Language-specific CPUs

[Jim Battle]

Chuck Guzis wrote:
...
> Well, the Burroughs B5000 was purportedly an Algol machine; there 
> have been CPU designs to eat UCSD Pascal bytecodes and Java bytecodes 
> and there have been various LISP machines.  But none, AFAIK, to 
> actually lexically parse program text input in hardware.  I suppose 
> 1401 Autocoder might be in that league, if you consider Autocoder to 
> be a "language".

I remember reading a computer architecture book back in the early/mid 80s, I think it was 
by Stone.  The subject was "advanced" architectures.  One section described on attempt to 
build a timesharing system for running a BASIC-like subset, and everything was hardwired 
-- parsing was via gate-level state machines, not microcode.  The intended audience was 
college-level computer classes.  As I recall, they gave up after getting a simplified 
version going.

> I believe that Intel actively discouraged programming in assembly on 
> the i860, given the mind-bending instruction scheduling issues.

The exposed pipe hazards weren't the real issue.  The problem was exceptions.  In certain 
states, there was no simple way to restore the pipe, so the interrupt handler had to 
detect when one of those bad cases existed, then nudge the state along one instruction at 
a time until it go to a point where it could restore the state fully and really return 
from the interrupt.

I never saw it, but I heard the return from interrupt code was a couple thousand lines of 
tricky assembly.