www.ppclinux.co.uk will still work for another year
ref: http://www.ppclinux.co.uk/wiki/maclin/OpenFirmware
OpenFirmware
Fundamentals of Open Firmware, Part I: The User Interfacehttp://developer.apple.com/technotes/tn/tn1061.html
Fundamentals of Open Firmware, Part II: The Device Tree
http://developer.apple.com/technotes/tn/tn1062.html
IEEE 1275 Open Firmware Home Page
http://playground.sun.com/1275/home.html
A podcast about openfirmware by Klaatu: The open firemware part starts at about 35mins.
http://www.thebadapples.info/audiophile/badAppleLinux_3x12.ogg
The Blog post with the show notes are Dated Dec 8th 2008 the rss link is below.
http://www.binrev.com/forums/index.php?autocom=blog&blogid=5&showentry=118
Other open firmware stuff...