I have successfully been able to "listen in" to an early 90's vintage alarm system through modification of the Arduino software serial library to accept a non-standard baud rate and skip an interrupt bit. The interrupt bit appears after the 8 bits of data, but before the stop bit. By basically taking the software delay designed to skip the stop bit and multiplying by 2, I can ignore the 9th bit. I've also been able to pass the 9th bit on the output data, but so far it has not appeared useful.
My question... is there a way to do something similar with the pi, without having to use an arduino and interface? I read that the pl011 uart can possibly do 2 stop bits, but it appears that maybe that isn't readily available on the GPIO pins without some serious hacking? I've already read that by modifying one of the system clocks, the baud rate can be changed to something non standard. I can always fall back on the arduino "software serial" interface method, but it would be nice to be able to interface directly through the pi with a simple C program or perl script.
Thanks in advance.