FPU Power Consumption

RE: FPU Power Consumption

Lorenzo — Thu, 27 Jun 2019 14:24:13 GMT

Hi Simon,

thanks for your answer. I've tried your solution (note that __set_FPSCR() and __get_FPSCR() require two initial underscores):

void idle_state_handle(void)
{   
    if (NRF_LOG_PROCESS() == false)
    {  
       #if (__FPU_USED == 1)
        __set_FPSCR(__get_FPSCR() & ~(0x0000009F)); 
        (void) __get_FPSCR();
        NVIC_ClearPendingIRQ(FPU_IRQn);
      #endif
      __WFE();
      nrf_pwr_mgmt_run();
    }
}

I had another problem, I was using nrf_delay_ms() to delay readings, now I've used a timer and everything is low power. Thanks again for your help.

RE: FPU Power Consumption

Lorenzo — Thu, 27 Jun 2019 14:18:17 GMT

Hi awneil, yeah that's from Bosch, however it needs to be used together with their BSEC Library (coming as a binary blob where I cannot do much) to get some special functions such as IAQ calculation.

RE: FPU Power Consumption

Simonr — Thu, 27 Jun 2019 13:25:17 GMT

Hi Gino

This is an erratum in our nRF52832 chips where the CPU is awoken from System ON Idle after FPU has been used. To prevent unexpected wake-ups from System ON Idle, you have to add this code snippet before entering sleep:

#if (__FPU_USED == 1)
 _set_FPSCR(_get_FPSCR() & ~(0x0000009F)); 
 (void) __get_FPSCR();
 NVIC_ClearPendingIRQ(FPU_IRQn);
#endif
 __WFE();

Best regards,

Simon

RE: FPU Power Consumption

awneil — Thu, 27 Jun 2019 11:04:47 GMT

That's Bosch, isn't it?

I've not used that one, but for some others, their low-level driver doesn't require FP.
Or they might have some non-FP code in app notes?

But I am also interested in the FPU question ...