Programming Guide
159
Memory map
Memory map system call, mmap (), allows the mapping of device
memory directly into a user processor’s address space. From
device viewpoint, Direct Memory Access (DMA) operations pro-
vide peripherals with direct access to system memory without
CPU processing. This can save large of time and loading that
application or driver doesn’t need to move data from devices to
system memory. Here we give and example showing how to set 4
buffer queues which store video data in turn.
/* global variables */
struct buffer {
void *start;
size_t length;
};
struct buffer *buffers = NULL;
static unsigned int n_buffers = 0;
void init_mmap(void)
{
struct v4l2_requestbuffers req;
memset (&req, 0, sizeof (reg));
req.count = 4;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (-1 == ioctl (fd, VIDIOC_REQBUFS, &req))
{
if (EINVAL == errno) {
fprintf (stderr, "%s does not
support " "memory mapping\n",
dev_name);
exit (EXIT_FAILURE);
} else {
exit (EXIT_FAILURE);
}
}
if (req.count < 2) {
fprintf (stderr, "Insufficient buffer
memory on %s\n", dev_name);
exit (EXIT_FAILURE);
}
buffers = calloc (req.count, sizeof
(*buffers));
Summary of Contents for cRTV-24
Page 4: ......
Page 8: ...List of Tables iv Table 5 2 C C Data Types 83 Table 5 3 Pixel Data 122 ...
Page 10: ......
Page 18: ...8 Introduction ...
Page 34: ...24 Hardware Reference Figure 2 8 STRG Address Jumpers ...
Page 55: ...Installation Guide 45 Figure 3 2 cRTV 24 3U cPCI ...
Page 61: ...Installation Guide 51 ...
Page 62: ...52 Installation Guide ...
Page 64: ...54 Installation Guide The Device Manager should be as follows ...
Page 67: ...Installation Guide 57 ...
Page 68: ...58 Installation Guide 3 When the following window appears please click Con tinue Anyway ...
Page 70: ...60 Installation Guide The Device Manager should be as follows ...
Page 72: ...62 Installation Guide 3 Click the Finish button to finish the installation ...
Page 76: ...66 Installation Guide ...
Page 144: ...134 Function Library ...
Page 174: ...164 Programming Guide ...
