Clock polarity and phase (CPOL, CPHA) in Embedded C - Mini Project: Build & Apply

Clock polarity and phase (CPOL, CPHA) configuration in embedded C

📖 Scenario: You are working on a microcontroller project that communicates with a sensor using SPI protocol. To ensure correct data transfer, you need to configure the SPI clock settings properly.The SPI clock has two important settings: Clock Polarity (CPOL) and Clock Phase (CPHA). These settings control when data is sampled and the idle state of the clock line.

🎯 Goal: Build a simple embedded C program that sets up SPI clock polarity and phase using variables CPOL and CPHA. Then, use these settings to configure a control register SPI_CR1 with the correct bits.

📋 What You'll Learn

Create variables CPOL and CPHA with exact values 1 and 0 respectively

Create a variable SPI_CR1 initialized to 0

Use bitwise operations to set bit 1 of SPI_CR1 to CPOL

Use bitwise operations to set bit 0 of SPI_CR1 to CPHA

Print the final value of SPI_CR1 as an unsigned integer

💡 Why This Matters

🌍 Real World

Configuring SPI clock polarity and phase is essential in embedded systems to communicate correctly with sensors and other devices.

💼 Career

Embedded software engineers often need to set hardware registers like SPI_CR1 to control communication protocols precisely.

1

Create SPI clock polarity and phase variables

Create two integer variables called CPOL and CPHA with values 1 and 0 respectively.

Embedded C

# Create variables CPOL and CPHA with values 1 and 0
// Your code here

Need a hint?

Use int CPOL = 1; and int CPHA = 0; to create the variables.

2

Initialize SPI control register variable

Create an unsigned integer variable called SPI_CR1 and initialize it to 0.

Embedded C

int CPOL = 1;
int CPHA = 0;

// Create SPI_CR1 variable initialized to 0
// Your code here

Need a hint?

Use unsigned int SPI_CR1 = 0; to create the control register variable.

3

Set CPOL and CPHA bits in SPI_CR1

Use bitwise operations to set bit 1 of SPI_CR1 to the value of CPOL and bit 0 of SPI_CR1 to the value of CPHA. Use shift operators and bitwise OR to do this.

Embedded C

int CPOL = 1;
int CPHA = 0;

unsigned int SPI_CR1 = 0;

// Set bit 1 of SPI_CR1 to CPOL and bit 0 to CPHA
// Your code here

Need a hint?

Use SPI_CR1 |= (CPOL << 1); and SPI_CR1 |= CPHA; to set the bits.

4

Print the SPI_CR1 register value

Write a printf statement to print the value of SPI_CR1 as an unsigned integer.

Embedded C

int CPOL = 1;
int CPHA = 0;

unsigned int SPI_CR1 = 0;

SPI_CR1 |= (CPOL << 1);
SPI_CR1 |= CPHA;

// Print SPI_CR1 value
// Your code here

Need a hint?

Use printf("%u\n", SPI_CR1); to print the value.