RE: nRF_LOG UART draws ~300uA

Radiohead — Fri, 18 Aug 2017 07:53:17 GMT

Thank you for your reply Stian. However this fix isn't working for me with SDK13.1.0. I've tried with both NRF_UART0->TASKS_STOPTX and the m_uart variable in the uart_event_handler within nrf_log_backend_serial.c as shown below:

 #if (NRF_LOG_BACKEND_SERIAL_USES_UART)
static void uart_event_handler(nrf_drv_uart_event_t * p_event, void * p_context)
{
    // Dummy handler since is_busy feature is used for determining readiness.
    if (p_event->type == NRF_DRV_UART_EVT_RX_DONE)
    {
        m_rx_done = true;
    }
		
		if (p_event->type == NRF_DRV_UART_EVT_TX_DONE)
		{
			//NRF_UART0->TASKS_STOPTX = 1;
			//m_uart.reg.p_uart->TASKS_STOPTX = 1;		
		}
}
#endif //NRF_LOG_BACKEND_SERIAL_USES_UART

While debugging the event is called and the TASK_STOPTX is executed, but power consumption remains ~300uA. When I disable the NRF_LOG_BACKEND_SERIAL_USES_UART, the power consumption drop to a few uA.

My while loop is as following:

    while (true)
{	
				/* Handle the Application statemachine each time the nRF52832 wakes-up. */
				ApplicationStatemachine();
			
				// When the NRF LOG has been processed, go to a low power mode to conserve energy. The nRF will wake up on interrupt of anything; RTC, timers, SPI transfers, etc.
				if (NRF_LOG_PROCESS() == false)
    {
      power_manage();
    }		
}

RE: nRF_LOG UART draws ~300uA

Stian Røed Hafskjold — Thu, 17 Aug 2017 18:27:21 GMT

The UART it self does not draw 300uA while it's not in TX/RX mode. So, this seems to be an issue with how the log module works together with the nrf_drv_uart driver.

I noticed that the TASKS_STOPTX task is never called after the logging module is finished transmitting the buffer. I tried adding the following code to the uart_event_handler() in nrf_log_backend_serial.c, and the current was reduced to normal idle current:

if (p_event->type == NRF_DRV_UART_EVT_TX_DONE)
{
    NRF_UART0->TASKS_STOPTX = 1;
}

I have not tested this thoroughly, but it seems to work, so you can try it as well. I will report the issue internally so it will be fixed in future SDK releases. I tried this on SDK 13.