Multiple .write() slow ?

Core Library Questions

astrixstar

in Core Library Questions • 2 years ago

I need to send a high rate of data to my arduino.
Sending calling more than one .write() call in my loop seems to be dramatically slowing my processes.

my first call would return about 80fps:

myport.write(hex("#ff9900",6));

if I add in another call it slows to 30 fps:

myport.write("N");

myport.write(hex("#ff9900",6));

if I put all values into one call, and even add more data I get my 80 fps back again:

myport.write("N" + i + hex("#ff9900",6));

does this seem odd to anyone? Is there an easy fix?

Replies(5)

PhiLho

Not odd, and you found the easy fix...
Each write supposes a transaction over the serial port (handshaking, acknowledge, etc.), so it is rather slow. If you combine several writes into one, you reduce the number of protocol exchanges over the size of the sent data.

astrixstar

Re: Multiple .write() slow ?

2 years ago

Thats interesting. So theoretically rather than doing one call inside a loop ie:

for (i=0; i<30; i++)

{

myport.write(i + "669900");

}

I'd be better off doing something like:

String sendString = "";

for (i=0; i<30; i++)

{

sendString = sendString + i + "669900";

}

myport.write(sendString);

astrixstar

Re: Multiple .write() slow ?

2 years ago

Turns out no, the second example drops the frame rate to 20fps! Nasty. What a quirky library processing.serial seems to be.

PhiLho

Re: Multiple .write() slow ?

2 years ago

First, it is better to use a StringBuilder to do such concatenation. Note that if the string is constant, you should build it in setup(), ie. only once.
Second, it is not the fault of the library (AFAIK) but a problem inherent to the serial protocol. Now, I don't know well the library (I don't have serial devices), but perhaps you can set up a higher bit rate.

astrixstar

Re: Multiple .write() slow ?

2 years ago

Yeah I'm using the max baud rate for arduino pro / xbee. Thanks for your replies phi.lho.

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