Missing bytes sended through serial from C# app

Question

I am trying to store values sended by C# app in EEPROM via Arduino UNO. Here is a C# code that reads bytes from file (I'm 100% sure that there are, and always will be 256 bytes) and sends the buffer via SerialPort

 SerialPort port = new SerialPort("COM3", 9600);
 const string fileName = @"filepath";
 port.Open();
 byte[] buffer = File.ReadAllBytes(fileName);
 port.Write("W");
 port.Write(buffer, 0, buffer.Length);

Here is Arduino Code

int flag;
int datasize = 256;
byte byteBuffer[256];
void setup() {
 Serial.begin(9600);
 //read_write();
}
void loop() {
 readEEPROM();
 writeEEPROM();
 delay(500);
}
void readEEPROM() {
 if (Serial.available()) {
 flag = Serial.read();
 if (flag == 'R') {
 for (int i = 0; i < datasize; i++) {
 byteBuffer[i] = ME.read(i);
 }
 flag = 'S';
 Serial.write(byteBuffer, datasize);
 }
 }
}
void writeEEPROM() {
 if (Serial.available()) {
 flag = Serial.read();
 if (flag = 'W') {
 int bytesRead = 0;
 digitalWrite(LED_BUILTIN, HIGH);
 delay(500);
 while (bytesRead < 256) {
 if (Serial.available() > 0) {
 byteBuffer[bytesRead] = Serial.read();
 bytesRead++;
 }
 }
 digitalWrite(LED_BUILTIN, LOW);
 for (int i = 0; i < datasize; i++) {
 digitalWrite(LED_BUILTIN, HIGH);
 delay(50);
 ME.writeEnable();
 ME.write(i, byteBuffer[i]);
 ME.writeDisable();
 digitalWrite(LED_BUILTIN, LOW);
 delay(50);
 }
 flag = 'S';
 }
 }
 }

As you can see in writeEEPROM function arduino turns on BUILTIN_LED before it starts reading serial, sadly the LED is never turning off, which makes me think like there are never 256 bytes in SerialPort, whats more, when i turn the c# program on again, the arduino successfully leaves the while loop, but the data is deformed, I mean the values are different.

• jsotola: why don't you know if there are 256 bytes received by the serial port?
• Majenko: Don't forget that the Arduino reboots every time you open the serial port from the computer - and the bootloader runs for a second or two gobbling up any serial data you send its way...
• Shizzle: @jsotola Well, to leave the while loop arduino needs to enter into if(Serial.available()) 255 times, right now it is not leaving while loop, that's why i assume that there are couple of bytes missing or something like that :/
• Shizzle: @Majenko How can I solve this then ? :)
• Majenko: It can't help but get into "w" - you're assigning with = not comparing with ==.

Answer 1

There's two basic things wrong here.

First is your way of opening the serial port and immediately sending data. The Arduino is reset when you open the serial port and the bootloader runs. This takes a second or so, and during that time any data that you send is lost.

Secondly you're not checking for a flag of "W" but instead you're assigning "W" to the flag, which always succeeds.

The line

if (flag = 'W') {

should read

if (flag == 'W') {

To get around the first problem you can either just put a delay (however you do that in C#) after opening the port and before sending the "W", or you could implement a "Are you there?" handshake to look for the Arduino.

One example would be to add an extra flag of (say) "?" to which the Arduino simply responds "Y".

The PC then sends "?" and, if it doesn't receive "Y" within a certain timeout it loops sending "?" again.

Once it receives "Y" then it knows the Arduino is there and ready to receive data, so you can send the "W" command and the data.