Add hardware probe and single-pixel test commands

- probe: toggles LD/CLK, reads DI state at each step, tests single pixel
- pixel0/pixel1: single pixel at max brightness for testing
- Increased LD pulse timing to 20us
- Increased CLK timing to 2us
- NeoPixel brightness raised to 80

include/pixel_stomp_mux.h

@@ -21,6 +21,7 @@ public:
     void show();
 
     void dump();
+    void probe();
 
 private:
     uint8_t pin_dat;

src/main.cpp

@@ -30,12 +30,14 @@ void midi_task(void* parameter) {
 void handle_serial_command(const String& cmd) {
     if (cmd == "dump" || cmd == "d") {
         mux.dump();
+    } else if (cmd == "probe" || cmd == "p") {
+        mux.probe();
     } else if (cmd == "ledon") {
         for (int i = 0; i < 8; i++) {
             mux.set_led_color(i, 255, 255, 255);
         }
         mux.show();
-        Serial.println("[CMD] All LEDs ON");
+        Serial.println("[CMD] All LEDs WHITE");
     } else if (cmd == "ledoff") {
         mux.clear_all();
     } else if (cmd == "ledtest") {
@@ -68,8 +70,28 @@ void handle_serial_command(const String& cmd) {
     } else if (cmd == "blue") {
         for (int i = 0; i < 8; i++) mux.set_led_color(i, 0, 0, 255);
         mux.show();
+    } else if (cmd == "pixel0") {
+        mux.set_led_brightness(255);
+        mux.set_led_color(0, 255, 255, 255);
+        mux.show();
+        Serial.println("[CMD] Pixel 0 WHITE (max brightness)");
+    } else if (cmd == "pixel1") {
+        mux.set_led_brightness(255);
+        mux.set_led_color(1, 255, 255, 255);
+        mux.show();
+        Serial.println("[CMD] Pixel 1 WHITE (max brightness)");
+    } else if (cmd == "help") {
+        Serial.println("[CMD] Commands:");
+        Serial.println("  dump    - show button states");
+        Serial.println("  probe   - hardware diagnostic");
+        Serial.println("  ledon   - all LEDs white");
+        Serial.println("  ledoff  - all LEDs off");
+        Serial.println("  ledtest - colour cycle");
+        Serial.println("  read    - raw button read");
+        Serial.println("  red/green/blue - solid colour");
+        Serial.println("  pixel0/pixel1 - single pixel test");
     } else {
-        Serial.println("[CMD] Commands: dump, ledon, ledoff, ledtest, read, red, green, blue");
+        Serial.println("[CMD] Unknown command. Type 'help'");
     }
 }
 

src/pixel_stomp_mux.cpp

@@ -16,21 +16,22 @@ void PixelStompMux::begin() {
 
     strip = new Adafruit_NeoPixel(NUM_LEDS, pin_dat, NEO_GRB + NEO_KHZ800);
     strip->begin();
-    strip->setBrightness(50);
+    strip->setBrightness(80);
     strip->clear();
     strip->show();
 
     Serial.printf("[MUX] Init DAT=%d LD=%d CLK=%d DI=%d\n",
                   pin_dat, pin_ld, pin_clk, pin_di);
-    Serial.printf("[MUX] 74HC165 for %d buttons, WS2812C for %d LEDs\n",
-                  NUM_BUTTONS, NUM_LEDS);
+    Serial.printf("[MUX] 74HC165 x2 daisy-chain for %d buttons\n", NUM_BUTTONS);
+    Serial.printf("[MUX] WS2812C for %d LEDs\n", NUM_LEDS);
+    Serial.printf("[MUX] DI pin reads: %d\n", digitalRead(pin_di));
 }
 
 uint8_t PixelStompMux::read_buttons() {
     digitalWrite(pin_ld, HIGH);
-    delayMicroseconds(5);
+    delayMicroseconds(20);
     digitalWrite(pin_ld, LOW);
-    delayMicroseconds(5);
+    delayMicroseconds(20);
 
     last_button_state = shift_in_74hc165();
     return last_button_state;
@@ -65,7 +66,7 @@ void PixelStompMux::show() {
 
 void PixelStompMux::dump() {
     uint8_t buttons = read_buttons();
-    Serial.printf("[MUX] Buttons: 0x%02X (binary: ", buttons);
+    Serial.printf("[MUX] Buttons: 0x%02X (", buttons);
     for (int i = 7; i >= 0; i--) {
         Serial.print((buttons >> i) & 1);
     }
@@ -85,10 +86,48 @@ uint8_t PixelStompMux::shift_in_74hc165() {
             data |= (1 << i);
         }
         digitalWrite(pin_clk, HIGH);
-        delayMicroseconds(1);
+        delayMicroseconds(2);
         digitalWrite(pin_clk, LOW);
-        delayMicroseconds(1);
+        delayMicroseconds(2);
     }
 
     return data;
 }
+
+void PixelStompMux::probe() {
+    Serial.println("[MUX] === Hardware Probe ===");
+
+    Serial.printf("  DI (GPIO %d) raw: %d\n", pin_di, digitalRead(pin_di));
+
+    Serial.println("  Testing LD pin...");
+    digitalWrite(pin_ld, LOW);
+    delayMicroseconds(10);
+    Serial.printf("  LD=LOW,  DI=%d\n", digitalRead(pin_di));
+    digitalWrite(pin_ld, HIGH);
+    delayMicroseconds(10);
+    Serial.printf("  LD=HIGH, DI=%d\n", digitalRead(pin_di));
+    digitalWrite(pin_ld, LOW);
+    delayMicroseconds(10);
+
+    Serial.println("  Toggling CLK 16 times, reading DI...");
+    for (int i = 0; i < 16; i++) {
+        bool bit = digitalRead(pin_di);
+        Serial.printf("  CLK %2d: DI=%d\n", i, bit);
+        digitalWrite(pin_clk, HIGH);
+        delayMicroseconds(5);
+        digitalWrite(pin_clk, LOW);
+        delayMicroseconds(5);
+    }
+
+    Serial.println("  Testing NeoPixel DAT pin...");
+    if (strip) {
+        strip->setPixelColor(0, strip->Color(255, 255, 255));
+        strip->show();
+        Serial.println("  Set pixel 0 to WHITE - check if it lights up");
+        delay(1000);
+        strip->clear();
+        strip->show();
+    }
+
+    Serial.println("[MUX] === Probe Complete ===");
+}