ESP32-S3 parallel communication with Serial & Serial0 (USB & UART)

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1

Hi Guys

I have a use case where I would need to communicate via the USB & UART whenever required, and the code should be able to check and act accordingly wherever the data is available (whether over Serial or Serial0). I have tried to do this with the below platformio.ini and a small cpp code snippet. Individually, the communication works with Serial (when connected to USB) & Serial0 (when connected via UART). I would appreciate it if someone could give me a few insights on how I might achieve my goal of making both communications work simultaneously.

Platformio.ini :

[env:esp32cam]
platform = espressif32@^6.5.0
board = esp32-s3-devkitc-1
framework = arduino

platform_packages = 
	platformio/tool-openocd-esp32

board_build.mcu = esp32s3
board_build.flash_mode = dio 
board_build.partitions = huge_app.csv
board_upload.flash_size: 4MB
board_build.memory_type= dio_opi
board_build.f_flash = 80000000L
board_build.f_cpu = 240000000L
board_upload.maximum_ram_size = 2097152         ;RAM - 2MB
board_upload.maximum_size = 4194304             ;FLASH - 4MB

build_unflags = -std=gnu++11

build_flags = 
        -std=gnu++17
        -DBOARD_HAS_PSRAM
        -DARDUINO_ESP32S3_DEV
        -DARDUINO_USB_CDC_ON_BOOT=1
        ; -DARDUINO_USB_MODE=1           

lib_deps = 
	espressif/esp32-camera@^2.0.4
	bblanchon/ArduinoJson @ ^7.0.3
	fhessel/esp32_https_server @^1.0.0

upload_speed = 115200
monitor_speed = 115200

In my application code, I try to handle this in this way (open to suggestions and feedback):

Serial.begin(115200);
Serial0.begin(115200);

Stream *stream;
    // Check which Serial interface has available data
    if (Serial.available()) {
        stream = &Serial;    
    } else if(Serial0.available()) {
        stream = &Serial0;
    }
    ...
    ...
    ...
    if (Serial0.available() || Serial.available()) {
        stream->println("Data available");

I really appreciate any help you can provide. :slight_smile:

2

Unfortunately, this is unclear (to me).
What do you want to acheive exactly?

Do you want to have a kind of bridge where everything received on Serial0 is written to Serial and vice versa?

3

Hi @sivar2311

Thanks for your response.

Umm no, not really a bridge between Serial and Serial0. Rather, 2 bridges in parallel, both ready to work whenever required. For example, if I send data using Serial, the code should send the response back through Serial. If I send data through Serial0, the response should be received back through Serial0.

Does this make sense at all?

Thanks,
Garvit

4

This is getting more and more confusing for me - sorry.
What do you mean by “send data” and response back through?

If you send data to Serial0 : Serial0.println("Some data"); this is already sent to Serial0… what response do you mean here?

5

Ah, my apologies for this confusion. Let me try harder.

Let’s say the ESP32 is connected through both USB (Serial) and UART (Serial0). I have an application code that expects some kind of request. Let’s say, esp32 is waiting for a command through Serial or Serial0 (both should be listening). For the response, I have to print “Command received”. So, I should know whether the request came through Serial or Serial0 so that I could accordingly do Serial.print("Command received"); or Serial0.print("Command received");

That’s why I was trying something like this:

Serial.begin(115200);
Serial0.begin(115200);

Stream *stream;
    // Check which Serial interface has available data
    if (Serial.available()) {
        stream = &Serial;    
    } else if(Serial0.available()) {
        stream = &Serial0;
    }
    ...
    ...
    ...
    if (Serial0.available() || Serial.available()) {
        stream->println("Command received");

Is it better now?

Thanks a lot for your patience. I really appreciate it.

6

Ok, I got it now. Thanks for the explenation.

The issue with your code might be that after reading from the Stream object (Serial / Serial0) another call to available() will always return 0 (if all data has been read from that stream).

Maybe this is what you’re looking for:

void processStream(Stream* stream) {
  int available = stream->available();

  if (!available) return; // nothing to process? -> return

  char buf[available];
  stream->readBytes(buf, available); // after this line stream->available() returns 0!

  // process content of buf
  // ...

  // send response
  stream->println("Command received");
}

void loop() {
  processStream(&Serial);
  processStream(&Serial0);
}
7

Thanks so much for your solid suggestions.
I will give these a go and let you know the outcome. :slight_smile:

1 Like
8

@sivar2311 Thanks so much. I worked on your suggestions and was able to fulfil my requirements. Really appreciate your support!! :smiley: