updated code (untested)

mainboard/CMakeLists.txt

@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.16.0)
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(mainboard)

mainboard/src/CMakeLists.txt

@@ -0,0 +1,6 @@
+# This file was automatically generated for projects
+# without default 'CMakeLists.txt' file.
+
+FILE(GLOB_RECURSE app_sources ${CMAKE_SOURCE_DIR}/src/*.*)
+
+idf_component_register(SRCS ${app_sources})

mainboard/src/main.cpp

@@ -4,21 +4,68 @@
 #define ROWS 2
 #define COLS 2
 
+int ROW[] = {15,2};
+int COL[] = {0,4};
+
+//Stores The Raw Report of the Keyboard
+uint8_t keyboard_report[ROWS][COLS];
+
+//Stores The Mapping of Each of The Key. Mapping is based of the ASCII value of that key.
+//Mappings are in the 2D Space - it's shifted version is 32 bits more than the original
+//Thus to get shifted version of M which is 0x4D we can add it by 32 which would be 0x6D
+//
+// Potential Improvements: 
+// It may be possible to make a firmware by just altering this variable to the mappings are reconfigurable. 
+// It may be possible to use more than 2 dimension of the array to allocate for special "shift" keys found on SFF keyboards
+uint8_t keyboard_mapping[ROWS][COLS] = {
+  {0x4D,0x69},
+  {0x4B,0x55},
+};
+
+//Temporary variable to store old and new keyoard report.
+//This way we only change the keyboard state when there is a change in the raw data.
+//This allows us to hold keys and press multiple at the same time
+//Rather than sending individual keystroke each press
+uint8_t old_report;
+uint8_t new_report;
+
 BleKeyboard bleKeyboard("ModularKeyboard_MainBoard");
 
 void setup() {
   Serial.begin(115200);
   Serial.println("Starting BLE work!");
   bleKeyboard.begin();
+  for (int i=0; i<COLS; i++){
+    pinMode(ROW[i], INPUT);
+    pinMode(COL[i], OUTPUT);
+  }
 }
 
 void loop() {
   if(bleKeyboard.isConnected()){
+    // Reset keyboard report
+    for (int i = 0; i < 2; i++) {
+      for (int j = 0; j < 2; j++) {
+          keyboard_report[i][j] = 0x0;
+      }
+    }
+    //Read keyboard report and send
     for(int i=0; i < COLS; i++){
-      //TURN ON ROW
+      //Write to the column
+      digitalWrite(COL[i], HIGH);
       for(int j=0; j < ROWS; j++){
-        //READ EACH ROW
-        //ENABLE KEY IN THAT PIN
+        //Read row input
+        old_report = keyboard_report[i][j];
+        new_report = digitalRead(ROW[j]);
+        if(old_report!=new_report){
+          if(new_report){
+            bleKeyboard.press(keyboard_mapping[i][j]);
+          }else{
+            bleKeyboard.release(keyboard_mapping[i][j]);
+            bleKeyboard.release(keyboard_mapping[i][j] + 32); //Shifted version
+          }
+          keyboard_report[i][j] = new_report; 
+        }
       }
     }
   }