Setting 16 Bit SPI Mode Fails for Raspberry Pi

[emaq]

Setting 16 bit SPI mode fails for the Raspberry Pi 3 board when using Analog Devices ADIS16xxx IMUs. I know this is because the SPI controller of Raspberry Pi only supports 8 bit mode.

How to modify the transferhword in https://github.com/PX4/PX4-Autopilo...42699f4f/src/lib/drivers/device/posix/SPI.cpp to mask the 16 bit SPI mode so that it works for 8 bit SPI as well?

 

[KlausST]

Hi,

In all my decades of professionally using SPI I never used (non standard) 16 bit mode.

I always used the standard 8 bits mode. Instead sending 16 bits it's just sending two 8 bits.
Doesn't this work for you? If not, why?

Currently I'm working on a project with 7 (different) devices on the same SPI. Different speeds, different phase and clock modes, .. accessed blocking, via ISR, via DMA...

Klaus

 

[emaq]

I always used the standard 8 bits mode. Instead sending 16 bits it's just sending two 8 bits.

Do you think the following WRITE sequence works?

1st byte sent: the first bit of the DIN sequence is a 1, followed by a 0 and finally the 6-bit address of the target register.
2nd byte sent: the 8-bit data command containing [15:8] bits of the 16-bit data.
3rd byte sent: the 8-bit data command containing [7:0] bits of the 16-bit data.

To read and verify the same 16-bit target register, the following READ sequence is used.

1st byte sent: the first two bits in the DIN sequence are 0, followed by the upper byte address of the 16-bit register.
1st byte received: the DOUT sequence contains the register’s upper 8-bit data.
2nd byte sent: the first two bits in the DIN sequence are 0, followed by the lower byte address of the 16-bit register.
2nd byte received: the DOUT sequence contains the register’s lower 8-bit data.

I tried this but no luck so far!

 

[KlausST]

Hi,

Show your code.
.. and give a link to the manufacturer's web site of the device. ... where we can find all related cocuments.
.. and the exact part name

Klaus

 

[emaq]

The code is located here...
**broken link removed**
Look at the functions, RegisterWrite and RegisterRead which are explained below.

The SPI::transfer function is defined in...

PX4-Autopilot/src/lib/drivers/device/posix/SPI.cpp at master · Pskoog3/PX4-Autopilot

PX4 Autopilot Software. Contribute to Pskoog3/PX4-Autopilot development by creating an account on GitHub.

github.com

Following is the WRITE sequence which is a bit different from what I mentioned in my last reply.

1st byte sent: the first bit of the DIN sequence is a 1, followed by a 0 and finally the LOWER 6-bit address of the 16-bit target register.
2nd byte sent: the 8-bit data command containing [7:0] bits of the 16-bit data.
3rd byte sent: the first bit of the DIN sequence is a 1, followed by a 0 and finally the UPPER 6-bit address of the 16-bit target register.
4th byte sent: the 8-bit data command containing [15:8] bits of the 16-bit data.

Following READ sequence is used which is again a bit different from what I explained in my last reply.

1st byte sent: the first two bits in the DIN sequence are 0, followed by the LOWER byte address of the 16-bit register.
1st byte received: the DOUT sequence contains the register’s LOWER 8-bit data.
2nd byte sent: the first two bits in the DIN sequence are 0, followed by the UPPER byte address of the 16-bit register.
2nd byte received: the DOUT sequence contains the register’s UPPER 8-bit data.
Finally the UPPER and LOWER 8-bit data is combined into a 16-bit word.

The ADIS16354 IMU datasheet is located at...

https://www.analog.com/media/en/technical-documentation/obsolete-data-sheets/ADIS16354.pdf