Setting the TX Power and checking it in the terminal

[AlexandraK_04]

Hello

I'm working with the nRF21540 and the nRF Connect SDK 2.6.2.

I would like to set my TX Power to 20 dBm and also check this value. Currently my configuration looks like this:

CONFIG_BT=y
CONFIG_BT_BROADCASTER=y
CONFIG_BT_EXT_ADV=y
CONFIG_BT_PER_ADV=y
CONFIG_BT_DEVICE_NAME="PAwR adv sample"

CONFIG_BT_MAX_CONN=1
CONFIG_BT_CENTRAL=y
CONFIG_BT_PER_ADV_SYNC_TRANSFER_SENDER=y

CONFIG_BT_PER_ADV_RSP=y

CONFIG_BT_REMOTE_INFO=y
CONFIG_BT_GATT_CLIENT=y

CONFIG_LOG=y

CONFIG_BT_CTLR=y

# floating-point support
CONFIG_NEWLIB_LIBC=y
CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y

# PHY
CONFIG_BT_CTLR_PHY_2M=y

# FEM
CONFIG_MPSL=y
CONFIG_MPSL_FEM=y
CONFIG_MPSL_FEM_NRF21540_GPIO=y
CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y
CONFIG_BT_CTLR_TX_PWR_ANTENNA=20

# RSSI 
CONFIG_BT_CTLR_CONN_RSSI=y

Unfortunately, I don't know if that's correct. I tried to test the value as follows:

static void response_cb(struct bt_le_ext_adv *adv, struct bt_le_per_adv_response_info *info,
		     struct net_buf_simple *buf)
{
	if (buf) {
		printk("Response: subevent %d, slot %d\n", info->subevent, info->response_slot);
		bt_data_parse(buf, print_ad_field, info);
		printk("RSSI: %d dBm\t", info->rssi);
		printk("TX Power: %d dBm\n", info->tx_power);
		increment_responses();
		
	} else {
		printk("Failed to receive response: subevent %d, slot %d\n", info->subevent,
		       info->response_slot);
		
	}
	
	
}

If I output the value for the TX Power, I always get a value of 127, the RSSI value is in a range between -17 and -22 dBm.

Is there something wrong with this in general or how can I set the TX Power to 20 dBm and then check it?

Thank you and best regards,

Alexandra

[Simonr]

Hi

Okay, my bad. I thought the CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB_POUTA would also set the TX power, but it just forwards the FEM status to the MPSL, and CONFIG_BT_CTLR_TX_PWR_ANTENNA should be the right config to set the actual TX output.

So, then the next mystery is why you get the value of 127. This is the maximum, which points to an invalid value. That could be because the TX power you get from the scanner side isn't the TX power the kit sends with. I think you can use the following function to get the correct TX power here. https://docs.nordicsemi.com/bundle/ncs-2.4.1/page/nrfxlib/mpsl/doc/api.html#c.mpsl_fem_pa_is_configured 

Best regards,

Simon