.. -*- coding: utf-8; mode: rst -*- .. _radio: *************** 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. 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 :c:type:`v4l2_capability` returned by the :ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of capability flags are reserved for future extensions. Supplemental Functions ====================== Radio devices can support :ref:`controls `, and must support the :ref:`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. Programming =========== Radio devices may have a couple audio controls (as discussed in :ref:`control`) such as a volume control, possibly custom controls. Further all radio devices have one tuner or modulator (these are discussed in :ref:`tuner`) 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 :ref:`VIDIOC_G_TUNER ` or :ref:`VIDIOC_G_MODULATOR ` ioctl reports the supported frequency range.