Advice sought on implementing a new homebrew IR receiver

[Martyn W. <ma...@we...>]

Hi All,

I have been using LIRC on and off for quite a few years now and I'd just 
like to say that's for such a useful tool.

A while back I integrated a simple "homebrew" IR receiver and 
transmitter on a MythTV box that both my partner and I have become 
rather attached to. One thing I have noticed is that, I assume due to 
the method used to control the timing for the pulses, video playback 
stutters a little when the remote is used. I doesn't happen when I use a 
wireless keyboard...

This got me to thinking about implementing a microcontroller based 
receiver/transmitter to resolve the issue. I know about the UIRT hex 
files and schematics that can be found on the internet, however I 
haven't had much luck creating a reliable conf file using the hex files 
I can find for the UIRT and I haven't been able to track down the code. 
I'm also aware that I can probably buy something to do exactly what I 
want, but wheres the challenge in that?!

So I started to play. :-)

I currently have a PIC based circuit, connected to a serial port and a 
IR receiver. Looking at the LIRC website I noticed the description of 
the "LIRC_MODE_MODE2" protocol which I believe is used by lirc_serial. 
After a few hours playing around I have so far managed to get some 
verbose serial output which currently tracks the state of the IR signal 
to 0.1ms.

I realize this as accurate as the 1us provided by dev_serial, but I 
think I might be able to get there with a bit more hacking. My aim 
currently is to be able to provide serial output as provided by the 
above mentioned mode and use a modified/simplified version of whatever 
uses the dev_serial kernel module. This will offload the tight timing 
requirements to the PIC, which I hope will stop the stuttering.

This raises a few questions:

1) Am I re-implementing something that's already done and I've just missed?
2) Is this a reasonable approach or can you suggest a better one?
3) Is 1us accuracy a requirement or is some of this accuracy thrown away 
during signal detection (i.e. could I get away with being less accurate?)

If I can get something working I'm planning to upload schematics, code, 
hex files and a description to either my website and/or I'd be happy for 
it to be added to the LIRC website/project. The PIC code is being 
written in C at this stage and compiled using SDCC. Yes, the code will 
be GPLed. I'd happily place the schematics and hex files under a 
suitable open source license as well.

Martyn