v4l2 heisenbug, krkrkr

Fonderie/glitches.c

@@ -100,7 +100,7 @@ int random_blocks(FloatImg *picture, int percent)
 {
 int		x, y;
 
-if ( (picture->width%16) || (picture->height%8) )
+if ( (picture->width%16) || (picture->height%16) )
 	{
 	fprintf(stderr, "%s: %d%d bad dims\n", __func__,
 				picture->width, picture->height);
@@ -173,9 +173,7 @@ h = picz->height;		w = picz->width;
 for (y=BB; y<h-BB; y++) {
 
 	dy = (float)y * omega;		/* normalize vertical position */
-
 	x = xpos + x_delta(dy, phi);	/* add sinus deviation */
-
 	/* compute bounding box */
 	if ( (x>BB) && (x<w-BB) ) {
 		/* an make the glitch */
@@ -184,7 +182,6 @@ for (y=BB; y<h-BB; y++) {
 		if (rand() & 8)
 			fimg_plot_rgb(picz, x-1, y, fv, fv, fv);
 		if (rand() & 8)
-		// XXX else
 			fimg_plot_rgb(picz, x+1, y, fv, fv, fv);
 		}
 	}

v4l2/grabvidseq.c

@@ -33,7 +33,6 @@
 /*	compilation control */
 
 #define SAVE_AS_CUMUL	1
-#define SAVE_AS_PNM	0
 #define SAVE_AS_FIMG	0
 
 /* --------------------------------------------------------------------- */
@@ -190,6 +189,8 @@ if ((fmt.fmt.pix.width != width) || (fmt.fmt.pix.height != height)) {
 			    fmt.fmt.pix.width, fmt.fmt.pix.height);
 	}
 
+fprintf(stderr,"--- Ok 1\n");
+
 CLEAR(req);
 req.count = 2;
 req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
@@ -242,19 +243,20 @@ else	{
 fimg_clear(&cumul);
 cumul.fval = 255.0;		/* must be read from camera XXX */
 cumul.count = 0;
-
 to_save = &cumul;
 #endif
 
-
 type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 xioctl(fd, VIDIOC_STREAMON, &type);
 
-#if 0
-if (verbosity)	fprintf(stderr,"pid %d grabbing %d picz...\n",
+#if 1
+if (verbosity)	fprintf(stderr,"pid %d is going to grab %d picz...\n",
 					getpid(), nbre_capt);
 #endif
 
+/*
+ *		START ON THE GRABBING LOOP
+ */
 for (i = 0; i < nbre_capt; i++) {
 	do	{
 		FD_ZERO(&fds);
@@ -269,35 +271,22 @@ for (i = 0; i < nbre_capt; i++) {
 
 	if (r == -1) {
 		perror("select");
-		return errno;
+		return errno;			/* WTF ? a rogue return
+						   from the main() ? */
 		}
 
 	if(verbosity > 1) {
-		printf("%6d / %6d      %9.3f\r", i, nbre_capt,
+		fprintf(stderr, "%6d / %6d      %9.3f\n", i, nbre_capt,
 						fimg_timer_get(0));
+		fflush(stderr);
 		}
 
-
 	CLEAR(buf);
 	buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 	buf.memory = V4L2_MEMORY_MMAP;
 	xioctl(fd, VIDIOC_DQBUF, &buf);
 
-#if SAVE_AS_PNM
-	/* at this time,we'v got a picture in-memory,
-	   so we can blast in on storage */
-	sprintf(out_name, "%s/%05d.ppm", dest_dir, i);
-	if (verbosity > 1) fprintf(stderr, "--> %s\n", out_name);
-	fout = fopen(out_name, "w");
-	if (!fout) {
-		perror("Cannot open image");
-		exit(EXIT_FAILURE);
-		}
-	fprintf(fout, "P6\n%d %d 255\n",
-			    fmt.fmt.pix.width, fmt.fmt.pix.height);
-	fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
-	fclose(fout);
-#endif
+	fprintf(stderr, "xioctl VIDIOC_DQBUF done\n"); fflush(stderr);
 
 #if SAVE_AS_CUMUL
 	if (upscaling) {

v4l2/notes.txt

@@ -0,0 +1,25 @@
+
+
+Heisenbug dans la capture d'image
+=================================
+
+Contexte : Debian 10 32 bits sur Sony Vaio,
+           webcam Logitech classique.
+
+Mon soft 'grabvidseq' part _parfois_ en torche oo, à la louche une
+fois sur cent. Mais toujours au même endroit, au début de la boucle
+de capture des images, précisément dans cet appel système :
+
+	CLEAR(buf);
+	buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+	buf.memory = V4L2_MEMORY_MMAP;
+	xioctl(fd, VIDIOC_DQBUF, &buf);
+
+Quand le programme semble figé, un strace -p <pi> sort le même
+message en rafale _très_ féroce :
+
+ioctl(3, VIDIOC_DQBUF, {type=V4L2_BUF_TYPE_VIDEO_CAPTURE}) = -1 EAGAIN (Resource temporarily unavailable)
+ioctl(3, VIDIOC_DQBUF, {type=V4L2_BUF_TYPE_VIDEO_CAPTURE}) = -1 EAGAIN (Resource temporarily unavailable)
+ioctl(3, VIDIOC_DQBUF, {type=V4L2_BUF_TYPE_VIDEO_CAPTURE^Cstrace: Process 11181 detached
+
+WTF ?