On Wed, 3 Jan 1996 01:39:03 +0100 
 "Arne H. Juul" <arnej@pvv.unit.no> wrote:

 > But in NetBSD the current spl() structure is not strictly hierarchic;
 > splnet() can block just network interrupts, splbio() just disk interrupts,
 > spltty() just serial interrupts and so on.  [This is a simplified picture
 > of course, ignoring parallel ports etc...] At least this is my current
 > understanding of the NetBSD source code.  Of course many machines must
 > have the spl() routines in a hierarchy anyway, because of the hardware
 > construction.

Actually, this is problably machine-dependent.  For example, if you have 
an HP-IB controller at ipl3 and a SCSI controller at ipl5 on an hp300, 
blocking HP-IB "disk" interrupts does not block SCSI "disk" interrupts.  
However, some architecures may have interrupt "bitmasks" where each type 
of interrupt (network, disk, serial line) corresponds to a "bit" in the 
mask ... This is guesswork on my part.  I'm not about to say I 
completely understand how interrupts work on the i386, alpha, or pmax.

 > Now what about another (maybe stupid) idea:  Most boxes doesn't
 > necessarily run slip or ppp at all.  What about making splimp() not
 > block tty interrupts if slip/ppp is not configured?  This *might*
 > be a huge win on many machines for serial port reliability, which
 > would be nice for driving printers / terminals.  [Of course, you need
 > serial port reliability when using slip/ppp too!]

Which boxes won't run SLIP or PPP?  (Actually, do some ports change 
splimp() if PPP and SLIP are both not present?  I thought so...)

--------------------------------------------------------------------------
Jason R. Thorpe                                       thorpej@nas.nasa.gov
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