How do I go from an integer value to a q31_t? Do I need to normalize the in32_t to a value between -1 and 1 and then pass to arm_pid_q31 to complete the calculation?

[AIsma]

I am using the arm pid library and I do not know how to use the arm_pid_q31 call. I need to give it an error as a q31_t, however, I am not entirely sure how to go from an int32_t to a q31_t. Do I need to normalize the in32_t to a value between -1 and 1 and then pass to arm_pid_q31 to complete the calculation?

[Tesla DeLorean]

You're expect to pass an array with numbers in your selected fixed point format.

Review the "data representation" expectations and diagrams.

Values are going to need to be less than 1

If you have a 12-bit signed ADC value

q31 = adc12i << 20;

q31 = (q31_t)(fltvalue * ((float)(1 << 31)));

[AIsma]

I don't understand entirely, so I wanted to clarify a few things:

1. You said the expectation is to pass an array with numbers, however, arm_pid_q31 accepts a q31_t, not a q31_t*. Are you saying arm_pid_q31 needs to be called multiple times.
2. You mentioned reviewing expectations and diagrams, could you point me to them?
3. Thanks for the help :)

[Tesla DeLorean]

It is passed an array of q31 values https://www.keil.com/pack/doc/CMSIS/DSP/html/structarm__pid__instance__q31.html

You understand how bits are held in bytes and word, and how floating point and fixed point values are held, and data in memory?

https://www.tutorialspoint.com/fixed-point-and-floating-point-number-representations

With q31 you've got 1 sign bit, and 31 fractional bits. Given this is entirely fractional bits holding the value, it will need to always be less than ONE (positive or negative), it could arguably represent -1 but unhelpfully.