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Old 12-03-2003, 12:48 PM   #1
Wim_Woittiez
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DMA underrun detected


Hi all,

Can anyone tell me what it means if an old 8-bit ISA Ethernet adapter (Racal Interlan NI5210, using ni52 kernel module) often gives "DMA underrun detected" messages, but continues to work nonetheless? What does the message really mean? I couldn't come up with an answer on Google... Speed is about 90 KB/s, which isn't really 10Mbit/s, is it?

Thanks,

Wim
 
Old 12-03-2003, 05:08 PM   #2
jailbait
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"What does the message really mean?"

I think that it means that the ISA Ethernet is so slow that the DMA unit is timing out waiting for data that does not arrive soon enough. Since the data does arrive eventually your CPU is simply wasting time recovering from non existant errors.

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Old 12-04-2003, 02:13 AM   #3
Wim_Woittiez
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Thanks for the info, Steve.

Do you know if there's any way I can increase some timeout, or have larger blocks DMA'd less often or something?

Do you suppose the 90KB/s speed is due to the errors, or would a 10Mbit card really be that slow?

Wim
 
Old 12-04-2003, 09:44 AM   #4
jailbait
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"Do you know if there's any way I can increase some timeout, or have larger blocks DMA'd less often or something?"

There is a way to turn off dma for a particular device but I don't remember what it is. People use it sometimes when they have buggy IDE controllers that don't respond to DMA correctly. Search the forum for hard drive problems that are solved by turning DMA off and you can find out how to turn DMA off for a particular device.

"Do you suppose the 90KB/s speed is due to the errors, or would a 10Mbit card really be that slow?"

The speed might be limited by something other than the card. It could be line speed. It could be the speed of whatever is at the other end of the line. And yes it could be that the hardware is fooling around a lot recovering from non existant errors.


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