[PATCHv11,8/8] FM TX: si4713: Add document file

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+Driver for I2C radios for the Silicon Labs Si4713 FM Radio Transmitters
+
+Copyright (c) 2009 Nokia Corporation
+Contact: Eduardo Valentin <eduardo.valentin@nokia.com>
+
+
+Information about the Device
+============================
+This chip is a Silicon Labs product. It is a I2C device, currently on 0×63 address.
+Basically, it has transmission and signal noise level measurement features.
+
+The Si4713 integrates transmit functions for FM broadcast stereo transmission.
+The chip also allows integrated receive power scanning to identify low signal
+power FM channels.
+
+The chip is programmed using commands and responses. There are also several
+properties which can change the behavior of this chip.
+
+Users must comply with local regulations on radio frequency (RF) transmission.
+
+Device driver description
+=========================
+There are two modules to handle this device. One is a I2C device driver
+and the other is a platform driver.
+
+The I2C device driver exports a v4l2-subdev interface to the kernel.
+All properties can also be accessed by v4l2 extended controls interface, by
+using the v4l2-subdev calls (g_ext_ctrls, s_ext_ctrls).
+
+The platform device driver exports a v4l2 radio device interface to user land.
+So, it uses the I2C device driver as a sub device in order to send the user
+commands to the actual device. Basically it is a wrapper to the I2C device driver.
+
+Applications can use v4l2 radio API to specify frequency of operation, mute state,
+etc. But mostly of its properties will be present in the extended controls.
+
+When the v4l2 mute property is set to 1 (true), the driver will turn the chip off.
+
+Properties description
+======================
+
+The properties can be accessed using v4l2 extended controls.
+Here is an output from v4l2-ctl util:
+/ # v4l2-ctl -d /dev/radio0 --all -L
+Driver Info:
+        Driver name   : radio-si4713
+        Card type     : Silicon Labs Si4713 Modulator
+        Bus info      :
+        Driver version: 0
+        Capabilities  : 0x00080800
+                RDS Output
+                Modulator
+Audio output: 0 (FM Modulator Audio Out)
+Frequency: 1408000 (88.000000 MHz)
+Video Standard = 0x00000000
+Modulator:
+        Name                 : FM Modulator
+        Capabilities         : 62.5 Hz stereo rds
+        Frequency range      : 76.0 MHz - 108.0 MHz
+        Subchannel modulation: mono+rds
+
+User Controls
+
+                           mute (bool) : default=1 value=0
+
+FM Radio Modulator Controls
+
+                 rds_program_id (int)  : min=0 max=65535 step=1 default=0 value=0
+               rds_program_type (int)  : min=0 max=31 step=1 default=0 value=0
+           rds_signal_deviation (int)  : min=0 max=90000 step=10 default=200 value=200 flags=slider
+                    rds_ps_name (str)  : min=0 max=97 value='Si4713  '
+                 rds_radio_text (str)  : min=0 max=385 value='Si4713  \r'
+  audio_limiter_feature_enabled (bool) : default=1 value=1
+     audio_limiter_release_time (int)  : min=250 max=102390 step=50 default=5010 value=5010 flags=slider
+        audio_limiter_deviation (int)  : min=0 max=90000 step=10 default=66250 value=66250 flags=slider
+audio_compression_feature_enabl (bool) : default=1 value=1
+         audio_compression_gain (int)  : min=0 max=20 step=1 default=15 value=15 flags=slider
+    audio_compression_threshold (int)  : min=-40 max=0 step=1 default=-40 value=-40 flags=slider
+  audio_compression_attack_time (int)  : min=0 max=5000 step=500 default=0 value=0 flags=slider
+ audio_compression_release_time (int)  : min=100000 max=1000000 step=100000 default=1000000 value=1000000 flags=slider
+     pilot_tone_feature_enabled (bool) : default=1 value=1
+           pilot_tone_deviation (int)  : min=0 max=90000 step=10 default=6750 value=6750 flags=slider
+           pilot_tone_frequency (int)  : min=0 max=19000 step=1 default=19000 value=19000 flags=slider
+          pre_emphasis_settings (menu) : min=0 max=2 default=1 value=1
+               tune_power_level (int)  : min=0 max=120 step=1 default=88 value=88 flags=slider
+         tune_antenna_capacitor (int)  : min=0 max=191 step=1 default=0 value=109 flags=slider
+/ #
+
+Here is a summary of them:
+
+* Pilot is an audible tone sent by the device.
+
+pilot_frequency - Configures the frequency of the stereo pilot tone.
+pilot_deviation - Configures pilot tone frequency deviation level.
+pilot_enabled - Enables or disables the pilot tone feature.
+
+* The si4713 device is capable of applying audio compression to the transmitted signal.
+
+acomp_enabled - Enables or disables the audio dynamic range control feature.
+acomp_gain - Sets the gain for audio dynamic range control.
+acomp_threshold - Sets the threshold level for audio dynamic range control.
+acomp_attack_time - Sets the attack time for audio dynamic range control.
+acomp_release_time - Sets the release time for audio dynamic range control.
+
+* Limiter setups audio deviation limiter feature. Once a over deviation occurs,
+it is possible to adjust the front-end gain of the audio input and always
+prevent over deviation.
+
+limiter_enabled - Enables or disables the limiter feature.
+limiter_deviation - Configures audio frequency deviation level.
+limiter_release_time - Sets the limiter release time.
+
+* Tuning power
+
+power_level - Sets the output power level for signal transmission.
+antenna_capacitor - This selects the value of antenna tuning capacitor manually
+or automatically if set to zero.
+
+* RDS related
+
+rds_ps_name - Sets the RDS ps name field for transmission.
+rds_radio_text - Sets the RDS radio text for transmission.
+rds_pi - Sets the RDS PI field for transmission.
+rds_pty - Sets the RDS PTY field for transmission.
+
+* Region related
+
+preemphasis - sets the preemphasis to be applied for transmission.
+
+RNL
+===
+
+This device also has an interface to measure received noise level. To do that, you should
+ioctl the device node. Here is an code of example:
+
+int main (int argc, char *argv[])
+{
+        struct si4713_rnl rnl;
+        int fd = open("/dev/radio0", O_RDWR);
+        int rval;
+
+        if (argc < 2)
+                return -EINVAL;
+
+        if (fd < 0)
+                return fd;
+
+        sscanf(argv[1], "%d", &rnl.frequency);
+
+        rval = ioctl(fd, SI4713_IOC_MEASURE_RNL, &rnl);
+        if (rval < 0)
+                return rval;
+
+        printf("received noise level: %d\n", rnl.rnl);
+
+        close(fd);
+}
+
+The struct si4713_rnl and SI4713_IOC_MEASURE_RNL are defined under
+include/media/si4713.h.
+
+Stereo/Mono and RDS subchannels
+===============================
+
+The device can also be configured using the available sub channels for
+transmission. To do that use S/G_MODULATOR ioctl and configure txsubchans properly.
+Refer to v4l2-spec for proper use of this ioctl.
+
+Testing
+=======
+Testing is usually done with v4l2-ctl utility for managing FM tuner cards.
+The tool can be found in v4l-dvb repository under v4l2-apps/util directory.
+
+Example for setting rds ps name:
+# v4l2-ctl -d /dev/radio0 --set-ctrl=rds_ps_name="Dummy"
+