8.42. ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER

8.42.1. Name

VIDIOC_G_TUNER - VIDIOC_S_TUNER - Get or set tuner attributes

8.42.2. Synopsis

int ioctl(int fd, VIDIOC_G_TUNER, struct v4l2_tuner *argp)
int ioctl(int fd, VIDIOC_S_TUNER, const struct v4l2_tuner *argp)

8.42.3. Arguments

fd
File descriptor returned by open().

argp

8.42.4. Description

To query the attributes of a tuner applications initialize the index field and zero out the reserved array of a struct v4l2_tuner and call the VIDIOC_G_TUNER ioctl with a pointer to this structure. Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds. To enumerate all tuners applications shall begin at index zero, incrementing by one until the driver returns EINVAL.

Tuners have two writable properties, the audio mode and the radio frequency. To change the audio mode, applications initialize the index, audmode and reserved fields and call the VIDIOC_S_TUNER ioctl. This will not change the current tuner, which is determined by the current video input. Drivers may choose a different audio mode if the requested mode is invalid or unsupported. Since this is a write-only ioctl, it does not return the actually selected audio mode.

SDR specific tuner types are V4L2_TUNER_SDR and V4L2_TUNER_RF. For SDR devices audmode field must be initialized to zero. The term ‘tuner’ means SDR receiver in this context.

To change the radio frequency the VIDIOC_S_FREQUENCY ioctl is available.

v4l2_tuner
struct v4l2_tuner
__u32 index Identifies the tuner, set by the application.
__u8 name[32]

Name of the tuner, a NUL-terminated ASCII string.

This information is intended for the user.

__u32 type Type of the tuner, see v4l2_tuner_type.
__u32 capability

Tuner capability flags, see Tuner and Modulator Capability Flags. Audio flags indicate the ability to decode audio subprograms. They will not change, for example with the current video standard.

When the structure refers to a radio tuner the V4L2_TUNER_CAP_LANG1, V4L2_TUNER_CAP_LANG2 and V4L2_TUNER_CAP_NORM flags can’t be used.

If multiple frequency bands are supported, then capability is the union of all capability fields of each struct v4l2_frequency_band.

__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, or if the capability flag V4L2_TUNER_CAP_1HZ is set, in units of 1 Hz. If multiple frequency bands are supported, then rangelow is the lowest frequency of all the frequency bands.
__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, or if the capability flag V4L2_TUNER_CAP_1HZ is set, in units of 1 Hz. If multiple frequency bands are supported, then rangehigh is the highest frequency of all the frequency bands.
__u32 rxsubchans

Some tuners or audio decoders can determine the received audio subprograms by analyzing audio carriers, pilot tones or other indicators. To pass this information drivers set flags defined in Tuner Audio Reception Flags in this field. For example:

    V4L2_TUNER_SUB_MONO receiving mono audio
    STEREO | SAP receiving stereo audio and a secondary audio program
    MONO | STEREO receiving mono or stereo audio, the hardware cannot distinguish
    LANG1 | LANG2 receiving bilingual audio
    MONO | STEREO | LANG1 | LANG2 receiving mono, stereo or bilingual audio
   

When the V4L2_TUNER_CAP_STEREO, _LANG1, _LANG2 or _SAP flag is cleared in the capability field, the corresponding V4L2_TUNER_SUB_ flag must not be set here.

This field is valid only if this is the tuner of the current video input, or when the structure refers to a radio tuner.

__u32 audmode

The selected audio mode, see Tuner Audio Modes for valid values. The audio mode does not affect audio subprogram detection, and like a User Controls it does not automatically change unless the requested mode is invalid or unsupported. See Tuner Audio Matrix for possible results when the selected and received audio programs do not match.

Currently this is the only field of struct struct v4l2_tuner applications can change.

__u32 signal

The signal strength if known.

Ranging from 0 to 65535. Higher values indicate a better signal.

__s32 afc

Automatic frequency control.

When the afc value is negative, the frequency is too low, when positive too high.

__u32 reserved[4]

Reserved for future extensions.

Drivers and applications must set the array to zero.

v4l2_tuner_type
enum v4l2_tuner_type
V4L2_TUNER_RADIO 1 Tuner supports radio
V4L2_TUNER_ANALOG_TV 2 Tuner supports analog TV
V4L2_TUNER_SDR 4 Tuner controls the A/D and/or D/A block of a Software Digital Radio (SDR)
V4L2_TUNER_RF 5 Tuner controls the RF part of a Software Digital Radio (SDR)
Tuner and Modulator Capability Flags
V4L2_TUNER_CAP_LOW 0x0001 When set, tuning frequencies are expressed in units of 62.5 Hz instead of 62.5 kHz.
V4L2_TUNER_CAP_NORM 0x0002 This is a multi-standard tuner; the video standard can or must be switched. (B/G PAL tuners for example are typically not considered multi-standard because the video standard is automatically determined from the frequency band.) The set of supported video standards is available from the struct v4l2_input pointing to this tuner, see the description of ioctl ioctl VIDIOC_ENUMINPUT for details. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.
V4L2_TUNER_CAP_HWSEEK_BOUNDED 0x0004 If set, then this tuner supports the hardware seek functionality where the seek stops when it reaches the end of the frequency range.
V4L2_TUNER_CAP_HWSEEK_WRAP 0x0008 If set, then this tuner supports the hardware seek functionality where the seek wraps around when it reaches the end of the frequency range.
V4L2_TUNER_CAP_STEREO 0x0010 Stereo audio reception is supported.
V4L2_TUNER_CAP_LANG1 0x0040 Reception of the primary language of a bilingual audio program is supported. Bilingual audio is a feature of two-channel systems, transmitting the primary language monaural on the main audio carrier and a secondary language monaural on a second carrier. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.
V4L2_TUNER_CAP_LANG2 0x0020 Reception of the secondary language of a bilingual audio program is supported. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.
V4L2_TUNER_CAP_SAP 0x0020

Reception of a secondary audio program is supported. This is a feature of the BTSC system which accompanies the NTSC video standard. Two audio carriers are available for mono or stereo transmissions of a primary language, and an independent third carrier for a monaural secondary language. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.

Note

The V4L2_TUNER_CAP_LANG2 and V4L2_TUNER_CAP_SAP flags are synonyms. V4L2_TUNER_CAP_SAP applies when the tuner supports the V4L2_STD_NTSC_M video standard.

V4L2_TUNER_CAP_RDS 0x0080 RDS capture is supported. This capability is only valid for radio tuners.
V4L2_TUNER_CAP_RDS_BLOCK_IO 0x0100 The RDS data is passed as unparsed RDS blocks.
V4L2_TUNER_CAP_RDS_CONTROLS 0x0200 The RDS data is parsed by the hardware and set via controls.
V4L2_TUNER_CAP_FREQ_BANDS 0x0400 The ioctl VIDIOC_ENUM_FREQ_BANDS ioctl can be used to enumerate the available frequency bands.
V4L2_TUNER_CAP_HWSEEK_PROG_LIM 0x0800 The range to search when using the hardware seek functionality is programmable, see ioctl VIDIOC_S_HW_FREQ_SEEK for details.
V4L2_TUNER_CAP_1HZ 0x1000 When set, tuning frequencies are expressed in units of 1 Hz instead of 62.5 kHz.
Tuner Audio Reception Flags
V4L2_TUNER_SUB_MONO 0x0001 The tuner receives a mono audio signal.
V4L2_TUNER_SUB_STEREO 0x0002 The tuner receives a stereo audio signal.
V4L2_TUNER_SUB_LANG1 0x0008 The tuner receives the primary language of a bilingual audio signal. Drivers must clear this flag when the current video standard is V4L2_STD_NTSC_M.
V4L2_TUNER_SUB_LANG2 0x0004 The tuner receives the secondary language of a bilingual audio signal (or a second audio program).
V4L2_TUNER_SUB_SAP 0x0004

The tuner receives a Second Audio Program.

Note

The V4L2_TUNER_SUB_LANG2 and V4L2_TUNER_SUB_SAP flags are synonyms. The V4L2_TUNER_SUB_SAP flag applies when the current video standard is V4L2_STD_NTSC_M.

V4L2_TUNER_SUB_RDS 0x0010 The tuner receives an RDS channel.
Tuner Audio Modes
V4L2_TUNER_MODE_MONO 0 Play mono audio. When the tuner receives a stereo signal this a down-mix of the left and right channel. When the tuner receives a bilingual or SAP signal this mode selects the primary language.
V4L2_TUNER_MODE_STEREO 1

Play stereo audio. When the tuner receives bilingual audio it may play different languages on the left and right channel or the primary language is played on both channels.

Playing different languages in this mode is deprecated. New drivers should do this only in MODE_LANG1_LANG2.

When the tuner receives no stereo signal or does not support stereo reception the driver shall fall back to MODE_MONO.

V4L2_TUNER_MODE_LANG1 3 Play the primary language, mono or stereo. Only V4L2_TUNER_ANALOG_TV tuners support this mode.
V4L2_TUNER_MODE_LANG2 2 Play the secondary language, mono. When the tuner receives no bilingual audio or SAP, or their reception is not supported the driver shall fall back to mono or stereo mode. Only V4L2_TUNER_ANALOG_TV tuners support this mode.
V4L2_TUNER_MODE_SAP 2

Play the Second Audio Program. When the tuner receives no bilingual audio or SAP, or their reception is not supported the driver shall fall back to mono or stereo mode. Only V4L2_TUNER_ANALOG_TV tuners support this mode.

Note

The V4L2_TUNER_MODE_LANG2 and V4L2_TUNER_MODE_SAP are synonyms.

V4L2_TUNER_MODE_LANG1_LANG2 4 Play the primary language on the left channel, the secondary language on the right channel. When the tuner receives no bilingual audio or SAP, it shall fall back to MODE_LANG1 or MODE_MONO. Only V4L2_TUNER_ANALOG_TV tuners support this mode.
Tuner Audio Matrix
  Selected V4L2_TUNER_MODE_
Received V4L2_TUNER_SUB_ MONO STEREO LANG1 LANG2 = SAP LANG1_LANG2 [1]
MONO Mono Mono/Mono Mono Mono Mono/Mono
MONO | SAP Mono Mono/Mono Mono SAP Mono/SAP (preferred) or Mono/Mono
STEREO L+R L/R Stereo L/R (preferred) or Mono L+R Stereo L/R (preferred) or Mono L+R L/R (preferred) or L+R/L+R
STEREO | SAP L+R L/R Stereo L/R (preferred) or Mono L+R SAP L+R/SAP (preferred) or L/R or L+R/L+R
LANG1 | LANG2 Language 1 Lang1/Lang2 (deprecated [2]) or Lang1/Lang1 Language 1 Language 2 Lang1/Lang2 (preferred) or Lang1/Lang1

8.42.5. 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 struct v4l2_tuner index is out of bounds.
[1]This mode has been added in Linux 2.6.17 and may not be supported by older drivers.
[2]Playback of both languages in MODE_STEREO is deprecated. In the future drivers should produce only the primary language in this mode. Applications should request MODE_LANG1_LANG2 to record both languages or a stereo signal.