> On Sun, Oct 25, 1998, Vojtech Pavlik <vojtech-lists@twilight.ucw.cz> wrote:
>
> >Thus writing a winmodem driver should be possible even on normal Linux,
> >while softmodem might be much harder to implement, and might need a
> >fair amount of either RT or kludges in the kernel.
>
> There is at least two softmodems on MacOS (Apple's Geoport and SAT ISDN
> adapter) and they work.
Poor example. Both Windows and MacOS are highly amenable to kernel hacks.
Now if you wanted to say a software modem was available for NeXT, this
would be more interesting. (In fact, I believe NeXT included a software
modem from the beginning -- but it only ran at 300 baud. Not so
interesting after all.)
> The trick is to have some hardware support for DMA transfer of the
> synchronous data flow. This way, you can have the HW transfert quite
> large frames of samples and separately (asynchronously) process them
> (from a kernel thread or an interrupt handler). This will slow down the
> kernel but it looks possible. I think the SAT ISDN adapter also works
> without DMA support (polling or interrupt every 3 byte) but the machines
> slows down horribly.
Yes, that's part of it, but another part is sufficient RT support to
explain to the kernel that this process has priority, and, conversely,
explain when a slightly lossy modem is OK. Remember, you aren't just
getting the data here and back again, but doing a bit of math on it in the
meantime.
-- Kenneth Albanowski (kjahds@kjahds.com, CIS: 70705,126)
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