Add screenshot USB-C support

App/app/uart.c

@@ -677,14 +677,26 @@ bool UART_IsCommandAvailable(uint32_t Port)
         return false;
     }
 
-    while (1)
+    // Limit iterations to prevent long loops when buffer is full of non-command data
+    uint16_t maxIterations = ReadBufSize + 1;
+
+    while (maxIterations--)
     {
         if ((*pReadPointer) == DmaLength)
             return false;
 
-        while ((*pReadPointer) != DmaLength && ReadBuf[*pReadPointer] != 0xABU)
+        // Find 0xAB with iteration limit
+        uint16_t searchLimit = ReadBufSize;
+        while ((*pReadPointer) != DmaLength && ReadBuf[*pReadPointer] != 0xABU && searchLimit--)
             *pReadPointer = DMA_INDEX((*pReadPointer), 1, ReadBufSize);
 
+        if (searchLimit == 0)
+        {
+            // Too many bytes without finding 0xAB - sync to current position and exit
+            *pReadPointer = DmaLength;
+            return false;
+        }
+
         if ((*pReadPointer) == DmaLength)
             return false;
 
@@ -702,6 +714,13 @@ bool UART_IsCommandAvailable(uint32_t Port)
         *pReadPointer = DMA_INDEX(*pReadPointer, 1, ReadBufSize);
     }
 
+    if (maxIterations == 0)
+    {
+        // Safety: too many outer loop iterations
+        *pReadPointer = DmaLength;
+        return false;
+    }
+
     Index = DMA_INDEX(*pReadPointer, 2, ReadBufSize);
     Size  = (ReadBuf[DMA_INDEX(Index, 1, ReadBufSize)] << 8) | ReadBuf[Index];
 
@@ -847,4 +866,4 @@ void UART_HandleCommand(uint32_t Port)
     #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
         gUART_LockScreenshot = 20; // lock screenshot
     #endif
-}
+}

App/driver/vcp.c

@@ -37,3 +37,25 @@ void VCP_Init()
     NVIC_SetPriority(USBD_IRQn, 3);
     NVIC_EnableIRQ(USBD_IRQn);
 }
+
+bool VCP_ScreenshotPing(void)
+{
+    static uint32_t read_ptr = 0;
+
+    uint32_t write_ptr = VCP_RxBufPointer;
+
+    while (read_ptr != write_ptr)
+    {
+        uint8_t b = VCP_RxBuf[read_ptr];
+
+        read_ptr++;
+        if (read_ptr >= VCP_RX_BUF_SIZE)
+            read_ptr = 0;
+
+        if (b == 0x55)
+        {
+            return true;
+        }
+    }
+    return false;
+}

App/driver/vcp.h

@@ -19,6 +19,7 @@
 
 #include <stdint.h>
 #include <string.h>
+#include <stdbool.h>
 #include "usb_config.h"
 
 #define VCP_RX_BUF_SIZE 256
@@ -27,6 +28,7 @@ extern uint8_t VCP_RxBuf[VCP_RX_BUF_SIZE];
 extern volatile uint32_t VCP_RxBufPointer;
 
 void VCP_Init();
+bool VCP_ScreenshotPing(void);
 
 static inline void VCP_Send(const uint8_t *Buf, uint32_t Size)
 {

App/misc.c

@@ -202,7 +202,8 @@ volatile bool     gTxTimeoutReached;
         volatile uint16_t gRxTimerCountdown_500ms;
     #endif
     #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
-         volatile uint8_t  gUART_LockScreenshot = 0; // lock screenshot if Chirp is used
+        volatile uint8_t  gUART_LockScreenshot = 0; // lock screenshot if Chirp is used
+        bool gUSB_ScreenshotEnabled = false;
     #endif
 #endif
 

App/misc.h

@@ -321,6 +321,7 @@ extern volatile bool         gTxTimeoutReached;
     #endif
     #ifdef ENABLE_FEAT_F4HWN_SCREENSHOT
         extern volatile uint8_t  gUART_LockScreenshot; // lock screenshot if Chirp is used
+        extern bool gUSB_ScreenshotEnabled;
     #endif
 #endif
 

App/screenshot.c

@@ -18,7 +18,16 @@
 #include "driver/st7565.h"
 #include "screenshot.h"
 #include "misc.h"
-#include <string.h>
+#include "driver/vcp.h"
+
+static void Screenshot_Send(const uint8_t *buf, uint16_t len)
+{
+    if (gUSB_ScreenshotEnabled) {
+        cdc_acm_data_send_with_dtr(buf, len);
+    } else {
+        UART_Send(buf, len);
+    }
+}
 
 // SRAM optimization: minimize static allocations
 // - previousFrame: 1024 bytes (REQUIRED - need to compare for delta)
@@ -43,6 +52,12 @@ void getScreenShot(bool force)
 
     if (UART_IsCableConnected()) {
         keepAlive = 10;
+        gUSB_ScreenshotEnabled = false;
+    }
+
+    if (VCP_ScreenshotPing()) {
+        keepAlive = 10;
+        gUSB_ScreenshotEnabled = true;
     }
 
     if (keepAlive > 0) {
@@ -114,7 +129,7 @@ void getScreenShot(bool force)
     // New format: sends 0xFF before header
     // Old format: doesn't exist, so viewers can differentiate
     uint8_t versionMarker = 0xFF;
-    UART_Send(&versionMarker, 1);
+    Screenshot_Send(&versionMarker, 1);
 
     // ==== Send header ====
     uint8_t header[5] = {
@@ -123,7 +138,7 @@ void getScreenShot(bool force)
         (uint8_t)(deltaLen & 0xFF)
     };
 
-    UART_Send(header, 5);
+    Screenshot_Send(header, 5);
 
     // ==== SECOND PASS: Send only changed chunks ====
     uint8_t chunk[9];
@@ -136,12 +151,12 @@ void getScreenShot(bool force)
         chunk[0] = chunkIdx;
         memcpy(&chunk[1], cur, 8);
         
-        UART_Send(chunk, 9);
+        Screenshot_Send(chunk, 9);
         
         // Update previousFrame for next comparison
         memcpy(prev, cur, 8);
     }
 
     uint8_t end = 0x0A;
-    UART_Send(&end, 1);
+    Screenshot_Send(&end, 1);
 }