Re: [NTLK] Connecting my Newton-Questions!

On 13.08.2008, at 01:27, James Wages wrote:

> On 8/13/08 1:37 AM, "Sonny Hung" <sonnyhung@gmail.com> wrote:
>> Yes you should be able to connect using Simon Bell's NCX
>
> If you're like me and want to use a serial cable, keep in mind you
> may get
> lockups when transferring several megabytes of data at once via NCX
> in OS X
> under Tiger. At least, I do. However, when I connect via serial
> (even at
> 57,600bps, via patch) with my SE/30 on the patched version of NCU, I
> never
> ever have any transmission failures.
>
> NCX is great for single packages or adding little things to the
> Newton (when
> using serial anyway).

Having had my head inside the serial communications code for the last
month, I think I know what is going on here. The MP2x00 uses a DMA (a
hardware approch to copy incoming data right into the RAM of the
machine without involving the CPU). Unfortunatley, there is a delay
from the time when the DMA is done to the reaction of the Newton OS
(the interrupt). During that time, additional data sent via the serial
port can in some cases cause a buffer overrun, triggering yet another
interrupt, which seems to create the data loss or even lockup.

The earlier models use software to shuffle data around and a slower
CPU, so they may have other issues, whcih I did not check.

There is a solution to this problem. "Slowdown" creates a side effect
which can be used to keep traffic down, and a similar thing could be
done on the Mac, but the true solution would be to write a serial port
driver (there are open source examples around for both OS's) which
interpretes the V.42/Block structure of Newton communication (easy!)
and adds pauses to data transmission at the end of every transmitted
block, giving the Newton enough time to react to the interrupt.
"slowdown" would be obsolete and the transfers on the Mac side should
be safer as well.

Now we need someone to write these drivers... .

Matthias

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