Hi,
You need to send correct commands to firmware. Plz check http://www.coreboot.org/AMD_IMC for a summary. Then I would say the interface did not change much, so looking into some agesa code will tell you how to program stuff there (there are files like imcEnv.c iirc) I need run now, plz ask if you want more info.
Also, you will need to enable the IMC and load firmware. The agesa has some straps override for this. You just need to place the imc.bin in cbfs on right offset.
Thanks Rudolf