Hello everyone,
i've worked recently on my source code for the image capturing duties.
With the Hint of Mr. Herbrechtsmeier to use YUV everything worked quite
well and now i get no failure message anymore and even the image.txt
file gets filled with values separated by tabulators and a newline after
each "picture" line.
This numerical values should represent the colour values of each pixel.
Now the main proble is, that every value is zero...
Hint: the initialisation of mmap with NULL let's the system choose an
empty area in the stack where the values from the camera memory can be
mapped to.
Now my question is. Has anyone an idea why there are only zeros?
Is it an failure in the program flow?
Is there something missing?
Do i need an loop or delays for the image capturing process?
I hope that someone can give me a hint or a solution for my problem.
Regards,
Kai Tiwisina
Stefan Herbrechtsmeier schrieb:
Hi,
Kai Tiwisina schrieb:
Hello everyone,
here is a little update to my question and to the source code.
After i implemented an function with the VIDIOC_ENUM_FMT ioctl i
recognized, that only two formats are support by the driver by now.
(Thanks to Mr. Liakhovetski by the way ;) )
The output.txt shows the output of this function and mentions the two
different types.
One is definately the V4L2_PIX_FMT_YUYV format but i don't know the
other one exactly...
I changed my set_format function after i got this information and
unfortunately nothing has changed...
Perhaps there are some further possibilities to solve this Problem.
Maybe there have some other v4l2 structures to be initialized, befor
the VIDIOC_S_FMT ioctl runs?
You have to set fmt.fmt.pix.field toV4L2_FIELD_ANY and only YUV is
supported at the moment.
Regards,
Stefan
Guennadi Liakhovetski wrote:
Hi Kai
On Mon, 23 Nov 2009, Kai Tiwisina wrote:
Hello,
my name is Kai Tiwisina and i'm a student in germany and i'm trying
to communicate with a Omnivision ov9655 camera which is atteched
with my embedded linux system via the v4l commands.
I've written a small testprogram which should grow step by step
while i'm trying one ioctl after another.
Everything worked fine until i tried to use the VIDIOC_S_FMT ioctl.
It's always giving me an "invalid argument" failure and i don't
know why.
Since you don't seem to have the source of the driver at hand, I'd
suggest to use the VIDIOC_ENUM_FMT
http://v4l2spec.bytesex.org/spec/r8367.htm ioctl to enumerate all
pixel formats supported be the driver. If the driver you're using is
the same, that Stefan (cc'ed) has submitted to the list, then indeed
it does not support the V4L2_PIX_FMT_RGB555 format, that you're
requesting, only various YUV (and a Bayer?) formats.
Perhaps someone of you is able to help me with this ioctl and give
an advice for a simple flow chart for a single frame image capture.
Which ioctl steps are neccessary and where do i need loops and for
what, because the capture-example.c from bytesex.org is way too
general for my purpose.
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
/*
============================================================================
Name : stream_test.c
Author : Kai Tiwisina
Version :
Copyright :
Description : Output of camera stream in text file
============================================================================
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h> // open() is in here
#include <unistd.h> // close() is in here
#include <errno.h> // used for desolving error
numbers
#include <sys/ioctl.h> // ioctl() is in here
#include <sys/mman.h>
#include <linux/videodev.h> // jpeg_markers are defined in here
#include <asm/types.h> // for videodev2.h
#include <linux/videodev2.h> // VIDIOC_QUERYCAP & struct v4ls_capability are
defined in here
#define CLEAR(x) memset(&(x), 0, sizeof(x))
#define v4l2_fourcc(a,b,c,d)
(((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24))
#define NUMEL 2 // the BeBot cam doesn't
support more formats!
void print_errno(char *s); //returns errno argument as value and expression
void open_device(); //opens a v4l device returning new file descriptor and
gives error info if necessary
void query_cap();
void request_buffer();
void stream_on();
void query_buffer();
void memory_mapping();
void stream_off();
void get_format();
void set_format();
void enum_format();
static struct v4l2_requestbuffers buffer;
static struct v4l2_buffer q_buffer;
static struct v4l2_format f_type;
static int fd; // fd
is the file descriptor
int main(void)
{
open_device();
printf("\n\n*New file descriptor: %i*\n\n",fd);
query_cap();
request_buffer();
enum_format();
set_format();
get_format();
stream_on();
query_buffer();
memory_mapping();
stream_off();
close(fd); //closes
connection to device
return 0;
}
void print_errno(char *s)
{
printf("Process %s failed %d, %s\n", s, errno, strerror(errno));
exit(EXIT_FAILURE);
}
void open_device()
{
int status;
status=open("/dev/video",O_RDWR); //Look up arguments for v4l2
open() in v4l_doku.pdf
if(status==-1) //Device_name
has to include the whole path, here /dev
{
print_errno("open_device");
}
else
{
fd=status;
}
}
void query_cap()
{
int status;
struct v4l2_capability camera_cap; // camera_cap should be
representative for the bebot's cam
status=ioctl(fd,VIDIOC_QUERYCAP,&camera_cap); // description on Page
188 in v4l_doku.pdf
if(status==-1)
{
print_errno("Determination of device capabilities");
}
else
{
printf("driver:\t%s\n",camera_cap.driver);
printf("card:\t%s\n",camera_cap.card);
printf("bus_info:\t%s\n",camera_cap.bus_info);
printf("version:\t%u.%u.%u\n",(camera_cap.version >>
16)&0xFF,(camera_cap.version >> 8)&0xFF,camera_cap.version&0xFF);
printf("capabilities:\t%x(HEX)\n",camera_cap.capabilities);
}
}
void request_buffer()
{
int status;
memset(&buffer,0,sizeof(buffer));
buffer.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
buffer.memory=V4L2_MEMORY_MMAP;
buffer.count=3;
status=ioctl(fd,VIDIOC_REQBUFS,&buffer);
if(status==-1)
{
print_errno("request buffer");
}
else
{
printf("buffer allocated %i times
%i\n",sizeof(buffer),sizeof(unsigned char));
}
}
void stream_on()
{
int status;
status=ioctl(fd,VIDIOC_STREAMON,&buffer.type);
if(status==-1)
{
print_errno("activating streaming device");
}
else
{
printf("streaming device activated\n");
}
}
void query_buffer()
{
int status;
q_buffer.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
q_buffer.field=V4L2_MEMORY_MMAP;
q_buffer.index=2;
status=ioctl(fd,VIDIOC_QUERYBUF,&q_buffer);
if(status==-1)
{
print_errno("querying buffer informations");
}
else
{
printf("index:\t%u\n",q_buffer.index);
printf("buffer_type:\t%u\n",q_buffer.type);
printf("bytes used:\t%u\n",q_buffer.bytesused);
printf("flags:\t%u\n",q_buffer.flags);
printf("field:\t%u\n",q_buffer.field);
//printf("time_stamp:\t%i\n",q_buffer.timestamp);
//printf("time_code:\t%i\n",q_buffer.timecode);
printf("sequence:\t%u\n",q_buffer.sequence);
printf("memory:\t%u\n",q_buffer.memory);
printf("offset:\t%u\n",q_buffer.m.offset);
printf("user_pointer:\t%lu\n",q_buffer.m.userptr);
printf("length:\t%u\n",q_buffer.length);
printf("input:\t%u\n",q_buffer.input);
}
}
void memory_mapping()
{
int i,j,status;
unsigned int *mem,*temp;
FILE* fp;
printf("\n\npage size %i\n\n",getpagesize());
mem=mmap(NULL,q_buffer.length,PROT_READ|PROT_WRITE,MAP_SHARED,fd,q_buffer.m.offset);
printf("mapped memory address %x\n\n",(unsigned int)mem);
if(mem==MAP_FAILED)
{
print_errno("memory mapping");
}
else
{
temp=mem;
get_format(fd);
fp=fopen("/home/root/image.txt","r+");
for(i=0;i<f_type.fmt.pix.height;i++)
{
for(j=0;j<(2*f_type.fmt.pix.width);j++)
{
fprintf(fp,"%u\t",*temp);
if(j==(f_type.fmt.pix.width-1))
{
fprintf(fp,"\n");
// de-interlace
}
temp++;
}
fprintf(fp,"\n");
}
status=munmap(mem,q_buffer.length);
if(status==-1)
{
print_errno("memory unmapping");
}
}
}
void stream_off()
{
int status;
status=ioctl(fd,VIDIOC_STREAMOFF,&buffer.type);
if(status==-1)
{
print_errno("deactivating streaming device");
}
else
{
printf("streaming device deactivated\n");
}
}
void get_format()
{
int status;
//struct v4l2_format f_type;
f_type.type=1;
status=ioctl(fd,VIDIOC_G_FMT,&f_type);
if(status==-1)
{
print_errno("get_format");
}
else
{
printf("\n\nbuffer type:\t%i\n",f_type.type);
printf("image size:\t%ix%i pixels
\n",f_type.fmt.pix.width,f_type.fmt.pix.height);
printf("pixelformat:\t%i\n",f_type.fmt.pix.pixelformat);
printf("v4l2 field-type:\t%i\n",f_type.fmt.pix.field);
printf("bytes per line:\t%i\n",f_type.fmt.pix.bytesperline);
printf("image size:\t%i\n",f_type.fmt.pix.sizeimage);
printf("v4l2_colorspace-type:\t%i\n",f_type.fmt.pix.colorspace);
}
}
void set_format()
{
int status;
CLEAR(f_type);
f_type.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
f_type.fmt.pix.pixelformat=V4L2_PIX_FMT_YUYV;
f_type.fmt.pix.field=V4L2_FIELD_ANY;
f_type.fmt.pix.height=240;
f_type.fmt.pix.width=320;
status=ioctl(fd,VIDIOC_S_FMT,&f_type);
if(status==-1)
{
print_errno("set_format");
}
else
{
printf("\n\nbuffer type:\t%i\n",f_type.type);
printf("image size:\t%ix%i pixels
\n",f_type.fmt.pix.width,f_type.fmt.pix.height);
printf("pixelformat:\t%i\n",f_type.fmt.pix.pixelformat);
printf("v4l2 field-type:\t%i\n",f_type.fmt.pix.field);
printf("bytes per line:\t%i\n",f_type.fmt.pix.bytesperline);
printf("image size:\t%i\n",f_type.fmt.pix.sizeimage);
printf("v4l2_colorspace-type:\t%i\n",f_type.fmt.pix.colorspace);
}
}
void enum_format()
{
int i,status;
struct v4l2_fmtdesc formats[NUMEL];
for(i=0;i<NUMEL;i++)
{
formats[i].index=i;
formats[i].type=1;
status=ioctl(fd,VIDIOC_ENUM_FMT,&formats[i]);
if(status==-1)
{
print_errno("enum_format");
}
else
{
printf("\n\nindex:\t%i\n",formats[i].index);
printf("buffer type:\t%i\n",formats[i].type);
printf("compressed:\t%i\n",formats[i].flags);
printf("sescription:\t%s\n",formats[i].description);
printf("pixelformat:\t%i\n",formats[i].pixelformat);
}
}
}
