Radio Service
Overview
NOTE: The verbs/events below are out of date, refer to protos/radio.proto for the new gRPC API until this documentation gets updated.
Radio Service allows tuning of rtl-sdr based devices to radio stations and receive respective audio stream.
Verbs
| Name | Description | JSON Parameters |
|---|---|---|
| subscribe | subscribe to radio events | Request: {"value": "frequency"} |
| unsubscribe | unsubscribe to radio events | Request: {"value": "frequency"} |
| frequency | get/set tuned radio frequency | Request: {"value": 101100000} |
| band | get/set current band type (e.g. AM, FM) | Request: {"value": "FM"} Response: {"band": "FM"} |
| band_supported | check if a certain band is supported | Request: {"band": "FM"} Response: {"supported": 1} |
| frequency_range | get frequency range for band type | Request: {"band": "FM"} Response: {"min": ..., "max": ...} |
| frequency_step | get frequency step/spacing for band type | Request: {"band": "FM"} Response: {"step": 200000} |
| start | start radio playback | |
| stop | stop radio playback | |
| scan_start | start scanning for station | Request: {"direction": "forward" or "backward"} |
| scan_stop | stop scanning for station | |
| stereo_mode | get/set stereo or mono mode | Request: {"value": "stereo" or "mono"} |
| rds | get current RDS data | |
| quality | get station quality | |
| alternative_frequency | check an alternative frequency and retune | Request: {"value": 104900000} |
Events
frequency Event JSON Response
JSON response has a single field value which is the currently tuned frequency.
station_found Event JSON Response
JSON response has a single field value of the frequency of the discovered radio station.
status Event JSON Response
JSON response has a single field value with one of the values "playing" or "stopped".
rds Event JSON Response
JSON response has 13 fields:
- name which is the Programme Service (PS) name;
- radiotext which is the Radio Text (RT) message;
- alternatives which is an array of Alternative Frequencies (AF);
- minute which is the current local time minute;
- hour which is the current local time hour;
- day which is the current day;
- month which is the current month;
- year which is the current year;
- pi which is the current Programme Identification (PI) code;
- pty which is the current Programme Type (PTY) code;
- ta which is the Traffic Announcement (TA) code;
- tp which is the Traffic Programme (TP) Identification code;
- ms which is the Music Speech (MS) code.
AGL Radio Tuner Binding
FM Band Plan Selection
The FM band plan may be selected by adding:
fmbandplan=X
to the [radio] section in /etc/xdg/AGL.conf, where X is one of the following strings:
US = United States / Canada JP = Japan EU = European Union ITU-1 ITU-2
Example:
[radio]
fmbandplan=JP
Implementation Specific Confguration
USB RTL-SDR adapter
The scanning sensitivity can be tweaked by adding:
scan_squelch_level=X
to the [radio] section in /etc/xdg/AGL.conf, where X is an integer. Lower values make the scanning more sensitive. Default value is 140.
Example:
[radio]
scan_squelch_level=70
M3ULCB Kingfisher Si4689
The scanning sensitivity can be tweaked by adding:
scan_valid_snr_threshold=X
scan_valid_rssi_threshold=Y
to the [radio] section in /etc/xdg/AGL.conf, where X and Y are integers between -127 and 127. The SNR value is in units of dB, and the RSSI is in units of dBuV. Lower values make the scanning more sensitive. Default values in the Si4689 are 10 and 17, respectively. You may determine the values that the Si4689 is seeing when tuning by examining the results of tuning in the systemd journal, looking for lines like:
Example:
[radio]
scan_valid_snr_threshold=7
scan_valid_rssi_threshold=10
Known Issues
M3ULCB Kingfisher
Initial setup for a new Kingfisher board requires booting an image with Kingfisher support and running the commands:
si_init
si_firmware_update
This installs the provided firmware into the flash attached to the Si4689.
Since all operations are currently done by calling a patched version of Cogent Embedded's si_ctl utility, scanning currently cannot be interrupted. Additionally, sometimes a failure in scanning seems to result in muted state that currently has not been debugged.