nrf52820 power control not working from samples

[Dmitrii Zav]

We use nrf connect sdk under linux.

I need to control tx power to be able to adjust working range.

I take example from zephyr/samples/bluetooth/hci_pwr_ctrl

Add segger_rtt 

CONFIG_LOG_MINIMAL=n
CONFIG_CONSOLE=y
CONFIG_RTT_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_LOG=y
CONFIG_LOG_DEFAULT_LEVEL=3
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=n
CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=512
CONFIG_LOG_BUFFER_SIZE=512
CONFIG_LOG_PROCESS_THREAD=y
CONFIG_DEBUG_OPTIMIZATIONS=n
CONFIG_LOG_PRINTK=y
CONFIG_PRINTK=y
CONFIG_LOG_PRINTK_MAX_STRING_LENGTH=512

Slightly increase stack size to prevent stack overflow errors

Run it on the board and get errors

00> Set Tx power level to 4
00> 
00> Actual Tx Power: 4
00> 
00> Get Tx power level -> [00:00:15.010,467] <wrn> bt_hci_core: opcode 0xfc0f status 0x01
00> Read Tx power err: -5 reason 0x00
00> 
00> TXP = -1
00> 
00> Set Tx power level to 0
00> 
00> Actual Tx Power: 0
00> 
00> Get Tx power level -> [00:00:20.011,260] <wrn> bt_hci_core: opcode 0xfc0f status 0x01
00> Read Tx power err: -5 reason 0x00
00> 
00> TXP = -1
00> 
00> Set Tx power level to -3
00> 
00> [00:00:20.011,657] <wrn> bt_hci_core: opcode 0xfc0e status 0x12
00> Set Tx power err: -5 reason 0x00
00> 
00> Get Tx power level -> [00:00:25.012,084] <wrn> bt_hci_core: opcode 0xfc0f status 0x01
00> Read Tx power err: -5 reason 0x00
00> 
00> TXP = -1
00> 
00> Set Tx power level to -8
00> 
00> Actual Tx Power: -8
00> 
00> Get Tx power level -> [00:00:30.013,000] <wrn> bt_hci_core: opcode 0xfc0f status 0x01
00> Read Tx power err: -5 reason 0x00
00> 
00> TXP = -1
00> 
00> Set Tx power level to -15
00> 
00> [00:00:30.013,427] <wrn> bt_hci_core: opcode 0xfc0e status 0x12
00> Set Tx power err: -5 reason 0x00
00> 

Where is my mistake? May be there are other ways to control tx power? 

[Simon]

I tested this with the nRF52840 and encountered the same errors. I had to set CONFIG_MAIN_STACK_SIZE=2048 first, to get around the stack overflow issues.

However, I was able to make it work using the Zephyr BLE Controller. Enable it by adding these to zephyr\samples\bluetooth\hci_pwr_ctrl\prj.conf

CONFIG_BT_LL_SOFTDEVICE=n
CONFIG_BT_LL_SW_SPLIT=y

It's working without any errors:

Set Tx power level to 4
Actual Tx Power: 4
Get Tx power level -> TXP = 4
Set Tx power level to 0
Actual Tx Power: 0
Get Tx power level -> TXP = 0
Set Tx power level to -3
Actual Tx Power: -4
Get Tx power level -> TXP = -4
Set Tx power level to -8
Actual Tx Power: -8
Get Tx power level -> TXP = -8
Set Tx power level to -15
Actual Tx Power: -16
Get Tx power level -> TXP = -16
Set Tx power level to -18
Actual Tx Power: -20
Get Tx power level -> TXP = -20
Set Tx power level to -23
Actual Tx Power: -40
Get Tx power level -> TXP = -40
Set Tx power level to -30
Actual Tx Power: -40
Get Tx power level -> TXP = -40
Set Tx power level to 4
Actual Tx Power: 4
Get Tx power level -> TXP = 4
Set Tx power level to 0
Actual Tx Power: 0
Get Tx power level -> TXP = 0
Set Tx power level to -3
Actual Tx Power: -4

Best regards,

Simon

[Dmitrii Zav]

Thanks you for fast replay

I cnage BLE stack as you said and it start working. It will be enough to finish project.

But i wonder, why with official softdevice it don't work, but Nordic says that it's sometimes better than open source stack?

[Simon]

I've asked internally about this, regarding the SoftDevice Controller. I'll keep you updated

[Simon]

The reason it fails for the nRF52840 and the SoftDevice Controller (SDC) is because the sample uses these powers {4, 0, -3, -8, -15, -18, -23, -30} and the nRF52840 supports these: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fradio.html&cp=4_0_0_5_19_13_46&anchor=register.TXPOWER. Each time the sample tries to set a power that the nRF52840 does not support, the SDC will return an error. This is not correct behaviour, instead of returning an error, the SDC should select one supported. We will get this fixed.

Best regards,

Simon