This is on an amd64 4600 x2 w/ AMD690G northbridge and SB600 south bridge.

Some debuggins is turned on,  Reads work ok as far as I can tell.

ahcisata0 port 0: device present, speed: 1.5Gb/s
wd0 at atabus0 drive 0wdattach
ahcisata0 port 1: device present, speed: 1.5Gb/s
: <ST506>
wd0: drive supports 1-sector PIO transfers, chs addressing
wd0: 69632 KB, 1024 cyl, 8 head, 17 sec, 512 bytes/sect x 139264 sectors
wd0: atap_dmatiming_mimi=0, atap_dmatiming_recom=0
dk0 at wd0: wd0e
dk0: 488397105 blocks at 63, type: lfs
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd0(ahcisata0:0:0): using PIO mode 4, DMA mode 2, Ultra-DMA mode 6 
(Ultra/133) (
using DMA)
wd1 at atabus1 drive 0wdattach
: <ST3160023AS>
wd1: quirks 2<FORCE_LBA48>
wd1: drive supports 16-sector PIO transfers, LBA48 addressing
wd1: 149 GB, 310101 cyl, 16 head, 63 sec, 512 bytes/sect x 312581808 sectors
wd1: atap_dmatiming_mimi=120, atap_dmatiming_recom=120

skd