VIDIOC_ENUM_FREQ_BANDS — Enumerate supported frequency bands
int ioctl( | int fd, |
| int request, | |
struct v4l2_frequency_band
*argp); |
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 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.
Table A.37. 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 Table A.88, “enum 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 Table A.89, “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 Table A.38, “Band Modulation Systems”. Note that 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 that functionality. | ||
| __u32 | reserved[9] | Reserved for future extensions. Applications and drivers must set the array to zero. | ||
Table A.38. 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. |
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.
The tuner or index
is out of bounds or the type field is wrong.