2010-05-29, 08:05 AM
Oh yes - this:
I'm pretty sure this is setting HL' to the required value for BASIC before exiting. The Basic interpreter (and in particular the Interrupt service routine) assume that IY is pointed at the system variables and HL' is set to a specific value. I assume this one. Otherwise the spectrum can crash hard when dropping to BASIC from machine code.
Code:
LD HL, $2758 ; ??
EXX
RETI'm pretty sure this is setting HL' to the required value for BASIC before exiting. The Basic interpreter (and in particular the Interrupt service routine) assume that IY is pointed at the system variables and HL' is set to a specific value. I assume this one. Otherwise the spectrum can crash hard when dropping to BASIC from machine code.