# Software Defined Radio Interface (SDR)

# Experimental

This is an experimental interface and may change in the future.

SDR is an abbreviation of Software Defined Radio, the radio device which uses application software for modulation or demodulation. This interface is intended for controlling and data streaming of such devices.

SDR devices are accessed through character device special files named `/dev/swradio0` to `/dev/swradio255` with major number 81 and dynamically allocated minor numbers 0 to 255.

# Querying Capabilities

Devices supporting the SDR receiver interface set the `V4L2_CAP_SDR_CAPTURE` and `V4L2_CAP_TUNER` flag in the capabilities field of &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device has an Analog to Digital Converter (ADC), which is a mandatory element for the SDR receiver.

Devices supporting the SDR transmitter interface set the `V4L2_CAP_SDR_OUTPUT` and `V4L2_CAP_MODULATOR` flag in the capabilities field of &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device has an Digital to Analog Converter (DAC), which is a mandatory element for the SDR transmitter.

At least one of the read/write, streaming or asynchronous I/O methods must be supported.

# Supplemental Functions

SDR devices can support controls, and must support the tuner ioctls. Tuner ioctls are used for setting the ADC/DAC sampling rate (sampling frequency) and the possible radio frequency (RF).

The `V4L2_TUNER_SDR` tuner type is used for setting SDR device ADC/DAC frequency, and the `V4L2_TUNER_RF` tuner type is used for setting radio frequency. The tuner index of the RF tuner (if any) must always follow the SDR tuner index. Normally the SDR tuner is #0 and the RF tuner is #1.

The &VIDIOC-S-HW-FREQ-SEEK; ioctl is not supported.

# Data Format Negotiation

The SDR device uses the format ioctls to select the capture and output format. Both the sampling resolution and the data streaming format are bound to that selectable format. In addition to the basic format ioctls, the &VIDIOC-ENUM-FMT; ioctl must be supported as well.

To use the format ioctls applications set the type field of a &v4l2-format; to `V4L2_BUF_TYPE_SDR_CAPTURE` or `V4L2_BUF_TYPE_SDR_OUTPUT` and use the &v4l2-sdr-format; sdr member of the fmt union as needed per the desired operation. Currently there is two fields, pixelformat and buffersize, of struct &v4l2-sdr-format; which are used. Content of the pixelformat is V4L2 FourCC code of the data format. The buffersize field is maximum buffer size in bytes required for data transfer, set by the driver in order to inform application.

## struct v4l2_sdr_format

&cs-str;
__u32 | pixelformat | The data format or type of compression, set by the application. This is a little endian four character code. V4L2 defines SDR formats in .
__u32 | buffersize | Maximum size in bytes required for data. Value is set by the driver.
__u8 | reserved[24] | This array is reserved for future extensions. Drivers and applications must set it to zero.

An SDR device may support read/write and/or streaming (memory mapping or user pointer) I/O.