Add alphabetical letters.

8By8/8By8.ino

@@ -1,10 +1,43 @@
 #include "TimerOne.h"
 
-#define TIME_PER_LAYER_IN_US 700
+#define TIME_PER_LAYER_IN_US 800
 #define BUS_START_PIN 22
 #define CLOCK_START_PIN 30
 #define SW_START_PIN 38
 
+const uint16_t numbers[10] = {
+    0xF6F, 0x592, 0xE57, 0xE8F, 0x979, 0xF8F, 0xF3F, 0xE54, 0xFEF, 0xFCF,
+};
+
+const uint64_t letters[26]{
+    0x3C66667E666666, // A
+    0x7C66667C66667C, // B
+    0x3C66606060663C, // C
+    0x7C66666666667C, // D
+    0x7E60607C60607E, // E
+    0x7E60607C606060, // F
+    0x3C6660606E663C, // G
+    0x6666667E666666, // H
+    0x3C18181818183C, // I
+    0x1E0C0C0C6C6C38, // J
+    0x666C7870786C66, // K
+    0x6060606060607E, // L
+    0x63777F6B636363, // M
+    0x63737B6F676363, // N
+    0x3C66666666663C, // O
+    0x7C6666667C6060, // P
+    0x3C6666666E3C06, // Q
+    0x7C66667C786C66, // R
+    0x3C66603C06663C, // S
+    0x7E5A1818181818, // T
+    0x6666666666663C, // U
+    0x66666666663C18, // V
+    0x6363636B7F7763, // W
+    0x6363361C366363, // X
+    0x6666663C181818, // Y
+    0x7E060C1830607E, // Z
+};
+
 class Cube {
 private:
   static int layer_count;
@@ -28,7 +61,9 @@ public:
         // In LED_status:
         // 0 = off
         // 4 = brightest
-            digitalWrite(BUS_START_PIN + j, ((LED_status[layer_count][i] >> (j * 2)) & 3) >= (3 - brightness_count));
+        digitalWrite(BUS_START_PIN + j,
+                     ((LED_status[layer_count][i] >> (j * 2)) & 3) >=
+                         (3 - brightness_count));
       }
       digitalWrite(CLOCK_START_PIN + i, HIGH);
       digitalWrite(CLOCK_START_PIN + i, LOW);
@@ -42,14 +77,148 @@ public:
       return;
     }
     brightness %= 4;
-    LED_status[z][x] = (LED_status[z][x] & (~(3 << (y * 2)))) | (brightness << (y * 2));
+    LED_status[z][x] =
+        (LED_status[z][x] & (~(3 << (y * 2)))) | (brightness << (y * 2));
+  }
+
+  static int get_status(int x, int y, int z) {
+    return LED_status[z][x] >> (y * 2) & 3;
+  }
+
+  static void clear() {
+    for (int i = 0; i < 8; i++) {
+      for (int j = 0; j < 8; j++) {
+        LED_status[i][j] = 0;
+      }
+    }
+  }
+
+  static void draw_num(int x, int y, int z, int num, int direction,
+                       int brightness) {
+    // 0 = look along x
+    // 1 = look reverse x
+    // 2 = look along y
+    // 3 = look reverse y
+    if (num > 9 || num < 0) {
+      return;
+    }
+    switch (direction) {
+    case 0: {
+      for (int i = 0; i < 3; i++) {
+        for (int j = 0; j < 4; j++) {
+          if ((numbers[num] >> (11 - (i + j * 3))) & 1) {
+            Cube::set_status(x, y - i, z - j, brightness);
+          } else {
+            Cube::set_status(x, y - i, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    case 1: {
+      for (int i = 0; i < 3; i++) {
+        for (int j = 0; j < 4; j++) {
+          if ((numbers[num] >> (11 - (i + j * 3))) & 1) {
+            Cube::set_status(x, y + i, z - j, brightness);
+          } else {
+            Cube::set_status(x, y + i, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    case 2: {
+      for (int i = 0; i < 3; i++) {
+        for (int j = 0; j < 4; j++) {
+          if ((numbers[num] >> (11 - (i + j * 3))) & 1) {
+            Cube::set_status(x + i, y, z - j, brightness);
+          } else {
+            Cube::set_status(x + i, y, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    case 3: {
+      for (int i = 0; i < 3; i++) {
+        for (int j = 0; j < 4; j++) {
+          if ((numbers[num] >> (11 - (i + j * 3))) & 1) {
+            Cube::set_status(x - i, y, z - j, brightness);
+          } else {
+            Cube::set_status(x - i, y, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    }
+  }
+
+  static void draw_letter(int x, int y, int z, int num, int direction, int brightness) {
+    // 0 = look along x
+    // 1 = look reverse x
+    // 2 = look along y
+    // 3 = look reverse y
+    if (num > 26 || num < 0) {
+      return;
+    }
+    switch (direction) {
+    case 0: {
+      for (int i = 0; i < 8; i++) {
+        for (int j = 0; j < 8; j++) {
+          if ((letters[num] >> (63 - (i + j * 8))) & 1) {
+            Cube::set_status(x, y - i, z - j, brightness);
+          } else {
+            Cube::set_status(x, y - i, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    case 1: {
+      for (int i = 0; i < 8; i++) {
+        for (int j = 0; j < 8; j++) {
+          if ((letters[num] >> (63 - (i + j * 8))) & 1) {
+            Cube::set_status(x, y + i, z - j, brightness);
+          } else {
+            Cube::set_status(x, y + i, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    case 2: {
+      for (int i = 0; i < 8; i++) {
+        for (int j = 0; j < 8; j++) {
+          if ((letters[num] >> (63 - (i + j * 8))) & 1) {
+            Cube::set_status(x + i, y, z - j, brightness);
+          } else {
+            Cube::set_status(x + i, y, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    case 3: {
+      for (int i = 0; i < 8; i++) {
+        for (int j = 0; j < 8; j++) {
+          if ((letters[num] >> (63 - (i + j * 8))) & 1) {
+            Cube::set_status(x - i, y, z - j, brightness);
+          } else {
+            Cube::set_status(x - i, y, z - j, 0);
+          }
+        }
+      }
+      break;
+    }
+    }
   }
 };
 
 int Cube::layer_count = 0;
 int Cube::brightness_count = 0;
 int Cube::LED_status[8][8] = {0};
-int bright = 3;
+int char_num = 0;
 
 void setup() {
   for (int i = 22; i < 46; i++) {
@@ -62,17 +231,32 @@ void setup() {
 
   Serial.begin(115200);
 
+  cli();
+  TCCR4A = 0; // set entire TCCR1A register to 0
+  TCCR4B = 0; // same for TCCR1B
+  TCNT4 = 0;  // initialize counter value to 0
+  // set compare match register for 1hz increments
+  OCR4A = 15624 / 1; // = (16*10^6) / (1*1024) - 1 (must be <65536)
+  // turn on CTC mode
+  TCCR4B |= (1 << WGM12);
+  // Set CS12 and CS10 bits for 1024 prescaler
+  TCCR4B |= (1 << CS12) | (1 << CS10);
+  // enable timer compare interrupt
+  TIMSK4 |= (1 << OCIE4A);
+  sei();
+
+  randomSeed(analogRead(0));
 }
 
 void loop() {
-    
-    for (int i = 7; i >= 0; i--) {
-        for (int j = 0; j < 8; j++) {
-            for (int k = 0; k < 8; k++) {
-                Cube::set_status(i, j, k, bright);
-                delay(5);
-            }
-        }
-    }
-    bright = (bright + 1) % 4;
+  // Ref:
+  // https://raw.githubusercontent.com/wiki/olikraus/u8glib/fontpic/u8g_font_u8glib_4.png
+  // Serial.println(i);
+  Cube::draw_letter(7, 7, 7, char_num, 3, 3);
+  delay(1000);
+}
+
+ISR(TIMER4_COMPA_vect) {
+  char_num = (char_num + 1) % 26;
+  Serial.println(char_num);
 }