; This patch turns the MAC assembler into a partial ZCPR3 utility. When it
; runs, it automatically sets the program error flag in the message buffer
; to show whether or not MAC encountered any errors in assembly. The flow
; control command IF ERROR can then be used to control command flow.
;
; (NOTE: int the original distribution of SYSFCP.ASM there is an error that
; reverses the sensing of the program error flag. You must either correct
; that error or use the reverse test IF ~ERROR. The com file IF12.COM has
; the correct sensing.)
;
; Jay Sage, sysop, Newton Centre (Massachusetts) Z-Node
; July 8, 1985
patch equ 2b70h ;place to intercept MAC
conout equ 2ac9h ;address called at patch originally
newcode equ 2e70h ;place to put new flag setting code
macstart equ 0128h ;where MAC code really begins
signon equ 2cd3h ;loacation of signon message
; First we patch the beginning of the program to make it look like a ZCPR3
; utility program. It can then be installed using Z3INS to know the address
; of the environment descriptor. From that it can find the program error
; flag in the message buffer and patch it into the flag-setting code at
; at newcode. The code patched in at 100h overwrites the copyright message.
org 100h
jmp start
db 'Z3ENV'
db 1 ;external environment
z3env: dw 0de00h ;this address set by Z3INS
start: lhld z3env ;get env address into hl
lxi d,22h ;offset to message buffer address
dad d ;hl points to address of message buf
mov a,m ;read address out
inx h
mov h,m
mov l,a ;hl now points to start of message buf
lxi d,6 ;offset to program error flag
dad d ;now hl points to program error flag
mvi m,0 ;set it to no error status
shld store+1 ;patch flag-setting code below
jmp macstart ;continue with original code
; We intercept MAC execution at address PATCH. The original instruction here
; was CALL CONOUT. We replace it with a call to our new code, which in turn
; will jump to conout.
; At NEWCODE, which appears to be some extra space at the end of MAC, we
; place the code to set the error flag.
org newcode
push psw ;make sure we don't mess anything up
mvi a,0ffh ;value to set the flag
store: sta 0 ;address will be filled in by code
pop psw ;restore registers
jmp conout ;go to where MAC went originally
; Just for the hell of it, patch the signon message to show it is a ZCPR3
; version. Twenty characters max, not including final mandatory carriage
; return.
