SP points to last-1 instead of last push

[Stokpan]

initial SP = 0000
run:

MVI A,F0H
INR A
PUSH PSW
HLT

SP = FFFD, it should be FFFE instead.

SP isn't pointing to the address containing the last PUSHed byte but rather the next available one. This is an error, according to Intel's specification (see 3-44, 3-45) it should be pointing to the address of the last one.

[FanisDeligiannis]

Nice catch! In order to adhere to that, I'm probably going to start the SP at address FFFE. It could still start at FFFF, but since every PUSH is pushing 16 bits, I'd like to keep those aligned nicely in the memory.

That way:

If SP=FFFE, the stack is empty
SP will always pointsto the last added data.
If SP > FFFE, you've popped an empty stack (which will, in the future, notify you and give you a warning).

Does that sound okay?

[Stokpan]

Sounds perfect, and FFFE is the starting address of some old, respected but outdated simulators.

[FanisDeligiannis]

Fixed as of edc7bc0.
Thank you!