7.42. ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER¶

7.42.1. Name¶

VIDIOC_G_TUNER - VIDIOC_S_TUNER - Get or set tuner attributes

7.42.2. Synopsis¶

int ioctl(int fd, VIDIOC_G_TUNER, struct v4l2_tuner *argp)¶

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

7.42.3. Arguments¶

fd: File descriptor returned by open().
argp: Pointer to struct v4l2_tuner.

7.42.4. 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

7.42.5. 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.