feat: deep sleep improvement for devkit2

[TuEmb]

This pull request aims to reduce deep sleep power consumption for the DevKit2 platform (and potentially for the OMI device as well). With these improvements, the power consumption decreases from approximately 1.2 mA to 7.8 µA.
As a result, with a 250 mAh battery, the device can operate in deep sleep mode for over three years.

QSPI Flash Deep Sleep

By default, the QSPI flash remains powered on without entering sleep mode.

Since the hardware is directly connected to the 3.3 V power source, we now initialize the flash and explicitly place it into deep sleep mode to minimize power consumption.

SD Card Power Management

Enhanced SD card power efficiency by suspending the SPI peripheral and disconnecting related GPIOs when the SD card is powered off, then restoring them upon reactivation.

Simply setting SD_EN = 0 does not completely power down the SD card — there is still potential current leakage through other connected pins. Therefore, all relevant GPIOs should also be disconnected to achieve true low-power operation.

MEASUREMENT RESULT

Before improvement:

After improvement:

[TuEmb]

Hi @beastoin,

Could you help me take a look at this PR ?

I’m really excited about this project! I recently ordered a DevKit2 to explore it further and noticed that the device runs out of battery after several days when using the latest firmware version.

After some investigation, I identified a few improvements that allow the device to enter deep sleep mode more effectively. Please correct me if I’m mistaken anywhere — I’m still new to this project and eager to learn and contribute more!

[beastoin]

that looks solid. will take a look then let you know.

btw, in the meantime, can you:

• check the sdcard functions so we can make sure it works after these changes?
• does zephyr have high-level apis support so you can use it instead of touching directly to nrf*?
• ah, we also have .overlay. take a look at this - the more elegant way is to use overlay/label but do not recall the pin directly.

also, feel free to ping me @thinh http://discord.omi.me

@TuEmb

[aaravgarg]

Nice! @TuEmb, it would also be cool to try reducing the power consumption of the device when it's actually being used.

ofc only after youre done with this PR haha

[TuEmb]

Hi @beastoin , @aaravgarg ,

1. check the sdcard functions so we can make sure it works after these changes?
--> yes, the SD card functions work well after wakeup from deepsleep (button press)

2. does zephyr have high-level apis support so you can use it instead of touching directly to nrf*?

--> yes, you are right. The zephyr supports the high level APIs to config the power management for qspi_flash.
Step to set the qspi_flash into deepsleep:

• Enable CONFIG_FLASH=y
• then just push it to deepsleep by pm_device_action_run(flash_dev, PM_DEVICE_ACTION_SUSPEND);

But, it seems the qspi_flash is still in standby mode (still better than before). We can save more ~10uA if it goes into deepsleep correctly. I read through the zephyr code in nrf sdk v2.7.0, it seems there is a bug (not sure) inside that can't let the qspi_flash into deepsleep

3. ah, we also have .overlay. take a look at this - the more elegant way is to use overlay/label but do not recall the pin directly.
--> I assumed you mentioned about the SD card pins. Let me explain about that issue:

From the schematic, the power for SD card is handled by P0.19 pin (SD_END), I tried to turn it off but the power is still there that let the SD consumes power. So I think the SPI pins that let the current leakage in SD cards (maybe it's related to hardware design), we need to isolate all pins to let SD card going off.

[TuEmb]

Conclusion:

To prevent adding a lot of code or touching directly to nrf pins, I tried to use the API from zephyr as much as possible:

• Added CONFIG_FLASH=y --> it will let the qspi_flash comes to standby mode (the current also reduces alot) --> still have a blocker that I need to investigate to push it into deepsleep mode (10uA saving).
• isolated the SPI pins and turned off the P0.19 to cut off the total power for SD card in deepsleep

Result: The total current consumption was reduced from 1.2 mA to 17 µA in deep sleep mode, ensuring the device can operate for over one year in this state.

[beastoin]

nice, lgtm @TuEmb

1 more thing, please create a new ticket that can help us save 10 uA more, but let it remain there.