Mathew Lewis
1f88150d03
Flashes the on-board LED as 3, 1, 4, 1, 5 with pauses between digits and a longer pause before repeating. The pattern is stepped from the hardware timer rather than blocking sleeps, so the USB serial port stays responsive and can reset the board back into BOOTSEL on request. Includes the original plain 250 ms blink under alt/ and prebuilt .uf2 images. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01FrCPgv2NGSEcyuN9KKQKHc
76 lines
2.3 KiB
Markdown
76 lines
2.3 KiB
Markdown
# pico-blinky
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Rust firmware for the Raspberry Pi Pico. Flashes the on-board LED with the
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digits of pi: three flashes, a pause, one flash, a pause, four, one, five,
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then a longer pause before it repeats.
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## Board
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This targets the **RP2040**, the original Pico. It will not run on a Pico 2.
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Check which one you have by holding BOOTSEL while plugging it in and looking
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at the volume that mounts:
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| Volume label | Chip | This firmware |
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|--------------|---------|---------------|
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| `RPI-RP2` | RP2040 | yes |
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| `RP2350` | RP2350 | no |
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## Build
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```
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rustup target add thumbv6m-none-eabi
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cargo install elf2uf2-rs --locked
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cargo build --release
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elf2uf2-rs target/thumbv6m-none-eabi/release/blinky pi-blink.uf2
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```
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## Flash
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Hold the BOOTSEL button down **before** the cable goes in, keep it held for a
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second after, then release. The button is only read at power-on, so pressing
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it while the board is already running does nothing.
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The board mounts as `RPI-RP2`. Copy the `.uf2` onto it. The volume ejects
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itself once the write completes, which is the bootloader confirming it took
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the image and jumped to it.
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Prebuilt images are in `uf2/` if you just want to drag one across.
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## Getting back into the bootloader
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The firmware exposes a USB serial port, so after the first flash you do not
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need the button again. Either:
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- send `b` to the serial port, or
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- open the port at 1200 baud and drop DTR, the convention `picotool` and the
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Arduino IDE use
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Both call `reset_to_usb_boot`, and the board comes back up as `RPI-RP2`.
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The LED pattern is driven from the hardware timer rather than blocking sleeps,
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so USB stays responsive while the sequence runs.
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## Layout
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```
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src/main.rs pi digits + USB reboot-to-bootloader
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alt/simple-blink.rs plain 250 ms on/off blink, the first version
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memory.x flash/RAM layout, reserves 0x100 for the boot2 stage
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build.rs puts memory.x on the linker search path
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uf2/ prebuilt images
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```
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## Timing
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Edit the constants at the top of `src/main.rs`:
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```rust
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const FLASH_ON_US: u64 = 150_000;
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const FLASH_OFF_US: u64 = 200_000;
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const DIGIT_GAP_US: u64 = 800_000;
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const CYCLE_GAP_US: u64 = 3_000_000;
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```
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`DIGIT_GAP_US` is the one worth raising if the sequence is hard to count by
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eye, since 1 and 4 sit next to each other and can run together.
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