[Question] Sending UBX protocol commands about neogps

[SlashDevin]

TBH, I've not tried putting the UBX message into PROGMEM. I think there is an initialization problem, something to do with the constructor needing to "execute" instead of the storage being evaluated by the compiler. You should be able to use send_request, though. I'm working up an example...

[SlashDevin]

Ok, there are three ways to send the reset command:

1. Construct a cfg_reset_t variable in RAM, set its members and use the send_request method.
2. Define a byte array in PROGMEM and send it with the utility function sendUBX (see ubloxRate.ino).
3. Cast the address of the PROGMEM byte array to a cfg_reset_t * and use send_request_P

Here is the code to do it all three ways:

static const uint8_t ubxReset[] __PROGMEM =
  { ublox::UBX_CFG, ublox::UBX_CFG_RST,
    UBX_MSG_LEN(ublox::cfg_reset_t), 0, // a word length... MSB is 0
    0x00, 0x00,    // Hotstart or...
    // 0x01, 0x00, // ... Warmstart or...
    // 0xff, 0xff, // ... Coldstart
    0x02,        // reset mode
    0x00         // reserved
  };

void resetGPS()
{
  const uint8_t WAY = 3; // pick 1,2 or 3
  
  switch (WAY) {
    case 1:
      {
        ublox::cfg_reset_t cfg_cold; // RAM local variable
        cfg_cold.clear_bbr_section =
          // Hotstart
          { false };

          // Warmstart
          // { true, false };

          // Coldstart
          // { true, true, true, true, true, true, true, true, true,
          //   true, // reserved1 is 2 bits
          //   true, true, true, 
          //   true, // reserved2 is 1 bit
          //   true };

        cfg_cold.reset_mode        = ublox::cfg_reset_t::CONTROLLED_SW_RESET_GPS_ONLY;
        cfg_cold.reserved          = 0;
        gps.send_request( cfg_cold );
      }
      break;

    case 2:
      sendUBX( ubxReset, sizeof(ubxReset) ); // just send the PROGMEM bytes
      break;

    case 3:
      {
        const ublox::cfg_reset_t *cfg_cold_ptr = (const ublox::cfg_reset_t *) ubxReset;
        gps.send_request_P( *cfg_cold_ptr );
      }
      break;
  }

} // resetGPS

There were two problems with the code you were trying:

1. The UBX message length does not include the header bytes, so the byte array had the wrong length value (see helper macro UBX_MSG_LEN).
2. The is a bug in send_request_P. It was not accessing the PROGMEM msgClass, msgID and length members correctly. I've checked in a new version of ubxGPS.cpp with a fix. This is not in the release yet, just get that one file.

[Redferne]

I tested option 3 and it worked perfectly! Thank you! Now I will implement a power off command to save battery usage on my device. Cheers! 👍