| .. -*- 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 <control>`, and must support |
| the :ref:`tuner or modulator <tuner>` 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 <VIDIOC_G_TUNER>` or |
| :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the |
| supported frequency range. |
