🚀 go-pugleaf

> I don't use a C compiler. But I'm curious about how they handle subroutines
> calls. Do they use a separate stack for parameters and local storage? Is
> the Stack Register used for subroutine calls? Are nesting of subroutines
> calls and used of hardware DO loop used sparingly?

For both g56k and g96k, we manage a software stack in addition to the
hardware stack. When a function is called, the jsr instruction is
used.  The callee will then transfer the saved program counter off of
the hardware stack and onto the software stack, thus freeing up that
stack location. At the end of the function, the saved program counter
is restored to the hardware stack, and the rts instruction is used.
Leaf functions, which make no function calls themselves, don't bother;
they just leave the program counter on the hardware stack. 

We, by default, issue up to three nested do loops. We won't issue a 
do loop if the loop body contains a function call for obvious reasons.
The number three was picked so that most of the do loop benefit would be 
derived in most cases, with plenty of room for interrupt nesting. The
user can change this limit. The user can also turn off leaf function 
optimizations.

	Jeff Enderwick
	jeff@dsp.sps.mot.com