Functioning I2C slave data receive

The slave now receives and prints data successfully.

prosjekt.X/i2c.c

@@ -1,6 +1,15 @@
 #include "i2c.h"
 
+// Heavily inspired by: https://github.com/microchip-pic-avr-examples/avr128db48-bare-metal-twi-mplab/blob/master/twi-client.X/peripherals/TWI/TWI_client.c
+
 void init_i2c(void) {
+  // Pin setup
+  PORTA.DIRSET = PIN2_bm | PIN3_bm;
+  PORTA.PINCTRLUPD = PIN2_bm | PIN3_bm;
+    
+  // Enable operating in debug
+  TWI0.DBGCTRL = TWI_DBGRUN_bm;
+    
   // Initialize the control A register
   TWI0.CTRLA = TWI_INPUTLVL_I2C_gc    // I2C voltage transition level
                | TWI_SDASETUP_4CYC_gc // Four clock cycles setup time
@@ -13,20 +22,60 @@ void init_i2c(void) {
 
   // Enable acting as a slave
   TWI0.SCTRLA = TWI_DIEN_bm     // Enable data interrupt
+                | TWI_APIEN_bm  // Enable more interrupts
                 | TWI_PIEN_bm   // Enable stop flag interrupt
-                | TWI_SMEN_bm   // Enable smart mode
+                | PIN2_bm       // Respond to all TWI addresses
                 | TWI_ENABLE_bm // Enable acting as a slave
       ;
 }
 
 // TODO: Figure out which interrupt does what
 
-// Interrupt vector
-ISR(TWI0_TWIS_vect) {
-    asm('nop');
+void i2c_write_handler(uint8_t data) {
+    printf("%u\n", data);
 }
 
-// Interrupt vector
-ISR(TWI0_TWIM_vect) {
-    asm('nop');
+void i2c_read_handler() {
+    printf("Master wanted to read.\n");
+}
+
+void i2c_stop_handler() {
+    printf("Stop, I guess\n");
+}
+
+// Address received
+ISR(TWI0_TWIS_vect) {
+    // Check for the data interrupt flag
+    if (TWI0.SSTATUS & TWI_DIF_bm) {
+        uint8_t data = 0;
+        
+        if ( ((TWI0.SSTATUS & TWI_DIR_bm) >> TWI_DIR_bp) == 0 ) {
+            // Data write Master -> Slave
+            data = TWI0.SDATA;
+            
+            // Send the data to the write handler
+            i2c_write_handler(data);
+        } else {
+            // Data read Master <- Slave
+            i2c_read_handler();
+            data = TWI0.SDATA;
+        }
+        
+        // Acknowledge having received
+        TWI0.SCTRLB = TWI_ACKACT_ACK_gc | TWI_SCMD_RESPONSE_gc;
+    }
+    
+    // Check for address match or STOP
+    if (TWI0.SSTATUS & TWI_APIF_bm) {
+        
+        if (TWI0.SSTATUS & TWI_AP_ADR_gc) {
+            // Address match, just send ack
+            TWI0.SCTRLB = TWI_ACKACT_ACK_gc | TWI_SCMD_RESPONSE_gc;
+        } else {
+            // STOP condition received
+            i2c_stop_handler();
+            // Send ACK
+            TWI0.SCTRLB = TWI_ACKACT_ACK_gc | TWI_SCMD_RESPONSE_gc;
+        }
+    }
 }

prosjekt.X/i2c.h

@@ -15,6 +15,8 @@ extern "C" {
 // Include the IO for I2C
 #include <avr/io.h>
 #include <avr/interrupt.h>
+#include "uart.h"
+#include <util/twi.h>
 
 // Initialize the I2C bus
 void init_i2c(void);

prosjekt.X/main.c

@@ -10,14 +10,18 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include "uart.h"
+#include "i2c.h"
 #include <util/delay.h>
 
-int main() {
+int main() {    
     init_uart((uint16_t)9600);
+    init_i2c();
     stdout = &USART_stream;
+    
+    sei();
 
     while (1) {
-        printf("Hello, world!\n");
+        printf("\n");
         _delay_ms(500);
     }
 }

prosjekt.X/nbproject/configurations.xml

@@ -171,6 +171,9 @@
         <property key="user-pack-device-support" value=""/>
         <property key="wpo-lto" value="false"/>
       </XC8-config-global>
+      <nEdbgTool>
+        <property key="debugoptions.useswbreakpoints" value="true"/>
+      </nEdbgTool>
     </conf>
   </confs>
 </configurationDescriptor>