[Gennoise]

Introduction

I was just looking through some of my Dune's system files, just minding my own business when I came across this proc entry: /proc/ir/button.
It looked interesting, but quick inspection using the cat program revealed that it doesn't return any text. I didn't think much of it at first, but then I tried to write to it using Echo commands. Curiously the echo commands did not throw any errors. So I tried to echo IR NEC codes (in reverse*) to the file to see what happens. Eureka! It was just as if I was pressing the buttons on my remote control.

How to

First you need to enable Telnet or SSH access. Having a working knowledge of linux filesystems and shell commands is helpful but not strictly necessary. I'm a total idiot when it comes down to linux myself so don't let it hold you back.

(If you need help setting up access, I've already made a little tutorial in my other thread here.)

The command that you need to use to emulate button presses is:

echo [ReverseNecCode] > /proc/ir/button

where [ReverseNecCode] is one of the codes listed on this page, in reverse*.

*: Why in reverse? I'm glad you asked!
The CPU uses the little-endian byte order to store bytes into memory. This means that in any given numeric value, the 'smallest' byte (least significant byte) is the first one in the array, and the 'largest' byte (most significant byte) is the last.


Example
To emulate the MUTE button, first we need to get the NEC code from the list. After a quick look through the document, we found the following value: 00 BF 46 B9
Now we need to reverse the bytes. In our example, 'B9' is the least significant byte, so that one comes first in the sequence. 00 BF 46 B9 becomes B9 46 BF 00.

Add it all together, and you have the final command:

echo B946BF00 > /proc/ir/button

Et voilà. That's all there is to it.

[ScottJ97]

Originally Posted by Gennoise For some reason, we can't send it just like that (if you know why, please post it below). For some reason, we need to reverse the bytes. 00 BF 46 B9 becomes B9 46 BF 00. Now it's ready to use.

Probably has to do with the endianness of the CPU, which is little-endian on the Dune.

Thanks for the writeup, although for most uses, the IP control is the more robust way to automate the Dune.

[Gennoise]

One particular thing I find it useful for is that you can write little shell scripts to automate button presses in a more organised way. I've not tried it (yet), but that would be alot harder to do client-side using batch files or vbscript. And you can access them on other computers without doing something funky like synchronising bookmarks.

But thanks for the tip. Seems like I have a bunch of reading to do on the endianness part. I don't know much about low-level stuff like that but I do want to get a better understanding of how it all comes together.