N900 FM radio receiver

2011-04-27T21:14:34Z

87.20.163.222: /* User */

The [[Nokia N900|N900]] FM receiver allows the reception of broadcast FM radio signals using the headset/headphones as an antenna.

==Hardware==

The FM radio is part of the [[N900 Hardware Bluetooth|Bluetooth chip]]. It receives FM radio signals using the headset or earphones plugged into the 3.5 mm socket as an antenna (actually arbitrary headset/headphones, or any other cable, for this purpose).

The audio output of the FM radio is connected to the audio codec chip.
This can be routed directly to the headphones - but possibly not the speaker due to concerns about speaker damage due to the speakers not being able to handle bass.

The existing software that uses the radio passes the audio through the CPU, implementing a software filter for speaker protection when the speakers are enabled.

==Software==

===Kernel===

The FM receiver is implemented as a video4linux radio device by the [http://mxr.maemo.org/fremantle/source/kernel/drivers/media/radio/radio-bcm2048.c bcm2048] module. This controls the receiver over the [[N900 Hardware Bus I2C]].

It appears as device <code>/dev/radio1</code>.
<pre>
v4l2-ctl --all -d /dev/radio1
Driver Info:
Driver name : bcm2048
Card type : Broadcom bcm2048 FM Radio Recei
Bus info : I2C: 0x22
Driver version: 1
Capabilities : 0x00050400
Tuner
Radio
Video input : 0
Frequency: 1518400 (94.900000 MHz)
Video Standard = 0x00000000
Streaming Parameters Video Capture:
Frames per second: 25.000 (25/1)
Read buffers : 0
Tuner:
Name : FM Receiver
Capabilities : 62.5 Hz stereo
Frequency range : 87.5 MHz - 108.0 MHz
Signal strength/AFC : 0%/0
Current audio mode : stereo
Available subchannels: stereo
</pre>

The module is only loaded when the radio is used.

It is also exposed under sysfs.
<pre>
/sys/class/i2c-adapter/i2c-3/3-0022# ls
audio_route fm_rssi rds_data
bus fm_search_mode_direction rds_pi
dac_output fm_search_rssi_threshold rds_pi_mask
driver fm_search_tune_mode rds_pi_match
fm_af_frequency modalias rds_ps
fm_best_tune_mode mute rds_rt
fm_carrier_error name rds_wline
fm_deemphasis power region
fm_frequency power_state region_bottom_frequency
fm_hi_lo_injection rds region_top_frequency
fm_rds_flags rds_b_block_mask subsystem
fm_rds_mask rds_b_block_match uevent
</pre>
The sysfs interface allows configuration of region (which affects frequency ranges and other parameters).

===User===

There are 3 userspace application that uses the FM receiver:

[http://maemo.org/packages/view/fmradio/ FMRadio],
[http://maemo.org/packages/view/qradio/ QRadio]
and
[http://maemo.org/packages/view/cfmradio/ C FM Radio]

[[Category:N900 Hardware]]

Maemo Wiki Mirror - User contributions [en]

N900 FM radio receiver