Sensor sampling and power/RAM retention

[Tim Adu]

I am trying to accomplish the following:

1. Read values from a number of sensors
2. Put the device in sleep mode (while keeping the samples from sensors in memory so that they can be reported when the device wakes up)
3. Wake up, report the samples and go back to sleep. After a programmed interval (in practice, this will be once or twice every 24 hours), the device wakes up and the process starts again from (1).

Questions:

1. What is the recommended "power down" mode for this? (System ON, System OFF, or some other mechanism). The most important issue here being that I absolutely need those samples to be available when the device wakes up.
2. When the device is powered-down; the device should be able to receive interrupts (GPIO and NFC). Again, what power down mode would be most suitable for this scenario?

Thanks. I'd really appreciate some suggestions before diving into this :)

[Simonr]

Hi Timothy

You should use System ON mode with RAM retention for this usecase. Please refer to chapter 5.2.1.1 in the product specification to see the various current consumption scenarios. I recommend either the ION_RAMON_EVENT or the ION_RAMON_GPIOTEPORT. 

Best regards,

Simon

[Tim Adu]

Thanks for the reply. How do I then configure full RAM retention?

[Simonr]

Hi Timothy

Please see the RAM retention example.

Best regards,

Simon

[Tim Adu]

Would this therefore make sense:

#define RAM_SECTIONS_TO_RETAIN      9



for(uint8_t i = 0; i < RAM_SECTIONS_TO_RETAIN; i++)
{
    NRF_POWER->RAM[i].POWERSET = (POWER_RAM_POWER_S0POWER_On << POWER_RAM_POWER_S0POWER_Pos)      |
                        (POWER_RAM_POWER_S1POWER_On      << POWER_RAM_POWER_S1POWER_Pos)      |
                        (POWER_RAM_POWER_S2POWER_On      << POWER_RAM_POWER_S2POWER_Pos)      |
                        (POWER_RAM_POWER_S3POWER_On      << POWER_RAM_POWER_S3POWER_Pos)      |
                        (POWER_RAM_POWER_S4POWER_On      << POWER_RAM_POWER_S4POWER_Pos)      |
                        (POWER_RAM_POWER_S5POWER_On      << POWER_RAM_POWER_S5POWER_Pos)      |
                        (POWER_RAM_POWER_S6POWER_On      << POWER_RAM_POWER_S6POWER_Pos)      |
                        (POWER_RAM_POWER_S7POWER_On      << POWER_RAM_POWER_S7POWER_Pos)      |
                        (POWER_RAM_POWER_S8POWER_On      << POWER_RAM_POWER_S8POWER_Pos)      |
                        (POWER_RAM_POWER_S9POWER_On      << POWER_RAM_POWER_S9POWER_Pos)      |
                        (POWER_RAM_POWER_S10POWER_On     << POWER_RAM_POWER_S10POWER_Pos)     |
                        (POWER_RAM_POWER_S11POWER_On     << POWER_RAM_POWER_S11POWER_Pos)     |
                        (POWER_RAM_POWER_S12POWER_On     << POWER_RAM_POWER_S12POWER_Pos)     |
                        (POWER_RAM_POWER_S13POWER_On     << POWER_RAM_POWER_S13POWER_Pos)     |
                        (POWER_RAM_POWER_S14POWER_On     << POWER_RAM_POWER_S14POWER_Pos)     |
                        (POWER_RAM_POWER_S15POWER_On     << POWER_RAM_POWER_S15POWER_Pos)     |
                        (POWER_RAM_POWER_S0RETENTION_On  << POWER_RAM_POWER_S0RETENTION_Pos)  |
                        (POWER_RAM_POWER_S1RETENTION_On  << POWER_RAM_POWER_S1RETENTION_Pos)  |
                        (POWER_RAM_POWER_S2RETENTION_On  << POWER_RAM_POWER_S2RETENTION_Pos)  |
                        (POWER_RAM_POWER_S3RETENTION_On  << POWER_RAM_POWER_S3RETENTION_Pos)  |
                        (POWER_RAM_POWER_S4RETENTION_On  << POWER_RAM_POWER_S4RETENTION_Pos)  |
                        (POWER_RAM_POWER_S5RETENTION_On  << POWER_RAM_POWER_S5RETENTION_Pos)  |
                        (POWER_RAM_POWER_S6RETENTION_On  << POWER_RAM_POWER_S6RETENTION_Pos)  |
                        (POWER_RAM_POWER_S7RETENTION_On  << POWER_RAM_POWER_S7RETENTION_Pos)  |
                        (POWER_RAM_POWER_S8RETENTION_On  << POWER_RAM_POWER_S8RETENTION_Pos)  |
                        (POWER_RAM_POWER_S9RETENTION_On  << POWER_RAM_POWER_S9RETENTION_Pos)  |
                        (POWER_RAM_POWER_S10RETENTION_On << POWER_RAM_POWER_S10RETENTION_Pos) |
                        (POWER_RAM_POWER_S11RETENTION_On << POWER_RAM_POWER_S11RETENTION_Pos) |
                        (POWER_RAM_POWER_S12RETENTION_On << POWER_RAM_POWER_S12RETENTION_Pos) |
                        (POWER_RAM_POWER_S13RETENTION_On << POWER_RAM_POWER_S13RETENTION_Pos) |
                        (POWER_RAM_POWER_S14RETENTION_On << POWER_RAM_POWER_S14RETENTION_Pos) |
                        (POWER_RAM_POWER_S15RETENTION_On << POWER_RAM_POWER_S15RETENTION_Pos);
}

Thanks.

[Simonr]

Hi Timothy

Sure, if you want to run it in a for-loop, I don't see why that should be a problem. The RAM retention example is great in that it works for multiple chips, and not just the nRF52840.

Best regards,

Simon