Arduino HardwareSerial flow control with handshake XON/XOFF

Question

I am sending large texts from PC to Arduino over Serial and I cannot simply copy-paste it, as Arduino is not fast enough to process it on the fly.

I need some flow control (probabely XON/XOFF) so Arduino would automatically send "I am bussy, stop sending" when its input buffer is about overflow and then "send more data" when the buffer is empty again.

(The Arduino program need to process the received text and it may take a time and there is not enought RAM to buffer all input. And on the other hand it should be responsive, so it should not wait for full buffer.)

(I had more projects with similar problems. The current is FORTH interpret on Arduino Uno (atmega328p) / Arduino Mega (atmega2560), where I want to copy-paste some programs first (say 1-5kB of text) and then continue with interactive communication (run some words, see results, play games ...)

What is the best solution?

• jsotola: examine avrdude
• gilhad: @jsotola - avrdude is used for "burning" binary code into flash via bootloader. I need to communicate with running program. How is avrdude suposed to help?
• jsotola: it sends large amount of data without error ... see how it is accomplished ... examine the source code for avrdude and for the bootloader
• gilhad: It uses internal protocol with known buffer size (256) and synchronisation messages dialog style ( such this ww1.microchip.com/downloads/aemDocuments/documents/OTH/… ). I would prefere something supproted by existing terminal programs if possible.
• halfbit: How often do you need this data transfer? And what is on the other side of transmission? Who is transmitting?

Answer 1

The Arduino Serial has no support for flow control, and neither does the serial port on the AVR microcontrollers. Unless you find a library that handles this for you, you will have to manage it on your own.

A typical way to handle serial input is to copy the incoming bytes from the Serial buffer into your own buffer and, when you see a message terminator (typically some end-of-line), you handle the whole message. Maybe something like this:

void loop() {
 /* Process incoming commands. */
 while (Serial.available()) {
 static char buffer[BUFFER_LENGTH];
 static int length = 0; // length received so far
 int data = Serial.read();
 if (data == '\r') { // on end-of-line:
 buffer[length] = '0円'; // terminate the string
 if (length) exec(buffer); // call the interpreter
 length = 0; // reset the buffer
 } else if (length < BUFFER_LENGTH - 1) {
 buffer[length++] = data; // buffer the incoming byte
 }
 }
}

If you are following this scheme, you could modify it to add your own XON/OFF support. Assuming the interpreter is the slow bit, you may simply replace exec(buffer); with:

{
 Serial.write(0x13); // send XOFF
 exec(buffer); // call the interpreter
 Serial.write(0x11); // send XON
}