Fix spectrum: reliable serial key input + USB-C unplug freeze fix (issue #212)

App/app/aircopy.c

@@ -139,7 +139,7 @@ static void AIRCOPY_clear()
         crc[i] = 0;
     }
     #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-        getScreenShot(true);
+        SCREENSHOT_Update(true);
     #endif
 }
 
@@ -167,7 +167,7 @@ static inline void AIRCOPY_CheckComplete(void)
     {
         gAircopyState = AIRCOPY_COMPLETE;
 #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-        getScreenShot(false);
+        SCREENSHOT_Update(false);
 #endif
     }
 }
@@ -212,7 +212,7 @@ bool AIRCOPY_SendMessage(void)
     if (CurrentSegmentIndex >= map->num_segments) {
         gAircopyState = AIRCOPY_COMPLETE;
         #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-            getScreenShot(false);
+            SCREENSHOT_Update(false);
         #endif
         return 0;
     }

App/app/app.c

@@ -1406,7 +1406,7 @@ void APP_TimeSlice10ms(void)
 
     #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
     if (gUpdateDisplayCurrent || gUpdateStatusCurrent) {
-        getScreenShot(false);
+        SCREENSHOT_Update(false);
     }
     #endif
 

App/app/breakout.c

@@ -484,7 +484,7 @@ void APP_RunBreakout(void) {
 
                     // For screenshot
                     #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-                        getScreenShot(false);
+                        SCREENSHOT_Update(false);
                     #endif
                 }
                 

App/app/spectrum.c

@@ -1667,6 +1667,12 @@ static void UpdateListening()
 
 static void Tick()
 {
+#ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
+    // Parse incoming packets on every tick so serial keys are never missed,
+    // regardless of whether the screen needs redrawing.
+    SCREENSHOT_ParseInput();
+#endif
+
     if (gNextTimeslice)
     {
         gNextTimeslice = false;
@@ -1737,7 +1743,7 @@ static void Tick()
         Render();
         // For screenshot
         #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-            getScreenShot(false);
+            SCREENSHOT_Update(false);
         #endif
         redrawScreen = false;
     }

App/driver/st7565.c

@@ -165,7 +165,7 @@ void ST7565_DrawLine(const unsigned int Column, const unsigned int Line, const u
     {
         ST7565_BlitScreen(line + 1);
         #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-            getScreenShot(true);  // Force immediate capture
+            SCREENSHOT_Update(true);  // Force immediate capture
         #endif
     }
 

App/driver/uart.c

@@ -155,43 +155,70 @@ void UART_LogSend(const void *pBuffer, uint32_t Size)
 
 #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
     bool UART_IsCableConnected(void) {
+        typedef enum {
+            STATE_IDLE = 0,
+            STATE_KA_1,
+            STATE_KA_2,
+            STATE_KA_3,
+            STATE_KEY_1,
+            STATE_KEY_2,
+            STATE_KEY_3,
+            STATE_KEY_3L,
+        } ParseState_t;
+
+        static uint8_t     read_ptr = 0;
+        static ParseState_t state   = STATE_IDLE;
+
         bool connected = false;
 
-        for (size_t i = 0; i < sizeof(UART_DMA_Buffer); i++) {
-            uint8_t b = UART_DMA_Buffer[i];
+        // DMA write position: NbData counts DOWN from 256
+        uint8_t write_ptr = (uint8_t)(sizeof(UART_DMA_Buffer) - 
+                                       LL_DMA_GetDataLength(DMA1, DMA_CHANNEL));
 
-            if (b == 0x55) {
-                // Keepalive byte — viewer is alive
-                UART_DMA_Buffer[i] = 0x00;
-                connected = true;
-            }
-            else if (b == 0xAA) {
-                // Possible start of a key packet: 0xAA 0x55 <type> <keycode>
-                // type 0x03 = short press, 0x04 = long press
-                size_t i1 = (i + 1) % sizeof(UART_DMA_Buffer);
-                size_t i2 = (i + 2) % sizeof(UART_DMA_Buffer);
-                size_t i3 = (i + 3) % sizeof(UART_DMA_Buffer);
-
-                if (UART_DMA_Buffer[i1] == 0x55 &&
-                    (UART_DMA_Buffer[i2] == UART_TYPE_KEY ||
-                     UART_DMA_Buffer[i2] == UART_TYPE_KEY_LONG))
-                {
-                    uint8_t type    = UART_DMA_Buffer[i2];
-                    uint8_t keyCode = UART_DMA_Buffer[i3];
-
-                    // Consume all 4 bytes
-                    UART_DMA_Buffer[i]  = 0x00;
-                    UART_DMA_Buffer[i1] = 0x00;
-                    UART_DMA_Buffer[i2] = 0x00;
-                    UART_DMA_Buffer[i3] = 0x00;
-
-                    if (type == UART_TYPE_KEY_LONG)
-                        KEYBOARD_InjectKeyLong(keyCode);
-                    else
-                        KEYBOARD_InjectKey(keyCode);
+        uint8_t processed = 0;
+        while (read_ptr != write_ptr && processed < sizeof(UART_DMA_Buffer))
+        {
+            uint8_t b = UART_DMA_Buffer[read_ptr++];
+            // read_ptr wraps naturally at 256 since it's uint8_t
+            processed++;
 
+            switch (state)
+            {
+                case STATE_IDLE:
+                    if      (b == 0x55) state = STATE_KA_1;
+                    else if (b == 0xAA) state = STATE_KEY_1;
+                    break;
+                case STATE_KA_1:
+                    state = (b == 0xAA) ? STATE_KA_2 : STATE_IDLE;
+                    break;
+                case STATE_KA_2:
+                    state = (b == 0x00) ? STATE_KA_3 : STATE_IDLE;
+                    break;
+                case STATE_KA_3:
+                    if (b == 0x00) connected = true;
+                    state = STATE_IDLE;
+                    break;
+                case STATE_KEY_1:
+                    state = (b == 0x55) ? STATE_KEY_2 : STATE_IDLE;
+                    break;
+                case STATE_KEY_2:
+                    if      (b == UART_TYPE_KEY)      state = STATE_KEY_3;
+                    else if (b == UART_TYPE_KEY_LONG) state = STATE_KEY_3L;
+                    else                              state = STATE_IDLE;
+                    break;
+                case STATE_KEY_3:
+                    KEYBOARD_InjectKey(b);
                     connected = true;
-                }
+                    state = STATE_IDLE;
+                    break;
+                case STATE_KEY_3L:
+                    KEYBOARD_InjectKeyLong(b);
+                    connected = true;
+                    state = STATE_IDLE;
+                    break;
+                default:
+                    state = STATE_IDLE;
+                    break;
             }
         }
 

App/screenshot.c

@@ -21,7 +21,26 @@
 #include "driver/vcp.h"
 #include "driver/keyboard.h"
 
-static void Screenshot_Send(const uint8_t *buf, uint16_t len)
+// SRAM optimization: minimize static allocations
+// - previousFrame: 1024 bytes (REQUIRED - need to compare for delta)
+// - No currentFrame or deltaFrame static buffers
+static uint8_t previousFrame[1024] = {0};
+static uint8_t forcedBlock = 0;
+static uint8_t keepAlive = 10;
+
+void SCREENSHOT_ParseInput(void)
+{
+    if (UART_IsCableConnected()) {
+        keepAlive = 10;
+        gUSB_ScreenshotEnabled = false;
+    }
+    if (VCP_ScreenshotPing()) {
+        keepAlive = 10;
+        gUSB_ScreenshotEnabled = true;
+    }
+}
+
+static void SCREENSHOT_Send(const uint8_t *buf, uint16_t len)
 {
     if (gUSB_ScreenshotEnabled) {
         cdc_acm_data_send_with_dtr(buf, len);
@@ -30,14 +49,7 @@ static void Screenshot_Send(const uint8_t *buf, uint16_t len)
     }
 }
 
-// SRAM optimization: minimize static allocations
-// - previousFrame: 1024 bytes (REQUIRED - need to compare for delta)
-// - No currentFrame or deltaFrame static buffers
-static uint8_t previousFrame[1024] = {0};
-static uint8_t forcedBlock = 0;
-static uint8_t keepAlive = 10;
-
-void getScreenShot(bool force)
+void SCREENSHOT_Update(bool force)
 {
     // Build frame in a temporary stack buffer
     // This is 1024 bytes but it's temporary and gets freed after the function
@@ -135,7 +147,7 @@ void getScreenShot(bool force)
     // New format: sends 0xFF before header
     // Old format: doesn't exist, so viewers can differentiate
     uint8_t versionMarker = 0xFF;
-    Screenshot_Send(&versionMarker, 1);
+    SCREENSHOT_Send(&versionMarker, 1);
 
     // ==== Send header ====
     uint8_t header[5] = {
@@ -144,7 +156,7 @@ void getScreenShot(bool force)
         (uint8_t)(deltaLen & 0xFF)
     };
 
-    Screenshot_Send(header, 5);
+    SCREENSHOT_Send(header, 5);
 
     // ==== SECOND PASS: Send only changed chunks ====
     uint8_t chunk[9];
@@ -157,12 +169,12 @@ void getScreenShot(bool force)
         chunk[0] = chunkIdx;
         memcpy(&chunk[1], cur, 8);
         
-        Screenshot_Send(chunk, 9);
+        SCREENSHOT_Send(chunk, 9);
         
         // Update previousFrame for next comparison
         memcpy(prev, cur, 8);
     }
 
     uint8_t end = 0x0A;
-    Screenshot_Send(&end, 1);
+    SCREENSHOT_Send(&end, 1);
 }

App/screenshot.h

@@ -17,6 +17,7 @@
 #ifndef SCREENSHOT_H
 #define SCREENSHOT_H
 
-void getScreenShot(bool force);
+void SCREENSHOT_Update(bool force);
+void SCREENSHOT_ParseInput(void);
 
 #endif

App/ui/welcome.c

@@ -222,7 +222,7 @@ void UI_DisplayWelcome(void)
         ST7565_BlitFullScreen();
 
         #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-            getScreenShot(true);
+            SCREENSHOT_Update(true);
         #endif
     }
 }

App/usb/usbd_cdc_if.c

@@ -190,8 +190,13 @@ void cdc_acm_data_send_with_dtr(const uint8_t *buf, uint32_t size)
     {
         ep_tx_busy_flag = true;
         usbd_ep_start_write(CDC_IN_EP, buf, size);
-        while (ep_tx_busy_flag)
+        uint32_t timeout = 100000;
+        while (ep_tx_busy_flag && --timeout)
             ;
+        if (!timeout) {
+            ep_tx_busy_flag = false;
+            dtr_enable = 0;  // Consider USB disconnected
+        }
     }
 }