write and then read data synchronously from device over usb OTG

Question

I am working with ESP32 (CP2102 USB to UART Bridge Controller). I need to send text command to this device and then immediately read response synchronously in the same function to return data. I tried two libraries: usb-serial-for-android and UsbSerial but without success. I checked also on Arduino Uno Rev 3 and the same issue.

my sample from usb-serial-for-android

//....
usbSerialPort.open(usbConnection)
usbSerialPort.setParameters(
SERIAL_BAUD_RATE,
UsbSerialPort.DATABITS_8,
UsbSerialPort.STOPBITS_1,
UsbSerialPort.PARITY_NONE
)
//.....

private fun requestData(textMessage: String): String {
    send(textMessage)
    return read()
}

private fun send(textMessage: String) {
    val messageByteArray = "$textMessage$NEW_LINE".toByteArray()
    val writeResult = usbSerialPort.write(messageByteArray, USB_WRITE_TIMEOUT)
}
fun read(): String {
    val messageByteArray = ByteArray(1024)  //16384   multiply of 64
    val readDataLength = usbSerialPort.read(messageByteArray, USB_READ_TIMEOUT)
    return messageByteArray.decodeToString()
}

const val SERIAL_BAUD_RATE = 115200 //57600 //115200
const val VENDOR_ID = 4292 // ESP32 4292   //arduino 9025
const val PRODUCT_ID = 60000 // ESP32 60000  //arduino 67
const val USB_READ_TIMEOUT = 3000
const val USB_WRITE_TIMEOUT = 1000
const val NEW_LINE = "\n"

and from UsbSerial

//....
if (serialPort.syncOpen()) {
  Log.d(TAG, "port opened successfully!")
  serialPort.setBaudRate(SERIAL_BAUD_RATE)
  serialPort.setDataBits(UsbSerialInterface.DATA_BITS_8)
  serialPort.setStopBits(UsbSerialInterface.STOP_BITS_1)
  serialPort.setParity(UsbSerialInterface.PARITY_NONE)
  /**
   * Current flow control Options:
   * UsbSerialInterface.FLOW_CONTROL_OFF
   * UsbSerialInterface.FLOW_CONTROL_RTS_CTS only for CP2102 and FT232
   * UsbSerialInterface.FLOW_CONTROL_DSR_DTR only for CP2102 and FT232
   */
  serialPort.setFlowControl(UsbSerialInterface.FLOW_CONTROL_OFF)
}
//.....


private fun requestData(textMessage: String): String {
    send(textMessage)
    return read()
}

private fun send(textMessage: String) {
    val messageByteArray = "$textMessage$NEW_LINE".toByteArray()
    val writeResult = serialPort.syncWrite(messageByteArray, USB_WRITE_TIMEOUT)
}
fun read(): String {
    val messageByteArray = ByteArray(1024)  //16384   multiply of 64
    val readDataLength = serialPort.syncRead(messageByteArray, USB_READ_TIMEOUT)
    return messageByteArray.decodeToString()
}

const val SERIAL_BAUD_RATE = 115200 //57600 //115200
const val VENDOR_ID = 4292 // ESP32 4292   //arduino 9025
const val PRODUCT_ID = 60000 // ESP32 60000  //arduino 67
const val USB_READ_TIMEOUT = 3000
const val USB_WRITE_TIMEOUT = 1000
const val NEW_LINE = "\n"

In both examples syncWrite/write is returning result > 0 but messageByteArray from syncRead/read is empty or sometimes contains not cut and messy data.

My sample code from ESP32 / Arduino

#include <Wire.h>

void setup() {
  Serial.begin(115200);
  while (!Serial) {
    delay (100);
  }
}

void loop() {
  String serialANDROID = "";
  if (Serial.available()) {
     serialANDROID = Serial.readStringUntil('\n');
  if (serialANDROID == "command1") {
     Serial.println ("someData = [123456789123456]/nEND/n/n");
  }
  else if (serialANDROID == "command2"){
    Serial.println("OK/nEND/n/n"); 
  }
  else if (serialANDROID == "command3"){
    Serial.println("test=true/nEND/n/n");
  }
  else if (serialANDROID == "command4") {
    Serial.println ("someExtraData = [1234567891234568685645334354]/nEND/n/n");
  }
  else {
    Serial.println("error"); 
  }
 }
}

Is it Android OS limitation ? Someone tried this ? Thanks in advance

score 0 · Answer 1 · answered Jan 23 '21 at 12:02

Firstly, the newlines in your ESP code are backwards, /n instead of \n. Fix those.

Secondly, I suggest trying out your ESP code without the Android counterpart to verify it's behaving correctly. Connect the ESP to a computer, open a serial terminal, enter the commands and check if the responses are arriving as expected.

write and then read data synchronously from device over usb OTG

1 Answers1