difference btw splnet & splimp

[Ron Natalie]

>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.