read address bits from GPIO

main.c

@@ -47,7 +47,13 @@
 #define HD44780_DB7_PIN PD3
 
 // the I²C address of this slave
-#define I2C_ADDR 0x47U
+static uint8_t i2c_addr = 0x47U;
+#define A0_PORT GPIO_PD
+#define A0_PIN PD4
+#define A1_PORT GPIO_PD
+#define A1_PIN PD5
+#define A2_PORT GPIO_PD
+#define A2_PIN PD6
 
 // the functions we can call over I²C
 enum i2c_mode_t {
@@ -283,6 +289,29 @@ void main(void)
 	HD44780_DB4_PORT->CR1.reg |= HD44780_DB4_PIN; // use in push-pull mode
 	hd44780_data_direction(false); // configure pins as output
 
+	// read I²C address bits
+	A0_PORT->DDR.reg &= ~A0_PIN; // switch pin to input
+	A0_PORT->CR1.reg |= A0_PIN; // enable pull-up
+	if (A0_PORT->IDR.reg & A0_PIN) {
+		i2c_addr |= 0x01;
+	} else {
+		i2c_addr &= ~0x01;
+	}
+	A1_PORT->DDR.reg &= ~A1_PIN; // switch pin to input
+	A1_PORT->CR1.reg |= A1_PIN; // enable pull-up
+	if (A1_PORT->IDR.reg & A1_PIN) {
+		i2c_addr |= 0x02;
+	} else {
+		i2c_addr &= ~0x02;
+	}
+	A2_PORT->DDR.reg &= ~A2_PIN; // switch pin to input
+	A2_PORT->CR1.reg |= A2_PIN; // enable pull-up
+	if (A2_PORT->IDR.reg & A2_PIN) {
+		i2c_addr |= 0x04;
+	} else {
+		i2c_addr &= ~0x04;
+	}
+
 	// configure I²C
 	GPIO_PB->CR1.reg |= (PB4 | PB5); // enable internal pull-up on SCL/SDA
 	GPIO_PB->DDR.reg &= ~(PB4 | PB5); // set SCL/SDA as input before it is used as alternate function by the peripheral
@@ -298,7 +327,7 @@ void main(void)
 	//I2C_CR1 |= I2C_CR1_ENGC; // enable general call (I was not able to have slave select with address 0x00 ACKed)
 	I2C_CR2 |= I2C_CR2_ACK; // enable acknowledgement if address matches
 	// since we are slave and not master, we don't have to set CCR
-	I2C_OARL = (I2C_ADDR << 1U); // set slave address
+	I2C_OARL = (i2c_addr << 1U); // set slave address
 	I2C_ITR |= (I2C_ITR_ITBUFEN | I2C_ITR_ITEVTEN); // enable buffer and event interrupts
 
 	// configure auto-wakeup (AWU) to be able to refresh the watchdog