Add example for slave mode operation with the Pi Pico

i2c/CMakeLists.txt

@@ -2,4 +2,5 @@ if (NOT PICO_NO_HARDWARE)
     add_subdirectory(bus_scan)
     add_subdirectory(lcd_1602_i2c)
     add_subdirectory(mpu6050_i2c)
+    add_subdirectory(slave_mode)
 endif ()

i2c/slave_mode/CMakeLists.txt

@@ -0,0 +1,8 @@
+add_executable(i2c_slave_mode main.c)
+
+target_link_libraries(i2c_slave_mode pico_stdlib hardware_gpio hardware_i2c)
+
+pico_enable_stdio_usb(i2c_slave_mode 1)
+pico_enable_stdio_uart(i2c_slave_mode 0)
+
+pico_add_extra_outputs(i2c_slave_mode)

i2c/slave_mode/main.c

@@ -0,0 +1,112 @@
+#include <stdio.h>
+#include <string.h>
+#include "pico/stdlib.h"
+#include "hardware/gpio.h"
+#include "hardware/i2c.h"
+
+#define bus i2c0
+#define SDA 16
+#define SCL 17
+#define FIFO_SIZE 16
+
+/**
+ * @brief initialize i2c bus on specified address
+ * 
+ * @param address slave address (0x21 seems to be causing problem for some reasons I cannot understand)
+ */
+void init_i2c_bus(uint8_t address) {
+	i2c_init(bus, 100000); // BUS SPEED IS 400kHz, Clock Stretching is enabled
+	gpio_set_function(SCL, GPIO_FUNC_I2C);
+	gpio_set_function(SDA, GPIO_FUNC_I2C);
+	gpio_pull_up(SDA);
+	gpio_pull_up(SCL);
+	i2c_set_slave_mode(bus, true, address);
+}
+
+
+/**
+ * @brief Listen for i²c commands in the RX FIFO. Wait until transmit from master side is finished.
+ * 
+ * @param i2c i2c instance
+ * @param handler_function function to handle the 16 byte message that the slave can read
+ */
+void i2c_listener(i2c_inst_t *i2c, void (*handler_function)(i2c_inst_t*, uint8_t*)) {
+	uint8_t buffer[FIFO_SIZE];
+	memset(buffer, 0, FIFO_SIZE);
+	int available;
+
+	for( ;; ) {
+		available = i2c_get_read_available(i2c);
+
+		if( available > 0 ) {
+
+			int old_available;
+			do {
+				old_available = available;
+				sleep_us(100);
+				available = i2c_get_read_available(i2c);
+			} while( available != old_available );
+
+			// read and execute handler function
+			i2c_read_raw_blocking(i2c, buffer, available);
+			handler_function(i2c, buffer);
+			memset(buffer, 0, FIFO_SIZE);
+		}
+	}
+}
+
+/**
+ * @brief Handler function called from the listener
+ * 
+ * @param i2c i2c instance
+ * @param message 16 byte i2c message, the first byte is assumed to be the command byte
+ */
+void on_message(i2c_inst_t *i2c, uint8_t *message) {
+	printf("\nRECEIVED MESSAGE\n");
+	printf("----------PAYLOAD--------------\n");
+	for( int i = 0; i < FIFO_SIZE; i++ ) {
+		printf("%02x ", message[i]);
+	}
+	printf("\n-------------------------------\n");
+
+	// check the first byte in command for command type
+	switch( message[0] ) { // handle commands in the array
+
+		// TOGGLE LED
+		case 0x10:
+			printf("LED SIGNAL!!!\n");
+			gpio_put(25, !gpio_get(25));
+			break;
+
+		// ECHO SOME BYTES BACK TO MASTER
+		case 0x20:
+			printf("ECHO SIGNAL!!!\n");
+			const uint8_t buffer[2] = {0x20,0x30};
+			i2c_write_raw_blocking(i2c0, buffer, 2);
+			break;
+
+		// NONE OF THE COMMAND BYTES APPLY
+		default:
+			printf("NO MATCHING COMMAND\n");
+			break;
+	}
+}
+
+int main() {
+
+	// STDOUT over usb serial
+	stdio_usb_init();
+
+	// set address 0x31
+	init_i2c_bus(0x31);
+
+	// setup LED
+	gpio_init(25);
+	gpio_set_dir(25, GPIO_OUT);
+
+	// start listener. This can be launched in a second core if neccecary
+	// connect i2c num and handler function
+	i2c_listener(bus, on_message);
+
+	return 0;
+}