Sunday, December 18, 2016

Using an MCE Remote with Mythbuntu

As I chronicled in a previous post, I've been using MythMote on my (Android) cell phone to serve as a remote control for my MythTV installation (running on Mythbuntu) when watching recordings  or live TV. For the most part this works fine, but there are little inconveniences associated with it, so I decided it was time buckle down and get one of my (many) remote controls to do the job. As it happens, I have Windows Media Center infrared receiver attached to the machine via USB drive, so the associated remote control was the logical choice.

I took the better part of a day to get it working, so I'll chronicle here the things I learned. Everything here is specific to MythTV running on some version of Linux, and much of it may require adjustment if MythTV is not installed on Mythbuntu, Ubuntu or maybe Linux Mint or Debian.

Ignore LIRC


As with any of my MythTV adventures, I started by consulting Google. It turns out a lot of the information out there is obsolete if you have a remotely recent operating system. Many (most?) of the posts I found discussed how to work with Linux Infrared Remote Control (LIRC), an add-on package for Linux. The catch is that infrared remote support is baked into recent kernels, so you don't need LIRC unless you want to use certain extended capabilities that it apparently provides. I don't know what they are, and I don't need them.

One Ring to Control Them All


Get to know the ir-keytable command, which will be your friend through all this.  Running it (with no options) in a terminal told me that my system understood that I had an MCE receiver attached (on /dev/input/event3, as it turns out ... yours may differ). Running

ir-keytable --device /dev/input/event3 --test

then let me test which key events were detected when each button on the remote was pressed.

BIOS Nonsense


This led to the first "minor" problem: according to ir-keytable, none of the buttons on my remote were registering. The LEDs on the remote and receiver both lit with each button press, so the receiver was "hearing" the remote; it just wasn't being believed by the system. Further consultation with Google led me to this post, which suggested that the problem lies in how some BIOSes support USB 3. The IR receiver was plugged into a USB 2 hub, and I don't have anything attached to the machine via USB 3 (I'm not even sure it has a USB 3 jack), but whatever. I rebooted, got into the BIOS editor, found the setting for USB 3 support (every damn BIOS seems to hide it in a different place, so I can't tell you exactly where to look), and turned it off, then booted back into Mythbuntu. This achieved a partial success: ir-keytable in test mode could see button presses! That's the good news. The bad news is that only a few were interpreted correctly.

Remapping the Buttons


The next step is to remap the buttons on the remote. The drill is to map buttons to the keys you would use if you were controlling MythTV with a keyboard. An important note here is that I'm only concerned with "playback" controls, not with controlling operating system menus or other applications. Here are some helpful links for that.
  • The MythTV wiki Keybindings page lists keyboard keys associated with various operations (e.g., "P" for pause/resume playback). Keep this handy as a reference.
  • "HOWTO: Get MCE USB remote working in Ubuntu without using LIRC for MythTV or Kodi (xbmc)" is a blog post with detailed, step-by-step instructions. Use this as your main guide. I will say that I deviated a bit here and there. In particular, the author has you generate the default button mapping and save it directly its final destination. This is the line

    sudo ir-keytable --read --device=/dev/input/event10 > /etc/rc_keymaps/myrc6_mce

    in his post. I found it much easier to write the file to the desktop, edit it there, experiment until I got it right, and only then move it to /etc/rc_keymaps. (The move requires superuser rights; editing on the desktop does not.)
  • "MythTV: Use All Buttons of Your Remote Control - Without LIRC" is another handy post on the same subject. In particular, it has a table at the end of all possible key codes, which you may find useful as a reference (to tell, for instance, that the escape key is KEY_ESC rather than KEY_ESCAPE).

My Remapping


There was some trial-and-error getting to a mapping I liked, but ultimately I was successful. The "HOWTO" blog post identifies an issue with key codes greater than 255 (those with three digit hexadecimal codes). Apparently X11 does not like them. I found, however, that some of the two digit key codes did not work as specified, either, and had to be remapped to other two digit codes. My remote is an RC6 type (the first of the two black ones shown here -- although I'm in the US, not the UK or AU). Reproduced below are just the key mappings I changed in the "myrc6_mce" file.

scancode 0x800f0400 = KEY_0 # was KEY_NUMERIC_0 (0x200)
scancode 0x800f0401 = KEY_1 # was KEY_NUMERIC_1 (0x201)
scancode 0x800f0402 = KEY_2 # was KEY_NUMERIC_2 (0x202)
scancode 0x800f0403 = KEY_3 # was KEY_NUMERIC_3 (0x203)
scancode 0x800f0404 = KEY_4 # was KEY_NUMERIC_4 (0x204)
scancode 0x800f0405 = KEY_5 # was KEY_NUMERIC_5 (0x205)
scancode 0x800f0406 = KEY_6 # was KEY_NUMERIC_6 (0x206)
scancode 0x800f0407 = KEY_7 # was KEY_NUMERIC_7 (0x207)
scancode 0x800f0408 = KEY_8 # was KEY_NUMERIC_8 (0x208)
scancode 0x800f0409 = KEY_9 # was KEY_NUMERIC_9 (0x209)
scancode 0x800f040a = KEY_BACKSPACE # was KEY_DELETE (0x6f)
scancode 0x800f040d = KEY_M # was KEY_MEDIA (0xe2)
scancode 0x800f040e = KEY_F9 # was KEY_MUTE (0x71)
scancode 0x800f040f = KEY_I # was KEY_INFO (0x166)
scancode 0x800f0410 = KEY_F11 # was KEY_VOLUMEUP (0x73)
scancode 0x800f0411 = KEY_F10 # was KEY_VOLUMEDOWN (0x72)
scancode 0x800f0412 = KEY_UP # was KEY_CHANNELUP (0x192)
scancode 0x800f0413 = KEY_DOWN # was KEY_CHANNELDOWN (0x193)
scancode 0x800f0414 = KEY_RIGHT # was KEY_FASTFORWARD (0xd0)
scancode 0x800f0415 = KEY_LEFT # was KEY_REWIND (0xa8)
scancode 0x800f0416 = KEY_P # was KEY_PLAY (0xcf)
scancode 0x800f0418 = KEY_P # was KEY_PAUSE (0x77)
scancode 0x800f0419 = KEY_SPACE # was KEY_STOP (0x80)
scancode 0x800f041a = KEY_END # was KEY_NEXT (0x197)
scancode 0x800f041b = KEY_HOME # was KEY_PREVIOUS (0x19c)
scancode 0x800f0422 = KEY_ENTER # was KEY_OK (0x160)
scancode 0x800f0423 = KEY_ESC # was KEY_EXIT (0xae)
scancode 0x800f0426 = KEY_S # was KEY_EPG (0x16d)
scancode 0x800f046e = KEY_P # was KEY_PLAYPAUSE (0xa4)
scancode 0x800f0481 = KEY_P # was KEY_PLAYPAUSE (0xa4)

 

Stuttering


Update 12/28/16: The one issue I discovered with the remote was a tendency for button presses to be counted twice (occasionally, not always). This can be moderately annoying when running through menus or trying to pause/resume and terribly annoying when trying to fast forward or reverse.

Fortunately, the solution is simple, and hinges on the fact that the button presses are being treated as keyboard input. In Mythbuntu's main menu, navigate to Settings > Accessibility > Keyboard > Slow Keys. Select the check box for "Use slow keys" and set the "Acceptance delay" slider to something around 100 ms. The menu location may vary with other distributions, and you may need to tinker with the delay. Caveat: This will also affect typing on your keyboard. If you are a "hunt and peck" typist, the impact may not be too bad. If you are a touch typist, it can get really annoying, possibly more annoying than the remote button stutter.

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