NRF52840 SAADC High Current with FreeRTOS SDK15.2

RE: NRF52840 SAADC High Current with FreeRTOS SDK15.2

Susheel Nuguru — Wed, 22 Jan 2020 20:46:11 GMT

good to hear that we were on the right track and you fixed the issue.

RE: NRF52840 SAADC High Current with FreeRTOS SDK15.2

Jimmy Wong — Wed, 22 Jan 2020 02:31:52 GMT

Hi,

You can refer to the description what I did.

https://jimmywongiot.com/2019/07/31/current-consumption-with-freertos-on-nordic-nrf5-sdk/
https://jimmywongiot.com/2019/07/29/how-to-add-the-battery-service-in-current-optimization

RE: NRF52840 SAADC High Current with FreeRTOS SDK15.2

kdubovenko — Wed, 22 Jan 2020 00:42:22 GMT

Checked the exact FPU flags and am getting the IXC - Inexact cumulative exception bit. This seems to imply that the result is "inexact" and needs to be rounded. The rounding is what throws the exception. I guessing this is because at some point of the calculation I get a repeating decimal.

RE: NRF52840 SAADC High Current with FreeRTOS SDK15.2

kdubovenko — Tue, 21 Jan 2020 23:48:40 GMT

Hi Susheel, your advice to check NVIC->ISPR was spot on. I saw that the FPU interrupt was active, this is becasue the data collected from ADC was converted to voltage using floating point math, I didn't connect the issue with that until I check the NVIC register. I used the solution from this thread to fix it. Specifically, I enabled the FPU interrupt handler. I added the following to my initialization code:

//Configure FPU interrupts
NVIC_SetPriority(FPU_IRQn, APP_IRQ_PRIORITY_LOW);
NVIC_EnableIRQ(FPU_IRQn);

I also added the interrupt that clears FPU exceptions (apparently I'm throwing an exception although when I redo the calculations they are sound ... need to investigate further):

#define FPU_EXCEPTION_MASK 0x0000009F

void FPU_IRQHandler(void)
{
    uint32_t *fpscr = (uint32_t *)(FPU->FPCAR+0x40);
    (void)__get_FPSCR();

    *fpscr = *fpscr & ~(FPU_EXCEPTION_MASK);
}

With this code, I'm getting proper functionality and the current draw is low, as expected. Thanks again!

RE: NRF52840 SAADC High Current with FreeRTOS SDK15.2

Patrick — Fri, 17 Jan 2020 20:08:31 GMT

I have noticed in a few instances that the SAADC uses a large amount of current if I never calibrate it. I haven't seen anyone else with this issue but might be worth a look.

RE: NRF52840 SAADC High Current with FreeRTOS SDK15.2

Susheel Nuguru — Fri, 17 Jan 2020 13:43:38 GMT

Just to understand if this is related to FreeRTOS and/or BLE solely, what happens if you disable BLE and keep the SAADC functionality exercised ? does the power consumption stays high?

If the answer to the above is yes, then most likely it is something that keeps the chip awake even though your app is (assuming) sleeping in tickless idle sleep. Possibly some interrupt is being pended and not serviced, you can check that in you read NVIC->ISPR register.