[J-core] Is a small Linux distribution available for J2 on Numato Mimas?

Rich Felker dalias at libc.org
Sat Aug 6 09:53:26 EDT 2016

On Sat, Aug 06, 2016 at 05:50:20AM +0000, Brian Bartholomew wrote:
> Has anyone compiled a small Linux distribution for J2 on the Numato
> Mimas?  By "small" I mean has emacs and can build packages natively,
> but doesn't have X-Windows.

A native toolchain takes about 15 seconds to compile and link a hello
world application, after the toolchain binaries have been executed
once and cached in ram, so while it's possible a native toolchain is
not very practical. This is largely a consequence of the FPGA running
at just 50 MHz, and probably also the small (8k) icache and dcache

I'm pretty sure emacs is not nommu-compatible due to the "dumper"
architecture, which depends on being loaded at the same logical
(=physical, for nommu) address it was running at when it was dumped.
Emacs can be built without the dumper, but then it takes 30 seconds to
load its elisp on a 1.5 GHz x86. On J2 I would expect it to take
several hours to load like that. A J3 with mmu would overcome this

Other editors should work reasonably well. I know I've used nano, and
it's smooth for typing within a line, but feels noticably slow for
inserting/removing lines. This is probably due to a largeish memmove
in nano or in ncurses.

In terms of actual distributions, Rob has a build script at
https://github.com/j-core/mkroot that can produce just a minimal
working userspace, and Buildroot can be convinced to target J2
reasonably well if you give it an external toolchain. Getting
better/native support upstream in Buildroot is an ongoing goal.
OpenEmbedded might also work; I'm not sure. With anything much bigger
than that, I don't think you'll find distros where anyone has put any
thought into supporting nommu, so you'll have better luck once there's
a J3.


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