1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3 .. _radio: 4 5 *************** 6 Radio Interface 7 *************** 8 9 This interface is intended for AM and FM (analog) radio receivers and 10 transmitters. 11 12 Conventionally V4L2 radio devices are accessed through character device 13 special files named ``/dev/radio`` and ``/dev/radio0`` to 14 ``/dev/radio63`` with major number 81 and minor numbers 64 to 127. 15 16 17 Querying Capabilities 18 ===================== 19 20 Devices supporting the radio interface set the ``V4L2_CAP_RADIO`` and 21 ``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` flag in the 22 ``capabilities`` field of struct 23 :c:type:`v4l2_capability` returned by the 24 :ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of 25 capability flags are reserved for future extensions. 26 27 28 Supplemental Functions 29 ====================== 30 31 Radio devices can support :ref:`controls <control>`, and must support 32 the :ref:`tuner or modulator <tuner>` ioctls. 33 34 They do not support the video input or output, audio input or output, 35 video standard, cropping and scaling, compression and streaming 36 parameter, or overlay ioctls. All other ioctls and I/O methods are 37 reserved for future extensions. 38 39 40 Programming 41 =========== 42 43 Radio devices may have a couple audio controls (as discussed in 44 :ref:`control`) such as a volume control, possibly custom controls. 45 Further all radio devices have one tuner or modulator (these are 46 discussed in :ref:`tuner`) with index number zero to select the radio 47 frequency and to determine if a monaural or FM stereo program is 48 received/emitted. Drivers switch automatically between AM and FM 49 depending on the selected frequency. The 50 :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or 51 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the 52 supported frequency range.
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