Which i.MX 8 SOCs do/do not support FTM Quadrature Decoder?

[petero5]

Hi

i.MX 8DualX/8DualXPlus/8QuadXPlus Applications Processor Reference Manual, Rev. 0, 05/2020
p7198 16.1.2.14 FTM
"NOTE Quadrature decoder cannot be used since phase A and B inputs are not available"

Do I understand correctly that the imx8qxp has FTM Quadrature Decoder, but it is impossible to use, because PHA and PHB inputs are not available? And there is no connection between CH0/1 and PHA/B?

Where can we find a summary/table of which i.MX 8 SOCs do/do not support FTM Quadrature Decoder please?

If FTM quaddec is not possible, what is the next best method to support a rotary dial or scroll wheel connected to the imx8qxp please? A rotary control that is part of the device's keypad/human-machine interface.

Thank you
-- Peter

[petero5]

PS. Turns out, for our purposes (HMI), GPIO rotary encoder seems good enough:
https://github.com/nxp-imx/linux-imx/blob/lf-5.15.y/drivers/input/misc/rotary_encoder.c
https://github.com/nxp-imx/linux-imx/blob/lf-5.15.y/Documentation/devicetree/bindings/input/rotary-e...
https://github.com/nxp-imx/linux-imx/blob/lf-5.15.y/Documentation/input/devices/rotary-encoder.rst

[joanxie · Accepted solution]

yes, because FTM pins aren't pined out, maybe you can use software Quadrature Decoder, pls refer to the

AN3775  which is sample of sw Quadrature Decoder

[petero5]

Hi @joanxie 

Thank you for confirming, and the suggestion. If I understand correctly, none of the i.MX 8's have the FTM Quadrature Decoder pinned out, only some i.MX 7.

For the imx8qxp, do you have any recommendation re whether it would be best to implement a software Quadrature Decoder on the M4 core or on the A35 core (Linux)?

Thank you
-- Peter

[joanxie]

got information:

"AN3775 explaining how to implement a software quadradure decoded on a SoC without a dedicated hardware do it. Although it's not a CM4, the fundamentals are the same.

In summary, if the application is to read rotary switch encoders or slow speed motors, this AN should cover the basics and the CM4 is capable to handle the cpu load without the necessity to use the FTM/TPM"