Add MUX diagnostic commands and GPIO probe

Serial commands:
- dump: show button and LED state
- ledon/ledoff: toggle all LEDs
- ledtest: sequential LED test
- read: raw button read
- probe: check pin states and test LD toggle

src/main.cpp

@@ -27,6 +27,52 @@ void midi_task(void* parameter) {
     }
 }
 
+void handle_serial_command(const String& cmd) {
+    if (cmd == "dump" || cmd == "d") {
+        mux.dump();
+    } else if (cmd == "ledon") {
+        for (int i = 0; i < 10; i++) {
+            mux.set_led(i, true);
+            delay(50);
+        }
+        Serial.println("[CMD] All LEDs ON");
+    } else if (cmd == "ledoff") {
+        mux.clear_all();
+    } else if (cmd == "ledtest") {
+        for (int i = 0; i < 10; i++) {
+            mux.set_led(i, true);
+            delay(200);
+            mux.set_led(i, false);
+            delay(100);
+        }
+        Serial.println("[CMD] LED test complete");
+    } else if (cmd == "read") {
+        uint16_t raw = mux.read_buttons();
+        Serial.printf("[CMD] Raw button state: 0x%03X (binary: ", raw);
+        for (int i = 9; i >= 0; i--) {
+            Serial.print((raw >> i) & 1);
+        }
+        Serial.println(")");
+    } else if (cmd == "probe") {
+        Serial.println("[CMD] Probing MUX pins...");
+        Serial.printf("  DAT (GPIO %d) = %d\n", 9, digitalRead(9));
+        Serial.printf("  LD  (GPIO %d) = %d\n", 10, digitalRead(10));
+        Serial.printf("  CLK (GPIO %d) = %d\n", 11, digitalRead(11));
+        Serial.printf("  DI  (GPIO %d) = %d\n", 12, digitalRead(12));
+
+        Serial.println("  Toggling LD pin...");
+        for (int i = 0; i < 5; i++) {
+            digitalWrite(10, HIGH);
+            delayMicroseconds(100);
+            digitalWrite(10, LOW);
+            delayMicroseconds(100);
+        }
+        Serial.printf("  DI after LD toggle: %d\n", digitalRead(12));
+    } else {
+        Serial.println("[CMD] Commands: dump, ledon, ledoff, ledtest, read, probe");
+    }
+}
+
 void setup() {
     Serial.begin(115200);
     delay(2000);
@@ -66,12 +112,20 @@ void setup() {
     
     Serial.println("=================================");
     Serial.println("  All systems ready");
-    Serial.println("  Waiting for USB MIDI host...");
+    Serial.println("  Type 'help' for diagnostics");
     Serial.println("=================================");
     Serial.flush();
 }
 
 void loop() {
     controller.update();
+
+    if (Serial.available()) {
+        String cmd = Serial.readStringUntil('\n');
+        cmd.trim();
+        cmd.toLowerCase();
+        handle_serial_command(cmd);
+    }
+
     delay(10);
 }

src/pixel_stomp_mux.cpp

@@ -1,8 +1,6 @@
 #include "pixel_stomp_mux.h"
 #include <Arduino.h>
 
-static const char* TAG = "MUX";
-
 PixelStompMux::PixelStompMux(uint8_t dat, uint8_t ld, uint8_t clk, uint8_t di)
     : pin_dat(dat), pin_ld(ld), pin_clk(clk), pin_di(di),
       last_button_state(0), current_led_state(0) {
@@ -20,13 +18,31 @@ void PixelStompMux::begin() {
 
     Serial.printf("[MUX] Init DAT=%d LD=%d CLK=%d DI=%d\n",
                   pin_dat, pin_ld, pin_clk, pin_di);
+
+    Serial.println("[MUX] GPIO probe:");
+    Serial.printf("  DI (GPIO %d) reads: %d (should be 1 with pullup)\n",
+                  pin_di, digitalRead(pin_di));
+
+    for (int i = 0; i < 3; i++) {
+        digitalWrite(pin_clk, HIGH);
+        delayMicroseconds(10);
+        digitalWrite(pin_clk, LOW);
+        delayMicroseconds(10);
+    }
+    Serial.printf("  DI after 3 CLK pulses: %d\n", digitalRead(pin_di));
+
+    digitalWrite(pin_ld, HIGH);
+    delayMicroseconds(10);
+    digitalWrite(pin_ld, LOW);
+    delayMicroseconds(10);
+    Serial.printf("  DI after LD pulse: %d\n", digitalRead(pin_di));
 }
 
 uint16_t PixelStompMux::read_buttons() {
     pulse_pin(pin_ld, HIGH);
-    delayMicroseconds(5);
+    delayMicroseconds(10);
     pulse_pin(pin_ld, LOW);
-    delayMicroseconds(5);
+    delayMicroseconds(10);
 
     uint16_t state = shift_in(NUM_INPUTS);
     last_button_state = state;
@@ -44,8 +60,9 @@ bool PixelStompMux::is_button_pressed(uint8_t index) {
 void PixelStompMux::write_leds(uint16_t led_state) {
     current_led_state = led_state;
     shift_out(led_state, NUM_OUTPUTS);
+
     pulse_pin(pin_ld, HIGH);
-    delayMicroseconds(5);
+    delayMicroseconds(10);
     pulse_pin(pin_ld, LOW);
 }
 
@@ -73,19 +90,20 @@ void PixelStompMux::dump() {
     for (int i = 0; i < NUM_INPUTS; i++) {
         bool pressed = !(buttons & (1 << i));
         bool led_on = current_led_state & (1 << i);
-        if (pressed || led_on) {
         Serial.printf("  [%d] Button:%s LED:%s\n", i,
                       pressed ? "PRESS" : "off",
                       led_on ? "ON" : "off");
     }
-    }
 }
 
 void PixelStompMux::shift_out(uint16_t data, uint8_t bits) {
     for (int i = bits - 1; i >= 0; i--) {
         digitalWrite(pin_dat, (data >> i) & 1);
-        pulse_pin(pin_clk, HIGH);
+        delayMicroseconds(1);
-        pulse_pin(pin_clk, LOW);
+        digitalWrite(pin_clk, HIGH);
+        delayMicroseconds(1);
+        digitalWrite(pin_clk, LOW);
+        delayMicroseconds(1);
     }
 }
 
@@ -97,8 +115,10 @@ uint16_t PixelStompMux::shift_in(uint8_t bits) {
         if (bit) {
             data |= (1 << i);
         }
-        pulse_pin(pin_clk, HIGH);
+        digitalWrite(pin_clk, HIGH);
-        pulse_pin(pin_clk, LOW);
+        delayMicroseconds(1);
+        digitalWrite(pin_clk, LOW);
+        delayMicroseconds(1);
     }
 
     return data;