Speed of Multiple I/O Operations Using jSerialComm

[toddcplayer]

Hi. First, thanks for this great resource. I have a project I am working on that requires multiple read/write operations in a very short time. Right now, I can't achieve the performance I want due to the length of time it takes to open the port and then set the parameters like so:

ubxPort.openPort(50);
ubxPort.setComPortParameters(115200, 8, 1, 0);
ubxPort.setFlowControl(0);
out.write(command.getBytes());
out.flush();
out.close();
ubxPort.setComPortTimeouts(SerialPort.TIMEOUT_READ_SEMI_BLOCKING, 50, 0);
InputStream in =ubxPort.getInputStream(); // Read input from PLC device
byte[] newData = new byte[ubxPort.bytesAvailable()];
int numRead = ubxPort.readBytes(newData, newData.length);
response = new String(newData, "UTF-8");
System.out.println(response);
ubxPort.closePort();

My data returned is small. It's like "OK,1" or "ERROR". Very basic text strings.

I found the documentation about openPort() and setting that timeout and that helped quite a bit, but I am wondering if there are other tuning opportunities I can use to speed it up further. FYI, my app dispenses water, and when my delay to turn a valve off is 1/2 second, I still get quite a bit of water after clicking a button. One thought I had was to open the port and set parameters globally when the app launches but I have thus far been unsuccessful in that approach.

I appreciate any insight or suggestions you might be able to offer.

[hedgecrw]

Hi there, thanks for your question!

In general, your suggestion of opening the port when the application launches is 100% the correct approach. If your app is very time sensitive (such as dispensing water), you most certainly don't want to waste time configuring a serial port for every single command, nor would this be considered safe at all. Consider the case where you open the port, send a "start dispensing" command, close the port, and then try to re-open the port to send a "stop dispensing" command, but the open() call fails for some reason. You will end up with a flood on your hands. It's much safer to preconfigure all comms during application launch and only deal with reading/writing during the normal course of the application usage.

Regarding speed improvements, you're more than welcome to set all serial parameters and timeouts (setComPortParameters, setFlowControl, setComPortTimeouts, etc) ONCE before the port is opened (such as at application launch) and they will remain intact during each subsequent open() call, assuming you are using the same SerialPort object and no re-enumerating them every time. That will result in huge speed-ups. Also, you can set the open() delay to 0 instead of 50 to have it open instantaneously. Next, you are requesting an InputStream (getInputStream) from the serial port but never using it which wastes time, so just remove that line completely. And finally, for speed's sake, I would pre-allocate a read buffer of sufficient size (slightly larger than the longest serial string you expect to receive), and directly use and re-use that buffer when making readBytes calls instead of allocating a new byte[] buffer using bytesAvailable() every single time you want to read something.

The correct solution, however, would be to open and configure everything at launch time, and to pre-allocate a read buffer, so that your only two library calls during normal operation are writeBytes() and readBytes(). Hope that helps!

[toddcplayer]

Thank you for getting back to me. I made the changes and you were right about it making an absolutely huge difference in performance. Really appreciate it.