gistfile1.asm

;There was an interrupt by the timer!

;;;VM

PUSH PC  ; is current PC
PUSH 0   ; timer has no second argument
PUSH 1   ; timer interrupt is 1

; vm does the lookup job
; jumps to the handler

;;;HANDLER
:interruptHandler
; interrupt is in [SP]
; arg is in [SP+1]
; PC is in [SP+2]

; Turn off interrupts
XOR CR, 1

; Save all registers
PUSH A
PUSH B
PUSH C
PUSH X
PUSH Y
PUSH I
PUSH J

; Get new stack address somehow

; Set new stack address
SET SP, newStack

; We now are on the new stack of another task,
; that also pushed their registers
POP J
POP I
POP Y
POP X
POP C
POP B
POP A

; We restores the program

; Remove the interrupt info without clobbering
SUB SP,2

; Turn on interrupts
XOR CR, 1

; notch-code this is SET PC,POP
POP PC

; We now run not in the VM but the actual code again