Thank you. (Puzzling that the data interface selection would matter)

Could you also please show the axis orientation on the mechanical drawing?

The drawing above shows the bottom view of the BGA package with A1 at lower right, which fits with the top view's dot on lower left. Can I suggest that the drawing at https://openimu.readthedocs.io/en/latest/330BI/mechanical.html also label the pin view as bottom view (so a mirror image of the PCB footprint)? More importantly, the pin view in the spreadsheet at https://openimu.readthedocs.io/en/latest/330BI/pinout.html is labeled "top view" when in fact it's the bottom view (rotated but not mirrored).

I guess an issue will be the lack of a magnetometer - is there a way to disable that in the INS code? It seems to be buried in the sensor library for which I don't see any source.

Is there an internal pulldown on BOOT0, or should that be added on the board if not using that pin?

The OpenIMU300 MCU has 1M ROM 192K RAM.
The OpenIMU330 MCU has 128K ROM, 64K RAM.

The example IMU300 projects include IMU, VG/AHRS, and INS, but the IMU330 projects only have IMU and VG. When I build the IMU300 INS, it shows 152K ROM and 87K RAM, so I guess that's why there's no IMU330 INS. Removing debug output only saves about 10K ROM.

(I don't know how much work is needed to replace FreeRTOS with the HAL library as done in the IMU330 IMU example, or how much memory that saves.)

I'm wondering why the IMU330 uses STM32L431CB, when there are compatible parts with more memory

https://www.st.com/en/microcontrollers-microprocessors/stm32l4x1.html

I was hoping for an IMU330 application with full INS plus some custom additions.

Excellent, thank you. Is G3 connected to PB12?

Yes, my plan now is to use the UART interface for the host, and modify the firmware to rejigger SPI2 as a master.

Is there any documentation on which ARM M4 pins are connected to which IMU330BI module BGA pins? Specifically, I'd like to add an SPI master to the firmware. It looks like SPI1 is used internally for sensors and SPI2 is the user SPI interface, so is SPI3 available and accessible (ARM PC10-12 or PB3-5)?