+Systems

but I see there may be more to it than that, owing to the recent vintage of this particular development board.

Sofware tools for programming and debug, in particular, seem to be restricted in their range of choices.

The board itself seems amazingly inexpensive -- six of them will set ya back less than $20.00 at today's spot price, which makes it a very attractive choice.

If the project goes straight south for some reason, at least ya won't be out much.

Just my initial impression of the idea.  If anyone can help to get it running, the folks here on Retro-Comp can.

Later On,
David

[Alan Cox]

On Fri, 28 Jun 2024 at 12:50, Douglas Miller <durga...@gmail.com> wrote:
>
> I'm not sure everyone would agree that this is a "retro computer", but I see that Linux does have a "riscv" architecture so there does appear to be a "Unix-like" OS available for it. I'm not sure if anyone is producing a RISC-V GNU distro, though. Otherwise you'll need to build all the utilities yourself.

MMUless limits you to ucLinux stuff. You can run Linux on a fairly
minimal RISC-V that way. If you want to run on one without a load of
external RAM you are rather more limited. It doesn't really end up as
a "retrocomputer" though - even the microcontroller ones are Pentium
grade machines or better. The ones with an MMU will run a full Linux
or BSD style OS quite happily.

Many of them have annoying magic binary blobs for chunks of their
hardware (even if allegedly "open source") and some have interesting
binary blobs containing symbols and strings that suggest that
licensing is dubious to say the least, so some care is needed picking.

[Tadeusz Pycio]

I have been planning for some time to use the CH32V103 or CH32X035 as a universal I/O controller. I am interested in exactly these models because they can run on 5V which is better than the ARM STM chips used with some 5V tolerant pins. But I still have a dilemma whether using a modern RISC-V is still retro. There are some applications that could be justified e.g. an SD card controller working at a higher level (FAT->raw data). I have temporarily put the work on hold because I have not yet convinced myself that this is the right direction.

[Douglas Miller]

That is the big question: renovation vs. restoration. Do you want a 1932 Ford or a Deuce Coupe (or a fiber-glass reproduction of a Deuce Coupe)? Some of the shadow area for me is if the RISC-V (or ARM for that matter) runs (say) a Z80 emulation so that original programs can be executed. Or, if the device interfaces to a retro machine bus and allows you to run some combination of original hardware with modern - such as replacing floppy with something that "looks" like a floppy controller but uses SD-Card for media. Some rather blurry lines are involved. IMHO.

[Talos Thoren]

I'd like to write a simple forth language based firmware for 32-bit riscv microcontrollers. It would also be nice to have a simple monitor program for them.

I've been an early adopter and fervent follower of risc-v since its inception and its made rapid progress, far more rapid than even its developers ever estimated. It's an evolutionary, almost viral, success; proving fit for so many compute ecosystem needs that it's taking over at an unprecedented rate.

RISC-V is the future, which is to say, it's very not retro.

The risc-v 64 bit ecosystem went from a simple but powerful extension of the isa to real world, high-performance compute modules that dropped in cost dramatically and are suddenly available to the development community en-masse. These high performance compute platforms are going to primarily be linux systems and I see little point, outside of education (which is usually worth it,) to putting effort into development for risc-v64 if one is not contributing to the improvement of linux software support for the platform.

I also wouldn't consider any of the currently maintained BSD's retro, even if they are old. These systems are still maintained and work well with modern hardware and networked systems; they are modern operating systems in every sense.

All that being said, I don't think it's a bad idea, but we couldn't really call it retro, maybe retro-style. Even then, the toolchains for riscv are very modern so it wouldn't quite feel the same. I think the best target for this plan is the 32-bit microcontroller ecosystem. If you're developing for a linux capable chip, you're sort of wasting your hardware capabilities by writing something from scratch.

Anyway, just my thoughts.

Much obliged,

David

On Friday, June 28, 2024 at 7:18:49 AM UTC-5 Tadeusz Pycio wrote:

[Tom Storey]

There isn't really much difference between a RISC-V M[CP]U and a Pi Pico when it comes to retro-ness. :-)

It probably makes for another great platform for emulating certain things with retro spirit though.

On Fri, 28 Jun 2024 at 13:18, Tadeusz Pycio <ta...@wp.pl> wrote:

I have been planning for some time to use the CH32V103 or CH32X035 as a universal I/O controller. I am interested in exactly these models because they can run on 5V which is better than the ARM STM chips used with some 5V tolerant pins. But I still have a dilemma whether using a modern RISC-V is still retro. There are some applications that could be justified e.g. an SD card controller working at a higher level (FAT->raw data). I have temporarily put the work on hold because I have not yet convinced myself that this is the right direction.

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[7alken]

Hi Andrew and all ... 

as the date is 240701 still,  only quick view how I see retro - in fact more as software with constrains; these days, as 64+bit processors skipped 2G/4G virtual memory limit, we are limitless and this causes exploding of everything... while I like AI chat, it help a lot ME to think more, I really feel tha 64+ bit processor was something the devil owed to us ))

so, in relation to risc-v, rather RV32EM, and even binary modified, I am still working on my VMEX/ASLIX combo, the virtual engine and C-like hl-asm for it and not even that ... think as new even simplified (and for learning and simple cases usabe) smaller C (here also Fuzix limited C compiler/syntax is neat).

here it is, working progress ...
https://github.com/apws/230326-VMEX
... I am now more focused on hardware, so there is last hing added, the "crucial license note" ))

On the hardware side, I this weekend (hopefully) specified 2mm 2x15pin "7xbus", as decoupled pcmcia-like 16bit + spi (MIPI DBI B/C helped a lot)

Also, just today I finally decided for "7xmod" for memory modules (originally not expected, but the price of sdram/sram chips may be quite high, so better to mount them to bereusable somewhere, somehow), so the final 1.27mm 2x40pin "7xmod" for 32bit sync-sdram at max PC133, perhaps ...

more later ...... :-)

7alken

[Stefan V. Pantazi]

Hi Andrew, 

Not sure you've already considered it, but something like Project Oberon (https://www.projectoberon.net/) also ticks one of your the boxes (risc-v). Not 8-bit and debatable if it is "retro" enough, but what it has going for it is all that wonderful documentation and tools available, begging for new implementations and use.

Stefan