On Sun, 13 Jul 1997, Bill Studenmund wrote:

> Is there some way we can squeze the splsoft*'s between spl1 and spl0?
> Maybe multiply all the hardware interrupt levels by 2 and add level 1
> between 2 (hardware int 1) and 0 (hardwware int level 0). I heard an
> off-hand comment somewhere that vaxen used to do something like this,
> but I'm not sure... ??

I don't think VAXen ever did this, but they did have 32 interrupt levels,
16 of which were reserved for software use (0-15) and 16 for hardware's
use (16-31).  Hardware devices never interrupted at the lower levels, but
the VAX did provide a way to request a software interupt at a specified
IPL;  it also enforced the rule that interrupts always increased IPL while
interrupt exits always decreased it.

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