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Decimation on STM32 Eval board

I am trying to decimate my ADC values which are stored in a DMA buffer.


The functions I am using are:
1. HAL_ADC_Start_DMA();
2. arm_fir_decimate_init_f32();
3. arm_fir_decimate_f32();

I understand that the information from the 12 bit ADC are stored in a uin32_t type buffer in the DMA. However, to decimate these values, which are in the range of 0-4096, it requires me to convert the uint32_t DMA values to a float32_t data type.
I have tried casting the uint32_t values to a q31_t format and convert them to float32_t via the CMSIS lib: arm_q31_float, but to no avail. The output array of the decimation is always 0.
May I have some help pertaining to either the conversion from uint32_t to q31_t format, or an alternative way to decimate uint32_t values.

Thank you.

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  • looks good! you could also use a q15_t instead of q31_t if you'd like it to go a little faster.  CMSIS takes advantage of SIMD for q15_t when it's available on specific targets. For targets without SIMD, it probably won't make a difference though.  For q15_t just shift up 4 bits instead of 20.

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  • looks good! you could also use a q15_t instead of q31_t if you'd like it to go a little faster.  CMSIS takes advantage of SIMD for q15_t when it's available on specific targets. For targets without SIMD, it probably won't make a difference though.  For q15_t just shift up 4 bits instead of 20.

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