TWI causing nRF52 not to sleep

[RichieJH]

I am using sd_app_evt_wait() to put my nRF52 to sleep. Works fine except after I read from a TWI sensor. As soon as I do I see the nRF52 continuously jump out of sleep. I have put a log into my twi_handler and except when I write to/read from the sensor, the twi_handler is not getting called, so it's not jumping out of sleep due to a nrf_drv_twi_evt_t event.

This issue only arrises when I try to read from the sensor via

 err_code = nrf_drv_twi_rx(m_twi_instance, SI7020_BASE_ADDRESS, returned_over_I2C, 3)

When I write to begin the measurement it doesn't appear to be the cause of the nRF52 not to go to sleep.

So I thought I would take a reading and then uninit twi completely until it was needed again. I added this code immediately having read from the sensor

nrf_drv_twi_uninit(&m_twi_instance);
uint32_t *twim0_power = (uint32_t *)(NRF_TWIM0_BASE+0xFFC);
*twim0_power = 0;   //turn off TWIM0
*(volatile uint32_t *)twim0_power;  

However this does not appear to work in my case, I still see the nRF52 continuously jump out of sleep.

Any thoughts?

AMENDED 1:

Here are the txt files of the registries. The first is when no TWI reading is commenced. The second is when a TWI reading has occurred and is at the point immediately below sd_app_evt_wait()

Registers when no TWI read.txt

Registers when TWI read and immediately after jumping out of sleep

AMENDED 2:

So just in case it was an fpu issue and to draw a line under this I thought I would add a power manage function along the lines suggested by this post devzone.nordicsemi.com/.../. However it appears the pack for SES does not define FPU_IRQn since I get an undefined error in SES. Any guidance how I can manually define this?

[RK]

What interrupts are pending when it comes out of sleep mode? Look at the interrupt registers, all of them, including the standard cortex ones (like FPU).

[RichieJH]

Thanks RK. OK checking the Registers in Segger Embedded Studio shows that there are no obvious interrupts causing the nRF52 not to hold in sd_app_evt_wait(). I attach the txt outputs in my original question. The first one is when no sensor reading is begun. The second is after a sensor reading at the point immediately after sd_app_evt_wait()

[RK]

I don't see anything there either. I thought it might be the FPU exception but it's not, there's none shown. So I don't know why it keeps bumping out of sleep

[Susheel Nuguru]

I cannot see any pending interrupts either. Are you sure that you are sniffing the registers before the interrupt is serviced?

[RK]

I assumed that register state was after the sd_app_evt_wait() has returned so that would be after the interrupts (if there were any) had been serviced. If one wasn't cleared then it wouldn't ever get out of the interrupt handlers and return, so it's not that. It would have to be a pretty fast interrupt to keep the thing awake, does the twi driver use a timer for anything, wondered if it was a fast timeout timer which wasn't getting suppressed and was constantly waking it up