Re: dma hardware underrun

[Alan Cox]

> My debugging result shows the underrun goes away if I put 2 printf's in the 
> harddisk ISR. The printf is at milli-seconds whereas the duration of the 
> original ISR is at lower magnitude. In addition, I find a SATA-PCI harddisk 
> does not have the underrun problem. IDE-PCI device gets the trouble.

Is the SATA controller on the motherboard and the PATA one on the PCI
bus ?

> So, do you have any idea about where the root cause can be hiding? Or what 
> do you think of adding printf's in ISR? (performance? incurring other 
> problems by disabling interrupt too long?

On a standard PCI bus an IDE DMA disk can saturate the bus. That may be
your underlying problem ?
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