This file briefly explains how the SDI video API uses the
sysfs virtual filesystem.

Some interface parameters are controlled through sysfs.
These include the interface operating mode, number and size of buffers,
and transmitter frame mode.
These parameters may be changed by the root user
while the associated interface is not open.
Their values persist as long as the driver module is loaded.
Any user may read the parameters at any time.

For example,

	cat /sys/class/sdivideo/sdivideorx0/buffers

displays the number of buffers allocated by the first receive interface,
while

	echo 1843200 > /sys/class/sdivideo/sdivideotx1/bufsize

sets the size of the buffers on the second transmit interface to 1843200 bytes.

An example program called sdivideocfg is also provided
in the Examples/SDIVIDEO directory
which demonstrates how an application can read or change the parameters.

Each parameter has certain limits on the values it can take.
These limits are described below. If a parameter does not exist
on a given interface, that parameter is omitted.
Some interfaces do not support all possible values.

buffers
	Number of buffers in the driver buffer queue.
	Valid values:	2...32768

bufsize
	Size of each buffer in the driver buffer queue in bytes.
	Valid values:
		For transmitters,
			1024, 1028, 1032,...67108864
		For receivers,
			4, 8, 12,...67108864

clock_source
	Transmitter clock source.
	Valid values:
		0 - onboard oscillator (default)
		1 - external 525i or NTSC reference
		2 - external 625i or PAL reference
		3 - external 525p reference
		4 - external 625p reference
		5 - external 720p/60 reference
		6 - external 720p/59.94 reference
		7 - external 720p/50 reference
		8 - external 720p/30 reference
		9 - external 720p/29.97 reference
		10 - external 720p/25 reference
		11 - external 720p/24 reference
		12 - external 720p/23.98 reference
		13 - external 1080p/60 reference
		14 - external 1080p/59.94 reference
		15 - external 1080p/50 reference
		16 - external 1080p/30 reference
		17 - external 1080p/29.97 reference
		18 - external 1080p/25 reference
		19 - external 1080p/24 reference
		20 - external 1080p/23.98 reference
		21 - external 1080i/60 reference
		22 - external 1080i/59.94 reference
		23 - external 1080i/50 reference

frame_mode
	Transmitter frame mode.
	Valid values:
		1 - SMPTE 125M 486i 59.94 Hz
		2 - ITU-R BT.601 720x576i 50 Hz
		5 - SMPTE 260M 1035i 60 Hz
		6 - SMPTE 260M 1035i 59.94 Hz
		8 - SMPTE 274M 1080i 60 Hz
		9 - SMPTE 274M 1080psf 30 Hz
		10 - SMPTE 274M 1080i 59.94 Hz
		11 - SMPTE 274M 1080psf 29.97 Hz
		12 - SMPTE 274M 1080i 50 Hz
		13 - SMPTE 274M 1080psf 25 Hz
		14 - SMPTE 274M 1080psf 24 Hz
		15 - SMPTE 274M 1080psf 23.98 Hz
		16 - SMPTE 274M 1080p 30 Hz
		17 - SMPTE 274M 1080p 29.97 Hz
		18 - SMPTE 274M 1080p 25 Hz
		19 - SMPTE 274M 1080p 24 Hz
		20 - SMPTE 274M 1080p 23.98 Hz
		21 - SMPTE 296M 720p 60 Hz
		22 - SMPTE 296M 720p 59.94 Hz (default)
		23 - SMPTE 296M 720p 50 Hz
		24 - SMPTE 296M 720p 30 Hz
		25 - SMPTE 296M 720p 29.96 Hz
		26 - SMPTE 296M 720p 25 Hz
		27 - SMPTE 296M 720p 24 Hz
		28 - SMPTE 296M 720p 23.98 Hz

mode
	Interface operating mode.
	Valid values:
		0 - uyvy (default)
		1 - v210
		2 - v210 deinterlaced
		3 - raw

vanc
	Enable or disable vertical ancillary space.
	Valid values:
		0 - disable (default)
		non-zero - enable

Many methods of writing sysfs parameters do not check for errors.
Confirming the change by reading the value after a write is recommended
in these cases. Sdivideocfg checks for write errors.

