Add data receiving capabilities using a buffer with overflow protection

firmware/atmega/include/twi.h

@@ -0,0 +1,7 @@
+#ifndef TWI_H
+#define TWI_H
+
+void twiInit(void);
+void twiAlert(void);
+
+#endif

firmware/atmega/source/main.c

@@ -3,15 +3,21 @@
 #include <avr/sleep.h>
 #include <avr/wdt.h>
 #include <avr/interrupt.h>
+#include "config.h"
 #include "adc.h"
 #include "moisture.h"
 #include "pump.h"
+#include "twi.h"
 
 ISR(WDT_vect) {
     triggerMoistureRead();
 }
 
-void watchdogs(void) {
+ISR(TWI_vect) {
+    twiAlert();
+}
+
+static void watchdogs(void) {
     cli();
     MCUSR &= ~(1 << WDRF);
     WDTCSR |= (1 << WDCE) | (1 << WDE);
@@ -19,15 +25,16 @@ void watchdogs(void) {
     sei();
 }
 
-void enterSleep(void) {
+static inline void enterSleep(void) {
     set_sleep_mode(SLEEP_MODE_PWR_DOWN);
     sleep_enable();
     sleep_cpu();
     sleep_disable();
 }
 
-void setup(void) {
+static void setup(void) {
     adcInit();
+    twiInit();
     sensorsInit();
     pumpsInit();
     watchdogs();
@@ -39,10 +46,9 @@ int main(void) {
     while(true) {
         if (readSensors) {
             uint16_t result = moistureRead();
-            //espSend(VASE_NUM, result)
+            // nested if: (result outside range (see config.h)) {waterPlant()}
+
         }
-        // if(espGet("ask if i need to water plants") == true) {waterPlant()}
-        // or maybe it's better to do this with interrupts?
 
         readSensors = false;
         enterSleep();

firmware/atmega/source/twi.c

@@ -0,0 +1,58 @@
+#include <stdint.h>
+#include <avr/io.h>
+#include "config.h"
+
+#define BUFFER_SIZE 8
+
+static inline void twiReset(void) {
+    // Enable TWI; enable ACK; clear interrupt flag; enable twi external interrupt
+    TWCR = (1 << TWEN) | (1 << TWEA) | (1 << TWINT) | (1 << TWIE);
+}
+
+void twiInit(void) {
+    TWAR = TWI_ADDR; //address definition found in config.h
+    twiReset();
+}
+
+static inline void twiSendAck(void) {
+    TWCR = (1 << TWEA) | (1 << TWINT);
+}
+
+static inline void twiSendNack(void) {
+    TWCR = (TWCR & ~(1 << TWEA)) | (1 << TWINT);
+}
+
+static void twiRespond(int8_t response[]) {
+    // Respond to TWI requests
+}
+
+
+static void twiExecute(int8_t buffer[]) {
+    // Perform actions based on received message
+    // if needed:
+    // twiRespond();
+}
+
+void twiAlert(void) {
+    static int8_t twiBuffer[BUFFER_SIZE] = {0};
+    static uint8_t bufferIndex = 0;
+
+    switch (TWSR & 0xF8) {
+        case 0x60: // SLA+W received
+            twiSendAck();
+            break;
+        case 0x80: // data received
+            if(bufferIndex < BUFFER_SIZE) {
+                twiBuffer[bufferIndex++] = TWDR;
+                twiSendAck();
+            } else twiSendNack();
+            break;
+        case 0xA0: // stop condition
+            twiExecute(twiBuffer);
+            twiReset();
+            break;
+        default:
+            twiSendNack();
+            break;
+    }
+}