From: davidsen@ariel.crd.GE.COM (william E Davidsen) Subject: Re: Do I need intelligent serial I/O?? Date: Wed, 14 Apr 1993 13:50:37 GMT
In article <1993Apr13.203450.7748@dcs.warwick.ac.uk>, robin@dcs.warwick.ac.uk (Rob Rainton) writes:
| I'm thinking of getting a powerful PC and running Linux and X windows
| on it. I also hope to get a fast (V32bis with V42bis compression)
| modem to connect to an internet service in the UK.
Sounds good so far.
| How much CPU time will be consumed by blasting the claimed max data
| rate of 57,600 baud (14,400 x 4 times compression - I know this won't
| happen most of the time, but just assume best case) down a standard PC
| serial port?
I would get a card with a smart UART for starters, the 16550 part will
cut the interrupt rate by 5-8x, which should let you keep up with the
incoming. As far as burst rate goes, one of the users of my BBS uses a
2400 modem with V.42bis and serial line locked at 9600, and gets 670cps
on text transfers (avg for a 50k file). That's 2.8x compression average,
so I would believe that the burst would hit the 4x claimed at least once
in a while. Transferring compressed files will be essentially no
compression, of course.
|
| Will buying an intellegent serial I/O card with it's own processor
| help in this particular application? (I don't want my machine to be
| tied up by the serial I/O when ftping large sources)
I have my BBS on an old 386DX-16, about as slow as you can go, and
with two lines coming in at 19200 I see about 6% CPU use. WARNING: I am
not running Linux on that machine, I'm running commercial UNIX with the
FAS device driver. However, I would not expect more than that using
Linux and a reasonable 486, since the serial driver uses the 16550 if
present. Maybe someone can give you an exact figure, but I wouldn't
expect any problem with a single line.
|
| Also, is there any advantage over buying a modem card rather than use
| an external modem via a serial port?
No, buy the serial port and modem. Each can be used for other things,
you can use the modem with your next computer (might not be a PC) or
upgrade the modem without changing the box. I hear that ISDN is big in
Europe, you might be able to get one of those beautiful ISDN modems for
less than the pice of a car someday (64k bidirectional).
-- bill davidsen, GE Corp. R&D Center; Box 8; Schenectady NY 12345