$/**$ EX: $7\mathrm{.}0$

When configuring hardware peripherals to generate interrupts, it is

important to ensure that interrupts cannot be raised by other

peripherals while this configuration is taking place.

TASK: Disable interrupts globally before configuring the TCB$0$ peripheral

and re$-$enable interrupts globally afterwards.

HINT: Use the cli$()$ and sei$()$ functions provided by avr$/$interrupt$.$h$.$

$*/$

void clock$\_$init$($void$)$

$\{$

$/**$ CODE: Write your code for Ex $7\mathrm{.}0$ within this function. $*/$

$//$ TCB$0$ is a $16-$bit timer that has been configured to generate

$//$ an interrupt every $64$th of a second. This was done to increase

$//$ the resolution of the timer.

TCB$0.$CCMP $=52083$;

TCB$0.$CTRLB $=$ TCB$\_$CNTMODE$\_$INT$\_$gc;

TCB$0.$INTCTRL $=$ TCB$\_$CAPT$\_$bm;

TCB$0.$CTRLA $=$ TCB$\_$ENABLE$\_$bm;

$\}$

$/**$ EX: $7\mathrm{.}1$

The stopwatch will be controlled by pushbuttons S$1,$ S$2,$ and S$4.$

TASK: Write code to configure the pins connected to these pushbuttons

to generate an interrupt on falling edges.

See ATtiny$1626$ Datasheet $17\mathrm{.}4$ Register Summary $-$ PORTx on p$.153$ and

$17\mathrm{.}5\mathrm{.}12$ Pin n Control on p$.165.$

$*/$

void buttons$\_$init$($void$)$

$\{$

$/**$ CODE: Write your code for Ex $7\mathrm{.}1$ within this function. $*/$

$\}$

$/**$ EX: $7\mathrm{.}2$

To display the elapsed time on the $7-$segment display, we need to count

the number of times the TCB$0$ CAPT interrupt is invoked.

TASK: Declare a global variable called "count$\_64"$ that will be used

to store a count of $1/64$ seconds that have elapsed.

Ensure this variable is sufficiently large so that it can represent the

largest value that can be displayed on the $7-$segment display.

The stopwatch should initially display $0$x$00.$

$*/$

$/**$ CODE: Write your code for Ex $7\mathrm{.}2$ above this line. $*/$

$/**$ EX: $7\mathrm{.}3$

To allow pushbuttons S$1$ and S$2$ to control when the stopwatch is

counting, we need to keep track of the state of the stopwatch.

TASK: Declare a global variable called $"$is$\_$counting" that keeps track

of the stopwatch's state.

The stopwatch should initially be paused.

$*/$

$/**$ CODE: Write your code for Ex $7\mathrm{.}3$ above this line. $*/$

$/**$ EX: $7\mathrm{.}4$

TASK: Declare an interrupt service routine $($ISR$)$ for the TCB$0$ peripheral

that was configured in Ex $7\mathrm{.}0.$

$1.$ Find the vector number and name that correspond to the TCB$0$ CAPT

interrupt.

Refer to datasheet Section $8\mathrm{.}2$ Interrupt Vector Mapping on p$.63.$

$2.$ Given that vectors are of the form $"*\_$vect", find the appropriate

macro corresponding to the vector number identified in step $1.$

Type $"\_$vect" to invoke VSCode suggestions.

$3.$ Declare an ISR using the ISR$()$ macro syntax, where

is the macro identified in step $2.$

$4.$ If the stopwatch is currently counting, increment "count$\_64"$ by $1.$

Ensure that this variable does not exceed the value which represents

$15\mathrm{.}9375$ s $(0$xFF $*1/16$ s$).$

$5.$ As the value displayed on the $7-$segment display is a count of $1/16$ s$,$

define a local variable called "count$\_16"$ and convert "count$\_64"$ to

a count of $1/16$ s$.$

$6.$ Update the $7-$segment display to reflect the value of "count$\_16".$

$7.$ Acknowledge that the interrupt has been handled by clearing the CAPT

bit in the TCB$0.$INTFLAGS register.

See ATtiny$1626$ Datasheet $22\mathrm{.}5\mathrm{.}5$ Interrupt Flags on p$.260$ for

information on how to clear this bit.

NOTE: You may use display$\_$hex$()$ to display a number in hexadecimal on

the $7-$segment display. This function accepts an unsigned $8-$bit integer.

To find the maximum value of "count$\_64"$ in step $4$ and to perform the

conversion in step $5,$ you will need to use the following relationship to

convert between counts of $1/64$ s and counts of $1/16$ s:

$1/16$ second $=4*(1/64$ second$)$

$*/$

$/**$ CODE: Write your code for Ex $7\mathrm{.}4$ above this line. $*/$

$/**$ EX: $7\mathrm{.}5$

To allow the variables "count$\_64"$ and $"$is$\_$counting" to be shared between

compilation units $($i$.$e$.,$ src$/$timer$.$c and src$/$buttons$.$c$),$ we must declare

them as external variables.

TASK: Declare "count$\_64"$ and $"$is$\_$counting" as external variables.

NOTE: An external declaration must not provide an initialisation.

$*/$

$/**$ CODE: Write your code for Ex $7\mathrm{.}5$ above this line. $*/$

$/**$ EX: $7\mathrm{.}6$

TASK: Write an interrupt service routine for PORTA, that will be invoked

when a falling edge is detected on any pins connected to pushbuttons S$1,$

S$2,$ or S$4.$

This ISR should check which pin generated the interrupt, and perform

one of the following actions:

$-$ If S$1$ is pressed, start the stopwatch.

$-$ If S$2$ is pressed, pause the stopwatch.

$-$ If S$4$ is pressed, reset the stopwatch to $0$x$00.$

See ATtiny$1626$ Datasheet $17\mathrm{.}5\mathrm{.}10$ Interrupt Flags on p$.163$ for

information on how to clear these interrupt flags.

NOTE: Each pin has its own interrupt flag, and you must only clear the

interrupt flag for the pin that generated the interrupt.

$*/$

$/**$ CODE: Write your code for Ex $7\mathrm{.}6$ above this line. $*/$