I am trying to write a sample program to retrieve temperature data from SHT20 temperature sensor using serial port with apache plc4x library.
private void plcRtuReader() {
String connectionString =
"modbus:serial://COM5?unit-identifier=1&baudRate=19200&stopBits=" + SerialPort.ONE_STOP_BIT + "&parityBits=" + SerialPort.NO_PARITY + "&dataBits=8";
try (PlcConnection plcConnection = new PlcDriverManager().getConnection(connectionString)) {
if (!plcConnection.getMetadata().canRead()) {
System.out.println("This connection doesn't support reading.");
return;
}
PlcReadRequest.Builder builder = plcConnection.readRequestBuilder();
builder.addItem("value-1", "holding-register:258[2]");
PlcReadRequest readRequest = builder.build();
PlcReadResponse response = readRequest.execute().get();
for (String fieldName : response.getFieldNames()) {
if (response.getResponseCode(fieldName) == PlcResponseCode.OK) {
int numValues = response.getNumberOfValues(fieldName);
// If it's just one element, output just one single line.
if (numValues == 1) {
System.out.println("Value[" + fieldName + "]: " + response.getObject(fieldName));
}
// If it's more than one element, output each in a single row.
else {
System.out.println("Value[" + fieldName + "]:");
for (int i = 0; i < numValues; i++) {
System.out.println(" - " + response.getObject(fieldName, i));
}
}
}
// Something went wrong, to output an error message instead.
else {
System.out.println(
"Error[" + fieldName + "]: " + response.getResponseCode(fieldName).name());
}
}
System.exit(0);
} catch (PlcConnectionException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
Connection is established with the device using serial communication. But it fails to get data and instead prints the below warning messages continously.
debugger hangs at below line:
PlcReadResponse response = readRequest.execute().get();
with below logs printing continuously.
2021-06-03-17:41:48.425 [nioEventLoopGroup-2-1] WARN io.netty.channel.nio.NioEventLoop - Selector.select() returned prematurely 512 times in a row; rebuilding Selector org.apache.plc4x.java.transport.serial.SerialPollingSelector@131f8986.
2021-06-03-17:41:55.080 [nioEventLoopGroup-2-1] WARN io.netty.channel.nio.NioEventLoop - Selector.select() returned prematurely 512 times in a row; rebuilding Selector org.apache.plc4x.java.transport.serial.SerialPollingSelector@48c328c5.
With same URL data (i.e baudrate,stopBits etc..) using modpoll.exe it works and returns the data over RTU. I am not sure what is missing here. Kindly shed some light here.
