I don't want to learn Yocto, and it seems like Nix is the easy way to build a custom Linux image with patches.
This is lightly based off of the Cyclone V SoC GSRD, which describes how to build an image for a different board. I acquired that image and put it on my board and it didn't output anything on serial (dammit), so I realized I was in for just doing the whole thing myself, not that I expected better.
The images available from the board vendor Terasic are ancient (Ubuntu 16.04 is the latest), so they are not worth using. Thus, I am here porting a different distro because it's the same amount of work and more reusable than doing it with Yocto.
Resources:
In the configuration used here (see Cyclone V Hard Processor System Technical Reference Manual, version 20.1 page A-13 to A-14), the boot process is using the MBR mode.
The boot ROM will find a partition of type 0xA2, which it will load 64kb of into memory (the tiny OCRAM, not DDR3) and jump to. There are four copies of the second phase loader/"preloader" (U-Boot SPL) in this partition.
U-Boot SPL will configure various devices, initialize the SDRAM and then start U-Boot, which is also on the same partition.
U-Boot will execute /boot/u-boot.scr, enable the FPGA bridge, then load the
kernel image and initrd per /boot/extlinux/extlinux.conf.
Note: Currently I use the device tree from U-Boot which will continue into Linux. This is subject to revision, since it seems annoying to put that into the bootloader partition that won't get updated with the NixOS system.
This is all built out using a patched version of sd-image.nix from nixpkgs. My patches make a SD image for the device in one shot, rather than requiring later modification to add the bootloader.
I patched the use of a function that was removed in 2019, leading to linux-socfpga just not building on socfpga_defconfig. I have no idea what is the deal there so I just fixed it.
The kconfig here is the socfpga_defconfig plus some entries required by systemd/NixOS. It's pretty minimal.
You can hack on the kconfig with (FIXME probably shouldn't use qt5.full but it's the one that was most obvious):
[acquire linux-socfpga]
$ nix-shell -p pkgsCross.armv7l-hf-multiplatform.stdenv.cc stdenv gmp mpfr libmpc ncurses qt5.full --run zsh
$ make socfpga_defconfig ARCH=arm CROSS_COMPILE="armv7l-unknown-linux-gnueabihf-"
$ make xconfig ARCH=arm CROSS_COMPILE="armv7l-unknown-linux-gnueabihf-"
There are two critical bugs I patched in the device tree shipped by U-Boot for DE1-SoC that render the system unusable:
-
The frequency of the UART device is unspecified, which means that even the SPL can't output anything on serial. I found this in a forum post from mid-2021.
-
The watchdog0 is marked "disabled" in the u-boot device tree for the DE1-SoC. This was done by upstream since it should probably be marked disabled for U-Boot, but Linux needs to enable it, and so the system would reboot due to watchdog after 10 seconds or so.
This is not the best way to fix this, and it is likely that we will start using device trees shipped by NixOS instead.
I have commented out the FPGA loading in bootScript.nix, since I don't have a
suitable FPGA image to offer. For this purpose I suggest starting from the
DE1-SoC GHRD from the CD, as it contains various things that are not
conveniently written down such as DDR3 timings and so on, which it has
conveniently put into the qsys file for you, along with all the various wires
you have to do in the top level file.
I will note that the top level file in there does use some very old IP and functionality. It's likely some of it could be cleaned up if one were so motivated, but start from it since it definitely works.
See also: https://github.com/u-boot/u-boot/blob/master/doc/README.socfpga
To build a .rbf image which you need to program the FPGA in u-boot, use
quartus_cpf -c whatever.sof whatever.rbf.
- I haven't done anything about the fact that the Nix setup is kinda hardcoded to x86_64-linux right now. Just patch it if you are building from a more fun architecture.
Set MSEL to 4'b0000: all DIP switches "ON" (sic!). This enables u-boot to
program the FPGA fabric.
Per the DE1-SoC manual:
"FPGA configured from HPS software: U-Boot, with FPPx16 image stored on the SD card, like LXDE Desktop or console Linux with frame buffer edition."
Source: https://forum.rocketboards.org/t/cyclonev-programming-fpga-from-u-boot/2230/24
$ nix build .#sdImage
$ sudo dd of=/dev/YOUR_SD_CARD_PROBABLY_mmcblk0 if=result/sd-image/nixos-*.img bs=1M status=progress
Attach your computer to the mini USB on the board (not the USB type B; that one is JTAG).
$ picocom -q -b 115200 /dev/ttyUSB0
Add your ssh keys to the configuration for root:
{
# ...
users.users.root = {
openssh.authorizedKeys.keys = [
"ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDNldAg4t13/i69TD786The+U3wbiNUdW2Kc9KNWvEhgpf4y4x4Sft0oYfkPw5cjX4H3APqfD+b7ItAG0GCbwHw6KMYPoVMNK08zBMJUqt1XExbqGeFLqBaeqDsmEAYXJRbjMTAorpOCtgQdoCKK/DvZ51zUWXxT8UBNHSl19Ryv5Ry5VVdbAE35rqs57DQ9+ma6htXnsBEmmnC+1Zv1FE956m/OpBTId50mor7nS2FguAtPZnDPpTd5zl9kZmJEuWCrmy6iinw5V4Uy1mLeZkQv+/FtozbyifCRCvps9nHpv4mBSU5ABLgnRRvXs+D41Jx7xloNADr1nNgpsNrYaTh hed-bot-ssh-tpm-rsa"
"[email protected] AAAAGnNrLXNzaC1lZDI1NTE5QG9wZW5zc2guY29tAAAAIKYljH8iPMrH00lOb3ETxRrZimdKzPPEdsJQ5D5ovtOwAAAACnNzaDpzc2hrZXk= ssh:sshkey"
];
};
}Then you can use deploy your-de1-ip-address to deploy.
This desugars to:
NIX_SSHOPTS="-l root" nixos-rebuild switch --target-host your-de1-ip-address --fast --flake .#fpga
U-Boot SPL 2022.04 (Jan 01 1980 - 00:00:00 +0000)
Trying to boot from MMC1
U-Boot 2022.04 (Jan 01 1980 - 00:00:00 +0000)
CPU: Altera SoCFPGA Platform
FPGA: Altera Cyclone V, SE/A5 or SX/C5 or ST/D5, version 0x0
BOOT: SD/MMC Internal Transceiver (3.0V)
Watchdog enabled
DRAM: 1 GiB
Core: 21 devices, 12 uclasses, devicetree: separate
MMC: dwmmc0@ff704000: 0
Loading Environment from MMC... *** Warning - bad CRC, using default environment
In: serial
Out: serial
Err: serial
Model: Terasic DE1-SoC
Net:
Error: ethernet@ff702000 address not set.
No ethernet found.
=>
=> run bootcmd_mmc0
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:2...
Found /boot/extlinux/extlinux.conf
Retrieving file: /boot/extlinux/extlinux.conf
1: NixOS - Default
Retrieving file: /boot/extlinux/../nixos/666zyfzbbm1pmnpx25pjvbp6blaw240w-initrd-linux-armv7l-unknown-linux-gnueabihf-5.15.50-initrd
Retrieving file: /boot/extlinux/../nixos/i0q6qrpxn6s9niw07zl12xiklnb82q6y-linux-armv7l-unknown-linux-gnueabihf-5.15.50-zImage
append: init=/nix/store/4l6xz4cqhk4wyamlipvhw2gz5kzrj8h1-nixos-system-nixos-23.05.20230131.e1e1b19/init console=ttyS0,115200n8 loglevel=7
Kernel image @ 0x1000000 [ 0x000000 - 0x56d200 ]
## Flattened Device Tree blob at 3bf90630
Booting using the fdt blob at 0x3bf90630
Loading Ramdisk to 0978f000, end 09fffa07 ... OK
Loading Device Tree to 09787000, end 0978e88f ... OK
Starting kernel ...
Deasserting all peripheral resets
[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 5.15.50 (nixbld@localhost) (armv7l-unknown-linux-gnueabihf-gcc (GCC) 11.3.0, GNU ld (GNU Binutils) 2.39) #1-NixOS SMP Tue Jan 1 00:00:00 UTC 1980
[ 0.000000] CPU: ARMv7 Processor [413fc090] revision 0 (ARMv7), cr=10c5387d
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] OF: fdt: Machine model: Terasic DE1-SoC
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] efi: UEFI not found.