suspend i2c does NOT reduce current?

[kfcube]

Hi,

The custom board is 52832 with st lsm6dsr sensor.

I tried to suspend i2c by this code: 

#define I2C_INST DT_NODELABEL(i2c0)
const struct device *const i2c = DEVICE_DT_GET(I2C_INST);
int rc = pm_device_action_run(i2c, PM_DEVICE_ACTION_SUSPEND);
	if (rc < 0) {
		LOG_ERR("Could not suspend i2c (%d)\n", rc);
	}

It worked with no errors. 

But when I measure the current, its the same whether the i2c is suspended or resumed. There is NO power saving at all. I checked the config, it has following:
CONFIG_I2C_NRFX=y
CONFIG_I2C_NRFX_TRANSFER_TIMEOUT=500
CONFIG_I2C_0_NRF_TWI=y
CONFIG_I2C_INIT_PRIORITY=50 

Questions:
1. How to reduce current by suspend i2c/twi? Is there any configuration I should do?  When with SDK, disable twi can reduce significant current. 

2. For 52832, how to make it into low power mode?

Thanks,

[dejans]

Hi,

You could start by reading about recommendations for power optimization. Specifically, you could look at the example of putting external flash into sleep mode in inactivity periods. 

You could try to disable I2C interface in the sensor driver and see if this helps in current reduction.

Please let me know if you have any further questions.

Best regards,
Dejan

[kfcube]

Dejan，

Thanks for your reply. Yes I do want to know why there is no current reduction after i2c device suspended. I measured it keeps the high current even after disconnect. 

After flash, when the board start advertising, the current is 0.13mA.

With i2c active, the current is 1.6mA.

With sensor data notification, the current is 1.6mA.

Then stop data notification and disconnect, the current keeps 1.6mA.

How to put i2c off? 

Thanks,

[kfcube]

 I tested twim and it doesn't stop current either. 

[dejans]

Hi,

Did you get lower current value using twim?

Best regards,
Dejan

[kfcube]

NO, nothing better with twim. 

[dejans]

Hi,

Your nrf52832 chip could be potentially affected by this errata. Due to this anomaly current consumption could be higher than expected. You could try to use provided workaround.

Best regards,
Dejan

[kfcube]

As I have stated early on, the issue is the current NOT getting lower after i2c suspended.

It has nothing to do with the errata as that errata is about higher current than normal when using twim. When not using twim, the current is low. But my case is the current stayed once i2c used.

And you should know that errata only happened when using twim, not twi.

So please stop this kind of useless response and provided some useful suggestions.  

[dejans]

Hi,

You could try suggested workaround (described in the errata) after PM SUSPEND because this will power cycle the peripheral. If the power consumption remains high after that, the problem might not be with TWI.

Best regards,
Dejan

[kfcube]

OK. Thanks.

[Mike Austin (LPI)]

kfcube ,

Did you ever get this sorted out?  I'm having the same issue in my firmware (see this ticket).

If I don't enable &i2c0, then my idle state current is around 5uA.  If I enable it, and even if I don't actually use it in my firmware, then the idle current goes up to around 300uA.

Calling PM_SUSPEND on the i2c device doesn't change the idle state current at all

Cheers,

Mike