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To: Michael Vernick <vernick@cs.sunysb.edu>
cc: freebsd-hackers@FreeBSD.org
Subject: Re: help with splbio, splnet, spl... 
In-reply-to: Your message of "Thu, 30 Mar 95 18:34:13 EST."
             <199503302334.SAA24705@cs.sunysb.edu> 
From: David Greenman <davidg@Root.COM>
Reply-To: davidg@Root.COM
Date: Thu, 30 Mar 1995 15:44:02 -0800
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>Can someone point me to some documentation that explains how the spl
>interrupts work?  For example, in the Scsi code (scsi_scsi_cmd in
>scsi_base.c) just before a command is sent to the adapter, a call is
>made to splbio().  Does this mask all I/O interrupts? Network interrupts
>too?  

   It prevents interrupts from devices that are "bio" type. This is basically
all disk controllers. Tty devices (such as serial ports) are blocked with
spltty(). Network interrupts are blocked with splimp(). splhigh() and
splclock() block all interrupts except "fast" interrupts. "fast" interrupts
are special and can be explained if necessary; they are currently only used in
the sio driver.

-DG