suspend NRF_LOG to save power and then resume

[Peter Kenyon]

Help, I want to run NRF_LOG_ENABLED builds but occasionally I want the device to sleep for (many) minutes, so I wish to turn off the NRF_LOG_UART backend since it consumes 200-300 uA, and then renable when back running, I have tried various hacks but to no avail, is there any easy way to achieve this - thanks

[Peter Kenyon]

I tried the following and it sort of works... any thoughts

#if (NRF_LOG_ENABLED && LOG_POWER_SAVE)
  #include "nrf_drv_uart.h"
  extern nrf_drv_uart_t m_uart;  // nb used by uart logger
  extern "C" void nrf_log_backend_uart_init(void);
  static bool nrf_log_disabled;
#endif

void Hardware::power_on()
{
  // turn on LOGging - sneaky
#if (NRF_LOG_ENABLED && LOG_POWER_SAVE)
  if ( nrf_log_disabled )
  {
    nrf_log_backend_uart_init();
    NRF_LOG_INFO("...logging enabled" );
  }
  nrf_log_disabled = false;
#endif
  NRF_LOG_INFO(__PRETTY_FUNCTION__);

  //.....
}

void Hardware::power_off()
{
  //....
 
  // disable logging very sneaky
  // outstanding nordic request but this seems to work
#if (NRF_LOG_ENABLED && LOG_POWER_SAVE)
  // attempt to turn off LOG uart it consumes loads of power
  NRF_LOG_INFO("shutting down logging..." );
  NRF_LOG_FLUSH();
  NRF_LOG_FINAL_FLUSH();
  nrf_drv_uart_uninit( &m_uart);
  nrf_log_disabled = true;
#endif
}

[Stian Røed Hafskjold]

Hi, have you tried to stop UART RX and TX before going to sleep? I was able to get the current down by adding the following two lines to the idle_state_handle. It seems stable to me. The function is from the hrs example in SDK 15.2.0

static void idle_state_handle(void)
{
    ret_code_t err_code;

    err_code = nrf_ble_lesc_request_handler();
    APP_ERROR_CHECK(err_code);

    if (NRF_LOG_PROCESS() == false)
    {
        NRF_UARTE0->TASKS_STOPRX = 1;
        NRF_UARTE0->TASKS_STOPTX = 1;
        nrf_pwr_mgmt_run();

    }
} 

[Peter Kenyon]

although that saves a few precious electrons, I found the maximum saving by turning off the usart, in sleep that saves 300 uA, also most of the time if an interrupt occurs I am tracing anyway, but thanks for the suggestion, I will play some more