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From: ron@BRL (Ron Natalie)
Newsgroups: net.unix-wizards
Subject: Re:  difference btw splnet & splimp
Message-ID: <10367@brl-tgr.ARPA>
Date: Thu, 2-May-85 12:09:36 EDT
Article-I.D.: brl-tgr.10367
Posted: Thu May  2 12:09:36 1985
Date-Received: Sat, 4-May-85 05:33:46 EDT
Sender: news@brl-tgr.ARPA
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>What is the difference between "splnet" and "splimp"?   
>I had a look at machine instructions of them in /sys/machine/asm.sed, but
>I could not understand their roles completely becuase there is no description
>for register 0x16 in /sys/machine/mtpr.h. 
>What is the function of Reg.0x16?
>For the record, I am using VAX750/4.

Splnet is just a flag that locks the net queues.   Splimp turns off
the imp interface temporarily to lock the imp tables.  Splnet is
implemented by setting a very low but non-zero priority (spl1), since
there are no UNIBUS levels less than four, this does not stop any device
interrupts.  It's just a flag that can be tested for.  Splimp sets
priority five so that the hardware IMP interface won't interrupt
anymore.