Trouble identifying packet source in a 2TX one RX setup

Using Arduino Programming Questions
1

I have a setup consisting of two Tx's sending data to one receiver.
Since the package Data structure has aleary 31 bytes, I decided not to use a vaiable to identify each transmitter and assigned one pipe to each TX instead.
On the receiver side, data would be identified by this code:

 uint8_t pipe;
  pipe = 1;
// for debugging
 if(serialPrintFlag == true){
  Serial.print("before checking....pipe= ");
  Serial.println(pipe);
  }

  if (radio.available(&pipe)){               

// for debugging...
    if(serialPrintFlag == true){
     Serial.print("after checking..pipe= ");
     Serial.println(pipe);
  }

 if (pipe == 1){                   // Changed Jan 2024 check pipe 1 => Cisterna
    getCisternaData();       // Changed Jan 2024
    }

  if (pipe == 2){                 // Changed Jan 2024 check pipe 2 => Caixa
    getCaixaData();           // Changed Jan 2024
    }

but it does not work.
It is probably a stupid mistake for I have been reading forums & tutorial for hours now and I still don't get it.
Can anyone help?
PS I have not posted the entire Tx's & RX codes here because two of them has more than 1100 lines, so I am trying to stick to the issue and made the other people life easier.

2

You can always pick one of the bytes that will ALWAYS have a low numeric value and set the high order bit to 1 for one sender and to 0 for the other sender.

3

Post the exact data structure of the payload. I'd be willing to bet there's opportunity for compaction. Also, which Arduino board? On 32-bit architectures you can use the "packed" attribute to recover space "lost" to default data alignment.

4

Here is the data structure
In my setup there are two Arduinos ProMicro (the Tx's) send data for a ESP32 (the RX) so I took long time to figure out that I had to align the data.....

// Structure of our payload
// ESP32 group data in 4 bytes chunks, so data structure has to be rearranged 

//The data to be transmitted by lower and upper water tanks modules is:
//         type       cisterna     caixa superior
//        -------    ----------    --------------
//  1      float     Irms          auxVol   (last pumping cycle volume)
//  2      float     flow          flow
//  3      float     Pdisch        totalLiters
//  4      float     DpFilter      flowPoco (added July 2023)
//  5      float     Pinlet        dummy2
//  6      float     lampCurrent   dummy4  //added in March 2021
//  7      int       rawDp         rawDp
//  8      bool      flapstate     dummy3

// In Jan 2024 rev 0 on, dummy variables on Cx Superior will be assigned a value 0f -100, which will
// be used by the receiver to identify the data belongs to Caixa Superior

// Structure of our payload
struct payload_t      // 32 bytes max,  used=7*4+2+1 = 31 bytes OK! corrected March 2023
{
  uint32_t  counter;  // - 4 bytes number of packets transmitted
  float     val1;     // - 4 bytes
  float     val2;     // - 4 bytes
  float     val3;     // - 4 bytes
  float     val4;     // - 4 bytes
  float     val5;     // - 4 bytes
  float     val6;     // - 4 bytes
  int16_t   val7;     // - 2 bytes
  bool      val8;     // - 1 byte
};

 payload_t payload;  // create a variable with the above structure
5

I'm thinking have a data alignment problem. Print the 'sizeof()' macro result for that data structure on both the ProMicro and ESP32. I'm willing to bet they will be different. The int16_t and bool will likely occupy 4 bytes each on the ESP32. That's why I mentioned the packed attribute.

You also didn't specify the radio type. What are TX and RX?

As for the amount of data, you may need to break the payload into two packets. Then it gets even trickier as you'll need to identify the packet type AND it would be possible to receive interleaved packets from the two TXs causing even more confusion. You'll need to work out a protocol so the two TXs don't stomp on each other.

6

Thank you for your reply gfvalvo.
This data structure works, since I could receive the correct values of both transmitters when I was using the RF24Netork library.

7

That's interesting, because when I run this code on an ESP32:

struct payload_t      // 32 bytes max,  used=7*4+2+1 = 31 bytes OK! corrected March 2023
{
  uint32_t  counter;  // - 4 bytes number of packets transmitted
  float     val1;     // - 4 bytes
  float     val2;     // - 4 bytes
  float     val3;     // - 4 bytes
  float     val4;     // - 4 bytes
  float     val5;     // - 4 bytes
  float     val6;     // - 4 bytes
  int16_t   val7;     // - 2 bytes
  bool      val8;     // - 1 byte
};

void setup() {
  Serial.begin(115200);
  delay(2000);
  Serial.printf("Size of payload_t = %d\n", sizeof(payload_t));
}

void loop() {
}

I get:

Size of payload_t = 32

On an Uno (also a AVR processor, I don't have I Pro Micro):

struct payload_t
{
  uint32_t  counter;  // - 4 bytes number of packets transmitted
  float     val1;     // - 4 bytes
  float     val2;     // - 4 bytes
  float     val3;     // - 4 bytes
  float     val4;     // - 4 bytes
  float     val5;     // - 4 bytes
  float     val6;     // - 4 bytes
  int16_t   val7;     // - 2 bytes
  bool      val8;     // - 1 byte
};

void setup() {
  Serial.begin(115200);
  delay(2000);
  Serial.print("Size of payload_t = ");
  Serial.println(sizeof(payload_t));
}

void loop() {
}

Size of payload_t = 31

So, as I said (twice):

ESP32:

struct __attribute__ ((packed)) payload_t
{
  uint32_t  counter;  // - 4 bytes number of packets transmitted
  float     val1;     // - 4 bytes
  float     val2;     // - 4 bytes
  float     val3;     // - 4 bytes
  float     val4;     // - 4 bytes
  float     val5;     // - 4 bytes
  float     val6;     // - 4 bytes
  int16_t   val7;     // - 2 bytes
  bool      val8;     // - 1 byte
};

void setup() {
  Serial.begin(115200);
  delay(2000);
  Serial.printf("Size of payload_t = %d\n", sizeof(payload_t));
}

void loop() {
}

Size of payload_t = 31
8

Well, you're using at a minimum 8 bits to transfer what can be represented in a single bit. The unused 7 bits could be used to represent up to 128 unique data sources, if you wanted to do a little programming. Or, is the structure out of your control?

9

thank you for your reply [camsysca].

Yes, I can alter the structure if it helps

10

I would replace the bool with two uint8_t variables (to keep the 32 byte size for the structure). Use one for bit flags. Replace the bool with a bit flag and you have 7 left for future expansion. Use the other one for your ID (I assume you won't have more then 256 devices).

11

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