How to add support for a new remote from lircd.conf file

You have a remote for which the is no rc keymap, but you do have a lircd.conf file which works. That requires running the lirc daemon; nowadays you most likely don’t need to any more.

Automagic conversion from lircd.conf to toml keymap

I’ve written a python script which parses a lircd.conf file, and outputs a toml file. Now this script should cover most cases, but it won’t work in all cases. Get from the v4l-utils contrib. This requires python3 to work.

  • Make executable: chmod 755
  • Run ./ -o output.toml yourlircdfile.lircd.conf

Once you have the output toml file, it probably needs a little fixing up. First of all, lircd does not usually use linux keycodes, so those will need adjusting. Have a look at the linux input keycodes for the list keycodes and adjust the toml accordingly. Also make sure the name is set to a reasonable value. Once you have done that, test it using:

ir-keytable -c -w output.toml -t

Please do let me know how you get on and comment below. Alternatively, find us on the linux-media mailinglist or on irc #v4l on Freenode. If the keymap works fine please submit it to the mailinglist as a patch for v4l-utils.

What if doesn’t work

First of all, please ask. I’m eager to hear about people using this tool. Having said that, I should explain a little more about lircd.conf files work.

IR decoders in a rc-core world

In the toml file there is the “protocol” field, which can either match a kernel decoder or BPF decoder.

There are two types of IR decoders in the rc-core world. There are the hardcoded decoders in the kernel, which cover the most common protocols: rc-5, nec, rc-6, rc-mm, sony, sanyo, jvc, sharp, xmp. If your remote uses one of these protocols, you can use the method described in the previous post. However, you can try the method with too, it should work for most cases.

There are also protocol decoders written in BPF, which also have parameters. So if your remote has a regular protocol with non-standard signaling length, you can specify that in your keymap, much like the parameters in lircd.conf files.

The protocol in the lircd.conf is set in the “flags” field. lircd has a few:

  • space_enc: This is anything where bits are encoded using the distance between to pulses or spaces. Many of these are plain nec, but not all. Those that are not, can be decoded using the BPF pulse_distance decoder, or BPF pulse_length depending on whether the space length differs or the pulse length differs.
  • space_first: Not sure yet.
  • rc5 or shift_enc: This is just rc-5. Some versions use non-standard times, in which case you should use the BPF manchester decoder.
  • rc6: This is just rc-6.
  • rcmm: This is just rc-mm.
  • grundig: This is for some ancient grundig remotes. There is a BPF grundig decoder for them.
  • bo: This is a Bang & Olufsen IR protocol. There is no BPF decoder for this yet, patches welcome :)
  • goldstar: This for some ancient goldstar remotes. There is no BPF decoder for this yet, and supported has been removed from lirc too
  • serial: This is for IR receivers that decode IR and put it on a tty. Not supported in rc-core, as this should be done by a device driver.
  • xmp: This is just xmp.
  • raw_codes: This is just a plain dump of the pulse/spaces for each button. This is not supported in BPF yet (but so below).

The parameters for the BPF decoders can be seen in the source code, see the global ints declared at the beginning of the c files. Have a look at the output of ir-ctl -r and see if you can match things up. Also have a look a the lirc documentation for the lircd format.

How to deal with raw_codes

If you have a lircd.conf remote with a raw_codes protocol, then things are a bit harder to solve unfortunately. The format lists all the keys and the associated IR, by listing the raw IR. The first value is a pulse, then space, pulse, etc. Essentially the protocol is not reverse engineered so you are not much better off than without the lird.conf. This is a case where you should reverse engineer the protocol, like you would if you had no lircd.conf file at all.

It might be possible to support raw_codes in BPF, but loops are not allowed so this is not trivial. You would have to create the state machine of walking through the list, and unrolling the loop enough so that it can successfully decode the IR.

Note that some raw_codes are a well-known protocol but the author of the lircd.conf did not realise. For example, this hauppauge lircd.conf file uses raw_codes but it’s actually rc-5.