I am new to DSP things and I just built my first test project. This is a low pass filter with an order of 31, so 32 coefficients. Also I have an input buffer of 32 values that I designed as a ring buffer. With these I programmed a standard FIR filter algorithm in C. The input buffer is filled with one new value periodically at sample frequency with the output of an ADC. Then I run one filter calculation and get an output for this point in time. Filter output goes to an DAC. All this runs fine for me, feeding the system with a frequency sweep I can see on an oscilloscope the low pass function at DAC output signal.
Now I want to change this to CMSIS FIR functions to increase speed and test Q15 and Q31 types, but I struggle with my realtime approach with one new value for every calculation run. All the examples I found calculate a large number of stored samples and create a complete waveform output instead of just the current output value. What do I have to setup?
Is blocksize = 1? So *pSrc and *pDst point to only one value? Will the previous values remain stored in pState of arm_fir_instance_f32? How is the ring buffer realized or is it all in the CMSIS functions?
Then I found an STM32 application note (AN4841) stating that the fastest FIR calculation is with float32, followed by Q31, followed by Q15. I wonder how this can be. Don't the Q31 and Q15 use MAC instructions? Or are there the same instructions also in the FPU unit?
Thanks for any help
This application is a bit old, but might help to understand the concept of using CMSIS-DSP functions.