Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!sun-barr!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: Software-only network protocol standards
Message-ID: <119211@sun.Eng.Sun.COM>
Date: 2 Aug 89 22:27:33 GMT
References: <1789.AA1789@geo-works> <117428@sun.Eng.Sun.COM> <1993.AA1993@geo-works>
Sender: news@sun.Eng.Sun.COM
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 30

In article <1993.AA1993@geo-works> bryan@geo-works.UUCP (Bryan Ford) writes:
>I stand corrected.  Please clarify 'memory management':  You don't include
>memory protection, do you?  How could a pre-68020 provide memory protection
>unless it has some special protection hardware?  (Did it?)

Yes, most Sun products have custom MMU's that provide both page relocation
and protection. [not sure about the 386i or 3/80] The Sun-1's dual 68000 
design allowed it to fake instruction restart by keeping the state in the 
"other" CPU. The 68010 of course provided the required state and so the 
redundant CPU was removed. 

>So, you're saying that interrupts are too slow to do anything but busy-wait
>after the beginning of the packet has been detected?  Too bad.  I was
>hoping that some needy task could get some precious CPU between the bytes,
>but it looks like this was a hopeless hope.  :-)

Yes, given the design constraint of 200,000 baud. But from a systems standpoint
the if the packets are small, say 1K bytes, then and relatively infrequent
say 1 per second. Then the packet takes about .06 seconds to receive and
stuff into memory and that leaves you with 94% of the CPU to play around
with. If the packets were 10/sec on average then you get down to something
like 40% of the CPU left and that might suggest that you needed to invest
in some additional CPU horsepower (like a DMA based network interface). 
It is all a question of system design and allocating your resources to
the where they are most profitably used.

--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.
"A most excellent barbarian ... Genghis Kahn!"