Power Consumption with only the M4 running

[Daniel S.]

We are using a STM32MP157A-DK1 and try to reduce power consumption.

1) When A7 and M4 are running we measure around 300mA.

2) When A7 is in Suspend-To-Mem and the M4 is still running we measure around 80mA.

3) When the M4 also enters standby mode the power consumption drops to around 25mA.

We are using an inline USB-device so it measures the whole board and it's probably not giving the most accurate values.

Mostly we are wondering about the second case. Is this power consumption to be expected (plus/minus a few mA)? Or is there a way to have only the M4 running without using 80mA?

[ArmandG]

Hi @DS.5chulze​ ,

Finding 80mA with A7 in Cstop and M4 in Crun for the whole board seems to be what expected.

If you look at the datasheet https://www.st.com/resource/en/datasheet/stm32mp157a.pdf at page 139, you can see with 209MHz oscillator you have IddCore = 71 mA, we can imagine reaching 80 mA with other additional currents such as Idd. By the way it could be relevant to see at what frequency oscillators are running in your board, it could be a way to reduce the intensity.

Besides as the A7 is in Cstop you don't need to use the DDR so you can remove disable VTT if you want less power consumption.

I think this link might be useful : https://www.st.com/resource/en/application_note/dm00449434-stm32mp1-series-using-lowpower-modes-stmicroelectronics.pdf

Armand

[Daniel S.]

I feel like I should have found that datasheet myself. Thanks for pointing that out.

We do turn off VTT now (pin goes low) but we are wondering about VDD_DDR. When we shutdown the A7 (shutdown -h now) and have the M4 still running, we still see VDD_DDR. Is there a way to only have the M4 active and turn everything else off to save even more power?

[Daniel S.]

I will continue this thread, because nobody answered.

What we achieved so far:

• Enable the RetentionRam by setting RREN and BREN

• Load the program of the M4 into the Retention Ram [1] 

• The M4 runs for a few seconds and then enters stop mode and can be woken up by user-button 1 [2]

• Set MCU_BEN flag (secure mode is disabled)

• Shut the C7 off (shutdown -h)

Now we see a power consumption of about 20mA so that's fine.

But. Now it's not possible anymore to wake the M4 up by pressing the user-button. That kind of makes sense because all power rails are deactivated, so not only doesn't the button generate any edges but the M4 also doesn't have any power to wake up.

We can wake up the M4 by pressing the wakeup button (directly connected to the PMIC). The M4 than starts to run, flashes its LED and enters stop mode again after a few seconds.

But now it's not possible to wake the M4 up again and the C7 starts booting on its own after around 20 seconds.

Does the wakeup generate a system reset, so that MCU_BEN gets reset? [3] 

That would mean, that it's only possible to wake up one single time.

And why does the C7 start again on its own but not when we press the wake up button again?

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[1] https://wiki.st.com/stm32mpu/wiki/STM32MP15_RAM_mapping

[2] DeveloperPackage, PWR_STOP_CoPro, replace HAL_PWR_EnterSTOPMode() by HAL_PWR_EnterSTANDBYMode()

[3] RM0436, Page 725: "This register is reset when a system reset occurs, but not when the circuit exits from Standby (app_rst reset)."

[Olivier GALLIEN]

Hi @DS.5chulze​ ,

I understand your target scenario is facing limitation listed in Errata sheet chapter 2.3.12 and 2.3.13.

Olivier

[Daniel S.]

That basically makes the whole MCU_BEN feature useless because we always have to boot up the CA7. The resulting power consumption is way to high so we came to the conclusion that this microcontroller is just the wrong tool for the job and we moved on to another one.

Thanks for helping.