Add read-only pointer accessor for previously read moisture value

firmware/atmega/include/globals.h

@@ -0,0 +1,8 @@
+#ifndef GLOBALS_H
+#define GLOBALS_H
+
+#include <stdint.h>
+
+const uint16_t* moisturePtr(void);
+
+#endif

firmware/atmega/source/main.c

@@ -40,12 +40,17 @@ static void setup(void) {
     watchdogs();
 }
 
+static uint16_t lastMoistureVal = 0;
+
+// Encapsulate lastMoistureVal to read later from twi
+const uint16_t *moisturePtr(void) { return &lastMoistureVal; }
+
 int main(void) {
     setup();
 
     while(true) {
         if (readSensors) {
-            uint16_t result = moistureRead();
+            lastMoistureVal = moistureRead();
             // nested if: (result outside range (see config.h)) {waterPlant()}
 
         }

firmware/atmega/source/twi.c

@@ -1,6 +1,7 @@
 #include <stdint.h>
 #include <avr/io.h>
 #include "config.h"
+#include "globals.h"
 
 #define BUFFER_SIZE 8
 
@@ -26,9 +27,18 @@ static void twiRespond(int8_t response[]) {
     // Respond to TWI requests
 }
 
-
 static void twiExecute(int8_t buffer[]) {
-    // Perform actions based on received message
+    switch(buffer[0]) {
+        case 0x01: // Send moisture
+            twiRespond(*moisturePtr());
+            break;
+        case 0x02:
+            // Perform action for command 0x02
+            break;
+        default:
+            // twiRespond with unkown command
+            break;
+    }
     // if needed:
     // twiRespond();
 }