Part 3 of my PS3-on-Linux programming series just got posted. This one focuses on communication between the PPU and the SPU. You can see it here:
Part #2 and Part #3 were originally one article, so it probably makes the most sense if they are read together.
Part #2 is here: http://www-128.ibm.com/developerworks/power/library/pa-linuxps3-2/
Part #1 is here: http://www-128.ibm.com/developerworks/power/library/pa-linuxps3-1/
There is one more assembly-language article to go, and then the series will move up to C/C++.