Serial Library and Arduino

Core Library Questions

joined

in Core Library Questions • 7 months ago

Hi to everyone.

So, I'm using Processing to communicate with an Arduino through a Bluetooth serial port.

I'm trying to understand why when I write bytes to the Serial port, it's very slow.

Here's an example to understand:

import processing.serial.*;
Serial myPort;
byte arr[] = {0,1,2,3,4,5,6,7,8,9,
0,1,2,3,4,5,6,7,8,9,
0,1,2,3,4,5,6,7,8,9,
0,1,2,3,4,5,6,7,8,9,
0,1,2,3,4,5,6,7,8,9};
void setup()
{
size(400, 600);
myPort = new Serial(this, "/dev/tty.HC-05-DevB", 57600);
}
void draw()
{
myPort.write(arr);
//myPort.write((byte)1);
println(millis());
}

This gives me the following output:

3183
3200
3401
3652
3902
4152
4402
4652
4902
5152
5402
5655
5902
6152
..

So I'm sending a 'frame' of 50bytes 4 times a second. But the STRANGE thing is that if I send, instead of a 50bytes frame, just a single byte (uncommenting the 18th line and commenting the 17th), the result is EXACTLY the same.

How can this be possible? If the max speed is 4 bytes per second, how it comes that i can send 4 frames of 50 bytes in one second?

Thank you for the help, I've also tried looking in the Processing source code to understand how this works but no luck..

Replies(4)

akseidel

Re: Serial Library and Arduino

7 months ago

I think it seems exactly the same because it is exactly the same. Think about what might cause that. You may have demonstrated a valuable lesson if this is what I think it is. The draw loop executes at a fixed speed over and over. Apparently it looks like the array transmits faster than the draw loop cycle speed. Therefore the single byte and the array transmission time "seem" to be the same. Look into the draw loop speed settings.

joined

Re: Serial Library and Arduino

7 months ago

Yes, I thought that too but.. if I use a while(true) {code} loop the result is exactly the same.

akseidel

Re: Serial Library and Arduino

7 months ago

Bracket the myPort.writes with println commands. Then give it shot.

For example:

println("SA " + millis());

myPort.write(arr.);

println("EA " + millis()) ;

println("SB " + millis());

myPort.write((byte)1);

println("EB " + millis());

joined

Re: Serial Library and Arduino

7 months ago

Sketch:

import processing.serial.*;
Serial myPort;
byte arr[] = {0,1,2,3,4,5,6,7,8,9};
void setup()
{
size(400, 600);
myPort = new Serial(this, "/dev/tty.HC-05-DevB", 57600);
while (true)
{
println("SA " + millis());
myPort.write(arr);
println("EA " + millis());
println("SB " + millis());
myPort.write((byte)1);
println("EB " + millis());
}
}
void draw()
{
}

Result:

SA 3314
EA 3314
SB 3315
EB 3324
SA 3324
EA 3453
SB 3453
EB 3703
SA 3703
EA 3953
SB 3953
EB 4203
SA 4203
EA 4453
SB 4453
EB 4703
SA 4703
EA 4953
SB 4953
EB 5203
SA 5203
EA 5453
SB 5453

How the hell can be sending 10bytes faster than sending a single one?

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