How to Force UDMA100 Mode on Boot?

jason jason at
Tue Aug 16 00:28:46 GMT 2005

Mark Kane wrote:

> 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
Sounds like a cable issue, but could it be a buggy bios?  How about some 
information since I did not see your previous postings.

 > dmesg|grep DMA
atapci1: <nVidia nForce2 UDMA133 controller> port 
0xf000-0xf00f,0x376,0x170-0x177,0x3f6,0x1f0-0x1f7 at device 9.0 on pci0
ad0: 38172MB <MAXTOR 6L040J2/A93.0500> [77557/16/63] at ata0-master UDMA133

Also if I don't have a cd in the drive I get "acd0: CDRW <LITE-ON 
LTR-40125S/ZS0K> at ata1-master PIO4" for acd0.  If there is a disc in 
the drive it is set to UDMA66 at boot up.   Or first use  if it was not 
in at boot.

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