On Aug 4, Douglas Beeson wrote:
> Upon looking in /var/log/messages, I discovered that the older version
> was autoprobing for all its configuration parameters and had decided to
> use ft_fdc_dma=2 on my system, not 0 as I had been using.
There is no autoprobing for DMA. Ftape just takes the value most
floppy controllers are using.
> When I went back to my original kernel (no built-in ftape) and modified
> the "insert" script to load the ftape module with ft_fdc_dma=2, the
> "overrun" problem went away.
>
> What is this mysterious DMA thing anyway?
DMA stands for Direct Memory Access. It allows the floppy controllor
to put the data it reads via the DMA channel into the main memory.
The driver has to program the channel first and tell it the memory
address. There are multiple DMA channels, so different devices can
write to the memory simultanously. Unfortunately, for non plug'n play
ISA devices there is no way to find out which channel corresponds to a
device. If the wrong channel is programmed, the floppy controller
can't deliver its data and report an overrun error.
Jochen
