4.10. Radio Interface¶
This interface is intended for AM and FM (analog) radio receivers and transmitters.
Conventionally V4L2 radio devices are accessed through character device
special files named /dev/radio
and /dev/radio0
to
/dev/radio63
with major number 81 and minor numbers 64 to 127.
4.10.1. Querying Capabilities¶
Devices supporting the radio interface set the V4L2_CAP_RADIO
and
V4L2_CAP_TUNER
or V4L2_CAP_MODULATOR
flag in the
capabilities
field of struct
v4l2_capability
returned by the
ioctl VIDIOC_QUERYCAP ioctl. Other combinations of
capability flags are reserved for future extensions.
4.10.2. Supplemental Functions¶
Radio devices can support controls, and must support the tuner or modulator ioctls.
They do not support the video input or output, audio input or output, video standard, cropping and scaling, compression and streaming parameter, or overlay ioctls. All other ioctls and I/O methods are reserved for future extensions.
4.10.3. Programming¶
Radio devices may have a couple audio controls (as discussed in User Controls) such as a volume control, possibly custom controls. Further all radio devices have one tuner or modulator (these are discussed in Tuners and Modulators) with index number zero to select the radio frequency and to determine if a monaural or FM stereo program is received/emitted. Drivers switch automatically between AM and FM depending on the selected frequency. The VIDIOC_G_TUNER or VIDIOC_G_MODULATOR ioctl reports the supported frequency range.