DataTransfer.asm (Polling)

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 #600h, 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
start1: JNR dev1, start1
START dev1
start2: JNR dev2, start2
START dev2
start3: JNR dev3, start3
START dev3
routine0: JNR dev0, routine1                ; [POLLING] Copies data from each device until the related device counter hits zero
ADDB #0h, R0                                ; Dual check: prevents overflow (data might be transferred more than 100 times)
JZ check
INL dev0, (R4)+                             ; Updates the memory location with each following operation
SUBB #1h, R0                                ; Updates the counter
JMP check                                   ; Checks all counters
routine1: JNR dev1, routine2
ADDB #0h, R1
JZ check
INL dev1, (R4)+
SUBB #1h, R1
JMP check
routine2: JNR dev2, routine3
ADDB #0h, R2
JZ check
INL dev2, (R4)+
SUBB #1h, R2
JMP check
routine3: JNR dev3, routine0
ADDB #0h, R3
JZ check
INL dev3, (R4)+
SUBB #1h, R3
check: ADDB #0h, R0                         ; Adds 0 to each register to check if they are all empty
JNZ routine0                                ; Keeps skipping routines until data transfers are over
ADDB #0h, R1
JNZ routine1
ADDB #0h, R2
JNZ routine2
ADDB #0h, R3
JNZ routine3
exit: 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