Handle USART_RXC interrupt

src/main.c

@@ -2,6 +2,7 @@
 #include "serial.h"
 
 #include <stdio.h>
+#include <avr/interrupt.h>
 
 #define MAX_CMDBUF 256
 
@@ -17,6 +18,10 @@ int main(void)
 		return 1;
 	}
 
+	// Handle USART_RXC interrupt
+	UCSRB |= (1 << RXCIE);
+	sei();
+
 	USART_Init();
 
 	for (i = 1;; i++) {
@@ -24,6 +29,7 @@ int main(void)
 
 		sprintf(buf, "[CORE] Fetching sensors #%05lu...\r\n", i);
 		USART_Write(buf);
+		USART_Update();
 
 		// USART_Read(&cmd, MAX_CMDBUF);
 		// sprintf(buf, "[CORE] Checking cmdbuf=\"%s\"\r\n", cmd);

src/serial.c

@@ -1,18 +1,21 @@
 #include "common.h"
 #include "serial.h"
-#include <avr/io.h>
 
+#include <avr/io.h>
+#include <avr/interrupt.h>
 #include <stdio.h>
 
 #define USART_BAUDRATE 9600
 
+// TODO: Use ring buffer! https://stackoverflow.com/a/1771607
+
 // Ensure closest fit for target baudrate
 //#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)
 #define BAUD_PRESCALE ((((F_CPU / 16) + (USART_BAUDRATE / 2)) \
         / (USART_BAUDRATE)) - 1)
 
-static char USART_Rx(void);
-static void USART_Tx(char ch);
+static size_t cmdlen;
+static char cmdbuf[256];
 
 void USART_Init(void)
 {
@@ -22,31 +25,11 @@ void USART_Init(void)
 	UBRRL = BAUD_PRESCALE; // Baud rate lower byte
 }
 
-void USART_Read(char **buf, int size)
+void USART_Update(void)
 {
-	int n = 0;
-	char *p = *buf;
-	char ch;
-
-	if ((UCSRA & BIT(RXC)) == 0) {
-		p = '\0';
-		return;
-	}
-
-	do  {
-		// Discard messages exceeding
-		// given size limit quietly
-		if (n == size) {
-			p = '\0';
-			while (USART_Rx());
-			return;
-		}
-
-		ch = USART_Rx();
-		p[n] = ch;
-		n++;
-
-	} while (ch != '\0');
+	char buf[512];
+	sprintf(buf, "[CORE] CMDBUF='%s'\r\n", cmdbuf);
+	USART_Write(buf);
 }
 
 void USART_Write(const char *buf)
@@ -54,23 +37,26 @@ void USART_Write(const char *buf)
 	int n = 0;
 
 	while (buf[n] != '\0') {
-		USART_Tx(buf[n++]);
+		// Wait until UDR can receive data
+		while ((UCSRA & BIT(UDRE)) == 0);
+		UDR = buf[n++];
 	}
 }
 
-static char USART_Rx(void)
+// USART RX Interrupt
+ISR(USART_RXC_vect)
 {
-	// Anything to read from UDR?
-	if ((UCSRA & BIT(RXC)) == 0)
-		return '\0';
+	char ch;
 
-	return UDR;
-}
-
-static void USART_Tx(char ch)
-{
-	// Wait until UDR can receive data
-	while ((UCSRA & BIT(UDRE)) == 0);
-
-	UDR = ch;
+	ch = UDR;
+
+	// Exceeded buffer capacity?
+	if (cmdlen >= sizeof(cmdbuf)) {
+		if (ch == '\n') {
+			cmdlen = 0;
+		}
+		return;
+	}
+
+	cmdbuf[cmdlen++] = ch;
 }

src/serial.h

@@ -2,7 +2,8 @@
 #define MAD_SERIAL_H
 
 void USART_Init(void);
-void USART_Read(char **buf, int size);
+void USART_Update(void);
+//void USART_Read(char **buf, int size);
 void USART_Write(const char *buf);
 
 #endif // MAD_SERIAL_H