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  LC3 Car

LC3-Self-Driving-Car

Wrote the LC3 program for a self-driving robotic car that would follow a single black line on a given track. We decided to implement the control program for the robot car using the finite-state machine methodology and creating different states with different outputs at different points in the robots movement to stay on the line.

.orig x3000

DRIVE_STATE ;; The car is completely on the track

AND R0, R0, #0        ; R0 <- 0 (which is 0000 binary)
AND R2, R2, #0        ; Clear R2
AND R1, R1, #0        ; Clear R1

                       ; Use indirect addressing mode to write to WDCR (at address 0x4010)
sti R0, WDCR_ADDR      ; Drive forward (all four motors OFF)

ldi R1, LSDR_ADDR      ; Use indirect load to read LSDR (at address 0x4000)

add R2, R1, #-3        ; Is it equal to 3 (equals 11 binary)?
brz DRIVE_STATE        ; If yes, then stay in DRIVE state
                           ;If not fall back to reverse state

and R2, R2, #0        ; Clear R2
and R1, R1, #0        ; Clear R1
ldi R1, LSDR_ADDR      ; Use indirect load to read LSDR (at address 0x4000)
add R2, R1, #-1        ; Is it equal to 1 (equals 01 binary)?
brz TURN_LEFT        ; If yes, then go to turn right state

and R2, R2, #0        ; Clear R2
and R1, R1, #0        ; Clear R1
ldi R1, LSDR_ADDR      ; Use indirect load to read LSDR (at address 0x4000)
add R2, R1, #-2        ; Is it equal to 2 (equals 10 binary)?
brz TURN_LEFT        ; If yes, then go to turn left state

REVERSE_STATE ;; The car is at least partially off the track

and R0, R0, #0        ; Clear R0
and R2, R2, #0        ; Clear R2
and R1, R1, #0        ; Clear R1
add R0, R0, #15       ; R0 <- 15  (which is 1111 binary)

                       ; Use indirect addressing mode to write to WDCR
sti R0, WDCR_ADDR      ; Reverse (all four motors in REVERSE)

ldi R1, LSDR_ADDR      ; Use indirect load to view value at 0x4000 

and R2, R2, #0        ; Clear R2
and R1, R1, #0        ; Clear R1
ldi R1, LSDR_ADDR      ; Use indirect load to read LSDR (at address 0x4000)
add R2, R1, #-1        ; Is it equal to 1 (equals 01 binary)?
brz TURN_LEFT        ; If yes, then go to turn right state

and R2, R2, #0        ; Clear R2
and R1, R1, #0        ; Clear R1
ldi R1, LSDR_ADDR      ; Use indirect load to read LSDR (at address 0x4000)
add R2, R1, #-2        ; Is it equal to 2 (equals 10 binary)?
brz TURN_LEFT        ; If yes, then go to turn left state

add R2, R1, #-3        ; Is it equal to 3 (equals 11 binary)?
brz DRIVE_STATE        ; If yes, then move back to DRIVE state      

brnzp REVERSE_STATE       ; Stay within the REVERSE state

TURN_LEFT ;; Car is left of track

    and R0, R0, #0        ; Clear R0
and R2, R2, #0        ; Clear R2
and R1, R1, #0        ; Clear R1

add R0, R0, #10       ; R0 <- 10  (which is 1010 binary)

                       ; Use indirect addressing mode to write to WDCR
sti R0, WDCR_ADDR      ; Turn Left (left wheels powered back right wheels powered forward)

ldi R1, LSDR_ADDR      ; Use indirect load to view value at 0x4000 

add R2, R1, #-3        ; Is it equal to 3 (equals 11 binary)?
brz DRIVE_STATE        ; If yes, then move back to DRIVE state  

add R2, R1, #-1        ; Is it equal to 1 (equals 01 binary)?
brz TURN_RIGHT          ; If yes, then go to TURN_RIGHT STATE   

brnzp TURN_LEFT       ; Stay within the TURN_LEFT state

TURN_RIGHT ;; Car is right of track

    and R0, R0, #0        ; Clear R0
and R2, R2, #0        ; Clear R2
and R1, R1, #0        ; Clear R1
add R0, R0, #5        ; R0 <- 5  (which is 0101 binary)

                       ; Use indirect addressing mode to write to WDCR
sti R0, WDCR_ADDR      ; Turn Right(right wheels powered back left wheels powered forward)

ldi R1, LSDR_ADDR      ; Use indirect load to view value at 0x4000 

add R2, R1, #-3        ; Is it equal to 3 (equals 11 binary)?
brz DRIVE_STATE        ; If yes, then move back to DRIVE state  

add R2, R1, #-2        ; Is it equal to 2 (equals 10 binary)?
brz TURN_LEFT          ; If yes, then go to TURN_LEFT STATE

brnzp TURN_RIGHT       ; Stay within TURN-RIGHT

LSDR_ADDR ;; Helper variable which contains the memory mapped address used to read the sensors

.fill x4000

WDCR_ADDR ;; Another helper variable. Used to access the wheel/motor controls

.fill x4010
.end

Built With

• form-assembly
• lc3