8.35. ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR¶
8.35.1. Name¶
VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes
8.35.2. Synopsis¶
-
int
ioctl
(int fd, int request, struct v4l2_modulator *argp)¶
-
int
ioctl
(int fd, int request, const struct v4l2_modulator *argp)¶
8.35.3. Arguments¶
fd
- File descriptor returned by open().
request
- VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
argp
8.35.4. Description¶
To query the attributes of a modulator applications initialize the
index
field and zero out the reserved
array of a struct
v4l2_modulator and call the
VIDIOC_G_MODULATOR 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 modulators applications shall
begin at index zero, incrementing by one until the driver returns
EINVAL.
Modulators have two writable properties, an audio modulation set and the
radio frequency. To change the modulated audio subprograms, applications
initialize the index
and txsubchans
fields and the reserved
array and call the VIDIOC_S_MODULATOR ioctl. Drivers may choose a
different audio modulation if the request cannot be satisfied. However
this is a write-only ioctl, it does not return the actual audio
modulation selected.
SDR specific modulator types are V4L2_TUNER_SDR
and
V4L2_TUNER_RF
. For SDR devices txsubchans
field must be
initialized to zero. The term ‘modulator’ means SDR transmitter in this
context.
To change the radio frequency the VIDIOC_S_FREQUENCY ioctl is available.
__u32 | index |
Identifies the modulator, set by the application. | ||
__u8 | name [32] |
Name of the modulator, a NUL-terminated ASCII string. This information is intended for the user. | ||
__u32 | capability |
Modulator capability flags. No flags are defined for this field, the tuner flags in struct v4l2_tuner are used accordingly. The audio flags indicate the ability to encode audio subprograms. They will not change for example with the current video standard. | ||
__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. |
||
__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. |
||
__u32 | txsubchans |
With this field applications can determine how audio sub-carriers shall be modulated. It contains a set of flags as defined in Modulator Audio Transmission Flags. Note The tuner |
||
__u32 | type |
Type of the modulator, see enum v4l2_tuner_type. | ||
__u32 | reserved [3] |
Reserved for future extensions. Drivers and applications must set the array to zero. |
V4L2_TUNER_SUB_MONO |
0x0001 | Modulate channel 1 as mono audio, when the input has more
channels, a down-mix of channel 1 and 2. This flag does not
combine with V4L2_TUNER_SUB_STEREO or
V4L2_TUNER_SUB_LANG1 . |
V4L2_TUNER_SUB_STEREO |
0x0002 | Modulate channel 1 and 2 as left and right channel of a stereo
audio signal. When the input has only one channel or two channels
and V4L2_TUNER_SUB_SAP is also set, channel 1 is encoded as
left and right channel. This flag does not combine with
V4L2_TUNER_SUB_MONO or V4L2_TUNER_SUB_LANG1 . When the
driver does not support stereo audio it shall fall back to mono. |
V4L2_TUNER_SUB_LANG1 |
0x0008 | Modulate channel 1 and 2 as primary and secondary language of a
bilingual audio signal. When the input has only one channel it is
used for both languages. It is not possible to encode the primary
or secondary language only. This flag does not combine with
V4L2_TUNER_SUB_MONO , V4L2_TUNER_SUB_STEREO or
V4L2_TUNER_SUB_SAP . If the hardware does not support the
respective audio matrix, or the current video standard does not
permit bilingual audio the VIDIOC_S_MODULATOR ioctl shall
return an EINVAL error code and the driver shall fall back to mono
or stereo mode. |
V4L2_TUNER_SUB_LANG2 |
0x0004 | Same effect as V4L2_TUNER_SUB_SAP . |
V4L2_TUNER_SUB_SAP |
0x0004 | When combined with V4L2_TUNER_SUB_MONO the first channel is
encoded as mono audio, the last channel as Second Audio Program.
When the input has only one channel it is used for both audio
tracks. When the input has three channels the mono track is a
down-mix of channel 1 and 2. When combined with
V4L2_TUNER_SUB_STEREO channel 1 and 2 are encoded as left and
right stereo audio, channel 3 as Second Audio Program. When the
input has only two channels, the first is encoded as left and
right channel and the second as SAP. When the input has only one
channel it is used for all audio tracks. It is not possible to
encode a Second Audio Program only. This flag must combine with
V4L2_TUNER_SUB_MONO or V4L2_TUNER_SUB_STEREO . If the
hardware does not support the respective audio matrix, or the
current video standard does not permit SAP the
VIDIOC_S_MODULATOR ioctl shall return an EINVAL error code and
driver shall fall back to mono or stereo mode. |
V4L2_TUNER_SUB_RDS |
0x0010 | Enable the RDS encoder for a radio FM transmitter. |
8.35.5. 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_modulator
index
is out of bounds.