193 lines
6.7 KiB
ReStructuredText
193 lines
6.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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.. include:: <isonum.txt>
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The Silicon Labs Si4713 FM Radio Transmitter Driver
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===================================================
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Copyright |copy| 2009 Nokia Corporation
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Contact: Eduardo Valentin <eduardo.valentin@nokia.com>
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Information about the Device
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----------------------------
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This chip is a Silicon Labs product. It is a I2C device, currently on 0x63 address.
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Basically, it has transmission and signal noise level measurement features.
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The Si4713 integrates transmit functions for FM broadcast stereo transmission.
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The chip also allows integrated receive power scanning to identify low signal
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power FM channels.
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The chip is programmed using commands and responses. There are also several
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properties which can change the behavior of this chip.
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Users must comply with local regulations on radio frequency (RF) transmission.
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Device driver description
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-------------------------
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There are two modules to handle this device. One is a I2C device driver
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and the other is a platform driver.
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The I2C device driver exports a v4l2-subdev interface to the kernel.
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All properties can also be accessed by v4l2 extended controls interface, by
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using the v4l2-subdev calls (g_ext_ctrls, s_ext_ctrls).
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The platform device driver exports a v4l2 radio device interface to user land.
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So, it uses the I2C device driver as a sub device in order to send the user
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commands to the actual device. Basically it is a wrapper to the I2C device driver.
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Applications can use v4l2 radio API to specify frequency of operation, mute state,
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etc. But mostly of its properties will be present in the extended controls.
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When the v4l2 mute property is set to 1 (true), the driver will turn the chip off.
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Properties description
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----------------------
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The properties can be accessed using v4l2 extended controls.
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Here is an output from v4l2-ctl util:
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.. code-block:: none
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/ # v4l2-ctl -d /dev/radio0 --all -L
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Driver Info:
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Driver name : radio-si4713
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Card type : Silicon Labs Si4713 Modulator
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Bus info :
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Driver version: 0
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Capabilities : 0x00080800
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RDS Output
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Modulator
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Audio output: 0 (FM Modulator Audio Out)
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Frequency: 1408000 (88.000000 MHz)
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Video Standard = 0x00000000
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Modulator:
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Name : FM Modulator
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Capabilities : 62.5 Hz stereo rds
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Frequency range : 76.0 MHz - 108.0 MHz
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Subchannel modulation: stereo+rds
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User Controls
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mute (bool) : default=1 value=0
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FM Radio Modulator Controls
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rds_signal_deviation (int) : min=0 max=90000 step=10 default=200 value=200 flags=slider
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rds_program_id (int) : min=0 max=65535 step=1 default=0 value=0
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rds_program_type (int) : min=0 max=31 step=1 default=0 value=0
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rds_ps_name (str) : min=0 max=96 step=8 value='si4713 '
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rds_radio_text (str) : min=0 max=384 step=32 value=''
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audio_limiter_feature_enabled (bool) : default=1 value=1
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audio_limiter_release_time (int) : min=250 max=102390 step=50 default=5010 value=5010 flags=slider
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audio_limiter_deviation (int) : min=0 max=90000 step=10 default=66250 value=66250 flags=slider
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audio_compression_feature_enabl (bool) : default=1 value=1
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audio_compression_gain (int) : min=0 max=20 step=1 default=15 value=15 flags=slider
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audio_compression_threshold (int) : min=-40 max=0 step=1 default=-40 value=-40 flags=slider
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audio_compression_attack_time (int) : min=0 max=5000 step=500 default=0 value=0 flags=slider
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audio_compression_release_time (int) : min=100000 max=1000000 step=100000 default=1000000 value=1000000 flags=slider
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pilot_tone_feature_enabled (bool) : default=1 value=1
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pilot_tone_deviation (int) : min=0 max=90000 step=10 default=6750 value=6750 flags=slider
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pilot_tone_frequency (int) : min=0 max=19000 step=1 default=19000 value=19000 flags=slider
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pre_emphasis_settings (menu) : min=0 max=2 default=1 value=1
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tune_power_level (int) : min=0 max=120 step=1 default=88 value=88 flags=slider
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tune_antenna_capacitor (int) : min=0 max=191 step=1 default=0 value=110 flags=slider
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Here is a summary of them:
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* Pilot is an audible tone sent by the device.
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- pilot_frequency - Configures the frequency of the stereo pilot tone.
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- pilot_deviation - Configures pilot tone frequency deviation level.
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- pilot_enabled - Enables or disables the pilot tone feature.
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* The si4713 device is capable of applying audio compression to the
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transmitted signal.
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- acomp_enabled - Enables or disables the audio dynamic range control feature.
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- acomp_gain - Sets the gain for audio dynamic range control.
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- acomp_threshold - Sets the threshold level for audio dynamic range control.
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- acomp_attack_time - Sets the attack time for audio dynamic range control.
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- acomp_release_time - Sets the release time for audio dynamic range control.
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* Limiter setups audio deviation limiter feature. Once a over deviation occurs,
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it is possible to adjust the front-end gain of the audio input and always
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prevent over deviation.
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- limiter_enabled - Enables or disables the limiter feature.
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- limiter_deviation - Configures audio frequency deviation level.
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- limiter_release_time - Sets the limiter release time.
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* Tuning power
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- power_level - Sets the output power level for signal transmission.
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antenna_capacitor - This selects the value of antenna tuning capacitor
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manually or automatically if set to zero.
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* RDS related
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- rds_ps_name - Sets the RDS ps name field for transmission.
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- rds_radio_text - Sets the RDS radio text for transmission.
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- rds_pi - Sets the RDS PI field for transmission.
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- rds_pty - Sets the RDS PTY field for transmission.
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* Region related
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- preemphasis - sets the preemphasis to be applied for transmission.
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RNL
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---
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This device also has an interface to measure received noise level. To do that, you should
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ioctl the device node. Here is an code of example:
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.. code-block:: none
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int main (int argc, char *argv[])
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{
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struct si4713_rnl rnl;
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int fd = open("/dev/radio0", O_RDWR);
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int rval;
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if (argc < 2)
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return -EINVAL;
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if (fd < 0)
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return fd;
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sscanf(argv[1], "%d", &rnl.frequency);
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rval = ioctl(fd, SI4713_IOC_MEASURE_RNL, &rnl);
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if (rval < 0)
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return rval;
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printf("received noise level: %d\n", rnl.rnl);
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close(fd);
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}
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The struct si4713_rnl and SI4713_IOC_MEASURE_RNL are defined under
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include/linux/platform_data/media/si4713.h.
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Stereo/Mono and RDS subchannels
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-------------------------------
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The device can also be configured using the available sub channels for
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transmission. To do that use S/G_MODULATOR ioctl and configure txsubchans properly.
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Refer to the V4L2 API specification for proper use of this ioctl.
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Testing
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-------
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Testing is usually done with v4l2-ctl utility for managing FM tuner cards.
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The tool can be found in v4l-dvb repository under v4l2-apps/util directory.
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Example for setting rds ps name:
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.. code-block:: none
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# v4l2-ctl -d /dev/radio0 --set-ctrl=rds_ps_name="Dummy"
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