nixos-riscv/README.md

# NixOS on RISC-V

To boot the system in QEMU, first enter the development shell:

```
$ nix develop
```

Then run the boot script:

```
$ ./boot.sh
```

In u-boot use the following to boot:

```
=> booti 0x84000000 - ${fdtcontroladdr} 
```

## Use more than 1 CPU

With only 1 CPU some thigs are soo slow to work. For example, the ttyS0 device
doesn't arrive on time and the login fails. Or the SSH daemon doesn't start
until the third try. With -smp 32 seems to work ok.

## Compressed instructions

To see if a binary has compressed instructions or not, you can use objdump:

    hut% nix shell -vL nixpkgs#pkgsCross.riscv64.bintools
    hut% objdump -M no-aliases -D result/u-boot | grep 'c\.' | head -5
        80200000:   822a                    c.mv    tp,a0
        80200002:   84ae                    c.mv    s1,a1
        80200018:   52c1                    c.li    t0,-16
        8020001e:   0356                    c.slli  t1,0x15
        80200024:   850a                    c.mv    a0,sp

To dump a ROM without the ELF header:

    hut% objdump -b binary -m riscv:rv64 -M no-aliases -D result/u-boot.bin