MODIFICATIONS TO MAKE:

You must change this program so that:

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

$-$ Pressing switches will change the timer period by $1\mathrm{.}0$ seconds, either faster $($by pressing S$1)$ or slower $($by pressing S$2).$

$-$ Given the timer configuration and $1\mathrm{.}0$ seconds of the adjustment period, there are only three modes: $0$ second period $($i$.$e$.,$ pause$),1$ second period, and $2$ second period.

$//$ 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$0001$

ori t$3,$ t$3,\_$INTCON$\_$MVEC$\_$MASK

sw t$3,$ INTCON

li t$3,\_$IPC$2\_$T$1$IP$\_$MASK

sw t$3,$ IPC$2$

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

sw t$3,$ IPC$2$SET

li t$2,\_$IFS$0\_$T$1$IF$\_$MASK

sw t$2,$ IEC$0$

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

sw t$2,$ IEC$0$SET

add t$3,$ t$4,$ zero

or t$3,$ t$3,$ t$6$

sw t$3,$ CNEN$1$B

sw zero, CNEN$0$B

li t$3,\_$CNCONB$\_$ON$\_$MASK

ori t$3,$ t$3,\_$CNCONB$\_$CNSTYLE$\_$MASK

sw t$3,$ CNCONB

ei

li t$3,\_$T$1$CON$\_$TON$\_$MASK

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$8$

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

$.$global isrvector$9$

$.$ent isrvector$9$

isrvector$9$:

li t$4,\_$PORTB$\_$RB$7\_$MASK

li t$6,\_$PORTB$\_$RB$13\_$MASK

$//$ Check S$1$

lw t$8,$ CNFB

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

beq t$9,$ zero, checkS$2$

nop

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

sw t$4,$ CNFBCLR

jal delay

nop

lw t$2,$ PORTB

and t$2,$ t$2,$ t$4$

bne t$2,$ zero, checkS$2$

nop

$//$ ADD routine when a new S$1$ press

$//$ Check S$2$

checkS$2$:

and t$9,$ t$8,$ t$6$

beq t$9,$ zero, int$9$done

nop

$//$ S$2$ pressed$--$clear flag, then debounce and toggle if actually pressed

sw t$6,$ CNFBCLR

jal delay

nop

lw t$2,$ PORTB

and t$2,$ t$2,$ t$6$

bne t$2,$ zero, int$9$done

nop

$//$ ADD routine when a new S$2$ press

int$9$done:

li t$3,\_$IFS$0\_$CNBIF$\_$MASK ## Clear Port B change notification flag

sw t$3,$ IFS$0$CLR ## in IFS$0$

eret ## Return from interrupt

$.$end isrvector$9$

$.$global isrvector$11$

$.$ent isrvector$11$

isrvector$11$:

li t$2,\_$IFS$0\_$T$1$IF$\_$MASK

sw t$2,$ IFS$0$CLR

modify BEHAVIOR TO IMPLEMENT THE LED STATES DESCRIBED ABOVE $***/$

li t$0,\_$PORTA$\_$RA$0\_$MASK

li t$1,\_$PORTC$\_$RC$9\_$MASK

int$11$done:

eret

$.$end isrvector$11$