Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!ncar!husc6!bunny!cayman!brad
From: brad@cayman.COM (Brad Parker)
Newsgroups: comp.protocols.appletalk
Subject: Re: What is EtherTalk speed?
Message-ID: <1731@cayman.COM>
Date: 14 Dec 88 13:41:06 GMT
References: <6047@hoptoad.uucp>
Organization: Cayman Systems Inc., Cambridge Ma
Lines: 25

From article <6047@hoptoad.uucp>, by tim@hoptoad.uucp (Tim Maroney):
> A non-dedicated 8MHz 68000 cannot keep up with an Ethernet, period.

10 megabits per seconds / 8 = 1.2 megabytes per second.
Reading words gives 600,000 word reads per second. (assume we have hardware
which will read 16 bits into a register from the wire)

8Mhz cpu give 125ns per cycle; 

move.w An@,An@+ is 12 cycles (2 reads, 1 write),  12 x 125ns = 1.5 usecs/word
Which means I can do 666,667 word copies per second. 

Doesn't this mean I could hand copy the bytes off the wire and still keep
up? (assume the loop is unwound)

Or did I miss something? I often do my math wrong, but 

(assume that the sender will send small bursts
of "packet trains" which will give me some time to process the bytes
in between "trains".)

-brad
-- 

Brad Parker
Cayman Systems, Inc.		Cambridge, Ma.			brad@cayman.com