Update flake.nix to use latest Rust toolchain

.cargo/config.toml

@@ -1,5 +1,11 @@
 [target.thumbv6m-none-eabi]
-runner = "direnv exec . probe-rs run --chip RP2040"
+runner = "direnv exec . elf2uf2-rs -d"
+rustflags = [
+    "-C", "linker=rust-lld",
+    "-C", "link-arg=-Tlink.x",
+    "-C", "link-arg=-Tlink-rp.x",
+    "-C", "link-arg=-Tdefmt.x",
+]
 
 [build]
 target = "thumbv6m-none-eabi"

README.md

@@ -104,22 +104,32 @@ flatpak run org.example.rustdevshell
 
 This project is configured for seamless flashing from the IDE or terminal.
 
-### Troubleshooting: No Connected Probes
+### Flashing via USB (BOOTSEL mode)
 
-If you encounter the error `Error: No connected probes were found` or udev rule warnings, check the following:
+If you don't have a physical debugger, you can flash the Pico W directly via USB using the BOOTSEL mode:
 
-1.  **Hardware Connection**: Ensure your Raspberry Pi Pico W is connected via a compatible debugger (e.g., another Pico running `picoprobe`, a CMSIS-DAP debugger, or an ESP-Prog).
-2.  **Udev Rules (Linux)**: `probe-rs` needs permission to access the USB device.
-    -   Create a file named `/etc/udev/rules.d/69-probe-rs.rules`.
-    -   Add the rules provided by the [probe-rs documentation](https://probe.rs/docs/getting-started/probe-setup/).
+1.  **Enter BOOTSEL Mode**: Hold the `BOOTSEL` button on your Pico W while plugging it into your computer's USB port. It should appear as a USB mass storage device.
+2.  **Flash and Run**: Run the following command (or use the IDE "Run" button):
+    ```bash
+    cargo run --release
+    ```
+    This project is configured to use `elf2uf2-rs`, which automatically detects the Pico W in BOOTSEL mode, converts the binary to UF2 format, and flashes it.
+
+### Troubleshooting: Flashing Issues
+
+If you encounter issues flashing via USB:
+1.  **Check BOOTSEL mode**: Ensure the Pico W is mounted as a USB drive.
+2.  **Udev Rules (Linux)**: You may need permissions to access the USB device.
+    -   Create a file named `/etc/udev/rules.d/99-pico.rules`.
+    -   Add: `SUBSYSTEMS=="usb", ATTRS{idVendor}=="2e8a", ATTRS{idProduct}=="0003", MODE="0666"`
     -   Reload rules: `sudo udevadm control --reload` and `sudo udevadm trigger`.
-3.  **Group Membership**: Ensure your user is in the `plugdev` or `dialout` group (depending on your distro's udev rules).
+3.  **Cable**: Ensure you are using a data-sync USB cable, not just a charging cable.
 
 ### Flashing from IDE
 
 If you are using **RustRover** or **IntelliJ Rust**, you can use the "Flash Pico W" run configuration provided in the `.run` folder. Just select it from the run menu and click "Run".
 
-**Note:** The project is configured to use `direnv exec .` in `.cargo/config.toml` to ensure `probe-rs` is available. Ensure `direnv` is installed and allowed (`direnv allow`) on your system. For the best experience, we recommend installing the **direnv** plugin for your IDE.
+**Note:** The project is configured to use `direnv exec .` in `.cargo/config.toml` to ensure `elf2uf2-rs` is available. Ensure `direnv` is installed and allowed (`direnv allow`) on your system. For the best experience, we recommend installing the **direnv** plugin for your IDE.
 
 ### Flashing from Terminal
 
@@ -129,10 +139,10 @@ You can flash the Pico W by running:
 cargo run --release
 ```
 
-This uses `probe-rs` (configured in `.cargo/config.toml`) to flash and run the binary via a CMSIS-DAP debugger or similar.
+This uses `elf2uf2-rs` (configured in `.cargo/config.toml`) to flash the binary via the USB BOOTSEL mode.
 
-If you prefer to use the UF2 bootloader (dragging to the drive or using `elf2uf2-rs`), you can change the runner in `.cargo/config.toml` to:
-`runner = "elf2uf2-rs -d"`
+If you prefer to use a physical debugger (e.g. CMSIS-DAP), you can change the runner in `.cargo/config.toml` to:
+`runner = "direnv exec . probe-rs run --chip RP2040"`
 
 ## Testing & Development Features
 

memory.x

@@ -0,0 +1,9 @@
+MEMORY
+{
+  /* FLASH and RAM lengths must match the RP2040 */
+  BOOT2 : ORIGIN = 0x10000000, LENGTH = 0x100
+  FLASH : ORIGIN = 0x10000100, LENGTH = 2048K - 0x100
+  RAM   : ORIGIN = 0x20000000, LENGTH = 256K
+  SCRATCH_A : ORIGIN = 0x20040000, LENGTH = 4K
+  SCRATCH_B : ORIGIN = 0x20041000, LENGTH = 4K
+}

src/main.rs

@@ -3,6 +3,7 @@
 
 use defmt_rtt as _;
 use embassy_executor::Spawner;
+use embassy_rp as _;
 use panic_probe as _;
 
 #[embassy_executor::main]