{
  system = {
    crossSystem = {
      config = "mipsel-unknown-linux-musl";
      gcc = {
        abi = "32";
        arch = "mips32";          # mips32r2?
      };
    };
  };

  description = ''
    Zyxel NWA50AX
    ********************

    Zyxel NWA50AX is quite close to the GL-MT300N-v2 "Mango" device, but it is based on the MT7621
    chipset instead of the MT7628.

    Installation
    ============

    This device is pretty, but, due to its A/B capabilities, can be a bit hard
    to use completely.

    The stock vendor firmware is a downstream fork of U-Boot: <https://github.com/RaitoBezarius/uboot-nwa50ax>
    with restricted boot commands. Fortunately, OpenWrt folks figured out trivial command injections,
    so you can use most of the OpenWrt commands without trouble by just command injecting
    atns, atna or atnf, e.g. atns "; $real_command".

    From factory web UI, you can upload the result of the zyxel-nwa-fit output.
    From another operating system, you need to `dumpimage -T flat_dt -p 0 $zyxel-nwa-fit -o firmware.bin`,
    `flash_erase $(mtd partition of the target partition firmware or zy_firmware) 0 0`, then you complete by
    `nandwrite -p $(mtd partition of the target partition firmware or zy_firmware) firmware.bin`.

    How to put the firmware.bin on the machine is left to you as an exercise, e.g. SSH, TFTP, whatever.

    From serial, you have two choices:

    - Flash this system via U-Boot:
      same reasoning as from an existing Linux system, two choices:
      - ymodem the binary, perform the write manually, you can inspire yourself
      from the `script` contained in the vendor firmware, those are just a FIT containing a script.
      - prepare a FIT containing a script executing your commands, tftpboot this.

    - boot from an existing Liminix system, e.g. TFTPBOOT image.
    - boot from an OpenWrt system, i.e. follow OpenWrt steps.

    Once you are in a Linux system, understand that this device has A/B boot.

    OpenWrt provides you with `zyxel-bootconfig` to set/unset the image status and choice.

    The kernel is booted with `bootImage=<number>` which tells you which slot are you on.

    You should find yourself with 10ish MTD partitions, the most interesting ones are two:

    - firmware: 40MB
    - firmware_1: 40MB

    In the current setup, they are split further into kernel (8MB) and ubi (32MB).

    Once you are done with first installation, note that if you want to use the A/B feature,
    you need to write a _secondary_ image on the slot B. There is no proper flashing code
    that will set the being-updated slot to `new` and boot on it to verify if it's working.
    This is a WIP.

    Upgrading your system can be achieved via:

    - `liminix-rebuild` for the userspace.
    - `flash_erase` + `nandwrite` for the kernelspace to the other slot than the one you are booted on,
      note that you can just nandwrite the mtd partition corresponding to the *kernel* and not the whole firmware.

    If you soft-bricked your AP, i.e. you cannot boot anything in U-Boot, no worries, just plug the serial console,
    prepare a TFTP server (via `tufted` for example), download vendor firmware, set up `atns`, `atnf`, etc. and run `atnz`.

    This will reflash everything back to normal via TFTP.

    If you hard-bricked your AP, i.e. U-Boot is telling you to transfer a valid bootloader via ymodem, just extract
    a U-Boot from the vendor OS, send it via ymodem and use the previous operations to perform a full flash this time
    of all partitions.

    Note that if you erased your MRD partition, you lost your serial and MAC address. There's no way to recover the original one
    except by reading the physical label on your… device!

    If you super-hard-bricked your AP, i.e. no output on serial console, congratulations, you reached one of the rare state
    of this device. You need an external NAND flasher to repair it and write the first stage from Mediatek to continue the previous
    recovery operations.

    Development TODO list:

    - Better support for upgrade automation w.r.t. to A/B, e.g. automagic scripts.
    - Mount the logs partition, mount / as overlayfs of firmware ? rootfs and rootfs_data for extended data.
    - Jitter-based entropy injection? Device can be slow to initialize its CRNG and hostapd will reject few clients at the start because of that.
    - Defaults for hostapd based on MT7915 capabilities? See the example for one possible list.
    - Offer ways to reflash the *bootloader* itself to support direct boot via UBI and kernel upgrades via filesystem rewrite.

    Vendor web page: https://www.zyxel.com/fr/fr/products/wireless/ax1800-wifi-6-dual-radio-nebulaflex-access-point-nwa50ax

    OpenWrt web page: https://openwrt.org/inbox/toh/zyxel/nwa50ax
    OpenWrt tech data: https://openwrt.org/toh/hwdata/zyxel/zyxel_nwa50ax

  '';

  module = { pkgs, config, lib, lim, ...}:
    let
      inherit (pkgs.liminix.networking) interface;
      inherit (pkgs.liminix.services) oneshot;
      inherit (pkgs.pseudofile) dir symlink;
      inherit (pkgs) openwrt;

      mac80211 = pkgs.mac80211.override {
        drivers = [ "mt7915e" ];
        klibBuild = config.system.outputs.kernel.modulesupport;
      };
      # v204520220929
      wlan_firmware = pkgs.fetchurl {
        url = "https://github.com/openwrt/mt76/raw/1b88dd07f153b202e57fe29734806744ed006b0e/firmware/mt7915_wa.bin";
        hash = "sha256-wooyefzb0i8640+lwq3vNhcBXRFCtGuo+jiL7afZaKA=";
      };
      wlan_firmware' = pkgs.fetchurl {
        url = "https://github.com/openwrt/mt76/raw/1b88dd07f153b202e57fe29734806744ed006b0e/firmware/mt7915_wm.bin";
        hash = "sha256-k62nQewRuKjBLd5R3RxU4F74YKnQx5zr6gqMMImqVQw=";
      };
      wlan_firmware'' = pkgs.fetchurl {
        url = "https://github.com/openwrt/mt76/raw/1b88dd07f153b202e57fe29734806744ed006b0e/firmware/mt7915_rom_patch.bin";
        hash = "sha256-ifriAjWzFACrxVWCANZpUaEZgB/0pdbhnTVQytx6ddg=";
      };
    in {
      imports = [ 
        # We include it to ensure the bridge functionality
        # is available on the target kernel.
        ../../modules/bridge
        ../../modules/arch/mipsel.nix
        ../../modules/outputs/tftpboot.nix
        ../../modules/outputs/zyxel-nwa-fit.nix
        ../../modules/zyxel-dual-image
      ];

      filesystem = dir {
        lib = dir {
          firmware = dir {
            mediatek = dir {
              "mt7915_wa.bin" = symlink wlan_firmware;
              "mt7915_wm.bin" = symlink wlan_firmware';
              "mt7915_rom_patch.bin" = symlink wlan_firmware'';
            };
          };
        };
      };

      rootfsType = "ubifs";
      hardware = {
        # Taken from OpenWRT
        # root@OpenWrt:/# ubinfo /dev/ubi0
        # ubi0
        # Volumes count:                           2
        # Logical eraseblock size:                 126976 bytes, 124.0 KiB
        # Total amount of logical eraseblocks:     256 (32505856 bytes, 31.0 MiB)
        # Amount of available logical eraseblocks: 0 (0 bytes)
        # Maximum count of volumes                 128
        # Count of bad physical eraseblocks:       0
        # Count of reserved physical eraseblocks:  19
        # Current maximum erase counter value:     2
        # Minimum input/output unit size:          2048 bytes
        # Character device major/minor:            250:0
        # Present volumes:                         0, 1
        ubi = {
          minIOSize = "2048";
          logicalEraseBlockSize = "126976";
          physicalEraseBlockSize = "128KiB";
          maxLEBcount = "256";
        };

        flash.eraseBlockSize = 64 * 1024;

        # This is a FIT containing a kernel padded and
        # a UBI volume rootfs.
        defaultOutput = "zyxel-nwa-fit";

        loadAddress = lim.parseInt "0x80001000";
        entryPoint = lim.parseInt "0x80001000";
        # Aligned on 2kb.
        alignment = 2048;

        rootDevice = "ubi:rootfs";
        alternativeRootDevice = "ubi:rootfs";

        # Auto-attach MTD devices: ubi_a then ubi_b.
        ubi.mtds = [ "ubi_a" "ubi_b" ];

        dts = {
          # Strong DTB assumptions:
          # ubi_a and ubi_b are two MTD devices.
          # If those changes, disaster will occur.
          src = ./dtb/mt7621_zyxel_nwa50ax.dtsi;
          includes = [
            "${./dtb}"
            "${openwrt.src}/target/linux/ramips/dts"
          ];
        };
        networkInterfaces =
          let
            inherit (config.system.service.network) link;
          in {
            eth = link.build { ifname = "eth0"; };
            lan = link.build { ifname = "lan"; };
            wlan0 = link.build {
              ifname = "wlan0";
              dependencies = [ mac80211 ];
            };
            wlan1 = link.build {
              ifname = "wlan1";
              dependencies = [ mac80211 ];
            };
          };
      };

      boot = {
        # Critical because NWA50AX will extend your cmdline with the image number booted.
        # and some bootloader version.
        # You don't want to find yourself being overridden.
        commandLineDtbNode = "bootargs-override";

        imageFormat = "fit";
        tftp = {
          # 5MB is nice.
          freeSpaceBytes = 5 * 1024 * 1024;
          loadAddress = lim.parseInt "0x2000000";
        };
      };

      # Dual image management service in userspace.
      services.zyxel-dual-image = config.boot.zyxel-dual-image.build {
        ensureActiveImage = "primary";
        # TODO: use mtd names rather…
        # primary and secondary are always /dev/mtd3 by virtue of the 
        # dtb being not too wrong…
        # TODO: remove this hack.
        primaryMtdPartition = "/dev/mtd3";
        secondaryMtdPartition = "/dev/mtd3";
        bootConfigurationMtdPartition = "/dev/mtd12";
      };

      #  DEVICE_VENDOR := ZyXEL
      #  KERNEL_SIZE := 8192k
      #  DEVICE_PACKAGES := kmod-mt7915-firmware zyxel-bootconfig
      #  KERNEL := kernel-bin | lzma | fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb
      #  IMAGES += factory.bin ramboot-factory.bin
      #  IMAGE/factory.bin := append-kernel | pad-to $$(KERNEL_SIZE) | append-ubi | zyxel-nwa-fit
      #  IMAGE/ramboot-factory.bin := append-kernel | pad-to $$(KERNEL_SIZE) | append-ubi

      kernel = {
        src = pkgs.fetchurl {
          name = "linux.tar.gz";
          url = "https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.15.137.tar.gz";
          hash = "sha256-PkdzUKZ0IpBiWe/RS70J76JKnBFzRblWcKlaIFNxnHQ=";
        };
        extraPatchPhase = ''
          ${openwrt.applyPatches.ramips}

        '';
        config = {

          RALINK = "y";
          PCI = "y";
          PHY_MT7621_PCI = "y";
          PCIE_MT7621 = "y";
          SOC_MT7621 = "y";
          CLK_MT7621 = "y";
          CLOCKSOURCE_WATCHDOG = "y";

          SERIAL_8250_CONSOLE = "y";
          SERIAL_8250 = "y";
          SERIAL_CORE_CONSOLE = "y";
          SERIAL_OF_PLATFORM = "y";
          SERIAL_8250_NR_UARTS = "3";
          SERIAL_8250_RUNTIME_UARTS = "3";
          SERIAL_MCTRL_GPIO = "y";

          CONSOLE_LOGLEVEL_DEFAULT = "8";
          CONSOLE_LOGLEVEL_QUIET = "4";

          # MTD_UBI_BEB_LIMIT = "20";
          # MTD_UBI_WL_THRESHOLD = "4096";

          MTD = "y";
          MTD_BLOCK = "y";          # fix undefined ref to register_mtd_blktrans_dev
          MTD_RAW_NAND = "y";
          MTD_NAND_MT7621 = "y";
          MTD_NAND_MTK_BMT = "y";      # Bad-block Management Table
          MTD_NAND_ECC_SW_HAMMING= "y";
          MTD_SPI_NAND= "y";
          MTD_OF_PARTS = "y";
          MTD_NAND_CORE= "y";
          MTD_SPLIT_FIRMWARE= "y";
          MTD_SPLIT_FIT_FW= "y";

          PINCTRL = "y";
          PINCTRL_MT7621 = "y";

          I2C = "y";
          I2C_MT7621 = "y";

          SPI = "y";
          MTD_SPI_NOR = "y";
          SPI_MT7621 = "y";
          SPI_MASTER = "y";
          SPI_MEM = "y";

          REGULATOR = "y";
          REGULATOR_FIXED_VOLTAGE = "y";
          RESET_CONTROLLER = "y";
          POWER_RESET = "y";
          POWER_RESET_GPIO = "y";
          POWER_SUPPLY = "y";
          LED_TRIGGER_PHY = "y";

          PCI_DISABLE_COMMON_QUIRKS = "y";
          PCI_DOMAINS = "y";
          PCI_DOMAINS_GENERIC = "y";
          PCI_DRIVERS_GENERIC = "y";
          PCS_MTK_LYNXI = "y";

          SOC_BUS = "y";

          NET = "y";
          ETHERNET = "y";
          WLAN = "y";

          PHYLIB = "y";
          AT803X_PHY = "y";
          FIXED_PHY = "y";
          GENERIC_PHY = "y";
          NET_DSA = "y";
          NET_DSA_MT7530 = "y";
          NET_DSA_MT7530_MDIO = "y";
          NET_DSA_TAG_MTK = "y";
          NET_MEDIATEK_SOC = "y";
          NET_SWITCHDEV = "y";
          NET_VENDOR_MEDIATEK = "y";

          SWPHY = "y";

          GPIOLIB = "y";
          GPIO_MT7621 = "y";
          OF_GPIO = "y";

          EARLY_PRINTK = "y";

          NEW_LEDS = "y";
          LEDS_TRIGGERS = "y";
          LEDS_CLASS = "y";         # required by rt2x00lib
          LEDS_CLASS_MULTICOLOR = "y";
          LEDS_BRIGHTNESS_HW_CHANGED = "y";

          PRINTK_TIME = "y";
        } // lib.optionalAttrs (config.system.service ? vlan) {
          SWCONFIG = "y";
        } // lib.optionalAttrs (config.system.service ? watchdog) {
          RALINK_WDT = "y";  # watchdog
          MT7621_WDT = "y";  # or it might be this one
        };
      };
    };
}