Hello
I have 2 devices ,a central and a peripheral on a custom nRF52840 board
Using Zephyr SDK 2.5.0
The distance between the devices is 10.9 meters.
When TX power on the peripheral is set to 0 the central receives packets with RSSI around -65 dBM
When the power on the peripheral is set to a negative value -4, -8, -20 and even -40 the RSSI received by the central does not change much - still hovers around -65
The function that sets the tx power is below. - taken from a Zephyr sample. The function succeeds
It is invoked as follows
set_tx_power(1,-8); where 1 is the advertising set handle
Any ideas why the RSSI is not affected even at very low TX?
Thank you
Andy
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static int set_tx_power(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;
int err;
buf = bt_hci_cmd_create(BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL,sizeof(*cp));
if (!buf) {
LOG_ERR("Unable to allocate command buffer");
return -1;
}
cp = net_buf_add(buf, sizeof(*cp));
cp->handle = sys_cpu_to_le16(handle);
cp->handle_type = BT_HCI_VS_LL_HANDLE_TYPE_ADV;
cp->tx_power_level = tx_pwr_lvl;
err = bt_hci_cmd_send_sync(BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL, buf, &rsp);
if (!err) {
rp = (void *)rsp->data;
// Zephyr implementation returns no error if the tx power is invalid. Instead it just sets it to 0
// We need to propagate the error up the call chain
if(rp->selected_tx_power == tx_pwr_lvl){
LOG_INF("Actual Tx Power: %d", rp->selected_tx_power);
}else{
LOG_ERR("Tx power not set! Value %d not supported by the radio, actual tx power:%d",tx_pwr_lvl,rp->selected_tx_power);
errno = EINVAL; // so the caller can use strerror();
err = -EINVAL; // Zephyr uses negative error codes
}
}else{
uint8_t reason = (rsp ? ((struct bt_hci_rp_vs_write_tx_power_level *) rsp->data)->status : 0);
LOG_ERR("Set Tx power err: %d reason 0x%02x", err, reason);
}
if(rsp){
net_buf_unref(rsp);
}
return err;
}
