On a PIC$32$MM Curiosity Development Board $($MIPS $32)$ using the following code as a template to:

Initially, LEDs blink every $1\mathrm{.}0$ seconds.

Pressing S$2$ makes LEDs blink in $2\mathrm{.}0$ seconds.

Pressing S$1$ makes LEDs blink in $1\mathrm{.}0$ seconds again.

Pressing S$1$ makes LEDs pause blinking

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

#include

$//$ Interrupt vector setup

$.$globl $\_\_$vector$\_$dispatch$\_9$ ## Port B change notification $=$ vector #$9$

$.$section $.$vector$\_9,$ code, keep

$.$align $2$

$.$set nomips$16$

$.$ent $\_\_$vector$\_$dispatch$\_9$

$\_\_$vector$\_$dispatch$\_9$:

j isrvector$9$ ## Jump to actual ISR code, which is in text section

nop

$.$end $\_\_$vector$\_$dispatch$\_9$

$.$size $\_\_$vector$\_$dispatch$\_9,.-\_\_$vector$\_$dispatch$\_9$

$.$globl $\_\_$vector$\_$dispatch$\_11$ ## Timer $1$ interrupt $=$ vector #$11$

$.$section $.$vector$\_11,$ code, keep

$.$align $2$

$.$set nomips$16$

$.$ent $\_\_$vector$\_$dispatch$\_11$

$\_\_$vector$\_$dispatch$\_11$:

j isrvector$11$ ## Jump to actual ISR code, which is in text section

nop

$.$end $\_\_$vector$\_$dispatch$\_11$

$.$size $\_\_$vector$\_$dispatch$\_11,.-\_\_$vector$\_$dispatch$\_11$

$//$ Start of text section

$.$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

main:

$//$ Configure port A for output

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

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

li t$0,\_$PORTB$\_$RB$7\_$MASK

ori t$0,$ t$0,\_$PORTB$\_$RB$13\_$MASK

sw t$0,$ TRISB ## TRISB $=0$x$00002080-->$ pins $7$ & $13$ inputs

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

$//$ Configure Timer $1$

sw zero, T$1$CON ## Clear T$1$CON$--$disables timer to allow setup

$/***$

The desired initial delay is $0\mathrm{.}5$ sec between interrupts

ADD TIMER SETTINGS $($PRESCALE and PR$1)$ TO GET THE DESIRED DELAY

$***/$

$//$ Configure interrupts

lui t$3,0$x$0001$ ## Want INTCON bit $16($VS$<0>)=1$

## so vectors $8$ bytes apart

ori t$3,$ t$3,\_$INTCON$\_$MVEC$\_$MASK ## Enable multivectored interrupt mode

sw t$3,$ INTCON

li t$3,\_$IPC$2\_$T$1$IP$\_$MASK ## Set T$1$ interrupt priority level to $7$

sw t$3,$ IPC$2$ ## Implicitly sets subpriority level to $0$

li t$3,\_$IPC$2\_$CNBIP$\_$MASK

sw t$3,$ IPC$2$SET

li t$2,\_$IFS$0\_$T$1$IF$\_$MASK ## t$2=$ bit mask for checking Timer $1$ interrupt flag

sw t$2,$ IEC$0$ ## Enable Timer $1$ interrupts $($uses

## same bit mask as T$1$ interrupt flag$)$

li t$2,\_$IEC$0\_$CNBIE$\_$MASK

sw t$2,$ IEC$0$SET

add t$3,$ t$4,$ zero ## Set bits in CNEN$1$B $=1$ and CNEN$0$B $=0$

or t$3,$ t$3,$ t$6$ ## corresponding to switch positions

sw t$3,$ CNEN$1$B ## $($t$4=$ S$1$ bit mask; t$6=$ S$2$ bit mask$)$

sw zero, CNEN$0$B ## Will detect falling edges on these pins

li t$3,\_$CNCONB$\_$ON$\_$MASK ## Enables Port B change notification

ori t$3,$ t$3,\_$CNCONB$\_$CNSTYLE$\_$MASK ## Enables edge detection

sw t$3,$ CNCONB

ei ## Enable interrupts globally

li t$3,\_$T$1$CON$\_$TON$\_$MASK ## Enable Timer $1$ by setting $"$ON$"$ bit in T$1$CON

sw t$3,$ T$1$CONSET

$//$ Main loop: doing nothing, just waiting for an interrupt

mainloop:

j mainloop

nop

$.$end main

$//////////////////////////////////////////////////////////////////////////$

$//$ Delay loop for switch debouncing

$.$global delay

$.$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

jr ra

nop

$.$end delay

$//////////////////////////////////////////////////////////////////////////$

$//$ Handle Port B change interrupt$--$check switches and toggle appropriate LEDs

$.$global isrvector$9$

$.$ent isrvector$9$

isrvector$9$:

li t$4,\_$PORTB$\_$RB$7\_$MASK ## t$4=0$x$00000080-->$ mask for S$1$

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

$//$ Check S$1$

lw t$8,$ CNFB

and t$9,$ t$8,$ t$4$

beq t$9,$ zero, checkS$2$ ## If bit $7=0,$ S$1$ wasn't pressed

nop

$//$ S$1$ pressed$--$clear flag, then debounce and toggle if actually pressed

sw t$4,$ CNFBCLR ## Clear flag for S$1$

jal delay ## Delay to debounce

nop