softi2c_master: add timeout to prevent infinite loop

softi2c_master.c

@@ -19,10 +19,16 @@
 // half period to wait for I²C clock
 static uint16_t period = 0;
 
+// port for data line
 #define SDA_PORT GPIO_PB
+// pin for data line
 #define SDA_PIN PB5
+// port for clock line
 #define SCL_PORT GPIO_PB
+// pin for clock line
 #define SCL_PIN PB4
+// operation timeout (in half period)
+#define TIMEOUT 10U
 
 // delay for half a period
 static void I2C_delay(void)
@@ -84,7 +90,7 @@ bool softi2c_master_setup(uint16_t freq_khz)
 	SDA_PORT->CR1.reg &= ~SDA_PIN; // use in open-drain mode
 
 	I2C_delay(); // give time to get high
-	return (read_SCL() && read_SDA());
+	return (read_SCL() && read_SDA()); // line is ready when the two lines are high
 }
 
 void softi2c_master_release(void)
@@ -104,7 +110,14 @@ bool softi2c_master_start(void)
 		set_SDA();
 		I2C_delay();
 		set_SCL();
-		while (read_SCL() == 0); // Clock stretching
+		uint8_t timeout = TIMEOUT;
+		while (read_SCL() == 0 && timeout) { // Clock stretching
+			I2C_delay();
+			timeout--;
+		}
+		if (0 == timeout) {
+			return false;
+		}
 
 		// Repeated start setup time, minimum 4.7us
 		I2C_delay();
@@ -130,7 +143,14 @@ bool softi2c_master_stop(void)
 	I2C_delay();
 
 	set_SCL();
-	while (read_SCL() == 0); // Clock stretching
+	uint8_t timeout = TIMEOUT;
+	while (read_SCL() == 0 && timeout) { // Clock stretching
+		I2C_delay();
+		timeout--;
+	}
+	if (0 == timeout) {
+		return false;
+	}
 
 	I2C_delay(); // Stop bit setup time, minimum 4us
 
@@ -158,7 +178,15 @@ static bool softi2c_master_write_bit(bool bit) {
 	I2C_delay(); // SDA change propagation delay
 	set_SCL(); // Set SCL high to indicate a new valid SDA value is available
 	I2C_delay(); // Wait for SDA value to be read by slave, minimum of 4us for standard mode
-	while (read_SCL() == 0); // Clock stretching
+	uint8_t timeout = TIMEOUT;
+	while (read_SCL() == 0 && timeout) { // Clock stretching
+		I2C_delay();
+		timeout--;
+	}
+	if (0 == timeout) {
+		return false;
+	}
+
 	// SCL is high, now data is valid
 	if (bit && (read_SDA() == 0)) { // If SDA is high, check that nobody else is driving SDA
 		return false;
@@ -173,7 +201,14 @@ static bool softi2c_master_read_bit(void) {
 	set_SDA(); // Let the slave drive data
 	I2C_delay(); // Wait for SDA value to be written by slave, minimum of 4us for standard mode
 	set_SCL(); // Set SCL high to indicate a new valid SDA value is available
-	while (read_SCL() == 0); // Clock stretching
+	uint8_t timeout = TIMEOUT;
+	while (read_SCL() == 0 && timeout) { // Clock stretching
+		I2C_delay();
+		timeout--;
+	}
+	if (0 == timeout) {
+		return false;
+	}
 	I2C_delay(); // Wait for SDA value to be written by slave, minimum of 4us for standard mode
 	const bool bit = read_SDA(); // SCL is high, read out bit
 	clear_SCL(); // Set SCL low in preparation for next operation