I need help to porting coreboot Asus M4a785m on Asus M5a78l-m lx3.

I'm trying to porting coreboot on the motherboard Asus M5a78l-m lx3 (rs780l/sb710). I cannot find documentation for the northbridge rs780l.

My configuration:  cpu - Athlon 2 x2 220 (K10), memory - 2 + 2 Gb DDR3, video - Asus GT520, sata segate hdd 500Gb, sata asus dvd-rw.

I have a positive result for the configuration with memory 2Gb and external video card Asus GT520. I can load Linux kernel 2.6.

But, i have two problems:

1. I cannot load coreboot with internal graphics card (hd 3000). Coreboot stops loading and to print on console "Calling option ROM…". May be the problems with gfx configuration?

2. I cannot run Linux with memory 4Gb. Coreboot is loading, SeaBios is loading too, but  Linux stop load on usb3-2 and ata1 setup. May be the problems with memory map?

Please, help me. I can provide all the necessary information from the log coreboot, SeaBios and Linux.