Pixhawk pin definitions

ArduCopter Copter 4.6
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1

Hi

I wanted to do some changes to use external imu on spi bus (external) of Pixhawk1 (fmuv3) hardware. The pixhawk’s spi bus is spi1 or spi4?
From the fmuv3 hwdef, there is definition for spidev, mpu9250_ext is defined on spi4, but some google searching it comes as spi1. Another label has mpu9250 and it is on spi4.

I basically want to connect an external imu since my board only has one - mpu6000.

From my findings, I need to correctly define spidev definitions in hwdef of fmuv3. There is already some definitions related to mpu9250 (one is labelled ext and other is mpu9250) in hwdef spidev section.

Then, in Pixhawk1 hwdef, I need to add a line similar to the definition of mpu6000: with mpu9250 or mpu9250_ext and the needed rotation.

So, is the external bus spi1 or spi4 and what is its cs pin?

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Pixhawk Schematics: Hardware/FMUv3_REV_D/Schematic Print/Schematic Prints.PDF at master · pixhawk/Hardware · GitHub

Here, I found that the internal MPU6000 is connected to MPU_CS, which is defined in SPI1 in the SPIDEV section of hwdef. So, it seems like that the external bus is SPI4 and it uses mpu_ext_cs.

Could someone verify this?

Thanks

3

the change that i am doing is at ardupilot/libraries/AP_HAL_ChibiOS/hwdef/Pixhawk1/hwdef.dat at Copter-4.6.3 · ArduPilot/ardupilot · GitHub and I am adding the following at line 18:

IMU Invensense SPI:mpu9250_ext ROTATION_PITCH_180

4

I found another far better IMU - ICM45686
https://robu.in/product/601n1-icm45686-acceleration-gyroscope-sensor/#tab-warranty_tab

So for this IMU, I believe I can change Invensense to Invensensev3 in the Pixhawk hwdef. And add SPIDEV entry for this:

SPIDEV icm45686_ext  SPI4  DEVID6  MPU_EXT_CS  MODE3   2*MHZ 8*MHZ

And, in pixhawk1 hwdef

IMU Invensensev3 SPI:icm45686_ext ROTATION_PITCH_180

I hope this is correct