fmtools: simple V4L2 radio card programs
Maintained by Ben Pfaff <email@example.com>
Originally by Russell Kroll <firstname.lastname@example.org>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
This is a pair of hopefully useful control programs for Video for
Linux 2 (V4L2) radio card drivers. The focus is on control, so you
may find these programs a bit unfriendly. Users are encouraged to
investigate the source and create wrappers or new programs based on
fm - a simple tuner
fmscan - a simple band scanner
This is a simple program that will send commands to your V4L2 radio
cards. It was written mostly so I could have something to send
commands at the drivers being created or debugged here.
The usual mode of operation is to tell the radio to come on to a given
freqency. In these examples, 94.3 will be used since that's a station
that happens to get tuned here frequently.
To turn the radio on to that frequency at the default volume, you'd do
"fm 94.3" and call it done. If you wanted to crank it up to full
volume, another argument would be needed and the command becomes "fm
94.3 100". Volumes range from 0 (off) to 100 (full intensity).
There is a -q option that will suppress messages about tuning, volume
changes, and so forth. Keeping your tuner quiet may not seem like
such a useful thing at first, but it can be very handy inside an IRC
script. Having a program scribble on your channel window when you do
/KILO or similar is not enjoyable.
Besides direct tuning, there are also "on" and "off" commands. They
will turn the card on and off (mute) as you may have guessed.
Finally, there is volume control. To go up a notch, use +. To go
down a notch, use -. Simple.
You can create a file called .fmrc in your home directory that
contains values for the default volume and default volume stepping.
This way, you can have your radio card always come on at a certain
volume when you don't explicitly list it on the command line. The
volume stepping controls how much the volume changes during a - or +
This file is not required for operation of the program, and it will
not even give so much as a peep if it doesn't find it. The defaults
are used when you don't specify values. The values are 12.5% for
default volume and 10% for default volume stepping.
Here's what a real .fmrc might look like ...
Here we say the default volume is 50%. Then we say the increment
value for volume changes with + and - is 10%. These values were
obtained by playing around with the numbers until things behaved the
way I wanted. Be aware that some cards only have a couple of volume
steps, so you may not notice a change right away.
The Cadet hardware, for example, has two settings: off and *VERY
LOUD*. Any volume setting will turn it on. The Aztech card has 4
settings (off, low, medium, high) and you'll notice it change when you
cross the boundaries. The Aimslab RadioReveal card is actually based
on analog volume control, with 10 steps emulated within that range.
There are some other options available:
-d - select device. If you have more than one V4L2 radio card in your
system for some reason, use -d <device> to select the right one.
This is probably only useful if you like writing drivers for
-o - override card frequency range - Some radio card drivers don't
actively enforce the frequencies that you can tune to. Use this
switch and fm will send any frequency you want to the driver.
This alone will not make an unmodified card receive frequencies
from outside the design range. You have to change the tuner
hardware in order to enjoy such broadcasts.
-t - select tuner - Certain cards have multiple tuners - usually used
for different bands. The ADS Cadet driver is known to support
this, specifically using 0 for FM and 1 for AM. To tune AM
frequencies, remember that fm expects MHz style input, and do the
For 1200 kHz, enter 'fm -t 1 1.2', since 1.2 MHz == 1200 kHz.
Yes, tuning am frequencies with 'fm' seems backwards, but that's
life. Crafty hackers may want to add some code to make the
program check argv and behave differently.
This simple little program will command your radio card through the
radio band and show which ones have a accumulated signal strength of
50% or higher. This process can take awhile, and can vary greatly
depending on the radio card in use.
By default, the range scanned is 87.9-107.9 MHz in .2 MHz steps, since
that's the standard band here in the USA. Users in other regions
should set the appropriate information for best results.
V4L2 /dev entries
By default, these programs use /dev/radio0 to access the hardware. This
can be changed with -d <device> if you have more than one. If you have
been using v4l radio cards for awhile, you may already have a /dev/radio.
That is now "legacy", and should be symlinked to /dev/radio0. To create
the proper device entry, either do "make devices" as root, or create it
by hand with mknod (c 81 64).
The proper device listing looks something like this in 'ls -la' ...
lrwxrwxrwx 1 root root 11 Jan 20 03:19 /dev/radio -> /dev/radio0
crw-r--r-- 1 root root 81, 64 Jan 20 03:19 /dev/radio0
Other cards follow the same pattern - radio1 would be (81, 65), and so on.
The owner and permission data should be set to values that agree with
your system's personality. If it's mostly a solitary system with few or
no users, the above settings will be fine.
However, if you have other people running around on your system, consider
making the device part of a "radio" group or maybe even "console" if you
use such a thing. That will keep random individuals from doing odd things
to your radio like changing it to a classical station while you're
listening to some death metal (or vice versa). You have been warned.