power consumption in Idle

[ran]

Hi, 

We are starting to measure the power of our nrf52840 based design.

I'd like to establish the power number for Idle() , since system will be in Idle() most of the time. 

For that , I have used the following code, invoked from CLI : 

__disable_irq();
sd_app_evt_wait();

1. Is this code correct for keeping system in Idle() ? 

2. What Is the estimated nrf52840 SoC current consumption in this mode ?  

3. Our code is based on UART example

Thanks, 

Ran

[Simonr]

Hi Ran

Most of our examples use the idle_state_handle() function in order to go into idle mode, which will call the sd_app_evt_wait() function if you're using the SoftDevice. The idle_state_handle() will process any pending log operations, and then sleep until the next event occurs, so I recommend you use this function as well. You can see the ble_app_bps example to see how it is set up and what functions it calls.

You can see the idle current for various scenarios in section 5.2.1.1 Sleep in the nRF52840 product specification or here in the Infocenter. Depending on whether you want RAM retention, how you want to wake the device, etc. the current consumption will in system ON (Idle) mode will be between 1.3uA to ~20uA.

Best regards,

Simon

[ran]

Thanks, Will do. 

I am using UART fo CLI and LOG and SPI\I2C to communicate with the sensors. 

I am using "blocked" mode for I2C\SPI so it is safe to put them into LPM when going Idle(). 

Should I configured them ( SPI\I2C ) in a specific way or put them into LPM before going to Idle ? 

[ran]

Also - I came across "NRFFOSDK-11174" ( https://devzone.nordicsemi.com/f/nordic-q-a/32734/why-use-wfe-instead-of-sd_app_evt_wait-on-sdk15-freertos ) .

Is this still an Issue ? 

[Simonr]

Hi Ran

Are you using FreeRTOS? If not you won't have to worry about this. In any case, this is an issue in a few build codes of the nRF52832, so seeing as you use an nRF52840 this should not apply in any case.

You should not have to configure SPI/I2C when your device stays in system ON mode. Also, why would you have to disable interrupts to go to idle mode?

Best regards,

Simon

[ran]

Simon 

I am using embOS (by Segger) with tickless impl. (ported from freetos example) 

I have disabled interrupt before Idle for test purposes only - So HW guys can measure the "floor" . ( I've added a "sleep" command to our CLI ) 

Also, I've noticed that in "freetos" examples, the following line is being used  :

"SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk"  ( set Cortex-M0 sleep mode ) . 

But it is not used in any non-freetos example ? why is that ?