webcam: going right direction (EAGAIN)

ThomasFarstrike · ThomasFarstrike · commit d57aa554d121 · 2025-05-13T17:41:54.000+02:00
diff --git a/c_mpos/src/webcam.c b/c_mpos/src/webcam.c
@@ -6,7 +6,6 @@
 #include <linux/videodev2.h>
 #include <sys/mman.h>
 #include <string.h>
-#include <poll.h>
 
 #include "py/obj.h"
 #include "py/runtime.h"
@@ -24,7 +23,7 @@
 #define CAPTURE_HEIGHT 480
 #define OUTPUT_WIDTH 240   // Resize to 240x240
 #define OUTPUT_HEIGHT 240
-#define NUM_BUFFERS 4      // Use 4 buffers for continuous streaming
+#define NUM_BUFFERS 2      // Use 2 buffers, as it worked for two captures
 
 // Webcam object type
 typedef struct _webcam_obj_t {
@@ -73,16 +72,42 @@ static void resize_640x480_to_240x240(uint8_t *src, uint8_t *dst) {
 static mp_obj_t webcam_capture_grayscale(mp_obj_t self_in) {
     webcam_obj_t *self = MP_OBJ_TO_PTR(self_in);
 
-    // Poll for available buffer
-    struct pollfd pfd = { .fd = self->fd, .events = POLLIN };
-    WEBCAM_DEBUG_PRINT("webcam: Polling for available buffer\n");
-    if (poll(&pfd, 1, 1000) <= 0) { // 1-second timeout
-        WEBCAM_DEBUG_PRINT("webcam: Poll timeout or error (errno=%d)\n", errno);
-        mp_raise_OSError(ETIMEDOUT);
+    // Try to queue a buffer
+    struct v4l2_buffer buf = {0};
+    bool queued = false;
+    for (size_t i = 0; i < self->num_buffers; i++) {
+        memset(&buf, 0, sizeof(buf));
+        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        buf.memory = V4L2_MEMORY_MMAP;
+        buf.index = i;
+
+        WEBCAM_DEBUG_PRINT("webcam: Attempting to queue buffer (index=%zu)\n", i);
+        if (ioctl(self->fd, VIDIOC_QBUF, &buf) == 0) {
+            WEBCAM_DEBUG_PRINT("webcam: Successfully queued buffer (index=%zu)\n", i);
+            queued = true;
+            break;
+        }
+        WEBCAM_DEBUG_PRINT("webcam: Failed to queue buffer (index=%zu, errno=%d)\n", i, errno);
+    }
+
+    if (!queued) {
+        WEBCAM_DEBUG_PRINT("webcam: No buffers available for queuing\n");
+        mp_raise_OSError(EAGAIN); // Try again later
+    }
+
+    // Start streaming if not already started
+    if (!self->streaming) {
+        enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        WEBCAM_DEBUG_PRINT("webcam: Starting video streaming\n");
+        if (ioctl(self->fd, VIDIOC_STREAMON, &type) < 0) {
+            WEBCAM_DEBUG_PRINT("webcam: Failed to start video streaming (errno=%d)\n", errno);
+            mp_raise_OSError(errno);
+        }
+        self->streaming = true;
     }
 
     // Dequeue a buffer (capture frame)
-    struct v4l2_buffer buf = {0};
+    memset(&buf, 0, sizeof(buf));
     buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
     buf.memory = V4L2_MEMORY_MMAP;
     WEBCAM_DEBUG_PRINT("webcam: Dequeuing buffer\n");
@@ -184,7 +209,7 @@ static mp_obj_t webcam_init(void) {
 
     // Open the webcam device
     WEBCAM_DEBUG_PRINT("webcam: Opening device %s\n", VIDEO_DEVICE);
-    self->fd = open(VIDEO_DEVICE, O_RDWR | O_NONBLOCK); // Non-blocking for polling
+    self->fd = open(VIDEO_DEVICE, O_RDWR);
     if (self->fd < 0) {
         WEBCAM_DEBUG_PRINT("webcam: Failed to open device %s (errno=%d)\n", VIDEO_DEVICE, errno);
         mp_raise_OSError(errno);
@@ -216,7 +241,7 @@ static mp_obj_t webcam_init(void) {
         mp_raise_OSError(errno);
     }
     self->num_buffers = req.count;
-    if (self->num_buffers < 2) {
+    if (self->num_buffers < NUM_BUFFERS) {
         WEBCAM_DEBUG_PRINT("webcam: Insufficient buffers allocated (%zu)\n", self->num_buffers);
         close(self->fd);
         mp_raise_OSError(ENOMEM);
@@ -253,23 +278,6 @@ static mp_obj_t webcam_init(void) {
             close(self->fd);
             mp_raise_OSError(errno);
         }
-
-        // Queue the buffer upfront
-        memset(&buf, 0, sizeof(buf));
-        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
-        buf.memory = V4L2_MEMORY_MMAP;
-        buf.index = i;
-        WEBCAM_DEBUG_PRINT("webcam: Initial queuing of buffer %zu\n", i);
-        if (ioctl(self->fd, VIDIOC_QBUF, &buf) < 0) {
-            WEBCAM_DEBUG_PRINT("webcam: Failed to queue buffer %zu initially (errno=%d)\n", i, errno);
-            for (size_t j = 0; j <= i; j++) {
-                if (self->buffers[j].start != NULL) {
-                    munmap(self->buffers[j].start, self->buffers[j].length);
-                }
-            }
-            close(self->fd);
-            mp_raise_OSError(errno);
-        }
     }
 
     // Create a tuple to hold the webcam object and method references
