Two-wire interface does not work together with Bluetooth

[Jarmo]

Hi!

I am using nRF51822 evaluation kit and connecting it as a master to a pair of I2C-devices (using twi_hw_master.c). Everything works well, but when I integrated the TWI (I2C) example code with the Nordic example ble_app_hrs (hear rate monitor) the TWI stops working. The initialization function just blocks (twi_master_init()). However, if I remove ble_stack_init() and other BT-initializations it starts working. Adding back only the ble_stack_init() is enough to make the TWI to block again.

When debugging, the twi_hw_master initialization function twi_master_init() seems to block on this line:

NRF_PPI->CH[0].EEP        = (uint32_t)&NRF_TWI1->EVENTS_BB;

Questions: Q1: Is there some configuration issue in the examples so that TWI and BLE won't work together? Q2: Is there even some hardware related problem for that combination? Q3: In any case, do you have any ideas to solve the problem?

[Ole Morten]

This has been covered at length here before, so I'd recommend you to browse around a little, for instance looking at this question, or one of the multiple others here.

However, I just finished a quick example of how the TWI can be used with the softdevice on second revision chips, and that example is available here, including a modified version of twi_hw_master.c, taking advantage of the working SHORTS on second revision chips.

If you use first revision chips, you should instead follow the suggested workaround in the question I linked to above, using the sd_ppi_* interface.

[Jarmo]

Thanks for the quick answer! I will examine the thing tomorrow.

[Jarmo]

How can we check which revision we have in our Evaluation Board? Also, we have just ordered our custom PCBs and would need to check what is the revision of the chips that will be installed on them.

[Ole Morten]

The different revisions of the chip is shown in both the PAN and the PCN, and you can identify a chip by looking at its chip markings.

In summary, on a 256 kB nRF51822 anything later than QFAAFA on the second line are second revision chips.

[Jarmo]

Thanks, our order code is 949-NRF51822-QFAA-R7, so it looks like it is the second revision, right?