Re: CTS Stuff...

[mdavis@crash.cts.com (Morgan Davis)]

In <9211131547.AA14279@pwtc.tc.pw.com> Brendan_Hoar@notes.pw.com writes:

>>ModemWorks uses the Extended Firmware
>>routines in the Apple IIGS's serial interface.
>>I've not heard of any
>>ModemWorks-based systems having any trouble with hardware flow control.

>Interesting.  How often is hardware flow control exercised with MW3.0?

This is transparent to ModemWorks because the IIGS serial port firmware
takes care of it.  The answer to your question is: as often as is
necessary. Since ModemWorks operates using the IIGS's default 2K
interrupt buffer, flow control would be asserted when it became
approximately 3/4 full.

>To cause it to occur would require a situation like this: ProLine's port rate 
>at a higher rate  than the caller has his/her port rate set to or higher than 
>the modem can move the data, & a Zmodem download to a system that can't 
>handle the speed.

That's one scenario.  And, yes, ModemWorks wants to run with the port
set to a high fixed speed (to get the most out of high speed modems with
data compression).  You can say the same thing for a caller who is
connected at 300bps and is getting a file with 1K XMODEM.  The protocol
isn't the factor.  Flow control would also come into play if the caller
was simply bulk-reading messages in the conference system non-stop (raw
ASCII stream).

The only time I've ever heard of ModemWorks/ProLine systems having
trouble with flow control is when they've not been using a properly
wired HWFC cable.

>Does ModemWork's Zmodem stream (keep sending until naks appear -
>regardless of lack of acks) or does it have a relatively  small window
>size?  If the latter, then flow control might almost never be 
>exercised...

When sending, it waits for ACKs if the receiving end requires them. 
When receiving, the buffer size varies depending on available memory,
but 12K is average.  Receiving 12K could easily overflow the IIGS's 2K
serial buffer and/or the modem's internal buffer, so flow control would
be asserted.

Again, we've had no problems except with systems that aren't set up
properly to handle high speed communications (e.g. anemic cables).  Most
Mac and PC users of ProLine have had success in uploading and
downloading with ZMODEM.  ProLine/ProLine and ProLine/UNIX systems have
not had trouble exchanging large packet transfers at high speed.  But
the majority of users experiencing difficulty are Apple II users using
ProTERM.