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>Registering Video Capture Devices</H1
><P
> This time we need to add more functions for our camera device.
</P
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>static struct video_device my_camera
{
"My Camera",
VID_TYPE_OVERLAY|VID_TYPE_SCALES|\
VID_TYPE_CAPTURE|VID_TYPE_CHROMAKEY,
VID_HARDWARE_MYCAMERA,
camera_open.
camera_close,
camera_read, /* no read */
NULL, /* no write */
camera_poll, /* no poll */
camera_ioctl,
NULL, /* no special init function */
NULL /* no private data */
};
</PRE
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><P
> We need a read() function which is used for capturing data from
the card, and we need a poll function so that a driver can wait for the next
frame to be captured.
</P
><P
> We use the extra video capability flags that did not apply to the
radio interface. The video related flags are
</P
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><B
>Table 1. Capture Capabilities</B
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>VID_TYPE_CAPTURE</TD
><TD
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>We support image capture</TD
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><TR
><TD
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>VID_TYPE_TELETEXT</TD
><TD
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>A teletext capture device (vbi{n])</TD
></TR
><TR
><TD
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>VID_TYPE_OVERLAY</TD
><TD
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VALIGN="TOP"
>The image can be directly overlaid onto the
frame buffer</TD
></TR
><TR
><TD
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>VID_TYPE_CHROMAKEY</TD
><TD
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>Chromakey can be used to select which parts
of the image to display</TD
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>VID_TYPE_CLIPPING</TD
><TD
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>It is possible to give the board a list of
rectangles to draw around. </TD
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>VID_TYPE_FRAMERAM</TD
><TD
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VALIGN="TOP"
>The video capture goes into the video memory
and actually changes it. Applications need
to know this so they can clean up after the
card</TD
></TR
><TR
><TD
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>VID_TYPE_SCALES</TD
><TD
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VALIGN="TOP"
>The image can be scaled to various sizes,
rather than being a single fixed size.</TD
></TR
><TR
><TD
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>VID_TYPE_MONOCHROME</TD
><TD
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>The capture will be monochrome. This isn't a
complete answer to the question since a mono
camera on a colour capture card will still
produce mono output.</TD
></TR
><TR
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>VID_TYPE_SUBCAPTURE</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>The card allows only part of its field of
view to be captured. This enables
applications to avoid copying all of a large
image into memory when only some section is
relevant.</TD
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><P
> We set VID_TYPE_CAPTURE so that we are seen as a capture card,
VID_TYPE_CHROMAKEY so the application knows it is time to draw in virulent
purple, and VID_TYPE_SCALES because we can be resized.
</P
><P
> Our setup is fairly similar. This time we also want an interrupt line
for the 'frame captured' signal. Not all cards have this so some of them
cannot handle poll().
</P
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>
static int io = 0x320;
static int irq = 11;
int __init mycamera_init(struct video_init *v)
{
if(check_region(io, MY_IO_SIZE))
{
printk(KERN_ERR
"mycamera: port 0x%03X is in use.\n", io);
return -EBUSY;
}
if(video_device_register(&my_camera,
VFL_TYPE_GRABBER)==-1)
return -EINVAL;
request_region(io, MY_IO_SIZE, "mycamera");
return 0;
}
</PRE
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> This is little changed from the needs of the radio card. We specify
VFL_TYPE_GRABBER this time as we want to be allocated a /dev/video name.
</P
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