BNO055 power on reset issues

[brentbop]

I'm trying to resolve a persistent issue I'm having with a BNO055 IMU on a custom PCBA. I'm communicating via I2C and am experiencing different behavior between device reset (using "Power on Reset" reset pin) with and without power cycling. In situations where I reprogram my MCU and start directly into my application code without power cycling, the IMU will respond with NAKs to any and all read/write messages. If I power-cycle the system, it works correctly. In both scenarios I'm pulling the reset pin low for ~25ms, pulling the reset pin high, and then waiting for ~725ms before initiating I2C communication. All other signals (COM1, COM2, PS0, PS1, nBOOT_LOAD_PIN) are connected to VDD or GND directly or through a 10kΩ resistor. A partial schematic is attached.

The firmware is heavily based upon the BNO055 XPlained Pro example code and is being run on a SAMD21G18A.

Can you help me to understand the differences in behavior between device reset for the BNO055 from an 'unknown' state and from a power-on state? Do I need to set the SDA/SCL lines to a certain level before/during/after Power on Reset?

Attached are logic analyzer screenshots of the system failing without power cycle (BNO055_noPowerCycle.png) and working with power cycle (BNO055_withPowerCycle.png), as well as a partial schematic (BNO055_sch.png).

[brentbop]

I've tried bit-banging an empty I2C frame in case an I2C transmission was interrupted by the MCU being reprogrammed (the clumsy approach here: i2c-bus.org) but haven't seen any improvement from any number of clock pulses - 8, 9, 10, 16, 32.

[Vincent]

Can you leave a email address since we need some additional information for this issue

[chrisc]

I too am seeing this issue, the BNO055 works fine on on a power cycle, but issuing a reset by I2C seems to lock up the sensor.
Did you get this to work with help from Bosch? Thanks for any help in advance.

[o_o]

Hi chrisc and brentpop,

We recently discovered a bug in the reset process when the BNO055 expects a crystal to be connected. This means that the BNO055 will fail to reset if there is no external crystal attached.

To prevent the issue:

1. If possible, use an external crystal;
2. If 1 is not possible, avoid triggering a reset after the part has been turned on.

Current workaround:

• Until a new firmware is provided, to reset the BNO055 to a known state, write every configuration register to a known value of your choice, such as the default value (or other).

Future fix:

• Fixing this issue in the field will require a firmware update to the BNO055 pre-programmed firmware. For this, it will require the host MCU to have a connection to the nBOOT_LOAD_PIN in order to enter the bootloader. More details on the firmware update protocol will be disclosed when the new firmware is available.
• It is also possible, but not guaranteed, that future BNO055 will be pre-programmed with the fixed version fo the software.