; This code has been modified as suggested by Charles Irvine so that it will
; function correctly with interrupts enabled.
; This is header code that can be used at the beginning of a type-3-environment
; program so that it will abort with an error message when not loaded to the
; correct address (such as when a user tries to run it under CP/M or Z30).
entry:
jr start0 ; Must use relative jump
defb 0 ; Filler
db 'Z3ENV',3 ; Type-3 environment
z3env: dw 0 ; Filled in by Z33
dw entry ; Intended load address
start0:
ld hl,0 ; Point to warmboot entry
ld a,(hl) ; Save the byte there
di ; Protect against interrupts
ld (hl),0c9h ; Replace warmboot with a return opcode
rst 0 ; Call address 0, pushing RETADDR onto stack
retaddr:
ld (hl),a ; Restore byte at 0
dec sp ; Get stack pointer to point
dec sp ; ..to the value of RETADDR
pop hl ; Get it into HL and restore stack
ei ; We can allow interrupts again
ld de,retaddr ; This is where we should be
xor a ; Clear carry flag
push hl ; Save address again
sbc hl,de ; Subtract -- we should have 0 now
pop hl ; Restore value of RETADDR
jr z,start ; If addresses matched, begin real code
ld de,notz33msg-retaddr ; Offset to message
add hl,de
ex de,hl ; Switch pointer to message into DE
ld c,9
jp 0005h ; Return via BDOS print string function
notz33msg:
defb 'Not Z33+$' ; Abort message if not Z33-compatible
