Using MPLAB PIC$32$MM Curiousity Board Pressing S$2$ at any point should toggle whether the LEDs are blinking. Pressing the switch the first time pauses blinking; pressing it again restarts$/$resumes blinking. When paused, one or both LEDs may be off, depending on the mode of operation described below.

Pressing S$1$ should change between three modes of operation, which are:

LEDs blinking simultaneously $($initial$)$

Only LED$1$ blinking, with LED$2$ paused $($either on or off$)$

Only LED$2$ blinking, with LED$1$ paused $($either on or off$)$

Repeated presses of S$1$ should cycle between the modes in the order above $(1,2,$ then $3).$ After leaving mode $3,$ the program should return to mode $1.$ Port Test$3$ with added stuff from Lecture

$.$text ## Text section contains code

$.$set noreorder ## Disable instruction reordering

$.$globl main ## Define main label as a global entity

$.$ent main ## and an entry point

$//$ Including xc$.$h allows use of SFR names, bit masks, etc.

#include

main:

$/*$ Configure I$/$O ports$--$LEDs on Port A & C; switches on Port B $*/$

sw zero, TRISA ## TRISA $=0-->$ all PORTA bits $=$ output

sw zero, ANSELA ## ANSELA $=0-->$ all PORTA bits digital

not t$0,$ zero

sw t$0,$ TRISB ## TRISB $=0$xFFFFFFFF $-->$ all PORTB bits $=$ input

sw zero, ANSELB ## ANSELB $=0-->$ all PORTB bits digital

sw zero, TRISC ## TRISC $=0-->$ all PORTC bits $=$ output

sw zero, ANSELC ## ANSELC $=0-->$ all PORTC bits digital

li t$0,\_$PORTA$\_$RA$0\_$MASK ## t$0=0$x$00000001-->$ control LED$1$

li t$1,\_$PORTC$\_$RC$9\_$MASK ## t$1=0$x$00000200-->$ control LED$2$

li t$5,\_$PORTB$\_$RB$7\_$MASK ## t$5=0$x$00000080-->$ saved state of S$1$

li t$6,\_$PORTB$\_$RB$13\_$MASK ## t$6=0$x$00002000-->$ saved state of S$2$

li t$8,0$

$/*$ Repeatedly read $($poll$)$ switches; turn on LED if button pressed;

turn off LED if button released $*/$

$//$ Start with state of S$1$

pollS$1$:

lw t$2,$ PORTB ## Read Port B

andi t$3,$ t$2,\_$PORTB$\_$RB$7\_$MASK ## Check S$1$

## If button isn't pressed, t$3=0$x$00000080$

## If button is pressed, t$3=0$x$00000000$

bne t$3,$ zero, copyS$1$ ## If button not pressed $($RB$7=1),$

nop ## copy state and check S$2$

beq t$3,$ t$5,$ pollS$2$ ## If button pressed but hasn't changed

nop ## check state of S$2$

## Must be a new button press$--$wait ~$0\mathrm{.}009$ sec and check it again

jal delay ## Call debounce function for delay

nop

## Check if button still pressed

lw t$2,$ PORTB

andi t$3,$ t$2,\_$PORTB$\_$RB$7\_$MASK

bne t$3,$ zero, copyS$1$

nop

$//$ sw t$0,$ LATAINV ## Toggle LED$1$ if this is a new button press

addi t$8,$t$8,1$

div t$8,2$

mfhi t$9$

copyS$1$:

add t$5,$ t$3,$ zero ## t$5=$ saved state of S$1$

$//$ Check state of S$2$

pollS$2$:

andi t$4,$ t$2,\_$PORTB$\_$RB$13\_$MASK ## Check S$2$

bne t$4,$ zero, copyS$2$ ## If button not pressed $($RB$13=1),$

nop ## copy state and go back to checking S$1$

beq t$4,$ t$6,$ pollS$1$ ## If button pressed but hasn't changed

nop ## check state of S$1$

## Must be a new button press$--$wait ~$0\mathrm{.}01$ sec and check it again

jal delay ## Call debounce function for delay

nop

## Check if button still pressed

lw t$2,$ PORTB

andi t$4,$ t$2,\_$PORTB$\_$RB$13\_$MASK

bne t$4,$ zero, copyS$2$

nop

$//$ sw t$1,$ LATCINV ## Toggle LED$2$ if this is a new button press

copyS$2$:

add t$6,$ t$4,$ zero ## t$6=$ saved state of S$2$

beq t$9,0,$ toggle

nop

beq t$9,1,$pause

nop

toggle:

$//$implement toggling

j pollS$1$

nop

pause:

$//$implement pause

j pollS$1$

nop

j pollS$1$ ## Return to test S$1$

nop

spin:

j spin

nop

$.$end main

$.$ent delay

delay:

li t$7,0$x$61$A$8$ ## Set delay counter to $0$x$61$A$8=25,000$

## Since loop body has $3$ instructions,

## loop takes $25,000*3=75,000$

## cycles

## Remaining $3$ instructions take $3$ cycles

## ~$75,000$ cycles $/8$ MHz clock ~ $0\mathrm{.}009375$ sec delay

loop:

addi t$7,$ t$7,-1$ ## Decrement counter

bne t$7,$ zero, loop ## and continue doing that until we hit $0$

nop ## NOTE: This function originally branched

## to "done" if t$7!=$ zero, which means

## the delay loop was really no loop at all!

jr ra

nop

$.$end delay