| David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame^] | 1 | .. Permission is granted to copy, distribute and/or modify this |
| 2 | .. document under the terms of the GNU Free Documentation License, |
| 3 | .. Version 1.1 or any later version published by the Free Software |
| 4 | .. Foundation, with no Invariant Sections, no Front-Cover Texts |
| 5 | .. and no Back-Cover Texts. A copy of the license is included at |
| 6 | .. Documentation/media/uapi/fdl-appendix.rst. |
| 7 | .. |
| 8 | .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections |
| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 9 | |
| 10 | .. _radio: |
| 11 | |
| 12 | *************** |
| 13 | Radio Interface |
| 14 | *************** |
| 15 | |
| 16 | This interface is intended for AM and FM (analog) radio receivers and |
| 17 | transmitters. |
| 18 | |
| 19 | Conventionally V4L2 radio devices are accessed through character device |
| 20 | special files named ``/dev/radio`` and ``/dev/radio0`` to |
| 21 | ``/dev/radio63`` with major number 81 and minor numbers 64 to 127. |
| 22 | |
| 23 | |
| 24 | Querying Capabilities |
| 25 | ===================== |
| 26 | |
| 27 | Devices supporting the radio interface set the ``V4L2_CAP_RADIO`` and |
| 28 | ``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` flag in the |
| 29 | ``capabilities`` field of struct |
| 30 | :c:type:`v4l2_capability` returned by the |
| 31 | :ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of |
| 32 | capability flags are reserved for future extensions. |
| 33 | |
| 34 | |
| 35 | Supplemental Functions |
| 36 | ====================== |
| 37 | |
| 38 | Radio devices can support :ref:`controls <control>`, and must support |
| 39 | the :ref:`tuner or modulator <tuner>` ioctls. |
| 40 | |
| 41 | They do not support the video input or output, audio input or output, |
| 42 | video standard, cropping and scaling, compression and streaming |
| 43 | parameter, or overlay ioctls. All other ioctls and I/O methods are |
| 44 | reserved for future extensions. |
| 45 | |
| 46 | |
| 47 | Programming |
| 48 | =========== |
| 49 | |
| 50 | Radio devices may have a couple audio controls (as discussed in |
| 51 | :ref:`control`) such as a volume control, possibly custom controls. |
| 52 | Further all radio devices have one tuner or modulator (these are |
| 53 | discussed in :ref:`tuner`) with index number zero to select the radio |
| 54 | frequency and to determine if a monaural or FM stereo program is |
| 55 | received/emitted. Drivers switch automatically between AM and FM |
| 56 | depending on the selected frequency. The |
| 57 | :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or |
| 58 | :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the |
| 59 | supported frequency range. |