Add i2c_message_t and use it all across the codebase. This will allow handling variable-length I2C messages and validation with minimal effort. The test LED and brightness PWM update features got temporarily broken and will fix them soon.

shared/slave_protocol.h

@@ -1,6 +1,11 @@
 #ifndef __SLAVE_PROTOCOL_H__
 #define __SLAVE_PROTOCOL_H__
 
+// Macros:
+
+    #define I2C_MESSAGE_MAX_LENGTH 255
+    #define I2C_BUFFER_MAX_LENGTH (I2C_MESSAGE_MAX_LENGTH + 3)
+
 // Typedefs:
 
     typedef enum {
@@ -10,4 +15,10 @@
         SlaveCommand_JumpToBootloader,
     } slave_command_t;
 
+    typedef struct {
+        uint8_t length;
+        uint16_t crc;
+        uint8_t data[I2C_MESSAGE_MAX_LENGTH];
+    } __attribute__ ((packed)) i2c_message_t;
+
 #endif