76 lines
2.3 KiB
Markdown
76 lines
2.3 KiB
Markdown
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# 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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