RAM retention / shutdown

RE: RAM retention / shutdown

haakonsh — Fri, 01 Feb 2019 11:44:35 GMT

nRF52832 Product Specification v1.4

PDF

RE: RAM retention / shutdown

lee-marc — Fri, 01 Feb 2019 10:45:54 GMT

Could you please send me a link to the mentioned Prod Spec? Thanks.

RE: RAM retention / shutdown

haakonsh — Fri, 01 Feb 2019 10:04:49 GMT

See chapter 8 Memory, and 18 POWER — Power supply of the Prod Spec.

We do not have any example or library that covers this topic in our SDKs.

I suggest you start by storing a single variable in a section of RAM, turn on RAM retention on that section, go to SystemOFF and wake up again, then read back the variable to verify that your data has been retained.
Do note that the lower part of the RAM is used by the SoftDevice and application and it should not be used to retain data.

RE: RAM retention / shutdown

lee-marc — Thu, 31 Jan 2019 15:53:55 GMT

But how to do this?
Where can I find a documentation about implementing RAM retention correctly?

RE: RAM retention / shutdown

haakonsh — Wed, 23 Jan 2019 10:37:58 GMT

If you're using a basic state machine for program flow then you can save its state and continue its execution after you've reset the CPU and initialized whatever you need to initialize. You can also use retained RAM as storage.

RE: RAM retention / shutdown

lee-marc — Tue, 22 Jan 2019 14:23:34 GMT

Ok, I see. But I don't understand the benefit of RAM retention if it's not possible to resume program code.

I was thinking that nRF52832 could go into ultra low power mode and resume program code after going back to normal mode.

RE: RAM retention / shutdown

haakonsh — Tue, 22 Jan 2019 14:12:47 GMT

"What is the benefit of retaining RAM in system off mode if it will be reset at wakeup?"
The RAM is not reset at wakeup, but the CPU and its registers are.

"Which ultra low power state can retain RAM and return back into normal state without reset?

In our application we want to save power if the device is not used. But RAM must be retained."

System ON, IDLE.

RE: RAM retention / shutdown

lee-marc — Mon, 21 Jan 2019 15:18:57 GMT

What is the benefit of retaining RAM in system off mode if it will be reset at wakeup?

Which ultra low power state can retain RAM and return back into normal state without reset?

In our application we want to save power if the device is not used. But RAM must be retained.

RE: RAM retention / shutdown

haakonsh — Mon, 21 Jan 2019 15:05:27 GMT

SystemOFF can retain RAM, but the device WILL reset upon wakeup from SystemON. After a reset the CPU will start execution from the reset_vector and the CPU registers are gone.

RAM, CPU registers, and Call Stack are retained in SystemON.

RE: RAM retention / shutdown

lee-marc — Mon, 21 Jan 2019 14:40:08 GMT

[quote userid="13562" url="~/f/nordic-q-a/41858/ram-retention-shutdown/166876"]You can retain information in RAM in System OFF, but the device will still reset on wakeup from System OFF. [/quote]

If System OFF can't retain RAM, which state does?

[quote userid="13562" url="~/f/nordic-q-a/41858/ram-retention-shutdown/166876"]See nrf_pwr_mgmt_run API docs.[/quote]

I can't find any documentaion about RAM retention there.

RE: RAM retention / shutdown

haakonsh — Mon, 21 Jan 2019 14:21:42 GMT

See POWER — Power supply.

You can retain information in RAM in System OFF, but the device will still reset on wakeup from System OFF.

See nrf_pwr_mgmt_run API docs.

RE: RAM retention / shutdown

lee-marc — Mon, 21 Jan 2019 10:44:38 GMT

Hello haakonsh,

Thanks four your reply. What do you mean with SystemON and SystemOFF?
Commands SystemON and SystemOFF don't exist. Also sd_power_system_on() doesn't exit.

Is there any documentation about shutdown and RAM retention?

RE: RAM retention / shutdown

haakonsh — Wed, 02 Jan 2019 14:30:32 GMT

You need to use SystemON because SystemOFF resets the device on wake-up.