Idea for changing the VM

[kingpinzs]

I am wanting to to change the VM GUI so it acts like a real computer and can be used like one also. for example I can just tell it to load my ROM and it just shows the screen and the keyboard does not have to be invoked.
the example usage would be
open the VM
it prompts to load a ROM if it does not have win in an ini or command line instruction
after Rom loads it works like any other computer with interaction.
 
After that I want to add new virtual hardware pieces like a hard drive and mouse

Any ideas how I could get started. i have the source code but not sure what all files have to be edited to get it to work.

[ajoshguy]

Yes, I know the post is super old.  I'm currently working on a VM (for running the VM code) in Love 2D.  https://love2d.org  Lua isn't my favorite language but once you get over a few quirks it's pretty easy to learn and use.

So far I have a working screen, keyboard, and it boots up a simple "no OS" firmware (compiled with Jack).



I've been tweaking it but at this point it supports all the VM instructions, so I'll be trying something a bit more advanced soon.  You just drag and drop a folder with .VM files on top of the window and then it will load that into the VM and "reboot".

It's about 500 lines of Lua so far.  Writing the VM was pretty trivial (far simpler than writing the VM translator IMHO).  It just stores the textual instructions in a large indexed array.  During preprocessing labels are prefixed with the filename and there is also a jump table for labels/functions to associate the name with the location.  Otherwise it's just fetch/execute.

Actual opcodes look a bit like:

-- and
function op_and()
  a = _pop()
  b = _pop()
  _push(bit.band(a,b))
end

-- return
function op_return()
  -- save the end frame and return address so we don't clobber them
  end_frame = ram[LCL]
  returnaddress = ram[end_frame-5]
  ram[ram[ARG]] = _pop() -- reposition the return value
  -- restore our frame
  ram[THAT] = ram[end_frame-1]
  ram[THIS] = ram[end_frame-2]
  ram[ARG] = ram[end_frame-3]
  ram[LCL] = ram[end_frame-4]
  PC = returnaddress -- jump to return address
end

It'd probably be even easier to actually emulate the lower-lever hardware than to emulate the VM.  Only two instructions you have to worry about!