No sleep during nrf_drv_twi_rx with LIS3DH

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Jason — Fri, 21 May 2021 06:23:41 GMT

Oh wow, yes, good point! Thanks.

I might have been temped to waste even more time trying to check it needlessly.

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Nguyen Hoan Hoang — Fri, 21 May 2021 05:34:40 GMT

192Bytes in 5ms -> 38KBytes/s -> 384KBits/s. Your speed setting is 400KHz. You are get 384Kbits/s which is correct.

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Jason — Fri, 21 May 2021 05:06:30 GMT

I also think that I must have a communication problem with the LIS3DH because 5ms for 192 bytes implies ~38kbps.The datasheet has specific instructions about the i2c protocol it expects, but it is not obvious to me how the nrf_drv_twi calls might deviate from their expectations.

But 10Mhz seems far better than 400khz. and certainly better than 38kbps. So I think this is the best way to eliminate this problem. I can breadboard it using the Sparkfun LIS3DH board.

In fact I've also ordered the newer https://www.st.com/en/mems-and-sensors/ais2dw12.html

https://www.arrow.com/en/products/steval-mki206v1/stmicroelectronics

It claims even lower current and I think it might have lower noise levels.

Thanks again for your help

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Jason — Thu, 20 May 2021 19:21:17 GMT

I am not aware of anything else which might be running.

My earlier test showed that the LIS3DH draws ~1mA during this process. So based on your figures, I think we should see a combined ~3.5mA. (instead of ~8mA at the moment.)

Neither figure is really low enough and perhaps it would be better to use SPI instead of TWI. The LIS3DH supports SPI at 10Mhz. Do you expect this would use use less power?

Thanks again for your help.

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Håkon Alseth — Thu, 20 May 2021 13:49:00 GMT

Hi,

The CPU seems to be in sleep mode for most of the time.

Any current going through the pull-resistors should not be much higher than ~1 mA, and the sleep current with an active TWIM (w/DMA) should be around 1.5 mA.

The 192 bytes should be read in one transaction, but you have several wake-ups within this TWIM reception. Is there anything else running in your system while this process is on-going?

Kind regards,

Håkon

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Jason — Thu, 20 May 2021 13:30:58 GMT

Hi Hakon, did you see my comment below? I am not sure if you receive notifications for comments or just replies.

I do not understand why the current is so high when the NRF52840 is sleeping.

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Jason — Thu, 20 May 2021 09:15:00 GMT

There was no race condition.

I've made some significant progress that maybe you can help me with.

I changed the code to perform the first 3 (of 4) twi calls synchronously, and the 4th call is the time-consuming one which I run asynchronously. I also hooked up the PPK2 logic analyser to show where the time was spent. See screenshot below

Pins 0,1,2, show time spent in twi_tx, twi_rx, twi_tx.

Pin 3 show time spent receiving 192 bytes in twi_rx

Pin 4 shows the time spent processing the samples (moving averages etc)

Pin 5 shows time spent inside nrf_pwr_mgmt_run. This is the most interesting because it shows that lots of time is spent inside nrf_pwr_mgmt_run() but the current is still high.

I expected the current to drop to a few uA's while the NRF52840 is inside nrf_pwr_mgmt_run()

I am confused by this result because it seems to show that the code is inside nrf_pwr_mgmt_run but the current is still very high.

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Jason — Thu, 20 May 2021 04:11:57 GMT

I think I have a race condition because some nrf_drv_twi_ calls respond so quickly. I am working to debug it at the moment.

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Jason — Wed, 19 May 2021 13:39:09 GMT

Thanks, they're all marked as volatile and I don't get any error codes from the nrf_drv_twi_* calls.

Is there any way to know why it doesn't enter sleep mode?

My main loop calls nrf_pwr_mgmt_run() immediately after the nrf_drv_twi_* calls.

When I look at sd_app_evt_wait I see this comment about interrupts. The 2nd note sounds relevant.

Obviously I cannot step into sd_app_evt_wait.

Could the calls to nrf_drv_twi_* have immediately caused an interrupt?

It's really only the call to get eh 192 bytes of accelerometer data that I really care about and it appears to take >5ms to complete.

RE: No sleep during nrf_drv_twi_rx with LIS3DH

Håkon Alseth — Wed, 19 May 2021 12:51:25 GMT

Hi,

in your twi_handler, you should check the evt type to see if there's an error that has occurred.

You should also check the return code from the nrf_drv_twi_* calls.

Since you mention timers, and twi callbacks, you should look into declaring any variables incremented/set in those to volatile.

Kind regards,

Håkon