LP-EM-CC2745R10-Q1: changing TX power during runtime

Hi Aslam,

I apologize for the late response, though I was able to get it working on my side, so below are the steps.

1. Make sure that the TX power setting in sysconfig is set to The Controller will choose the Tx Power

You can find these settings in Broadcaster Configuration > Advertisement Set 1 > Advertisement Set Parameters 1

2. I then create a global tx_power variable, that will be externed into the app_peripheral.c file. First, we need to add the tx_power variable into simple_gatt_profile.c and then change the value:

uint8_t tx_power = 0; // My global variable that will be read in app_peripheral.c
bStatus_t SimpleGattProfile_writeAttrCB( uint16_t connHandle,
                                     gattAttribute_t *pAttr,
                                     uint8_t *pValue, uint16_t len,
                                     uint16_t offset, uint8_t method )
{
  bStatus_t status = SUCCESS;
  uint8 notifyApp = 0xFF;

  if ( pAttr->type.len == ATT_BT_UUID_SIZE )
  {
    // 16-bit UUID
    uint16 uuid = BUILD_UINT16( pAttr->type.uuid[0], pAttr->type.uuid[1]);
    switch ( uuid )
    {
      case SIMPLEGATTPROFILE_CHAR1_UUID:
      {
          // Simple logic for setting the tx_power
          // This could be done a variety of more robust ways.
          // I did it this way just for the example.
          if (*pValue <= 10)
          {
              tx_power = *pValue;
          }
      }

I modified simple_gatt_profile.c :: SimpleGattProfile_writeAttrCB but notice, in this function the validation of the value comes in the next case (SIMPLEGATTPROFILE_CHAR3_UUID) statement. I recommend refactoring this, so the value is always validated. However, for the sake of this example, I wanted this to be quick and I understand that your overall implementation will be different so don't pay too much attention to this. The goal is to set the tx_power variable via GATT so that our main application has access to that value, regardless of how that is accomplished.

3. Now we need to modify app_peripheral.c :: Peripheral_GAPConnEventHandler

In order to change the TX power, we will need to stop all connections and stop all advertisements to ensure that the radio is no longer in use. I haven't thoroughly tested this, however, I believe that when the radio is in use the tx power cannot be changed. Please see the BLEAPPUTIL_LINK_TERMINATED_EVENT.

extern uint8_t tx_power;

void Peripheral_GAPConnEventHandler(uint32 event, BLEAppUtil_msgHdr_t *pMsgData)
{
    switch(event)
    {
        case BLEAPPUTIL_LINK_ESTABLISHED_EVENT:
        {
            /* Check if we reach the maximum allowed number of connections */
            if(linkDB_NumActive() < linkDB_NumConns())
            {
                /* Start advertising since there is room for more connections */
                BLEAppUtil_advStart(peripheralAdvHandle_1, &advSetStartParamsSet_1);
            }
            else
            {
                /* Stop advertising since there is no room for more connections */
                BLEAppUtil_advStop(peripheralAdvHandle_1);
            }
            break;
        }

        case BLEAPPUTIL_LINK_TERMINATED_EVENT:
        {
            // Stop advertising completely.
            BLEAppUtil_advStop(peripheralAdvHandle_1);

            // Set the TX power.
            HCI_EXT_SetTxPowerDbmCmd(tx_power, 0);

            // Start advertising again.
            BLEAppUtil_advStart(peripheralAdvHandle_1, &advSetStartParamsSet_1);
            break;
        }

        default:
        {
            break;
        }
    }
}

Alternatively, you could trigger the termination of connections when you set the tx power, but I just manually disconnect from the device. This will cause a BLEAPPUTIL_LINK_TERMINATED_EVENT to trigger, thus setting the TX power for the advertisement.

In summary, in order to change the TX power for the advertisement during run time, you must ensure that the radio is not being used, and that the proper sysconfig parameters are in place.

I hope that helps.

Best,

Nima Behmanesh