difference btw splnet & splimp

[Chris Torek]

> What is the difference between "splnet" and "splimp"?   

splimp is about halfway between spl5 and spl6, and blocks IMP
interrupts (and thus redirects et al., which is why you find it in
routing code).  splnet is between spl1 and spl4 (there is no spl2 or
spl3) and blocks only software interrupts (net input is generally
queued first, then processed via software interrupts).

> 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. 

There isn't any reference to register 0x16; both splimp and splnet read
register 18 (IPL, the current interrupt priority level) and then stick
a new value in it.  "mtpr $0x16,$18" means put 16 in IPL, not put 18 in
register 0x16....
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251)
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