Test command parser state machine

README

@@ -0,0 +1,8 @@
+# USART Commands
+
+Instead of polling for input we use an interrupt vector
+to write data to a rx ring buffer when it's available.
+
+We parse commands using a state machine so we can deal
+with small chunks of characters at a time and spit out
+the parsed command when the transmission has finished.

src/main.c

@@ -3,24 +3,66 @@
 
 #include <avr/interrupt.h>
 
+
+// # Serial Input Data Flow
+//   USART INTERRUPT -> RING BUFFER -> COMMAND PARSER STATE MACHINE
+//
+// # Supported Commands
+//   (Optional decimal point for numbers)
+//   - START
+//   - RESET
+//   - STOP
+//   - SET TEMP 20
+//   - SET DEWP 60.0
+
+static int state;
+
+void parse(char ch)
+{
+	switch (state) {
+	case 0:
+		if (ch == 't')
+			state = 1;
+		break;
+	case 1:
+		if (ch == 'e')
+			state = 2;
+		else
+			state = 0;
+	case 2:
+		if (ch == 's')
+			state = 3;
+		else
+			state = 0;
+	case 3:
+		if (ch == 't')
+			state = 4;
+		else
+			state = 0;
+	case 4:
+		if (ch == '\n') {
+			USART_Printf("[CORE] Parsed 'test'!\r\n");
+			state = 0;
+		} else
+			state = 0;
+	}
+}
+
 int main(void)
 {
 	unsigned long i;
 	char ch;
 
-	// Handle USART_RXC interrupt
-	UCSRB |= (1 << RXCIE);
-	sei();
-
 	USART_Init();
 
 	for (i = 1;; i++) {
 		if (i >= 99999) i = 1;
 
-		ch = USART_GetChar();
+		while ((ch = USART_GetChar())) {
+			parse(ch);
+		}
+
 		USART_Printf("[CORE] Fetching sensors #%05lu...\r\n", i);
-		USART_Printf("[CORE] USART_GetChar() = '%c'\r\n",
-			(ch) ? ch : ' ');
 
 		Sleep(3000);
 	}

src/serial.c

@@ -20,6 +20,10 @@ void USART_Init(void)
 	rxhead = 0;
 	rxtail = 0;
 
+	// Handle RXC interrupt
+	UCSRB |= (1 << RXCIE);
+	sei();
+
 	UCSRB |= BIT(RXEN) | BIT(TXEN); // Enable rx and tx circuitry
 	UCSRC |= BIT(URSEL) | BIT(UCSZ0) | BIT(UCSZ1); // 8-bit chars
 	UBRRH = (USART_BAUD_PRESCALE >> 8); // Baud Rate upper byte