I had a terrible time trying to work out the finer points of the Z80 interrupt
handling with SDCC.
My tweaked crt0.s is below. I don't use the NMI so it's commented out. You can
also see that I use ex and exx and call _isr. And, I don't re-enable interrupts
in the immediate isr code.
Memory on my Z80 board is one 32K flash ROM and one 32K static RAM, so you can
see how I set up the stack at 0x7FFF
;; Generic crt0.s for a Z80
;;
;; regenerate using "as-z80 -o crt0.o crt0.s"
;;
.module crt0
.globl _main
.globl _isr
;; .globl _nmi_isr
.area _HEADER (ABS)
;; Reset vector
.org 0
jp init
.org 0x08
reti
.org 0x10
reti
.org 0x18
reti
.org 0x20
reti
.org 0x28
reti
.org 0x30
reti
.org 0x38
di
; push af
; push hl
ex af, af'
exx
call _isr
exx
ex af, af'
; pop hl
; pop af
; disable enabling interrupts so that we can handle rtc interrupt better
; ei
reti
; commented out the NMI for now
.org 0x66
; push af
; call _nmi_isr
; pop af
retn
.org 0x100
init:
;; Stack at the top of memory.
ld sp,#0xffff
;; enable interrupts
im 1
ei
;; Initialise global variables
call _main
jp _exit
;; Ordering of segments for the linker.
.area _HOME
.area _CODE
.area _GSINIT
.area _GSFINAL
.area _DATA
.area _BSS
.area _HEAP
.area _CODE
__clock::
ld a,#2
rst 0x08
ret
_exit::
;; Exit - special code to the emulator
ld a,#0
rst 0x08
1$:
halt
jr 1$
.area _GSINIT
;;gsinit::
;;
;; .area _GSFINAL
;; ret
My interrupt comes from an RTC, so it's not extremely time critical thus the
ISR sets a flag which is then tested in main.
//================================================================================
// the maskable interrupt service routine is here
// see crt0.s for the rest of ISR handler
//================================================================================
#pragma save
#pragma nooverlay
void isr (void)
{
interrupted=1;
}
#pragma restore
Finally, since "interrupted" is volatile, it must be defined as such:
static volatile unsigned char interrupted;
Excuse my older pragma directives. I haven't updated this code to the newer
standard (though I am working through that).
Hope this helps.
Mike------------------------------------------------------------------------------
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