Arduino: Add full Arduino code

This is the full working Arduino code, for writing and loading.

This shouldn not be used by students.

Arduino/SendCart/SendCart.ino

@@ -0,0 +1,98 @@
+#include <Wire.h>
+#include <inttypes.h>
+
+// Arduino constants
+static constexpr uint8_t i2c_buff_size = 32;
+static constexpr uint8_t serial_buff_size = 64;
+
+// EEPROM constants
+static constexpr int page_count = 512;
+static constexpr int page_size = 128;
+static constexpr int i2c_buff_per_page = page_size / i2c_buff_size;
+static constexpr uint8_t eeprom_addr = 0b1010000;
+
+uint8_t pageData[page_size] = {};
+uint16_t pageAddr = 0;
+
+// Send a two bytes address via I²C which selects an address within the EEPROM.
+void write_addr(uint16_t addr) {
+  Wire.write((uint8_t)(addr >> 8));
+  Wire.write((uint8_t)addr);
+}
+
+// When the receiver sums on its side, it can just add this sum and check that is 0.
+uint16_t sum_complement(const uint8_t data[page_size]) {
+        uint16_t sum = 0;
+        for (int i = 0; i<page_size; i += 2) {
+          sum += (data[i+1] << 8) | data[i];
+        }
+        return -sum;
+}
+
+void setup() {
+  Serial.begin(115200);
+  pinMode(LED_BUILTIN, OUTPUT);
+  Wire.begin();
+}
+
+/*
+ * Read data from the Serial port until a full message is read.
+ * This function is blocking and will not return early, use with caution.
+ * Use '\n' as a delimiter for a complete message, making it exit
+ * early if it is encountered before the count is done (invalid message).
+ */
+void read_message(char *buffer, const uint8_t match_len) {
+  uint8_t read_bytes = 0;
+  do {
+    // readBytesUntil should always be positive or zero, despite the documentation.
+    read_bytes += Serial.readBytesUntil('\n', buffer + read_bytes, match_len - read_bytes);
+  } while(read_bytes < match_len || Serial.peek() == '\n');
+  if (Serial.peek() == '\n')
+    Serial.read(); // Consume the delimiter if it is there.
+}
+
+void loop() {
+  char ret[4];
+  // Wait until we receive the start message.
+  do {
+    memset(ret, 0, 4);
+    read_message(ret, 2);
+  } while (strncmp(ret, "GO", 2) != 0);
+
+  // Reset the EEPROM internal address to 0. It autoincrements after.
+  Wire.beginTransmission(eeprom_addr);
+  write_addr(0);
+  Wire.endTransmission(false);
+
+  digitalWrite(LED_BUILTIN, HIGH);
+  /*
+   * We don't know the size of the cartridge, and it could be the whole EEPROM.
+   * Read and send all the pages (64kiB), it should not impact the final PNG.
+   */
+  for (int i = 0; i < page_count; i++) {
+    memset(pageData, 0, page_size);
+    // Arduino I2C buffer is 32 bytes, so we need multiple requests per page.
+    for (int j = 0; j < i2c_buff_per_page; j++) {
+      Wire.requestFrom(eeprom_addr, i2c_buff_size);
+      for (int k = 0; k < i2c_buff_size; k++) {
+        pageData[i2c_buff_size*j + k] = Wire.read();
+      }
+    }
+
+    // Try to send the full page via serial until the recipient ACKs.
+    uint16_t page_checksum = sum_complement(pageData);
+    do {
+      // The internal Serial buffer is smaller than a page, so send in bursts.
+      size_t written = 0;
+      while (written < page_size) {
+        written += Serial.write(pageData + written, min(page_size - written, serial_buff_size));
+      }
+      Serial.write((uint8_t*)&page_checksum, 2);
+
+      memset(ret, 0, 4);
+      read_message(ret, 3);
+    } while(strncmp(ret, "ACK", 3) != 0);
+  }
+
+  digitalWrite(LED_BUILTIN, LOW);
+}