Steve
[EMAIL PROTECTED] wrote:
Hi!, I just started learning v4l and I'm trying to make a little program in order to understand how it works.
It gives segfault, but I cannot understand why.
The error is:
[EMAIL PROTECTED]:~/video > ./ottavio
mmap: Invalid argument
Segmentation fault
[EMAIL PROTECTED]:~/video > gdb ottavio
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This GDB was configured as "i386-linux"...
(gdb) run
Starting program: /home/bott/video/ottavio
mmap: Invalid argument
Program received signal SIGSEGV, Segmentation fault.
0x40093d7d in mempcpy () from /lib/libc.so.6
(gdb) where
#0 0x40093d7d in mempcpy () from /lib/libc.so.6
#1 0x40089892 in _IO_file_xsputn () from /lib/libc.so.6
#2 0x40080f7a in fwrite () from /lib/libc.so.6
#3 0x08048602 in main () at ottavio.c:40
(gdb)
I can't find the error. Can you please help me?
Thank you.
Here's the code.
#include <stdio.h> #include <unistd.h> #include <fcntl.h> #include <sys/mman.h> #include <linux/ioctl.h> #include <linux/videodev.h>
main() { int fd, siz; short targaheader[9]={ 0,2,0,0,0,0,444,555,8216 }; /* 444 and 555 are fake */ void *map; struct video_mmap v;
v.format=VIDEO_PALETTE_RGB24; // ... GREY, RGB555, RGB565, RGB24, RGB32 v.frame=0; // 0 or 1 (buffer 0 or buffer 1) v.width=768; // from 32 to 924 (sometimes limited to 768) v.height=576; // from 32 to 576 siz=v.width*v.height*3; // rgb24:3, rgb32:4, rgb565:2, rgb555:2
targaheader[6]=v.width; targaheader[7]=v.height; // update targa header for frame
fd=open("/dev/video",O_RDONLY); // open video device if(fd<0) perror("/dev/video");
map=mmap(0, siz, PROT_READ, MAP_SHARED, fd, 0); // select memory-map if(map==MAP_FAILED) perror("mmap");
if(ioctl(fd, VIDIOCMCAPTURE, &v)<0) // start capturing a frame perror("VIDIOCMCAPTURE");
if(ioctl(fd, VIDIOCSYNC, &v.frame)<0) // wait for end of frame perror("VIDIOCSYNC");
fwrite(targaheader, sizeof(targaheader), // save header & data to stdout 1, stdout); fwrite(map, siz, 1, stdout); }
-- Steve Miller Software Engineer STMicroelectronics phone (602) 485-2014
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