pm-kit milestone 2: ST7796 display bring-up

Init the Kit's ST7796 320x480 over SPI0 (SCK=GP2, MOSI=GP3, CS=GP5, DC=GP6,
RST=GP7; BGR, colours inverted, 16 MHz) via mipidsi 0.9 + embedded-graphics, and
draw a panel + "PM-KIT / RUST OK" so SPI + the graphics stack are verifiable on
screen. GP25 LED keeps blinking as a heartbeat.

Compiles for thumbv8m; runtime (does it draw? colours/orientation right?) is the
on-device check. Next: tune orientation/colour if needed, then inputs + audio + pm-core.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

rust/pm-kit/Cargo.toml

@@ -2,13 +2,16 @@
 name = "pm-kit"
 version = "0.1.0"
 edition = "2021"
-description = "PM_K-1 firmware (RP2350 / Pico 2). Stage 3 bring-up: boot-proof blink, then drivers + pm-core."
+description = "PM_K-1 firmware (RP2350 / Pico 2). Stage 3 bring-up: boot blink → display → drivers + pm-core."
 
 [dependencies]
 rp235x-hal = { version = "0.3", features = ["binary-info", "critical-section-impl", "rt"] }
 cortex-m-rt = "0.7"
 panic-halt = "1"
 embedded-hal = "1"
+embedded-hal-bus = "0.2"
+mipidsi = "0.9"
+embedded-graphics = "0.8"
 
 [profile.release]
 opt-level = "s"

rust/pm-kit/src/main.rs

@@ -1,29 +1,44 @@
-//! PM_K-1 firmware — Stage 3 bring-up milestone 1: prove our Rust boots on the Pico 2 (RP2350).
+//! PM_K-1 firmware — Stage 3 bring-up.
-//!
+//! Milestone 1 (done): blink GP25 → proved boot/flash.
-//! Blinks the onboard LED (GP25). If it blinks, the whole path works: toolchain, RP2350 boot
+//! Milestone 2 (this): init the ST7796 320×480 display over SPI0 and draw to it.
-//! block, memory layout, flash, and the cortex-m-rt entry. Drivers (display / audio / inputs /
+//! Pins (from the CircuitPython firmware): SCK=GP2, MOSI=GP3, CS=GP5, DC=GP6, RST=GP7;
-//! USB-MIDI) and the `pm-core` engine come next, once boot is confirmed on hardware.
+//! BGR panel, colours inverted. LED on GP25 keeps blinking as a heartbeat.
 
 #![no_std]
 #![no_main]
 
+use embedded_graphics::{
+    mono_font::{ascii::FONT_10X20, MonoTextStyle},
+    pixelcolor::Rgb565,
+    prelude::*,
+    primitives::{PrimitiveStyle, Rectangle},
+    text::Text,
+};
 use embedded_hal::delay::DelayNs;
 use embedded_hal::digital::OutputPin;
+use embedded_hal_bus::spi::ExclusiveDevice;
+use mipidsi::interface::SpiInterface;
+use mipidsi::models::ST7796;
+use mipidsi::options::{ColorInversion, ColorOrder, Orientation};
+use mipidsi::Builder;
 use panic_halt as _;
 use rp235x_hal as hal;
+use hal::fugit::RateExtU32;
+use hal::Clock;
 
 /// Image definition block — the RP2350 bootrom looks for this to boot the image.
 #[link_section = ".start_block"]
 #[used]
 pub static IMAGE_DEF: hal::block::ImageDef = hal::block::ImageDef::secure_exe();
 
-const XTAL_FREQ_HZ: u32 = 12_000_000; // Pico 2 crystal
+const XTAL_FREQ_HZ: u32 = 12_000_000;
+const WIDTH: u16 = 320;
+const HEIGHT: u16 = 480;
 
 #[hal::entry]
 fn main() -> ! {
     let mut pac = hal::pac::Peripherals::take().unwrap();
     let mut watchdog = hal::Watchdog::new(pac.WATCHDOG);
-
     let clocks = hal::clocks::init_clocks_and_plls(
         XTAL_FREQ_HZ,
         pac.XOSC,
@@ -37,11 +52,50 @@ fn main() -> ! {
     .unwrap();
 
     let mut timer = hal::Timer::new_timer0(pac.TIMER0, &mut pac.RESETS, &clocks);
-
     let sio = hal::Sio::new(pac.SIO);
     let pins = hal::gpio::Pins::new(pac.IO_BANK0, pac.PADS_BANK0, sio.gpio_bank0, &mut pac.RESETS);
+
     let mut led = pins.gpio25.into_push_pull_output();
 
+    // --- ST7796 over SPI0 ---
+    let sclk = pins.gpio2.into_function::<hal::gpio::FunctionSpi>();
+    let mosi = pins.gpio3.into_function::<hal::gpio::FunctionSpi>();
+    let dc = pins.gpio6.into_push_pull_output();
+    let rst = pins.gpio7.into_push_pull_output();
+    let cs = pins.gpio5.into_push_pull_output();
+
+    let spi = hal::spi::Spi::<_, _, _, 8>::new(pac.SPI0, (mosi, sclk));
+    let spi = spi.init(
+        &mut pac.RESETS,
+        clocks.peripheral_clock.freq(),
+        16.MHz(),
+        embedded_hal::spi::MODE_0,
+    );
+    let spi_device = ExclusiveDevice::new_no_delay(spi, cs).unwrap();
+
+    let mut buffer = [0u8; 512];
+    let di = SpiInterface::new(spi_device, dc, &mut buffer);
+
+    let mut display = Builder::new(ST7796, di)
+        .reset_pin(rst)
+        .display_size(WIDTH, HEIGHT)
+        .color_order(ColorOrder::Bgr)
+        .invert_colors(ColorInversion::Inverted)
+        .orientation(Orientation::new())
+        .init(&mut timer)
+        .unwrap();
+
+    // background
+    display.clear(Rgb565::new(2, 4, 8)).unwrap();
+    // a panel + label so we can see SPI + the graphics stack working
+    Rectangle::new(Point::new(20, 60), Size::new((WIDTH - 40) as u32, 140))
+        .into_styled(PrimitiveStyle::with_fill(Rgb565::new(2, 40, 50)))
+        .draw(&mut display)
+        .unwrap();
+    let title = MonoTextStyle::new(&FONT_10X20, Rgb565::WHITE);
+    Text::new("PM-KIT", Point::new(40, 110), title).draw(&mut display).unwrap();
+    Text::new("RUST OK", Point::new(40, 150), title).draw(&mut display).unwrap();
+
     loop {
         led.set_high().unwrap();
         timer.delay_ms(250);
@@ -54,4 +108,4 @@ fn main() -> ! {
 #[link_section = ".bi_entries"]
 #[used]
 pub static PICOTOOL_ENTRIES: [hal::binary_info::EntryAddr; 1] =
-    [hal::binary_info::rp_program_name!(c"pm-kit blink")];
+    [hal::binary_info::rp_program_name!(c"pm-kit display")];