API bt_hci_cmd_send_sync() is returning -5 error

[Learner]

Hello,

I am trying to write some code that sets the BLE Tx power on the nRF52833 SoC.

I have based my code on the sample example code provided at C:\Zypher\v1.7.0\zephyr\samples\bluetooth\hci_pwr_ctrl\src\main.c and in particular in the function set_tx_power().

static result_t bluetooth_set_ble_tx_power( uint8_t handle_type, uint16_t handle, int8_t tx_pwr_lvl )
{
    struct bt_hci_cp_vs_write_tx_power_level    *cp;
    struct bt_hci_rp_vs_write_tx_power_level    *rp;
    struct net_buf                              *buf, *rsp = NULL;
    result_t                                    result = RESULT_ERROR;

    buf = bt_hci_cmd_create( BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL, sizeof(*cp) );
    if ( buf )
    {
        cp                  = net_buf_add( buf, sizeof(*cp) );
        cp->handle          = sys_cpu_to_le16( handle );
        cp->handle_type     = handle_type;
        cp->tx_power_level  = tx_pwr_lvl;

        result = bt_hci_cmd_send_sync( BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL, buf, &rsp );
        if ( result )
        {
            uint8_t reason = rsp ? ((struct bt_hci_rp_vs_write_tx_power_level *) rsp->data)->status : 0;
            LOG_WRN( "Set Tx power err: %d reason 0x%02x\n", result, reason );
            result = RESULT_ERROR;
        }
        else
        {
            rp = (void *)rsp->data;
            LOG_INF( "Actual Tx Power: %d\n", rp->selected_tx_power );
            net_buf_unref( rsp );
            result = RESULT_OK;
        }
    }
    else
    {
        LOG_WRN( "Unable to allocate command buffer\n" );
    }

    return result;
}

I am seeing the function bt_hci_cmd_send_sync() returning error -5.

Can you please help me find the cause of this error.

Thank you.

Kind regards

Mohamed

[Susheel Nuguru]

I would recommend to enable the BT_LOG to right level to be able to get more context on the error.

which controller are you using Softdevice Controller(SDC) or Zephyr Controller? The setting you have for CONFIG_BT_LL_SW_SPLIT?

[Learner]

Good Morning Susheel,

I am developing under zephyr using

Zephyr OS build v2.6.99-ncs1 

nRF Connect SDK v1.7.0 

LOG_MODULE_REGISTER(bt, LOG_LEVEL_INF);

This is the error I am getting:

<wrn> bt: Set Tx power err: -5 reason 0x00

Below is the content of my prj_debug.conf file.

# BLE
CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_GATT_CLIENT=y
CONFIG_BT_GATT_DYNAMIC_DB=y

# Turn off/reduce Bluetooth aspects
CONFIG_BT_LL_SW_SPLIT=y
CONFIG_BT_PHY_UPDATE=n
CONFIG_BT_GATT_CACHING=n
CONFIG_BT_GATT_SERVICE_CHANGED=y
CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS=n
CONFIG_BT_HCI_VS_EXT=n
CONFIG_BT_CTLR_PRIVACY=n
CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT=1
CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE=251
CONFIG_BT_CTLR_PHY_2M=n
CONFIG_BT_USER_DATA_LEN_UPDATE=n
CONFIG_BT_USER_PHY_UPDATE=n

# Increase BLE packet sizes
CONFIG_BT_DATA_LEN_UPDATE=y
CONFIG_HEAP_MEM_POOL_SIZE=2048
CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=n
CONFIG_BT_BUF_ACL_RX_SIZE=255
CONFIG_BT_ATT_PREPARE_COUNT=1
#Maximum number of pending TX buffers with a callback
#CONFIG_BT_CONN_TX_MAX=2
CONFIG_BT_CONN_TX_MAX=10
#Number of L2CAP TX buffers
CONFIG_BT_L2CAP_TX_BUF_COUNT=10
#CONFIG_BT_L2CAP_TX_BUF_COUNT=2
CONFIG_BT_L2CAP_TX_MTU=247
CONFIG_BT_CTLR_RX_BUFFERS=1
CONFIG_BT_BUF_ACL_TX_COUNT=1
CONFIG_BT_BUF_ACL_TX_SIZE=251
#NRF_SDH_BLE_GATT_MAX_MTU_SIZE=247

Can you spot anything in my config that could explain the error I am getting?

Thank you for your help.

Kind regards

Mohamed

[Susheel Nuguru]

You are using the Zephyr implementation of the controller (CONFIG_BT_LL_SW_SPLIT=y). I am not sure if this is due to this config and also not sure if the this hci command is supported in that version. 
Can you quickly test your application when you set BT_LL_SOFTDEVICE=y instead of CONFIG_BT_LL_SW_SPLIT?

[Learner]

Hi,

So, you want me to replace in prj_debug.conf the line 

CONFIG_BT_LL_SW_SPLIT=y

with

Susheel Nuguru said:

BT_LL_SOFTDEVICE=y

Isn't it CONFIG_BT_LL_SOFTDEVICE i.e. with the prefix 'CONFIG_'?

[Learner]

Hi Susheel,

bt_hci_cmd_send_sync() is working fine now after I made the following changes in prj_debug.conf. Both config items were set to 'n'.

CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y

CONFIG_BT_HCI_VS_EXT=y

Does this make sense?

Although the error from bt_hci_cmd_send_sync() is gone, the actual BLE TX power settings is not changing. I tried different values -40, -30, -20, 0 and 8 dBm and only -40 seems to work. Also, I noticed upon BLE disconnection the power level goes back to the default 0 dBm.

Can you please help?

Kind regards

Mohamed

[Susheel Nuguru]

Learner said:

CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y

CONFIG_BT_HCI_VS_EXT=y

Does this make sense?

Hi Mohammed,

Yes, this makes sense and CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL is necessary for the TX power control to work.

Learner said:

Although the error from bt_hci_cmd_send_sync() is gone, the actual BLE TX power settings is not changing. I tried different values -40, -30, -20, 0 and 8 dBm and only -40 seems to work.

There is a known issue with setting TX power before the advertising parameters are set. This is documented in known issues for the SDC. Apart from that, it should work as I tested this on other nRF52 variants. 

Learner said:

Also, I noticed upon BLE disconnection the power level goes back to the default 0 dBm.

This could be true that this setting is per role, I normally would call bluetooth_set_ble_tx_power for every role (just connected, disconnected, advertiser, scanner).