Hi,
I'm not sure if there's still anyone out there interested in such things,
but here goes!
I've pulled together bits and pieces that various people have done towards
getting a working GNU toolchain (binutils, GCC, etc.) and fixed them up a
bit so that they all work together -- and possibly produce code that'll run
on a real VC4, although I've not been able to test that so far.
This has consisted of:
* Rewriting a bunch of the binutils code so it uses CGEN -- in retrospect,
not such a great idea, because CGEN is kind of lacking in various regards,
particularly with respect to variable-length instruction sets -- but never
mind...
* Hacking CGEN to fix the above lossage.
* Rebasing David Given's GCC bits onto a (then-) current trunk GCC -- a
snapshot from some time before GCC 6.0 forked, IIRC. Fixed a bunch of
things, and stripped some stuff out: the compiler supports basic scalar
instructions, but not some of the trickier ones (no conditional insns, no
ALU+shift insns, no pre/post increment/decrement insns, definitely no
vector insns...).
* Doing a basic Newlib port that supports console output over an (emulated)
mini-UART, startup code, and a few necessary stub functions.
* Tweaking Mathias Gottschlag's "resim" VC4 emulator to use with the GCC
testsuite.
Possible next steps for anyone with the motivation are probably:
* Getting code running on the real hardware! It'd be nice to get a real Pi
substituting for resim in GCC tests (downloading each test successively
over serial, and automatically rebooting on crashes). That means enabling
SDRAM and "pivoting" to a small monitor of some sort from there, I think.
(This is about where I've run out of steam.)
* Incrementally adding more instructions to GCC and (lesserly) binutils.
* Not sure, getting some kind of RTOS running on the VC4, and enabling the
ARM?
The code's on my GitHub account at:
https://github.com/puppeh/vc4-toolchain
Cheers,
Julian
