Data Structures
struct	msp_fft_q15_params
	Parameter structure for Q15 real FFT functions. More...

struct	msp_fft_iq31_params
	Parameter structure for IQ31 real FFT functions. More...

Functions
msp_status	msp_fft_auto_q15 (const msp_fft_q15_params params, int16_t src, uint16_t *shift)
	Real forward FFT function with auto-scaling. More...

msp_status	msp_fft_fixed_q15 (const msp_fft_q15_params params, int16_t src)
	Real forward FFT function with fixed scaling by two at each stage. More...

msp_status	msp_fft_iq31 (const msp_fft_iq31_params params, int32_t src)
	Real forward FFT function without scaling. More...

msp_status	msp_ifft_auto_q15 (const msp_fft_q15_params params, int16_t src, uint16_t shift)
	Real result inverse FFT function with auto-scaling. More...

msp_status	msp_ifft_fixed_q15 (const msp_fft_q15_params params, int16_t src)
	Real result inverse FFT function with fixed scaling by two at each stage. More...

msp_status	msp_ifft_iq31 (const msp_fft_iq31_params params, int32_t src)
	Real result inverse FFT function without scaling. More...

Detailed Description

Functions for performing forward and inverse FFT of real 16-bit and 32-bit input data.

Function Documentation

msp_status msp_fft_auto_q15	(	const msp_fft_q15_params *	params,
		int16_t *	src,
		uint16_t *	shift
	)

Real forward FFT function with auto-scaling.

Details: Computes the forward discreet Fourier transform (DFT) of 16-bit real inputs. If the inputs are not already in bit reversed order the bit reversal parameter must be set. The output is monitored for overflow and scaled by a factor of two when an overflow risk is detected. The shift parameter contains the number of bit shifts that were applied to the output.

: This functions requires half the data storage and consumes roughly half the cycles and energy as running a complex FFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.

Pseudo code: y = fft(real(x)) * 2^-shift

Scaling: Scaling is applied as needed to prevent saturation of the output. The scale factor that was applied to the output is returned in the shift parameter and can be used to calculate the result by applying the following function.

: result = result * 2^shift

LEA Support: This function is supported by LEA and requires data to be placed into shared LEA memory with alignment equal to twice the data length (e.g. a 256-point real FFT requires 512-byte alignment). When allocating data the MSP_ALIGN_FFT_Q15 macro can be used to calculate correct alignment. The twiddle table pointer parameter is not used with LEA and can be null or uninitialized.

Parameters

params	Pointer to the real FFT parameter structure.
src	Pointer to the real data array to perform the FFT on.
shift	Auto-scaling shift that was applied to the output.

Returns: Status of the operation.

msp_status msp_fft_fixed_q15	(	const msp_fft_q15_params *	params,
		int16_t *	src
	)

Real forward FFT function with fixed scaling by two at each stage.

Details: Computes the forward discreet Fourier transform (DFT) of 16-bit real inputs. If the inputs are not already in bit reversed order the bit reversal parameter must be set. The output is scaled by a factor of two for each stage of the DFT.

: This functions requires half the data storage and consumes roughly half the cycles and energy as running a complex FFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.

Pseudo code: y = fft(real(x)) ./ (N/2)

Scaling: Each stage of the real FFT, with the exception of the final split stage, scales the result by a factor of 0.5. The output format can either be interpreted as the same type with (N/2) scaling or a different fixed point data type. This can be helpful when using the IQmathLib to process the results of the FFT, such as computing the magnitude or phase angle of the complex result.

Length	Input Type	Result Type
16	_q15	_q12
32	_q15	_q11
64	_q15	_q10
128	_q15	_q9
256	_q15	_q8
512	_q15	_q7
1024	_q15	_q6
2048	_q15	_q5
4096	_q15	_q4

: The following table lists the applied scaling factor and resulting data type when the input is a 16-bit integer.

Length	Input Type	Result Type
16	int16_t	(int16_t)(result / 8)
32	int16_t	(int16_t)(result / 16)
64	int16_t	(int16_t)(result / 32)
128	int16_t	(int16_t)(result / 64)
256	int16_t	(int16_t)(result / 128)
512	int16_t	(int16_t)(result / 256)
1024	int16_t	(int16_t)(result / 512)
2048	int16_t	(int16_t)(result / 1024)
4096	int16_t	(int16_t)(result / 2048)

LEA Support: This function is supported by LEA and requires data to be placed into shared LEA memory with alignment equal to twice the data length (e.g. a 256-point real FFT requires 512-byte alignment). When allocating data the MSP_ALIGN_FFT_Q15 macro can be used to calculate correct alignment. The twiddle table pointer parameter is not used with LEA and can be null or uninitialized.

Parameters

params	Pointer to the real FFT parameter structure.
src	Pointer to the real data array to perform the FFT on.

Returns: Status of the operation.

msp_status msp_fft_iq31	(	const msp_fft_iq31_params *	params,
		int32_t *	src
	)

Real forward FFT function without scaling.

Details: Computes the forward discreet Fourier transform (DFT) of 32-bit real inputs. If the inputs are not already in bit reversed order the bit reversal parameter must be set. The output is not scaled.

: This functions requires half the data storage and consumes roughly half the cycles and energy as running a complex FFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.

Pseudo code: y = fft(real(x))

LEA Support: This function is supported by LEA and requires data to be placed into shared LEA memory with alignment equal to four times the data length (e.g. a 256-point real FFT requires 1024-byte alignment). When allocating data the MSP_ALIGN_FFT_IQ31 macro can be used to calculate correct alignment. The twiddle table pointer parameter is not used with LEA and can be null or uninitialized.

Parameters

params	Pointer to the real FFT parameter structure.
src	Pointer to the real data array to perform the FFT on.

Returns: Status of the operation.

Examples:: transform_ex3_fft_iq31.c.

msp_status msp_ifft_auto_q15	(	const msp_fft_q15_params *	params,
		int16_t *	src,
		uint16_t	shift
	)

Real result inverse FFT function with auto-scaling.

Details: Computes the inverse discreet Fourier transform (DFT) of 16-bit complex inputs with real result. If the inputs are not already in bit reversed order the bit reversal parameter must be set. Automatic scaling is performed such that this is the direct inverse of the forward FFT with auto scaling.

: This functions uses half the data storage and consumes roughly half the cycles and energy as running a complex IFFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.

Pseudo code: y = (real(ifft(x)) * 2^shift) ./ (N/2)

LEA Support: This function is supported by LEA and requires data to be placed into shared LEA memory with alignment equal to twice the data length (e.g. a 256-point real FFT requires 512-byte alignment). When allocating data the MSP_ALIGN_FFT_Q15 macro can be used to calculate correct alignment. The twiddle table pointer parameter is not used with LEA and can be null or uninitialized.

Parameters

params	Pointer to the real FFT parameter structure.
src	Pointer to the real data array to perform the FFT on.
shift	Auto-scaling shift that was applied to the forward FFT.

Returns: Status of the operation.

msp_status msp_ifft_fixed_q15	(	const msp_fft_q15_params *	params,
		int16_t *	src
	)

Real result inverse FFT function with fixed scaling by two at each stage.

Details: Computes the inverse discreet Fourier transform (DFT) of 16-bit complex inputs with real result. If the inputs are not already in bit reversed order the bit reversal parameter must be set. Fixed scaling is performed such that this is the direct inverse of the forward FFT with fixed scaling.

: This functions uses half the data storage and consumes roughly half the cycles and energy as running a complex IFFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.

Pseudo code: y = real(ifft(x))

Scaling: This function is the direct inverse of the forward real FFT with fixed scaling. The following fixed point input types will all result in Q15 results.

Length	Input Type	Result Type
16	_q12	_q15
32	_q11	_q15
64	_q10	_q15
128	_q9	_q15
256	_q8	_q15
512	_q7	_q15
1024	_q6	_q15
2048	_q5	_q15
4096	_q4	_q15

LEA Support: This function is supported by LEA and requires data to be placed into shared LEA memory with alignment equal to twice the data length (e.g. a 256-point real FFT requires 512-byte alignment). When allocating data the MSP_ALIGN_FFT_Q15 macro can be used to calculate correct alignment. The twiddle table pointer parameter is not used with LEA and can be null or uninitialized.

Parameters

params	Pointer to the real FFT parameter structure.
src	Pointer to the real data array to perform the FFT on.

Returns: Status of the operation.

msp_status msp_ifft_iq31	(	const msp_fft_iq31_params *	params,
		int32_t *	src
	)

Real result inverse FFT function without scaling.

Details: Computes the inverse discreet Fourier transform (DFT) of 32-bit complex inputs with real result. If the inputs are not already in bit reversed order the bit reversal parameter must be set. Fixed scaling is performed such that this is the direct inverse of the forward FFT without scaling.

: This functions uses half the data storage and consumes roughly half the cycles and energy as running a complex IFFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.

Pseudo code: y = real(ifft(x)) ./ N

LEA Support: This function is supported by LEA and requires data to be placed into shared LEA memory with alignment equal to four times the data length (e.g. a 256-point real FFT requires 1024-byte alignment). When allocating data the MSP_ALIGN_FFT_IQ31 macro can be used to calculate correct alignment. The twiddle table pointer parameter is not used with LEA and can be null or uninitialized.

Parameters

params	Pointer to the real FFT parameter structure.
src	Pointer to the real data array to perform the FFT on.

Returns: Status of the operation.

Data Structures

Functions

Detailed Description

Function Documentation