DataTransfer.asm (Busy Waiting)

org 400h
dev0 EQU 0h                                 ; Declares all devices as constants for future use
dev1 EQU 4h
dev2 EQU 8h
dev3 EQU 12h
code
MOVB #64h, R0                               ; Initializes a counter per device (each device contains 100 data to be copied)
MOVB #64h, R1
MOVB #64h, R2
MOVB #64h, R3
MOVL #500h, R4                              ; Stores the memory location to start copying data to (works as a memory counter)
JSR files                                   ; Jumps to the subroutine that copies data from devices
files: PUSH R0                              ; Saves the counters
PUSH R1
PUSH R2
PUSH R3
PUSH R4
start0: JNR dev0, start0                    ; [BUSY WAITING] Starts each device when it's ready
START dev0
routine0: JNR dev0, routine0                ; [BUSY WAITING] Copies data from each device until the related device counter hits zero
INL dev0, (R4)+                             ; Updates the memory location with each following operation
SUBB #1h, R0                                ; Updates the counter
JNZ routine0                                ; Follows on with the next instruction when the counter hits zero
start1: JNR dev1, start1
START dev1
routine1: JNR dev1, routine1
INL dev1, (R4)+
SUBB #1h, R1
JNZ routine1
start2: JNR dev2, start2
START dev2
routine2: JNR dev2, routine2
INL dev2, (R4)+
SUBB #1h, R2
JNZ routine2
start3: JNR dev3, start3
START dev3
routine3: JNR dev3, routine3
INL dev3, (R4)+
SUBB #1h, R3
JNZ routine3
POP R4                                      ; Restores the registers used in the subroutine to their original state
POP R3
POP R2
POP R1
POP R0
RET                                         ; Returns from subroutine and continues program execution
halt
end