default.nix

let
  pkgs = import <nixpkgs> {};
  helloworld = { linker }: pkgs.pkgsCross.vc4.runCommandCC "helloworld-${linker}" {
    src = ./.;
    allowSubstitutes = false;
  } ''
    unpackPhase
    cd $sourceRoot
    vc4-elf-gcc helloworld.c -O2 -o hello.elf -T ${pkgs.pkgsCross.vc4.stdenv.cc.libc}/vc4-elf/lib/vc4-${linker}.ld
    vc4-elf-objcopy -O binary hello.elf hello.bin
    vc4-elf-objdump -d hello.elf
    mkdir $out
    cp -v hello.{elf,bin} $out/
  '';
  testit = pkgs.runCommandNoCC "testit" {
    buildInputs = with pkgs; [ resim strace socat ];
    blob = helloworld { linker = "sim"; };
  } ''
    mkdir $out
    cd $out
    socat create:uart.txt tcp-listen:12365 &
    ulimit -c unlimited
    ls -ld $blob
    vc4emul -verbose -log $blob/hello.bin 0 0
  '';
  testit2 = pkgs.runCommandNoCC "testit2" {
    buildInputs = with pkgs; [ resim strace socat ];
    succeedOnFailure = true;
  } ''
    mkdir $out
    cd $out
    socat create:uart.txt tcp-listen:12365 &
    ulimit -c unlimited
    vc4emul -verbose -log ${/home/clever/apps/rpi/rpi-eeprom/firmware/beta/main-body.bin} 0 0x200
  '';
in {
  inherit helloworld testit testit2;
}

helloworld.c

#include <stdio.h>
#include <stdint.h>
#include "vc4-regs.h"

static inline uint32_t cpuid() {
  uint32_t res;
  asm("version %0"
      : "=r"(res));
  return res;
}

int main (int argc, char* argv[])
{
  MMIO_WRITE (AUX_MU_BAUD_REG, SYSTEM_CLOCK / (TARGET_BAUD_RATE * 8) - 1);
  uint32_t id = cpuid();
  printf("Hello world! %lx\n", id);
  return 0;
}

vc4-regs.h

#ifndef VC4_REGS_H
#define VC4_REGS_H 1

#define GPFSEL1		0x200004
#define GPSET0		0x20001C
#define GPCLR0		0x200028
#define GPPUD		0x200094
#define GPPUDCLK0	0x200098

#define AUX_ENABLES	0x215004
#define AUX_MU_IO_REG	0x215040
#define AUX_MU_IER_REG	0x215044
#define AUX_MU_IIR_REG	0x215048
#define AUX_MU_LCR_REG	0x21504C
#define AUX_MU_MCR_REG	0x215050
#define AUX_MU_LSR_REG	0x215054
#define AUX_MU_MSR_REG	0x215058
#define AUX_MU_SCRATCH	0x21505C
#define AUX_MU_CNTL_REG	0x215060
#define AUX_MU_STAT_REG	0x215064
#define AUX_MU_BAUD_REG	0x215068

#define MMIO_BASE	0x7e000000

#define MMIO_READ(X) (*(volatile uintptr_t *) (MMIO_BASE + (X)))
#define MMIO_WRITE(X,V) (*(volatile uintptr_t *) (MMIO_BASE + (X))) = (V)

#define SYSTEM_CLOCK		19200000
//#define SYSTEM_CLOCK		250000000
#define TARGET_BAUD_RATE	115200

#define ST_CLO                  0x3004

#endif