Failure to decode messages from Multitech xDot

[bastilleresearch]

Failure to decode messages from Multitech xDot

[jcard0na]

I'm getting closer on this. I switched to a different driver for the xDot that exposes low level access to the radio and turn off the explicit header. I am configuring the radio as shown below, which I understand is a supported configuration:

int main()
{
    (...)
    radio.set_frf_MHz(915.5);
    lora.enable();
    lora.setBw_KHz(500);
    lora.setSf(8);
    lora.setHeaderMode(false);
    lora.setCodingRate(4);
    lora.setRxPayloadCrcOn(false);
 
    (...)

    /* constant payload length of four bytes */
    lora.RegPayloadLength = 1;
    radio.write_reg(REG_LR_PAYLOADLENGTH, lora.RegPayloadLength);

    for (;;) {
        radio.tx_buf[0] = 0x00;  /* set payload */
        lora.start_tx(lora.RegPayloadLength);   /* begin transmission */

        while (lora.service() != SERVICE_TX_DONE)   /* wait for transmission to complete */
            ;

        radio.set_opmode(RF_OPMODE_STANDBY);
        wait(1);  /* throttle sending rate */
        logInfo("waiting for 1s");
    }
}

As shown above, the payload is one byte (0) and now I'm receiving. If I change the payload to 0xff, the first nibble of the third byte changes from 0 to f.

***********************************
* MESSAGE DEBUG PRINT PDU VERBOSE *
()
pdu_length = 7
contents = 
0000: ef f6 0f c7 f2 24 22 
***********************************
* MESSAGE DEBUG PRINT PDU VERBOSE *
()
pdu_length = 7
contents = 
0000: ef f6 0f 47 72 2c 22 
***********************************
* MESSAGE DEBUG PRINT PDU VERBOSE *
()
pdu_length = 7
contents = 
0000: ef f6 0f e7 f2 2c 22 
***********************************
* MESSAGE DEBUG PRINT PDU VERBOSE *
()
pdu_length = 7
contents = 
0000: ef f6 0f c7 f2 b4 22 
***********************************

[jcard0na]

I was finally able to get this to work by changing

 lora.setHeaderMode(false);

with

 lora.setHeaderMode(true);

I had incorrectly assumed that setHeaderMode to true would add the explicit header, when it is the opposite.

After changing that I can send small payloads (<3 bytes) without errors. Yay!