BLE transmission errors when i2c sensors read in interrupt

[Yano]

Hi, we have a device that reads two sensors on separate i2c buses consecutively and transmits these using ble_nus_data_send().

The i2c sensors are read on an interrupt timer 100 readings a second.

The problem is we are dropping a lot of packets especially at the beginning of the transmission.

When we switch off the i2c sensors reading and just transmit dummy packetst he problem goes away.

We use ble_nus_data_send() to send data which is called from main and polls for sensor data.

How can the interrupt routines interfere with BLE transmissions? Are they not on higher interrupt priority?

Is there anything we can do to stop the i2c reading in interrupt interfering with BLE transmissions?

Thanks

[Jared]

Hi,

What pins are used for the I2C communication?

regards

Jared 

[Yano]

Hi Jared,

P0-30, P0-19 and P0-11, P0-31 

[Jared]

P0-30, P0.19 and P0-31 is marked as low frequency/low drive in the product specification. This means that they should not be used for serial communication, as we have seen that it can interfere with the radio. Can you try to use pins on the left side of the chip and see if it mitigate the issue?

[Yano]

Hi,

I've never seen this before, is there documentation on it?

We're only operating at 400KHz.

We're using an nRF52832 in a module ISP1507AX.

Are there similar restrictions with this?

Is there a way to mitigate this?

For example could we drop the i2c read speed?

Thanks

[Jared]

Hi,

From the documentation I linked in my previous reply:

Yes, this is relevant for all nRF52832. You can either decrease the frequency or try to schedule the I2C communication when the radio is off.

But first you should test with other pins and see if this is really the problem or not in your case.

regards

Jared