From 96d6da4e252b06dcfdc041e7df23e86161c33007 Mon Sep 17 00:00:00 2001 From: rihab kouki Date: Tue, 28 Jul 2020 11:24:49 +0100 Subject: Official ARM version: v5.6.0 --- docs/DSP/html/group__FIR__decimate.html | 258 +++++++++++++++----------------- 1 file changed, 124 insertions(+), 134 deletions(-) (limited to 'docs/DSP/html/group__FIR__decimate.html') diff --git a/docs/DSP/html/group__FIR__decimate.html b/docs/DSP/html/group__FIR__decimate.html index 6296034..01ca22b 100644 --- a/docs/DSP/html/group__FIR__decimate.html +++ b/docs/DSP/html/group__FIR__decimate.html @@ -32,7 +32,7 @@ Logo
CMSIS-DSP -  Version 1.5.2 +  Version 1.7.0
CMSIS DSP Software Library
@@ -116,30 +116,30 @@ $(document).ready(function(){initNavTree('group__FIR__decimate.html','');}); - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + +

Functions

void arm_fir_decimate_f32 (const arm_fir_decimate_instance_f32 *S, float32_t *pSrc, float32_t *pDst, uint32_t blockSize)
 Processing function for the floating-point FIR decimator. More...
 
void arm_fir_decimate_fast_q15 (const arm_fir_decimate_instance_q15 *S, q15_t *pSrc, q15_t *pDst, uint32_t blockSize)
 Processing function for the Q15 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4. More...
 
void arm_fir_decimate_fast_q31 (arm_fir_decimate_instance_q31 *S, q31_t *pSrc, q31_t *pDst, uint32_t blockSize)
 Processing function for the Q31 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4. More...
 
arm_status arm_fir_decimate_init_f32 (arm_fir_decimate_instance_f32 *S, uint16_t numTaps, uint8_t M, float32_t *pCoeffs, float32_t *pState, uint32_t blockSize)
 Initialization function for the floating-point FIR decimator. More...
 
arm_status arm_fir_decimate_init_q15 (arm_fir_decimate_instance_q15 *S, uint16_t numTaps, uint8_t M, q15_t *pCoeffs, q15_t *pState, uint32_t blockSize)
 Initialization function for the Q15 FIR decimator. More...
 
arm_status arm_fir_decimate_init_q31 (arm_fir_decimate_instance_q31 *S, uint16_t numTaps, uint8_t M, q31_t *pCoeffs, q31_t *pState, uint32_t blockSize)
 Initialization function for the Q31 FIR decimator. More...
 
void arm_fir_decimate_q15 (const arm_fir_decimate_instance_q15 *S, q15_t *pSrc, q15_t *pDst, uint32_t blockSize)
 Processing function for the Q15 FIR decimator. More...
 
void arm_fir_decimate_q31 (const arm_fir_decimate_instance_q31 *S, q31_t *pSrc, q31_t *pDst, uint32_t blockSize)
 Processing function for the Q31 FIR decimator. More...
 
void arm_fir_decimate_f32 (const arm_fir_decimate_instance_f32 *S, const float32_t *pSrc, float32_t *pDst, uint32_t blockSize)
 Processing function for floating-point FIR decimator. More...
 
void arm_fir_decimate_fast_q15 (const arm_fir_decimate_instance_q15 *S, const q15_t *pSrc, q15_t *pDst, uint32_t blockSize)
 Processing function for the Q15 FIR decimator (fast variant). More...
 
void arm_fir_decimate_fast_q31 (const arm_fir_decimate_instance_q31 *S, const q31_t *pSrc, q31_t *pDst, uint32_t blockSize)
 Processing function for the Q31 FIR decimator (fast variant). More...
 
arm_status arm_fir_decimate_init_f32 (arm_fir_decimate_instance_f32 *S, uint16_t numTaps, uint8_t M, const float32_t *pCoeffs, float32_t *pState, uint32_t blockSize)
 Initialization function for the floating-point FIR decimator. More...
 
arm_status arm_fir_decimate_init_q15 (arm_fir_decimate_instance_q15 *S, uint16_t numTaps, uint8_t M, const q15_t *pCoeffs, q15_t *pState, uint32_t blockSize)
 Initialization function for the Q15 FIR decimator. More...
 
arm_status arm_fir_decimate_init_q31 (arm_fir_decimate_instance_q31 *S, uint16_t numTaps, uint8_t M, const q31_t *pCoeffs, q31_t *pState, uint32_t blockSize)
 Initialization function for the Q31 FIR decimator. More...
 
void arm_fir_decimate_q15 (const arm_fir_decimate_instance_q15 *S, const q15_t *pSrc, q15_t *pDst, uint32_t blockSize)
 Processing function for the Q15 FIR decimator. More...
 
void arm_fir_decimate_q31 (const arm_fir_decimate_instance_q31 *S, const q31_t *pSrc, q31_t *pDst, uint32_t blockSize)
 Processing function for the Q31 FIR decimator. More...
 

Description

These functions combine an FIR filter together with a decimator. They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion. Conceptually, the functions are equivalent to the block diagram below:

@@ -151,31 +151,31 @@ Components included in the FIR Decimator functions

The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner. Instead of calculating all of the FIR filter outputs and discarding M-1 out of every M, only the samples output by the decimator are computed. The functions operate on blocks of input and output data. pSrc points to an array of blockSize input values and pDst points to an array of blockSize/M output values. In order to have an integer number of output samples blockSize must always be a multiple of the decimation factor M.

The library provides separate functions for Q15, Q31 and floating-point data types.

Algorithm:
The FIR portion of the algorithm uses the standard form filter: 
-    y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]
+     y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]
where, b[n] are the filter coefficients.
The pCoeffs points to a coefficient array of size numTaps. Coefficients are stored in time reversed order. 
-    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
+     {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
pState points to a state array of size numTaps + blockSize - 1. Samples in the state buffer are stored in the order: 
-    {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}
+     {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}
The state variables are updated after each block of data is processed, the coefficients are untouched.
Instance Structure
The coefficients and state variables for a filter are stored together in an instance data structure. A separate instance structure must be defined for each filter. Coefficient arrays may be shared among several instances while state variable array should be allocated separately. There are separate instance structure declarations for each of the 3 supported data types.
Initialization Functions
There is also an associated initialization function for each data type. The initialization function performs the following operations:
  • Sets the values of the internal structure fields.
  • Zeros out the values in the state buffer.
    • -
  • Checks to make sure that the size of the input is a multiple of the decimation factor. To do this manually without calling the init function, assign the follow subfields of the instance structure: numTaps, pCoeffs, M (decimation factor), pState. Also set all of the values in pState to zero.
    • +
  • Checks to make sure that the size of the input is a multiple of the decimation factor. To do this manually without calling the init function, assign the follow subfields of the instance structure: numTaps, pCoeffs, M (decimation factor), pState. Also set all of the values in pState to zero.
Use of the initialization function is optional. However, if the initialization function is used, then the instance structure cannot be placed into a const data section. To place an instance structure into a const data section, the instance structure must be manually initialized. The code below statically initializes each of the 3 different data type filter instance structures 
-arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};
-arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};
-arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};
+     arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};
+     arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};
+     arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};
where M is the decimation factor; numTaps is the number of filter coefficients in the filter; pCoeffs is the address of the coefficient buffer; pState is the address of the state buffer. Be sure to set the values in the state buffer to zeros when doing static initialization.
Fixed-Point Behavior
Care must be taken when using the fixed-point versions of the FIR decimate filter functions. In particular, the overflow and saturation behavior of the accumulator used in each function must be considered. Refer to the function specific documentation below for usage guidelines.

Function Documentation

- +
@@ -188,7 +188,7 @@ Components included in the FIR Decimator functions - + @@ -212,20 +212,18 @@ Components included in the FIR Decimator functions
Parameters
float32_t * const float32_t *  pSrc,
- - - - + + + +
[in]*Spoints to an instance of the floating-point FIR decimator structure.
[in]*pSrcpoints to the block of input data.
[out]*pDstpoints to the block of output data.
[in]blockSizenumber of input samples to process per call.
[in]Spoints to an instance of the floating-point FIR decimator structure
[in]pSrcpoints to the block of input data
[out]pDstpoints to the block of output data
[in]blockSizenumber of samples to process
-
Returns
none.
- -

References arm_fir_decimate_instance_f32::M, arm_fir_decimate_instance_f32::numTaps, arm_fir_decimate_instance_f32::pCoeffs, and arm_fir_decimate_instance_f32::pState.

+
Returns
none
- +
@@ -238,7 +236,7 @@ Components included in the FIR Decimator functions - + @@ -260,39 +258,36 @@ Components included in the FIR Decimator functions
q15_t * const q15_t *  pSrc,
+

Processing function for the Q15 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4.

Parameters
- - - - + + + +
[in]*Spoints to an instance of the Q15 FIR decimator structure.
[in]*pSrcpoints to the block of input data.
[out]*pDstpoints to the block of output data
[in]blockSizenumber of input samples to process per call.
[in]Spoints to an instance of the Q15 FIR decimator structure
[in]pSrcpoints to the block of input data
[out]pDstpoints to the block of output data
[in]blockSizenumber of input samples to process per call
Returns
none
-
Restrictions
If the silicon does not support unaligned memory access enable the macro UNALIGNED_SUPPORT_DISABLE In this case input, output, state buffers should be aligned by 32-bit
-

Scaling and Overflow Behavior:

-
This fast version uses a 32-bit accumulator with 2.30 format. The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit. Thus, if the accumulator result overflows it wraps around and distorts the result. In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (log2 is read as log to the base 2). The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result.
-
Refer to the function arm_fir_decimate_q15() for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion. Both the slow and the fast versions use the same instance structure. Use the function arm_fir_decimate_init_q15() to initialize the filter structure.
- -

References __SIMD32, __SMLAD(), arm_fir_decimate_instance_q15::M, arm_fir_decimate_instance_q15::numTaps, arm_fir_decimate_instance_q15::pCoeffs, and arm_fir_decimate_instance_q15::pState.

+
Scaling and Overflow Behavior
This fast version uses a 32-bit accumulator with 2.30 format. The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit. Thus, if the accumulator result overflows it wraps around and distorts the result. In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (log2 is read as log to the base 2). The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result.
+
Remarks
Refer to arm_fir_decimate_q15() for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion. Both the slow and the fast versions use the same instance structure. Use function arm_fir_decimate_init_q15() to initialize the filter structure.
- +
- + - + @@ -314,25 +309,23 @@ Components included in the FIR Decimator functions
void arm_fir_decimate_fast_q31 (arm_fir_decimate_instance_q31 * const arm_fir_decimate_instance_q31 *  S,
q31_t * const q31_t *  pSrc,
+

Processing function for the Q31 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4.

Parameters
- - - - + + + +
[in]*Spoints to an instance of the Q31 FIR decimator structure.
[in]*pSrcpoints to the block of input data.
[out]*pDstpoints to the block of output data
[in]blockSizenumber of input samples to process per call.
[in]Spoints to an instance of the Q31 FIR decimator structure
[in]pSrcpoints to the block of input data
[out]pDstpoints to the block of output data
[in]blockSizenumber of samples to process
Returns
none
-

Scaling and Overflow Behavior:

-
This function is optimized for speed at the expense of fixed-point precision and overflow protection. The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format. These intermediate results are added to a 2.30 accumulator. Finally, the accumulator is saturated and converted to a 1.31 result. The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result. In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2).
-
Refer to the function arm_fir_decimate_q31() for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision. Both the slow and the fast versions use the same instance structure. Use the function arm_fir_decimate_init_q31() to initialize the filter structure.
- -

References arm_fir_decimate_instance_q31::M, arm_fir_decimate_instance_q31::numTaps, arm_fir_decimate_instance_q31::pCoeffs, and arm_fir_decimate_instance_q31::pState.

+
Scaling and Overflow Behavior
This function is optimized for speed at the expense of fixed-point precision and overflow protection. The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format. These intermediate results are added to a 2.30 accumulator. Finally, the accumulator is saturated and converted to a 1.31 result. The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result. In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2).
+
Remarks
Refer to arm_fir_decimate_q31() for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision. Both the slow and the fast versions use the same instance structure. Use function arm_fir_decimate_init_q31() to initialize the filter structure.
- +
@@ -357,7 +350,7 @@ Components included in the FIR Decimator functions - + @@ -381,27 +374,28 @@ Components included in the FIR Decimator functions
Parameters
float32_t * const float32_t *  pCoeffs,
- - - - - - + + + + + +
[in,out]*Spoints to an instance of the floating-point FIR decimator structure.
[in]numTapsnumber of coefficients in the filter.
[in]Mdecimation factor.
[in]*pCoeffspoints to the filter coefficients.
[in]*pStatepoints to the state buffer.
[in]blockSizenumber of input samples to process per call.
[in,out]Spoints to an instance of the floating-point FIR decimator structure
[in]numTapsnumber of coefficients in the filter
[in]Mdecimation factor
[in]pCoeffspoints to the filter coefficients
[in]pStatepoints to the state buffer
[in]blockSizenumber of input samples to process per call
-
Returns
The function returns ARM_MATH_SUCCESS if initialization was successful or ARM_MATH_LENGTH_ERROR if blockSize is not a multiple of M.
-

Description:

-
pCoeffs points to the array of filter coefficients stored in time reversed order: 
-   {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
+
Returns
execution status
+

+
Details
pCoeffs points to the array of filter coefficients stored in time reversed order: 
+    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
 
 

-
pState points to the array of state variables. pState is of length numTaps+blockSize-1 words where blockSize is the number of input samples passed to arm_fir_decimate_f32(). M is the decimation factor. 

-
-
References ARM_MATH_LENGTH_ERROR, ARM_MATH_SUCCESS, arm_fir_decimate_instance_f32::M, arm_fir_decimate_instance_f32::numTaps, arm_fir_decimate_instance_f32::pCoeffs, arm_fir_decimate_instance_f32::pState, and status.

+
pState points to the array of state variables. pState is of length numTaps+blockSize-1 words where blockSize is the number of input samples passed to arm_fir_decimate_f32(). M is the decimation factor.
- +
@@ -426,7 +420,7 @@ Components included in the FIR Decimator functions - + @@ -450,27 +444,28 @@ Components included in the FIR Decimator functions
Parameters
q15_t * const q15_t *  pCoeffs,
- - - - - - + + + + + +
[in,out]*Spoints to an instance of the Q15 FIR decimator structure.
[in]numTapsnumber of coefficients in the filter.
[in]Mdecimation factor.
[in]*pCoeffspoints to the filter coefficients.
[in]*pStatepoints to the state buffer.
[in]blockSizenumber of input samples to process per call.
[in,out]Spoints to an instance of the Q15 FIR decimator structure
[in]numTapsnumber of coefficients in the filter
[in]Mdecimation factor
[in]pCoeffspoints to the filter coefficients
[in]pStatepoints to the state buffer
[in]blockSizenumber of input samples to process
-
Returns
The function returns ARM_MATH_SUCCESS if initialization was successful or ARM_MATH_LENGTH_ERROR if blockSize is not a multiple of M.
-

Description:

-
pCoeffs points to the array of filter coefficients stored in time reversed order: 
-   {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
+
Returns
execution status
+

+
Details
pCoeffs points to the array of filter coefficients stored in time reversed order: 
+    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
 
 

-
pState points to the array of state variables. pState is of length numTaps+blockSize-1 words where blockSize is the number of input samples to the call arm_fir_decimate_q15(). M is the decimation factor. 

-
-
References ARM_MATH_LENGTH_ERROR, ARM_MATH_SUCCESS, arm_fir_decimate_instance_q15::M, arm_fir_decimate_instance_q15::numTaps, arm_fir_decimate_instance_q15::pCoeffs, arm_fir_decimate_instance_q15::pState, and status.

+
pState points to the array of state variables. pState is of length numTaps+blockSize-1 words where blockSize is the number of input samples to the call arm_fir_decimate_q15(). M is the decimation factor.
- +
@@ -495,7 +490,7 @@ Components included in the FIR Decimator functions - + @@ -519,27 +514,28 @@ Components included in the FIR Decimator functions
Parameters
q31_t * const q31_t *  pCoeffs,
- - - - - - + + + + + +
[in,out]*Spoints to an instance of the Q31 FIR decimator structure.
[in]numTapsnumber of coefficients in the filter.
[in]Mdecimation factor.
[in]*pCoeffspoints to the filter coefficients.
[in]*pStatepoints to the state buffer.
[in]blockSizenumber of input samples to process per call.
[in,out]Spoints to an instance of the Q31 FIR decimator structure
[in]numTapsnumber of coefficients in the filter
[in]Mdecimation factor
[in]pCoeffspoints to the filter coefficients
[in]pStatepoints to the state buffer
[in]blockSizenumber of input samples to process
-
Returns
The function returns ARM_MATH_SUCCESS if initialization was successful or ARM_MATH_LENGTH_ERROR if blockSize is not a multiple of M.
-

Description:

-
pCoeffs points to the array of filter coefficients stored in time reversed order: 
-   {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
+
Returns
execution status
+

+
Details
pCoeffs points to the array of filter coefficients stored in time reversed order: 
+    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
 
 

-
pState points to the array of state variables. pState is of length numTaps+blockSize-1 words where blockSize is the number of input samples passed to arm_fir_decimate_q31(). M is the decimation factor. 

-
-
References ARM_MATH_LENGTH_ERROR, ARM_MATH_SUCCESS, arm_fir_decimate_instance_q31::M, arm_fir_decimate_instance_q31::numTaps, arm_fir_decimate_instance_q31::pCoeffs, arm_fir_decimate_instance_q31::pState, and status.

+
pState points to the array of state variables. pState is of length numTaps+blockSize-1 words where blockSize is the number of input samples passed to arm_fir_decimate_q31(). M is the decimation factor.
- +
@@ -552,7 +548,7 @@ Components included in the FIR Decimator functions - + @@ -576,23 +572,20 @@ Components included in the FIR Decimator functions
Parameters
q15_t * const q15_t *  pSrc,
- - - - + + + +
[in]*Spoints to an instance of the Q15 FIR decimator structure.
[in]*pSrcpoints to the block of input data.
[out]*pDstpoints to the location where the output result is written.
[in]blockSizenumber of input samples to process per call.
[in]Spoints to an instance of the Q15 FIR decimator structure
[in]pSrcpoints to the block of input data
[out]pDstpoints to the block of output data
[in]blockSizenumber of input samples to process per call
-
Returns
none.
-

Scaling and Overflow Behavior:

-
The function is implemented using a 64-bit internal accumulator. Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result. The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format. There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved. After all additions have been performed, the accumulator is truncated to 34.15 format by discarding low 15 bits. Lastly, the accumulator is saturated to yield a result in 1.15 format.
-
Refer to the function arm_fir_decimate_fast_q15() for a faster but less precise implementation of this function for Cortex-M3 and Cortex-M4.
- -

References arm_fir_decimate_instance_q15::M, arm_fir_decimate_instance_q15::numTaps, arm_fir_decimate_instance_q15::pCoeffs, and arm_fir_decimate_instance_q15::pState.

+
Returns
none
+
Scaling and Overflow Behavior
The function is implemented using a 64-bit internal accumulator. Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result. The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format. There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved. After all additions have been performed, the accumulator is truncated to 34.15 format by discarding low 15 bits. Lastly, the accumulator is saturated to yield a result in 1.15 format.
+
Remarks
Refer to arm_fir_decimate_fast_q15() for a faster but less precise implementation of this function.
- +
@@ -605,7 +598,7 @@ Components included in the FIR Decimator functions - + @@ -629,19 +622,16 @@ Components included in the FIR Decimator functions
Parameters
q31_t * const q31_t *  pSrc,
- - - - + + + +
[in]*Spoints to an instance of the Q31 FIR decimator structure.
[in]*pSrcpoints to the block of input data.
[out]*pDstpoints to the block of output data
[in]blockSizenumber of input samples to process per call.
[in]Spoints to an instance of the Q31 FIR decimator structure
[in]pSrcpoints to the block of input data
[out]pDstpoints to the block of output data
[in]blockSizenumber of samples to process
Returns
none
-

Scaling and Overflow Behavior:

-
The function is implemented using an internal 64-bit accumulator. The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit. Thus, if the accumulator result overflows it wraps around rather than clip. In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2). After all multiply-accumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format.
-
Refer to the function arm_fir_decimate_fast_q31() for a faster but less precise implementation of this function for Cortex-M3 and Cortex-M4.
- -

References arm_fir_decimate_instance_q31::M, arm_fir_decimate_instance_q31::numTaps, arm_fir_decimate_instance_q31::pCoeffs, and arm_fir_decimate_instance_q31::pState.

+
Scaling and Overflow Behavior
The function is implemented using an internal 64-bit accumulator. The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit. Thus, if the accumulator result overflows it wraps around rather than clip. In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2). After all multiply-accumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format.
+
Remarks
Refer to arm_fir_decimate_fast_q31() for a faster but less precise implementation of this function.
@@ -650,7 +640,7 @@ Components included in the FIR Decimator functions