7.17. ioctl VIDIOC_ENUM_FREQ_BANDS

7.17.1. Name

VIDIOC_ENUM_FREQ_BANDS - Enumerate supported frequency bands

7.17.2. Synopsis

int ioctl(int fd, VIDIOC_ENUM_FREQ_BANDS, struct v4l2_frequency_band *argp)

7.17.3. Arguments

fd

File descriptor returned by open().

argp

Pointer to struct v4l2_frequency_band.

7.17.4. Description

Enumerates the frequency bands that a tuner or modulator supports. To do this applications initialize the tuner, type and index fields, and zero out the reserved array of a struct v4l2_frequency_band and call the ioctl VIDIOC_ENUM_FREQ_BANDS ioctl with a pointer to this structure.

This ioctl is supported if the V4L2_TUNER_CAP_FREQ_BANDS capability of the corresponding tuner/modulator is set.

v4l2_frequency_band

struct v4l2_frequency_band

__u32	tuner	The tuner or modulator index number. This is the same value as in the struct v4l2_input tuner field and the struct v4l2_tuner index field, or the struct v4l2_output modulator field and the struct v4l2_modulator index field.
__u32	type	The tuner type. This is the same value as in the struct v4l2_tuner type field. The type must be set to V4L2_TUNER_RADIO for /dev/radioX device nodes, and to V4L2_TUNER_ANALOG_TV for all others. Set this field to V4L2_TUNER_RADIO for modulators (currently only radio modulators are supported). See v4l2_tuner_type
__u32	index	Identifies the frequency band, set by the application.
__u32	capability	The tuner/modulator capability flags for this frequency band, see Tuner and Modulator Capability Flags. The V4L2_TUNER_CAP_LOW or V4L2_TUNER_CAP_1HZ capability must be the same for all frequency bands of the selected tuner/modulator. So either all bands have that capability set, or none of them have that capability.
__u32	rangelow	The lowest tunable frequency in units of 62.5 kHz, or if the capability flag V4L2_TUNER_CAP_LOW is set, in units of 62.5 Hz, for this frequency band. A 1 Hz unit is used when the capability flag V4L2_TUNER_CAP_1HZ is set.
__u32	rangehigh	The highest tunable frequency in units of 62.5 kHz, or if the capability flag V4L2_TUNER_CAP_LOW is set, in units of 62.5 Hz, for this frequency band. A 1 Hz unit is used when the capability flag V4L2_TUNER_CAP_1HZ is set.
__u32	modulation	The supported modulation systems of this frequency band. See Band Modulation Systems. 注釈 Currently only one modulation system per frequency band is supported. More work will need to be done if multiple modulation systems are possible. Contact the linux-media mailing list (https://linuxtv.org/lists.php) if you need such functionality.
__u32	reserved[9]	Reserved for future extensions. Applications and drivers must set the array to zero.

Band Modulation Systems

V4L2_BAND_MODULATION_VSB	0x02	Vestigial Sideband modulation, used for analog TV.
V4L2_BAND_MODULATION_FM	0x04	Frequency Modulation, commonly used for analog radio.
V4L2_BAND_MODULATION_AM	0x08	Amplitude Modulation, commonly used for analog radio.

7.17.5. Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

EINVAL

The tuner or index is out of bounds or the type field is wrong.