From: Sam Moore <matches@ucc.asn.au>
Date: Wed, 9 Apr 2014 15:41:58 +0000 (+0800)
Subject: An interface for a FPU compiled from VHDL
X-Git-Url: https://git.ucc.asn.au/?p=ipdf%2Fcode.git;a=commitdiff_plain;h=1bab8e093f47967dc28a5a10030972407d7d0675;hp=1bab8e093f47967dc28a5a10030972407d7d0675

An interface for a FPU compiled from VHDL

I have tested with the FPU from https://github.com/jop-devel/jop

The way this works is really awful...

1. Make (or steal from jop) a VHDL FPU
2. Make (or steal from jop) a testbench that uses stdio to read operands and ops
   - The jop one reads from a generated file, but it is trivial to change to "STD_INPUT" and remove all the assertion tests.
3. Compile testbench into an executable with ghdl
4. Call VFPU::Start which does the following:
   - Create a socketpair(2)
   - fork(2) and in the child dup(2) stdin/stdout to the socketpair
     - Redirect stderr to /dev/null because the testbench generates 10^3 warning messages
   - in the child, exec(3) the testbench FPU
5. Call VFPU::Exec passing the desired operands and opcodes
   - The operands and opcodes are written as hex strings over the socketpair
   - The child executing the FPU program does its thing
   - The result is read back as a hex string
6. When finished, call VFPU::Halt to kill(2) the FPU

I tried to get ghdl and gcc/g++ to make a static library to call ghdl_main instead
of exec'ing things. But that didn't work. The fork and socketpair would have still been
required for that approach anyway.

TODO:
  - Make the interface (not the FPU) deal with arbitrary size registers
  - Wrap a Real type around it so we can #define REAL_SIMULATED_FPU

I haven't put any of the VHDL in the git repo for obvious reasons.
If I actually start messing with it, it will probably get a seperate repo.

This may end up being a complete waste of time?
Although potentially being able to run an arbitrary FPU albeit in a horrible manner does seem cool.
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