RE: Single float division causing ~7x higher current draw

Sigurd — Tue, 04 Jul 2017 10:32:11 GMT

Hi,

You seem to be running into errata [87] CPU: Unexpected wake from System ON Idle when using FPU. Add the workaround to the power_manage() function, and the problem should be solved:

 void power_manage(void)
{
  #if (__FPU_USED == 1)
  __set_FPSCR(__get_FPSCR() & ~(0x0000009F)); 
  (void) __get_FPSCR();
  NVIC_ClearPendingIRQ(FPU_IRQn);
  #endif
  uint32_t err_code = sd_app_evt_wait();
  APP_ERROR_CHECK(err_code);
}

RE: Single float division causing ~7x higher current draw

dingari — Tue, 04 Jul 2017 10:31:32 GMT

Should have dug around a bit more. I found the solution in this answer: devzone.nordicsemi.com/.../

It seems that just invoking the FPU and not clearing the interrupt, the nRF52 chip couldn't sleep.