difference btw splnet & splimp

[terryl at tekcrl.UUCP]

>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 VAX750/4.2BSD.

     splnet() and splimp() set the processor priority to different values,
and looking at the asm.sed, it looks like splnet() is between a spl1() and
spl4(), and splimp is between a spl5 and a spl6(), approx. Note I say approx.
`cause the VAX has 32(or is it 16?My reference books are all at work...)
different processor priority levels, and I'm trying to relate them to the
8 levels on a PDP.