LAB $1-$ STM$32$: Digital IO $-$ LED and Pushbutton and TIMER Introduction

This lab uses a STM$32$G$071$RBT$6$

Objectives

To install and setup STM$32$CubeIDE on your machine, which is essential to complete the lab tasks and the MCU project

To configure the GPIO registers within the STM$32$ to blink an LED that is controlled by reading an input from a push$-$button

To explore some basic debugging strategies in embedded systems

Activity #$1$: Preparation

Read through section $7$ of the STM$32$G$0$ datasheet.

Follow the guide "Getting Started on STM$32$ CubeIDE" and follow the steps to blink the LED at $1$Hz$.$

If the on$-$board LED is blinking at $1$Hz$,$ your system is ready for the lab.

Activity #$2$: Control an LED using a pushbutton

Modify the code to blink the onboard LED at $1$Hz $($or ON for $0\mathrm{.}5$ sec and OFF for $0\mathrm{.}5$ sec$)$ while the user pushbutton is pressed.

While the button is released, turn off the LED.

In your setup code, configure the port and pin connected to the user button $($built$-$in push button$)$ as an input

Determine which port and pin the button is connected to in section $6\mathrm{.}11$ of the STM$32$ Nucleo$-64$ board's user manual

Enable the clock to that port

Configure the pin to be an input

Determine if you should configure a pull$-$up or pull$-$down resistor using GPIOx$\_$PUPDR

In your main loop, read the value of the corresponding bit in GPIOx$\_$IDR.

To check a bit, you can use the following:

if $(($GPIOx$\_$IDR $>>$ n$)$ & $1)$

$\{$

$//$ Runs if the nth bit of GPIOx$\_$IDR is set

$\}$

Activity #$3$: Using the BSR

An alternative way of setting the output of a pin to be HIGH or LOW is to use the bit set reset register. Refer to section $7\mathrm{.}3\mathrm{.}5$ and $7\mathrm{.}4\mathrm{.}7$ of the datasheet.

In your code, instead of using the output data register $($ODR$),$ use the bit set reset register $($BSRR$)$ to turn on and off the LED.

Activity #$4$: Delay Function using TIM$2$ in Count up Overflow Mode

Configure TIM$2$ to overflow every $1$ms in count up mode to create your own HAL delay function. This is done by enabling TIM$2$ and setting the prescaler $($PSC$)$ and auto$-$reload value $($ARR$).$ It is recommended to read up on Chapter $22\mathrm{.}3\mathrm{.}2$ of the datasheet to understand the principles of different counter modes.

The instructions to do so are as follows.

Enable TIM$2$ in the $$Reset and Clock Control$.$

Set TIM$2$ in count up mode.

Set the Prescaler $($PSC$)$ and Auto$-$Reload Register $($ARR$)$ values.

Enable TIM$2$ on the $$Control Register.$$

Use TIM$2$ to generate your own HAL delay function.

To set the PSC and ARR values, the following relationship needs to be used.

Fevents $=$ FCLK $/($PSC $+1)($ARR $+1)$

Where the Fclk is the frequency of the system clock defined by the $$APB Timer Clocks$$ in CubeIDE$$s clock configuration. The overflow value is set by the ARR.

The delay function should have a similar format to what is shown. Call this function in

the main while loop and set a delay value $($in milliseconds$).$

void my$\_$delay$\_$ms$($uint$32\_$t ms$)$

$\{$

$//$ Read from TIM$2$ counter and increment a variable.

$//$ Clear the status register and repeat until the millis$\_$val.

TIM$2->$SR &$=$ ~;

$\}$

Appendices

Appendix $1$: Setting up Timer $2($TIM$2)$

Enable the TIM$2$ register in the $$APB peripheral clock enable register $1($RCC$\_$APBENR$1).$ The relevant information can be found in Chapter $5\mathrm{.}4\mathrm{.}15$ of the datasheet. To better understand how count up timer$$s work, refer to Chapter $22\mathrm{.}3\mathrm{.}1$ and $22\mathrm{.}3\mathrm{.}2$ in the

Datasheet.

The STM$32$ architecture has multiple timer signals that you can configure. By enabling

the clock for RCC$\_$APBENR$1,$ additional registers need to be set based on the purpose of the timer. These can be found in Chapter $22\mathrm{.}4$ of the datasheet. To configure the TIM$2$ Registers, the following procedure should be followed.

The timer must be set to count up mode. This is done by configuring $$control register $1$ and setting the Direction register. Refer to Chapter $22\mathrm{.}4\mathrm{.}1$ in the datasheet.

Set the prescaler $($PSC$)$ and Auto$-$Reload Values $($ARR$).$ The PSC and ARR values are set based on the required time interval and have the following relationship.

Fevents $=$ FCLK $/($PSC $+1)($ARR $+1)$

Where Fclk comes from the ABP peripheral clock, event frequency is how

frequent the timer increments. The prescaler is used to divide the clock signal

while the ARR is the maximum value to set for timer overflow. PSC and ARR

register values, in Chapters $22\mathrm{.}4\mathrm{.}14$ and $22\mathrm{.}4\mathrm{.}15$ of the datasheet.

Once these are set, the timer can then be enabled in $$Control Register $1$ and setting the counter enable register $($CEN$).$The count up diagram found in Chapter $22\mathrm{.}3\mathrm{.}2$ in the datasheet explains the timer operations. To generate the delay needed in the timer, an update event needs to occur, i$.$e$.$ when a counter overflows. This triggers an interrupt flag which needs to be read and reset. : Compared to AVR, this is an indicator this is an overflow has occured.