M1 complete: XIAO M0 drives LP5562 LEDs over I2C

Add error-resilient firmware with diagnostic LED blink patterns
(3 slow = alive, solid = I2C OK, fast burst = I2C error). Document
EVM external MCU wiring: disconnect P6 EN jumper, power VDD from
XIAO 5V, leave SCL/SDA jumpers in place with MSP430 unpowered.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/STATUS.md

@@ -1,6 +1,6 @@
 # xblink Project Status
 
-**Current Milestone**: M1 — LED Smoke Test (I2C verified via EVM USB bridge, XIAO M0 flash pending)
+**Current Milestone**: M2 — Engine Patterns
 **Last Updated**: 2026-03-05
 
 ---
@@ -24,7 +24,7 @@
 - [x] Update `main.rs` with I2C init + GPIO EN + LP5562 direct PWM test
 - [x] Verify `cargo build --release` compiles
 - [x] Verify LP5562 I2C control via EVM USB-to-I2C bridge (`tools/lp5562_evm.py`)
-- [ ] Flash XIAO M0 and verify RGBW LED channels with Rust firmware
+- [x] Flash XIAO M0 and verify RGBW LED channels with Rust firmware
 
 ### M2: Engine Patterns
 
@@ -142,7 +142,7 @@
 |------|--------|-------|
 | Seeed XIAO M0 | Available | Dev board MCU (SAMD21G18A) |
 | LP5562EVM | Available | TI eval module, RGBW LEDs, I2C addr 0x30 |
-| Mini-USB cable | Not on hand | Needed to flash XIAO M0 |
+| Mini-USB cable | Available | USB-C, used for flashing XIAO M0 |
 | NTAG5 Link Click | Available, partially wired | Missing I2C jumper to XIAO |
 | Hall effect sensor | Not available | Need to source — TI DRV5032FB (SOT-23) for prototype |
 | ACR1552 PCSC reader | Available | For ntag5sensor Python tooling |

docs/plans/2026-03-05-lp5562evm-protocol.md

@@ -88,3 +88,14 @@ The LP5562 EN pin is controlled by the MSP430's GPIO (EN-UC), connected through
 **Workaround**: Jumper EN directly to VDD (3.3V) on P1 or P6 header. This is acceptable because in the final xblink design, EN is controlled by a wired-AND circuit (MCU GPIO + hall sensor), not the EVM's MSP430.
 
 Without EN high, all I2C reads return status `02` (NAK) with data `00`.
+
+## Using EVM with External MCU (XIAO M0)
+
+When driving the LP5562 from an external MCU instead of the MSP430:
+
+1. **Disconnect EVM from USB** — the MSP430 must be unpowered to avoid I2C bus contention.
+2. **P6 header**: Remove the **EN jumper** to disconnect EN-UC (MSP430's EN output). Leave SCL/SDA jumpers in place — the unpowered MSP430's I/O pins go high-impedance.
+3. **P4 header**: Feed external VDD (e.g., XIAO 5V pin → P4 VDD). The on-board LP2985 3.3V LDO only runs from USB power.
+4. **Wiring**: XIAO A0 → P6 EN (LP5562 side), A4 → SDA, A5 → SCL, GND → GND, 5V → VDD.
+
+The LP5562 VDD range is 2.7–5.5V. Using 5V ensures headroom for white LED forward voltage (~3.0V) plus LP5562 current sink saturation (~0.4V).

src/main.rs

@@ -17,6 +17,16 @@ use pac::{CorePeripherals, Peripherals};
 mod led;
 use led::lp5562::{ClockSource, Lp5562, DEFAULT_ADDRESS};
 
+/// Blink the on-board LED n times (active-low: low=on, high=off)
+fn blink<D: embedded_hal::delay::DelayNs>(led: &mut bsp::Led0, delay: &mut D, times: u8, ms: u16) {
+    for _ in 0..times {
+        led.set_low().unwrap();
+        delay.delay_ms(ms as u32);
+        led.set_high().unwrap();
+        delay.delay_ms(ms as u32);
+    }
+}
+
 #[entry]
 fn main() -> ! {
     let mut peripherals = Peripherals::take().unwrap();
@@ -36,10 +46,14 @@ fn main() -> ! {
     let mut led: bsp::Led0 = pins.led0.into_push_pull_output();
     led.set_high().unwrap(); // LED off (active low)
 
+    // === DIAGNOSTIC: 3 slow blinks = firmware is alive ===
+    blink(&mut led, &mut delay, 3, 200);
+    delay.delay_ms(500u32);
+
     // LP5562 hardware enable on D0/A0 — drive high to power on
     let mut lp_en = pins.a0.into_push_pull_output();
     lp_en.set_high().unwrap();
-    delay.delay_ms(1u16); // Let LP5562 power stabilize
+    delay.delay_ms(10u32); // Let LP5562 power stabilize
 
     // I2C on A4 (SDA) / A5 (SCL) at 400 kHz
     let i2c = bsp::i2c_master(
@@ -53,35 +67,46 @@ fn main() -> ! {
 
     let mut lp = Lp5562::new(i2c, DEFAULT_ADDRESS);
 
-    // Enable chip, wait for startup (>500 us)
+    // Try to initialize LP5562 — blink error pattern on failure
-    lp.enable().unwrap();
+    let i2c_ok = (|| -> Result<(), led::lp5562::Error<_>> {
-    delay.delay_ms(1u16);
+        lp.enable()?;
+        delay.delay_ms(1u32); // >500us startup
+        lp.init_direct_control(ClockSource::Internal)?;
+        lp.set_all_current(50, 50, 50, 50)?;
+        Ok(())
+    })();
 
-    // Direct I2C PWM control, internal oscillator
+    match i2c_ok {
-    lp.init_direct_control(ClockSource::Internal).unwrap();
+        Ok(()) => {
+            // === DIAGNOSTIC: solid LED on = LP5562 init OK ===
+            led.set_low().unwrap();
+            delay.delay_ms(1000u32);
 
-    // 5 mA per channel (50 × 0.1 mA) — conservative for EH power budget
+            // M1 smoke test: cycle through RGBW channels
-    lp.set_all_current(50, 50, 50, 50).unwrap();
+            let on: u8 = 255;
+            let step: u16 = 500;
 
-    // Board LED on = LP5562 initialized OK
+            loop {
-    led.set_low().unwrap();
+                lp.set_all_pwm(on, 0, 0, 0).ok(); // Blue
-
+                delay.delay_ms(step as u32);
-    // M1 smoke test: cycle through RGBW channels
+                lp.set_all_pwm(0, on, 0, 0).ok(); // Green
-    let on: u8 = 255;
+                delay.delay_ms(step as u32);
-    let step: u16 = 500;
+                lp.set_all_pwm(0, 0, on, 0).ok(); // Red
-
+                delay.delay_ms(step as u32);
-    loop {
+                lp.set_all_pwm(0, 0, 0, on).ok(); // White
-        lp.set_all_pwm(on, 0, 0, 0).unwrap(); // Blue
+                delay.delay_ms(step as u32);
-        delay.delay_ms(step);
+                lp.set_all_pwm(on, on, on, on).ok(); // All on
-        lp.set_all_pwm(0, on, 0, 0).unwrap(); // Green
+                delay.delay_ms(step as u32);
-        delay.delay_ms(step);
+                let _ = lp.all_off();
-        lp.set_all_pwm(0, 0, on, 0).unwrap(); // Red
+                delay.delay_ms(step as u32);
-        delay.delay_ms(step);
+            }
-        lp.set_all_pwm(0, 0, 0, on).unwrap(); // White
+        }
-        delay.delay_ms(step);
+        Err(_) => {
-        lp.set_all_pwm(on, on, on, on).unwrap(); // All on
+            // === DIAGNOSTIC: fast blink forever = I2C error ===
-        delay.delay_ms(step);
+            loop {
-        lp.all_off().unwrap();
+                blink(&mut led, &mut delay, 5, 80);
-        delay.delay_ms(step);
+                delay.delay_ms(500u32);
+            }
+        }
     }
 }