extremely slow operations on ATI SB600 AHCI controller

[chriz74x]

I have this Acer t671 desktop pc, it uses ATI SR600-SB600 chipset. In the bios I disabled the IDE mode and enabled AHCI, I have two sata disks plugged to the MB, one has Windows, on the other one I installed Mavericks.

I am using the latest Clover but I also tried with an older one (33xx something version).

The problem is the whole process of scanning entries, showing up and then start booting is EXTREMELY slow, I am talking about 5 / 10 minutes on USB and even slower on HDD.

I am booting legacy as this pc doesn't have EFI, I set "boot block I/O" in clover setup or the disks won't show up, without this option clover shows up earlier but then it won't find any disk.

Any clue? I don't have debug enabled.