Notes

__MAIN

; The following lines are similar to Lab-1 but use a defined address to make it easier.
; They just turn off all LEDs
LDR R10, =LED_BASE_ADR ; R10 is a permenant pointer to the base address for the LEDs, offset of 0x20 and 0x40 for the ports

MOV R3, #0xB0000000 ; Turn off three LEDs on port 1
STR R3, [r10, #0x20]
MOV R3, #0x0000007C
STR R3, [R10, #0x40] ; Turn off five LEDs on port 2

; This line is very important in your main program
; Initializes R11 to a 16-bit non-zero value and NOTHING else can write to R11 !!
MOV R11, #0xABCD ; Init the random number generator with a non-zero number
loop BL RandomNum

BL COUNTER
B loop

;
; Display the number in R3 onto the 8 LEDs
DISPLAY_NUM STMFD R13!,{R1, R2, R4, R5, R14}

EOR R3, #0xFFFFFFFF ; flip everything

MOV R4, R3
AND R4, R4, #0x1F ; extract last 5 bits
RBIT R4, R4 ; reverse
LSR R4, R4, #25 ; shift off all 0s so now it's only the 5 bits
STR R4, [R10, #0x40] ; store into pin 2-6

MOV R4, R3
AND R4, R4, #0x20 ; extract 6th bit
LSL R4, #26 ; move into MSB part

MOV R5, R3
AND R5, R5, #0xC0 ; extract bits 7 and 8
RBIT R5, R5 ; reverse
LSL R5, R5, #4 ; put them in MSB 4th and 5th

ADD R4, R5, R4 ; add bits 6 and 7 and 8
STR R4, [R10, #0x20] ;

LDMFD R13!,{R1, R2, R15}

;
; R11 holds a 16-bit random number via a pseudo-random sequence as per the Linear feedback shift register (Fibonacci) on WikiPedia
; R11 holds a non-zero 16-bit number. If a zero is fed in the pseudo-random sequence will stay stuck at 0
; Take as many bits of R11 as you need. If you take the lowest 4 bits then you get a number between 1 and 15.
; If you take bits 5..1 you'll get a number between 0 and 15 (assuming you right shift by 1 bit).
;
; R11 MUST be initialized to a non-zero 16-bit value at the start of the program OR ELSE!
; R11 can be read anywhere in the code but must only be written to by this subroutine
RandomNum STMFD R13!,{R1, R2, R3, R14}

AND R1, R11, #0x8000
AND R2, R11, #0x2000
LSL R2, #2
EOR R3, R1, R2
AND R1, R11, #0x1000
LSL R1, #3
EOR R3, R3, R1
AND R1, R11, #0x0400
LSL R1, #5
EOR R3, R3, R1 ; the new bit to go into the LSB is present
LSR R3, #15
LSL R11, #1
ORR R11, R11, R3

LDMFD R13!,{R1, R2, R3, R15}

;
; Delay 0.1ms (100us) * R0 times
; aim for better than 10% accuracy
; The formula to determine the number of loop cycles is equal to Clock speed x Delay time / (#clock cycles)
; where clock speed = 4MHz and if you use the BNE or other conditional branch command, the #clock cycles =
; 2 if you take the branch, and 1 if you don't.

DELAY STMFD R13!,{R2, R14}

TEQ R0, #0
BEQ exitDelay

MultiplierLoop
MOV R2, #0x85

Loop
SUBS R2, #1
BNE Loop

SUBS R0, #1
BNE MultiplierLoop

exitDelay LDMFD R13!,{R2, R15}


COUNTER STMFD R13!, {R0-R2, R14}

MOV R0, #1000
MOV R2, #256
MOV R3, #0

LoopCount
BL DISPLAY_NUM
BL DELAY
ADD R3, R3, #1
TEQ R2, R3
BEQ LoopCount

LDMFD R13!, {R0-R2, R15}