Increase send-receive speed between Arduino and linux computer

Projects Networking, Protocols, and Devices
1

Hi,

I have a problem where i send data from a Teensy 3.6 which runs arduino to the computer, do some calculations on that data and send it back to the arduino using serial communiciation over a USB.
And I would like to do this as fast as possible. ​The computer runs on real time linux, but i'm not smart enough to understand any of that.

Underneath I have code (based on code found on this forum), where i send and recieve a short string (see underneath) and it is very slow. I can do the send-recieve loop at 200Hz.

Is there any ​way that I can make this faster? I have full control over what I can change on the computer and hardware. Installing other kernels, maybe ethernet or things like that. So any solutions are welcome.

Code on the arduino:

const byte buffSize = 40;
char inputBuffer[buffSize];
const char startMarker = '<';
const char endMarker = '>';
byte bytesRecvd = 0;
boolean readInProgress = false;
boolean newDataFromPC = false;

char messageFromPC[buffSize] = {0};


//=============

void setup() {
  Serial.begin(57600);
}

//=============

void loop() {
  getDataFromPC();
  replyToPC();
}

//=============

void getDataFromPC() {

    // receive data from PC and save it into inputBuffer
   
  if(Serial.available() > 0) {

    char x = Serial.read();

      // the order of these IF clauses is significant
     
    if (x == endMarker) {
      readInProgress = false;
      newDataFromPC = true;
      inputBuffer[bytesRecvd] = 0;
      strcpy(messageFromPC, inputBuffer); //not sure if this is still needed
    }
   
    if(readInProgress) {
      inputBuffer[bytesRecvd] = x;
      bytesRecvd ++;
      if (bytesRecvd == buffSize) {
        bytesRecvd = buffSize - 1;
      }
    }

    if (x == startMarker) {
      bytesRecvd = 0;
      readInProgress = true;
    }
  }
}


//=============

void replyToPC() {

  if (newDataFromPC) {
    newDataFromPC = false;
    Serial.print("<");
    Serial.print(messageFromPC);
    Serial.print(">");
  }
}

//============

Code on python (pyserial):

#=====================================

#  Function Definitions

#=====================================

def sendToArduino(sendStr):
    ser.write(sendStr.encode('utf-8')) # change for Python3


#======================================

def recvFromArduino():
    global startMarker, endMarker
   
    ck = ""
    x = "z" # any value that is not an end- or startMarker
    byteCount = -1 # to allow for the fact that the last increment will be one too many
   
    # wait for the start character
    while ord(x) != startMarker:
        x = ser.read()
   
    # save data until the end marker is found
    while ord(x) != endMarker:
        if ord(x) != startMarker:
            ck = ck + x.decode("utf-8") # change for Python3
            byteCount += 1
        x = ser.read()
   
    return(ck)


#============================

def waitForArduino():

    # wait until the Arduino sends 'Arduino Ready' - allows time for Arduino reset
    # it also ensures that any bytes left over from a previous message are discarded
   
    global startMarker, endMarker
   
    msg = ""
    while msg.find("Arduino is ready") == -1:

        while ser.inWaiting() == 0:
            pass
       
        msg = recvFromArduino()

        print (msg) # python3 requires parenthesis
        print ()
       
#======================================

def runTest():
    waitingForReply = False

    for i in range(1,1000):

        if waitingForReply == False:
            sendToArduino('<'+str(i)+'>')
            waitingForReply = True

        if waitingForReply == True:

            while ser.inWaiting() == 0:
                pass
           
            dataRecvd = recvFromArduino()
            print ("Reply Received  " + dataRecvd)

            waitingForReply = False
            print ("-------------------")


#======================================
# THE DEMO PROGRAM STARTS HERE
#======================================
# as sudo -s, doing this doesn't make a difference: setserial /dev/ttyACM0 low_latency
import serial
import time


# NOTE the user must ensure that the serial port and baudrate are correct
portname = "/dev/ttyACM0"
baudrate = 57600
ser = serial.Serial(portname,baudrate,timeout=1)

startMarker = 60
endMarker = 62
t1 = time.time()
runTest()
print(time.time()-t1) #between 4.98 and 5.2 seconds
ser.close()

I have tried the same via LibSerialPort via the julia programming lanuage instead of pyserial and i get exactly the same 200Hz. So i have a feeling that it is at the side of the computer that something can be done faster.

2

You can use a baud rate that is much faster. I use 250000 sometimes.

3

Thanks for the quick response.

I tried that too, but got the same results. I read here that Teensies have a fixed baud rate of 12 MB/s.

Also doubling the length of the data that is sent to the Teensy from the computer doesn't seem to have an effect.

4

If a higher baud rate doesn't help then I would suspect that the delay is on the Linux box.

Try putting some logging in on the python side to see where it is spending its time.

5

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