Reading from USB serial GPS

[mbcoder]

I've got a USB based GPS device which I'd like to read from. I've been following the documentation here to get me started.

I've proven my GPS device can be listened to by using Putty so I know its broadcasting on /dev/ttyUSB0 at 4800baud, 8 data bits, one stop bit. Of course I'm closing putty before running my Java app!

My code so far looks like this:

System.out.println("Starting serial...");

            pi4j = Pi4J.newAutoContext();


            serial = pi4j.create(Serial.newConfigBuilder(pi4j)
                .baud(Baud._4800)
                .dataBits_8()
                .parity(Parity.NONE)
                .stopBits(StopBits._1)
                .flowControl(FlowControl.NONE)
                .id("gps port")
                .device("/dev/ttyUSB0")
                //.provider("pigpio-serial"). --  Note I commended this out as my serial is on USB port!  Different val needed?
                .build());

            System.out.println("serial " + serial);
            serial.open();

            System.out.println("about to create runnable");

            

            Runnable runnable = new Runnable() {
                @Override
                public void run() {
                    System.out.println("Waiting till serial port is open");
                    while (!serial.isOpen()) {
                        try {
                            Thread.sleep(1000);
                            System.out.println("retry...");
                        } catch (InterruptedException e) {
                            throw new RuntimeException(e);
                        }
                    }

                    //opened now!
                    System.out.println("serial port is open!");

                    // Start a thread to handle the incoming data from the serial port
                    SerialReader serialReader = new SerialReader(serial);
                    Thread serialReaderThread = new Thread(serialReader, "SerialReader");
                    serialReaderThread.setDaemon(true);
                    serialReaderThread.start();

                }
            };
            System.out.println("about to start runnable");
            runnable.run();

So when I run the code, it waits for the serial port to open, but it never return true when I call serial.isOpen()

The example in the documentation worked using a serial connection connected to the GPIO port, but I'm wondering if the API works for a USB based device? Maybe I'm just doing something silly.

Any thoughts would be much appreciated.

[taartspi]

You need that .provider line. Without, the default '.build' operation has not created a usable device. With that line included your code gets into the SerialReader thread and fails for a bad handle, I do not have a /dev/ttyUSB0 in my tree. Hopefully this lets you debug further.

[mbcoder]

@taartspi thanks for your reply. I've had a dig into what the provider is and understand why its needed - basically in the background you are using the pigpio library.

When I added the provider back into the code, the .build didn't return and on killing the app, it bubbles up an exception like this:

Caused by: com.pi4j.library.pigpio.PiGpioException: PIGPIO ERROR: PI_INIT_FAILED; pigpio initialisation failed
        at com.pi4j.library.pigpio@2.3.0/com.pi4j.library.pigpio.impl.PiGpioBase.validateResult(PiGpioBase.java:265)
        at com.pi4j.library.pigpio@2.3.0/com.pi4j.library.pigpio.impl.PiGpioBase.validateResult(PiGpioBase.java:251)
        at com.pi4j.library.pigpio@2.3.0/com.pi4j.library.pigpio.impl.PiGpioNativeImpl.gpioInitialise(PiGpioNativeImpl.java:98)
        at com.pi4j.library.pigpio@2.3.0/com.pi4j.library.pigpio.PiGpio.initialize(PiGpio.java:159)
        at com.pi4j.plugin.pigpio@2.3.0/com.pi4j.plugin.pigpio.provider.serial.PiGpioSerialProviderImpl.create(PiGpioSerialProviderImpl.java:60)

I was looking around some other discussions on this forum and found that running my app with sudo makes it work and I don't get the exception.

So as a gradle app I run it as: sudo ./gradlew run and it all springs into life and I'm seeing my NMEA sentences.

So although I've got it working, is there a way of reading the serial port without running my java app from sudo?

I can run Putty via my own user and that works, so I'm wondering of there is some config I can do to make this work?

Thanks again - this is much appreciated!

[taartspi]

Sudo is required by the pigpio library to access the hardware. You can find conversations of people configuring the userID and pi to avoid this. I never researched if/how well it worked as my programs are used by me so adding sudo is not a problem Glad u have things moving.

[mbcoder]

@taartspi thanks again for your replies, I thought you'd be interested in the project I've applied this to which is in this Blog

Having used the pi4j API which is an great project backed up by good documentation, I feel that I could make some improvements and additions myself so I might pop in a ticket with my ideas.

[taartspi]

Your care in documentation will encourage interested folks to give it a try. When I read through your project my thought was to suggest you contact @FDelporte and this work be added to the Pi4j web but Frank beat me to it. Take care, Tom

[FDelporte]

Wow @mbcoder that's a really nice post where you combine two of my "darlings": Pi4J and JavaFX ;-)
Shared it here:
https://foojay.social/@pi4j/110654372808381876
https://pi4j.com/documentation/io-examples/serial/#code-example

Will also include it in the next JFX-Central LinksOfTheWeek!

Looking forward to your feedback for the Pi4J!