How to Force UDMA100 Mode on Boot?

[Mark Kane]

Hi everyone. I've had a thread going here on the lists about DMA 
problems in 133 mode. In a nutshell, some drives give DMA_WRITE and 
DMA_READ errors when in 133 mode with certain configurations, however 
don't have any problems in 100 or 66 mode. After looking in to many 
solutions I think I'm just going to run it at 100, since from my 
research the benefit isn't that noticeable.

I know about atacontrol to set it manually, but I'd like to set UDMA100 
mode automatically on boot since I have 5 hard drives. I also know the 
sysctl hw.ata.ata_dma, but that doesn't say anything about using 100 vs 133.

Thanks in advance.

-Mark