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mu/shell/README.md

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A prototype shell for the Mu computer

Currently runs a tiny dialect of Lisp. Steps to run it from the top-level:

  1. Build it:
$ ./translate shell/*.mu      # generates code.img

You can now already run it:

$ qemu-system-i386 code.img

But let's add some more 'meat' to play with.

  1. Create a data disk with a library of functions.
$ dd if=/dev/zero of=data.img count=20160
$ cat shell/data.limg |dd of=data.img conv=notrunc

Run with data disk (and 2GB of RAM):

$ qemu-system-i386 -m 2G -hda code.img -hdb data.img

Try typing in some expressions and hitting ctrl-s to see their results. Hit ctrl-m to focus on the ... after a run, and browse how the results were computed. Here's a demo. The bottom of the screen shows context-dependent keyboard shortcuts.

  1. If your Qemu installation supports them, one of these commandline arguments may speed up emulation:
  • -enable-kvm
  • -accel ___ (run with -accel help for a list of available options)

If you do this, I recommend also adjusting the responsiveness mask in shell/evaluate.mu, which controls how frequently the fake screen updates. Smaller values will seem more responsive, larger values will leave more time to run your programs. I like to see the screen update about once a second. Some suggested values depending on how fast your Qemu is running:

  • -enable-kvm on a T420s running Linux: 0xffff/responsiveness=64k
  • -accel tcg on a 2019 Mac: 0xfff/responsiveness=4k

Putting it all together, here's the command I typically use on Linux:

$ qemu-system-i386 -m 2G -enable-kvm -hda code.img -hdb data.img

Known issues

  • No mouse support.

  • Don't press keys too quickly (such as by holding down a key). The Mu computer will crash (and often Qemu will segfault).

  • Mu currently assumes access to 2GB of RAM. To increase that, modify the definition of Heap in 120allocate.subx, and then modify the -m 2G argument in the Qemu commands above. Mu currently has no virtual memory. If your Heap is too large for RAM, allocating past the end of RAM will succeed. However, accessing addresses not backed by RAM will fail with this error:

    lookup: failed