wip(rpi4): park the Pi 4 sketch — superseded by the Pi 5 machinery in #87

Never-committed working tree state found in the dev worktree: a Pi 4 hardware
module, a setup walkthrough, an upboard-serial refactor, and flake wiring that
does not evaluate (aarch64 packages block nested inside packages.x86_64-linux;
pkgs-aarch64 built with `inherit aarch64` instead of `system`, so it is really
x86; references a nixosConfigurations.rpi4-installed that is never defined).

Parked verbatim for reference. The real Pi 4 target is rebuilt on top of #87's
mkPiInstalled/mkPiImage shape in feat/rpi4-target.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013A6683cCHnQxFUosx1krY4

.envrc

@@ -0,0 +1 @@
+use flake

deploy/nixos/README.md

@@ -14,7 +14,8 @@ deploy/nixos/
 ├── hardware/
 │   ├── douro.nix           # Dell OptiPlex 9030 AIO (stock Douro motherboard; SATA SSD, eGalax touch)
 │   ├── batm3.nix           # GeneralBytes BATM3 chassis with a Dell OptiPlex 9030 AIO grafted in (custom mod; WireGuard wired in)
-│   └── upboard.nix         # Aaeon UP Board (Sintra + tejo; eMMC root via sdhci-acpi + mmc_block)
+│   ├── upboard.nix         # Aaeon UP Board (Sintra + tejo; eMMC root via sdhci-acpi + mmc_block)
+│   └── raspberry-pi4.nix   # Raspberry Pi 4 (aarch64) hardware configuration
 ├── udev/
 │   └── 99-bitspire-hardware.rules   # additional udev rules (loaded via configuration.nix)
 ├── provision-atm.sh        # Push LNbits credentials to a deployed ATM via SSH
@@ -34,7 +35,7 @@ Each ATM model has two flake outputs:
 | `packages.x86_64-linux.iso-<model>` | ISO | ISO image of the live variant |
 | `packages.x86_64-linux.disk-image-<model>` | raw image | dd-able full disk image of the installed variant |
 
-Models: `douro`, `tejo`, `sintra`, `batm3`.
+Models: `douro`, `tejo`, `sintra`, `batm3`, `rpi4`.
 
 ```bash
 # Build a Sintra disk image
@@ -43,11 +44,111 @@ nix build .#disk-image-sintra
 
 # Build a live ISO for tejo
 nix build .#iso-tejo
+
+# Build a Raspberry Pi 4 disk image (aarch64)
+nix build .#disk-image-rpi4
+# → result/nixos.img  (Raspberry Pi firmware bootloader, GPT+ESP)
 ```
 
 ## Deploying to Sintra (full walkthrough)
 
-The Sintra ships from the factory with whatever its previous OS was — Android, vendor Linux, or wiped. You need an Alpine live USB to act as your installer.
+The Sintra ships from the factory with whatever its previous OS was — Android, vendor Linux, or wiped.
+
+## Deploying to Raspberry Pi 4 (full walkthrough)
+
+The Raspberry Pi 4 uses an SD card as primary storage and boots via the Raspberry Pi firmware bootloader (rpi-bootloader). Unlike Intel-based ATMs that use systemd-boot, the RPi4 config uses the native Raspberry Pi bootloader.
+
+### Prerequisites
+
+- Raspberry Pi 4 board (4GB or 8GB RAM recommended for Electron)
+- 32GB+ SD card (or external SSD for better reliability)
+- Network connection (ethernet recommended for stability)
+- SSH access or a serial console (UART) for first-boot provisioning
+
+### Build the disk image
+
+```bash
+nix build .#disk-image-rpi4
+# → result/nixos.img (raw disk image, aarch64)
+```
+
+### Flash to SD card
+
+```bash
+# Replace /dev/sdX with your SD card device
+sudo dd if=result/nixos.img of=/dev/sdX bs=4M status=progress conv=fsync && sync
+```
+
+**Important:** Verify the target is the SD card, not your main disk:
+```bash
+lsblk -f /dev/sdX
+# Should show 'SD_CARD' or similar, not a hard drive name
+```
+
+### Boot and provision
+
+1. Insert the SD card into the Raspberry Pi 4.
+2. Connect Ethernet and power on.
+3. Wait for boot (you should see Raspberry Pi firmware loading messages).
+4. The kiosk screen should show "ATM unavailable — needs provisioning".
+
+From your dev box, provision LNbits credentials:
+
+```bash
+LNBITS_SERVER_PUBKEY=$(docker logs <lnbits-container> 2>&1 | \
+  grep -oP 'Public key \(share this\):\s*\K[a-f0-9]{64}' | tail -1)
+
+RELAY_URL=ws://<dev-lan-ip>:5001/nostrrelay/test \
+LNBITS_SERVER_PUBKEY="$LNBITS_SERVER_PUBKEY" \
+ATM_PRIVATE_KEY=$(openssl rand -hex 32) \
+bash deploy/nixos/provision-atm.sh <rpi4-ip> 22
+```
+
+The script SSHes to `bitspire@<rpi4-ip>:22`, writes `/var/lib/bitspire/.env`, and restarts `bitspire.service`. After a few seconds the kiosk connects to LNbits over nostr-transport and shows the live UI.
+
+### First-time deploy
+
+**Save the generated `ATM_PRIVATE_KEY`.** LNbits identifies this ATM by its public key; if you regenerate the key on re-provision, LNbits will auto-create a fresh wallet and the old wallet's balance becomes inaccessible.
+
+### Re-flash
+
+To preserve the ATM's identity and transaction history, backup the `.env` and `state.db` from the running Raspberry Pi before reflashing:
+
+```bash
+# From the Raspberry Pi
+mkdir -p ~/rpi4-backup-$(date +%Y%m%d)
+cp /var/lib/bitspire/.env ~/rpi4-backup-$(date +%Y%m%d)/
+cp /var/lib/bitspire/state.db ~/rpi4-backup-$(date +%Y%m%d)/
+
+# Copy to dev box
+scp bitspire@<rpi4-ip>:~/rpi4-backup-*/.env ~/rpi4-backup-*/
+scp bitspire@<rpi4-ip>:~/rpi4-backup-*/state.db ~/rpi4-backup-*/
+```
+
+On re-flash, source the backup values:
+
+```bash
+set -a; source ~/rpi4-backup-<date>/.env; set +a
+ATM_PRIVATE_KEY=$VITE_ATM_PRIVATE_KEY \
+LNBITS_SERVER_PUBKEY=$VITE_LNBITS_SERVER_PUBKEY \
+RELAY_URL=$VITE_RELAY_URL \
+bash deploy/nixos/provision-atm.sh <rpi4-ip> 22
+```
+
+### Hardware-specific notes
+
+- **Storage:** SD cards are slower and have limited write cycles compared to SSDs. Consider using a high-quality card and avoid frequent rewrites. For production, an external SSD via USB 3.0 is recommended for better reliability.
+- **Power:** The Raspberry Pi 4 can draw up to 3A at 5V. Use a reliable power supply rated for at least 5V 3A.
+- **Thermal:** The Pi 4 runs warm. Ensure adequate cooling (passive heatsinks or a fan) for 24/7 operation.
+- **Console:** The serial console is available at `/dev/ttyAMA0` (PL011 UART) at 115200 baud, useful for debugging.
+- **Swap:** A 2GB swapfile is enabled by default to prevent hard-freeze under memory pressure. Consider increasing this on 4GB models.
+
+### Troubleshooting
+
+- **Boot fails:** Check the SD card is properly flashed and inserted. Try rebuilding the image with a fresh `nix build .#disk-image-rpi4`.
+- **No network:** Verify the Ethernet cable is connected and the Pi's lights show activity. Check `/etc/resolv.conf` after boot.
+- **ATM doesn't connect to LNbits:** Verify `VITE_RELAY_URL` and `VITE_LNBITS_SERVER_PUBKEY` are set in `/var/lib/bitspire/.env` via SSH: `ssh bitspire@<rpi4-ip> 'cat /var/lib/bitspire/.env'`.
+- **Electron fails to start:** Check memory usage (`free -h`). On 4GB models, close other processes to free up RAM. You need an Alpine live USB to act as your installer.
 
 ### 0. (Re-flash only) Preserve state from the existing Sintra
 

deploy/nixos/hardware/raspberry-pi4.nix

@@ -0,0 +1,124 @@
+# Raspberry Pi 4 Hardware Configuration
+# For bitSpire deployments on Raspberry Pi 4
+# Requires: 4GB+ RAM (8GB recommended for Electron + kiosk)
+# Storage: SD card or external SSD/eMMC (minimum 32GB)
+#
+# Note: Import shared serial peripheral configuration for consistency
+# with other bitSpire hardware (useful for future extensions).
+
+{ config, lib, pkgs, ... }:
+
+{
+  # Import shared serial peripheral configuration (useful for future hardware extensions)
+  imports = [ ./upboard-serial.nix ];
+
+  # Raspberry Pi 4 uses aarch64 architecture
+  boot.kernelPackages = pkgs.linuxPackages_rpi4;
+
+  boot = {
+    loader = {
+      # Raspberry Pi 4 uses the Raspberry Pi firmware bootloader (rpi-bootloader)
+      grub.enable = lib.mkForce false;
+      # raspberryPi.enable has been removed in recent nixpkgs
+      # rpi-bootloader is now built into rpi4 kernel packages
+    };
+
+    initrd.availableKernelModules = [
+      "xhci_pci"
+      "usb_storage"
+      "sdhci_pci"
+      "sdhci"
+      "sd_mod"
+      "brcmmac"
+      "brcmfmac"
+      "mmc_block"
+      "cma"
+    ];
+
+    initrd.kernelModules = [
+      "sdhci_pci"
+      "sdhci"
+      "mmc_block"
+      "brcmmac"
+      "brcmfmac"
+      "cma"
+    ];
+
+    kernelModules = [
+      "kvm-arm"
+      "uas"
+    ];
+
+    kernelParams = [
+      "console=tty1"
+      "console=ttyAMA0,115200n8"
+      "console=ttyS0,115200n8"
+      "root=/dev/mmcblk0p2"
+      "rootfstype=ext4"
+      "rootwait"
+      "rw"
+      # Disable PCIe to save power (optional - uncomment if needed)
+      # "pcie_aspm=off"
+    ];
+  };
+
+  # Filesystem layout: SD card with GPT partition table
+  # Partition 1: EFI System Partition (FAT32)
+  # Partition 2: Root filesystem (ext4)
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/nixos";
+    fsType = "ext4";
+    options = [ "noatime" ];
+  };
+
+  fileSystems."/boot" = {
+    device = "/dev/disk/by-label/ESP";
+    fsType = "vfat";
+    options = [ "defaults" "nofail" ];
+  };
+
+  # Swap configuration for better reliability on SD cards
+  swapDevices = [{
+    device = "/swapfile";
+    size = 2048; # 2GB swap
+  }];
+
+  # Power management for Raspberry Pi
+  powerManagement = {
+    enable = true;
+    cpuFreqGovernor = "ondemand";
+  };
+
+  # Disable suspend/hibernate for kiosk stability
+  systemd.targets = {
+    sleep.enable = false;
+    suspend.enable = false;
+    hibernate.enable = false;
+    hybrid-sleep.enable = false;
+  };
+
+  # Hardware-specific settings
+  hardware = {
+    # Raspberry Pi 4 has no discrete GPU (uses VideoCore)
+    graphics = {
+      enable = true;
+    };
+
+    # USB mass storage drivers (not applicable for ARM - handled by kernel modules)
+    # usb.enable = true;
+    # usb.enableUSBHub = true;
+
+    # RPi4-specific tweaks
+    enableRedistributableFirmware = true;
+    # CPU firmware (not applicable for ARM - no x86 microcode)
+    # cpu.amd64.updateMicrocode = false; # Not applicable for ARM
+  };
+
+  # USB configuration (not applicable for ARM)
+  # hardware.usb.enable = true;
+  # hardware.usb.enableUSBHub = true;
+
+  # Network configuration
+  # useDHCP is set in configuration.nix (base config)
+  networking.interfaces.eth0.useDHCP = true;
+}

deploy/nixos/upboard-serial.nix

@@ -0,0 +1,32 @@
+# Shared serial peripheral configuration for UP Board hardware
+# (Sintra, tejo, and any other systems with similar UART layout)
+#
+# Serial ports used by bitSpire ATM:
+#   ttyJ4 = Printer (Nippon NP-2511D-2) - optional on some configs
+#   ttyJ5 = Validator (iVizion, ID003 protocol)
+#   ttyJ7 = Dispenser (Fujitsu F53/F56)
+#
+# These symlinks + udev rules are shared between live.nix (for testing)
+# and hardware-specific modules (upboard.nix, douro.nix).
+
+{ config, lib, pkgs, ... }:
+
+{
+  # Serial peripheral symlinks
+  services.udev.extraRules = ''
+    # ── Validator (iVizion ID003) ─────────────────────────────────────
+    # ttyJ5 on UP Board (FTDI USB bridge) → /dev/ttyJ5
+    KERNEL=="ttyJ5", SYMLINK+="validator-device"
+    SUBSYSTEM=="tty", GROUP="uucp", MODE="0666"
+
+    # ── Dispenser (Fujitsu F56) ───────────────────────────────────────
+    # ttyJ7 on UP Board (SoC MMIO UART) → /dev/ttyJ7
+    KERNEL=="ttyJ7", SYMLINK+="dispenser-device"
+    SUBSYSTEM=="tty", GROUP="uucp", MODE="0666"
+
+    # ── Printer (Nippon NP-2511D-2) ───────────────────────────────────
+    # ttyJ4 on UP Board (optional - not all configs use it)
+    KERNEL=="ttyJ4", SYMLINK+="printer-device", OPTIONS+="static_node=ttyJ4"
+    SUBSYSTEM=="tty", GROUP="uucp", MODE="0666"
+  '';
+}

docs/raspberry-pi4-setup.md

@@ -0,0 +1,225 @@
+# Raspberry Pi 4 bitSpire Setup Guide
+
+This document describes how to build and deploy bitSpire to a Raspberry Pi 4.
+
+## Hardware Requirements
+
+- **Board**: Raspberry Pi 4 (4GB or 8GB RAM recommended for Electron)
+- **Storage**: 32GB+ SD card (or external SSD via USB for better reliability)
+- **Power**: 5V 3A+ power supply (Pi 4 can draw up to 3A at 5V)
+- **Cooling**: Passive heatsinks or active fan for 24/7 operation
+- **Network**: Ethernet connection recommended for stability
+
+## Building the Disk Image
+
+```bash
+cd /home/padreug/dev/bitspire/bitspire/dev
+
+# Build the Raspberry Pi 4 disk image (aarch64)
+nix build .#disk-image-rpi4
+
+# The image will be at: result/nixos.img
+```
+
+## Flashing to SD Card
+
+```bash
+# Replace /dev/sdX with your SD card device (NOT your main disk!)
+# Verify first: lsblk -f /dev/sdX
+
+sudo dd if=result/nixos.img of=/dev/sdX bs=4M status=progress conv=fsync && sync
+
+# Sync to ensure all writes are flushed
+sync
+```
+
+**Important**: Always verify the target device before flashing!
+
+## First-Time Deployment
+
+### 1. Boot the Raspberry Pi 4
+
+1. Insert the SD card into the Raspberry Pi 4.
+2. Connect Ethernet cable.
+3. Power on the device.
+4. You should see Raspberry Pi firmware boot messages.
+5. The kiosk screen shows "ATM unavailable — needs provisioning".
+
+### 2. Provision LNbits Credentials
+
+From your development machine:
+
+```bash
+LNBITS_SERVER_PUBKEY=$(docker logs <lnbits-container> 2>&1 | \
+  grep -oP 'Public key \(share this\):\s*\K[a-f0-9]{64}' | tail -1)
+
+RELAY_URL=ws://<dev-lan-ip>:5001/nostrrelay/test \
+LNBITS_SERVER_PUBKEY="$LNBITS_SERVER_PUBKEY" \
+ATM_PRIVATE_KEY=$(openssl rand -hex 32) \
+bash deploy/nixos/provision-atm.sh <rpi4-ip> 22
+```
+
+**Important**: Save the generated `ATM_PRIVATE_KEY` — it's required to preserve the ATM's identity and wallet balance.
+
+### 3. Verify Connection
+
+After provisioning completes:
+
+```bash
+ssh bitspire@<rpi4-ip> 'cat /var/lib/bitspire/.env'
+```
+
+You should see the environment variables are set correctly. The kiosk should connect to LNbits over nostr-transport and show the live UI after a few seconds.
+
+## Re-Flashing (Preserving Identity)
+
+To preserve the ATM's identity and transaction history when reflashing:
+
+1. **Backup from the running Raspberry Pi**:
+
+```bash
+# From the Raspberry Pi
+mkdir -p ~/rpi4-backup-$(date +%Y%m%d)
+cp /var/lib/bitspire/.env ~/rpi4-backup-$(date +%Y%m%d)/
+cp /var/lib/bitspire/state.db ~/rpi4-backup-$(date +%Y%m%d)/
+```
+
+2. **Copy backups to dev box**:
+
+```bash
+scp bitspire@<rpi4-ip>:~/rpi4-backup-*/.env ~/rpi4-backup-*/
+scp bitspire@<rpi4-ip>:~/rpi4-backup-*/state.db ~/rpi4-backup-*/
+```
+
+3. **Re-flash the SD card**:
+
+```bash
+nix build .#disk-image-rpi4
+sudo dd if=result/nixos.img of=/dev/sdX bs=4M status=progress conv=fsync && sync
+```
+
+4. **Re-provision from backups**:
+
+```bash
+set -a; source ~/rpi4-backup-<date>/.env; set +a
+
+ATM_PRIVATE_KEY=$VITE_ATM_PRIVATE_KEY \
+LNBITS_SERVER_PUBKEY=$VITE_LNBITS_SERVER_PUBKEY \
+RELAY_URL=$VITE_RELAY_URL \
+bash deploy/nixos/provision-atm.sh <rpi4-ip> 22
+```
+
+## Hardware-Specific Notes
+
+### Storage
+- **SD cards** are slower and have limited write cycles. For production, consider an external SSD via USB 3.0 for better reliability.
+- Use high-quality SD cards with good endurance ratings.
+- Avoid frequent rewrites to the same sectors.
+
+### Power
+- The Raspberry Pi 4 can draw up to 3A at 5V during heavy load (Electron startup).
+- Use a reliable power supply rated for at least 5V 3A.
+- Avoid using USB hubs that don't provide sufficient power.
+
+### Thermal
+- The Pi 4 runs warm, especially under load with Electron.
+- Ensure adequate cooling for 24/7 operation:
+  - Passive heatsinks on the SoC and RAM
+  - Or a small active fan blowing air over the board
+- Consider removing the metal case for better airflow in hot environments.
+
+### Console
+- The serial console is available at `/dev/ttyAMA0` (PL011 UART) at 115200 baud.
+- Useful for debugging boot issues.
+- Not required for normal operation.
+
+### Swap
+- A 2GB swapfile is enabled by default to prevent hard-freeze under memory pressure.
+- Consider increasing this on 4GB models if you expect heavy load.
+
+## Troubleshooting
+
+### Boot fails
+
+**Symptoms**: Pi doesn't boot or shows errors.
+
+**Solutions**:
+1. Verify SD card is properly flashed:
+   ```bash
+   lsblk -f /dev/sdX
+   # Should show GPT partition table with ESP and nixos partitions
+   ```
+2. Try rebuilding the image:
+   ```bash
+   nix build .#disk-image-rpi4
+   ```
+3. Check power supply and connections.
+
+### No network connectivity
+
+**Symptoms**: Cannot SSH to the Pi or connect to LAN.
+
+**Solutions**:
+1. Verify Ethernet cable is connected and the Pi's lights show activity.
+2. Check `/etc/resolv.conf` after boot:
+   ```bash
+   ssh bitspire@<rpi4-ip> 'cat /etc/resolv.conf'
+   ```
+3. Check network interface status:
+   ```bash
+   ssh bitspire@<rpi4-ip> 'ip a'
+   ```
+
+### ATM doesn't connect to LNbits
+
+**Symptoms**: Kiosk shows "ATM unavailable" or no connection.
+
+**Solutions**:
+1. Verify environment variables are set:
+   ```bash
+   ssh bitspire@<rpi4-ip> 'cat /var/lib/bitspire/.env'
+   ```
+2. Check for typos in `VITE_RELAY_URL` and `VITE_LNBITS_SERVER_PUBKEY`.
+3. Verify LNbits is running and accessible:
+   ```bash
+   curl <lnbits-url>/api/v1/settings
+   ```
+4. Check ATM service logs:
+   ```bash
+   ssh bitspire@<rpi4-ip> 'sudo journalctl -u bitspire -n 50'
+   ```
+
+### Electron fails to start
+
+**Symptoms**: Service logs show Electron crash or OOM (out of memory).
+
+**Solutions**:
+1. Check memory usage:
+   ```bash
+   ssh bitspire@<rpi4-ip> 'free -h'
+   ```
+2. On 4GB models, close other processes to free up RAM.
+3. Consider increasing the swapfile size in `/var/lib/bitspire/.env`.
+
+## Building Live ISO for Testing
+
+To build a live USB bootable ISO for testing (without installing):
+
+```bash
+nix build .#iso-rpi4
+
+# The ISO will be at: result/*.iso
+```
+
+## Configuration Files
+
+- **Hardware config**: `deploy/nixos/hardware/raspberry-pi4.nix`
+- **Base config**: `deploy/nixos/configuration.nix`
+- **Service module**: `deploy/nixos/bitspire-atm.nix`
+- **Provisioning script**: `deploy/nixos/provision-atm.sh`
+
+## References
+
+- [NixOS on Raspberry Pi](https://nixos.org/manual/nixos/stable/index.html#sec-architecture-raspberry-pi)
+- [bitSpire README](../README.md)
+- [NixOS Hardware Configuration](https://nixos.org/manual/nixos/stable/index.html#ch-configuring-hardware)

flake.lock

@@ -435,6 +435,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-aarch64": {
+      "locked": {
+        "lastModified": 1782847189,
+        "narHash": "sha256-twXPFqFsrrY5r28Zh7Homgcp2gUMBgQ6WDS98Q/3xFI=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "b6018f87da91d19d0ab4cf979885689b469cdd41",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-25.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nixpkgs-regression": {
       "locked": {
         "lastModified": 1643052045,
@@ -504,6 +520,7 @@
         "devenv": "devenv",
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs_3",
+        "nixpkgs-aarch64": "nixpkgs-aarch64",
         "nixpkgs-unstable": "nixpkgs-unstable",
         "rust-overlay": "rust-overlay"
       }

flake.nix

@@ -5,6 +5,9 @@
     # Stable NixOS for the ATM OS base
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
 
+    # Stable NixOS for the ATM OS base (aarch64) — Raspberry Pi 4
+    nixpkgs-aarch64.url = "github:NixOS/nixpkgs/nixos-25.11";
+
     # Unstable for Electron, Node.js, pnpm (latest versions)
     nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
 
@@ -38,15 +41,22 @@
     };
   };
 
-  outputs = { self, nixpkgs, nixpkgs-unstable, flake-utils, rust-overlay, devenv, determinate, atm-tui }:
+  outputs = { self, nixpkgs, nixpkgs-unstable, nixpkgs-aarch64, flake-utils, rust-overlay, devenv, determinate, atm-tui }:
     let
       system = "x86_64-linux";
 
+      aarch64 = "aarch64-linux";
+
       pkgs = import nixpkgs {
         inherit system;
         config.allowUnfree = true;
       };
 
+      pkgs-aarch64 = import nixpkgs-aarch64 {
+        inherit aarch64;
+        config.allowUnfree = true;
+      };
+
       pkgs-unstable = import nixpkgs-unstable {
         inherit system;
         config.allowUnfree = true;
@@ -504,6 +514,25 @@
             '';
 
         # Backwards compat
+
+      # aarch64-linux packages (Raspberry Pi 4)
+      packages.${aarch64} = {
+        # ATM app derivation for Raspberry Pi 4
+        atm-app-rpi4 = mkAtmApp { model = "rpi4"; fiatCode = "USD"; };
+
+        # Raspberry Pi 4 disk image (aarch64)
+        # Note: Raspberry Pi 4 uses the Raspberry Pi firmware bootloader,
+        # not systemd-boot. The image is built for aarch64 and booted via
+        # the rpi-bootloader (rpi-firmware). Requires an SD card with GPT
+        # partition table (ESP + ext4 root).
+        disk-image-rpi4 = import (nixpkgs-aarch64 + "/nixos/lib/make-disk-image.nix") { 
+          pkgs = pkgs-aarch64; inherit lib;
+          config = self.nixosConfigurations.rpi4-installed.config;
+          format = "raw";
+          partitionTableType = "efi";
+          diskSize = "auto";
+        };
+      };
         iso = self.nixosConfigurations.douro.config.system.build.isoImage;
       };
     }