xtos_signal_ssvep_feature

Sums rounded-bin harmonic power and neighboring noise, then computes SNR and dB.

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Declaration

#include <xtos/signal.h>

int xtos_signal_ssvep_feature(const double *input,
                              size_t n,
                              uint32_t sample_rate_hz,
                              double target_frequency_hz,
                              size_t harmonic_count,
                              size_t neighbor_bins,
                              struct xtos_ssvep_feature *result);

Parameters

Parameter	Type	Description
input	const double *	Non-NULL input with at least n doubles; it is not modified, but NaN/Inf are not checked.
n	size_t	A nonzero power of two used as the internal DFT length.
sample_rate_hz	uint32_t	Sampling rate in Hz, greater than zero.
target_frequency_hz	double	Target frequency in Hz, in (0, fs/2); finite is not explicitly checked.
harmonic_count	size_t	Number of target harmonics, greater than zero, with the highest harmonic bin in range.
neighbor_bins	size_t	Neighbor bins on each side, greater than zero.
result	struct xtos_ssvep_feature *	Non-NULL caller-provided output structure.

Output fields

Field	Type	Meaning
signal_power	double	Sum of squared-magnitude power at target harmonic bins, without automatic normalization.
noise_power	double	Average power of valid neighboring bins.
snr	double	Linear signal-to-noise ratio, signal_power / noise_power.
snr_db	double	Signal-to-noise ratio 10×log10(snr), in dB.
target_bin	size_t	Rounded target-frequency bin index.
harmonics_used	size_t	Number of target harmonics included in the accumulation.

Return value

Returns 0 and writes result on success; returns -1 on failure. signal_power sums target bins and noise_power averages valid neighbors.

Errors

errno	Condition
EINVAL	A pointer is NULL, n is not a power of two, frequency range is invalid, target bin is zero, or a harmonic bin is out of range.
ENOMEM	Allocation of the internal power or FFT temporary arrays failed.
EDOM	There are no valid neighbors or noise power is not positive.

Notes

The implementation allocates heap memory for power and the FFT; it does not check input or target_frequency_hz NaN/Inf, so callers must validate first.
Overlapping neighborhoods may count a noise bin more than once; this is not CCA, stimulus identification, or artifact rejection.

Example

Source

This reference describes headers and implementation at OpenXTOS commit dd313955ad57542bcd2af8827157d1bbd0cf5e83.