#include <cstdint>
using float32_t = float;
typedef struct
{
uint16_t numTaps; /**< number of filter coefficients in the filter. */
float32_t *pState; /**< points to the state variable array. The array is of length numTaps+blockSize-1. */
float32_t *pCoeffs; /**< points to the coefficient array. The array is of length numTaps. */
} arm_fir_instance_f32;
static void arm_fir_f32(const arm_fir_instance_f32 * S, float32_t * pSrc, float32_t * pDst, uint32_t blockSize);
Sample* process_data(Samples samples)
{
// 1. Define our array sizes (Be sure to set Run > Set buffer size... to below value!)
constexpr unsigned int buffer_size = 500;
constexpr unsigned int filter_size = 100;
// 2. Define our filter and the working arrays
static float filter[filter_size] = {
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,
.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f,.01f
};
static float input[buffer_size];
static float output[buffer_size];
static float working[buffer_size + filter_size];
// 3. Scale 0-4095 interger sample values to +/- 1.0 floats
for (unsigned int i = 0; i < SIZE; i++)
input[i] = (samples[i] - 2048) / 2048.f;
// 4. Compute the FIR
arm_fir_instance_f32 fir { filter_size, working, filter };
arm_fir_f32(&fir, input, output, SIZE);
// 5. Convert float results back to 0-4095 range for output
for (unsigned int i = 0; i < SIZE; i++)
samples[i] = output[i] * 2048.f + 2048;
return samples;
}
// Below taken from the CMSIS DSP Library (find it on GitHub)
void arm_fir_f32(
const arm_fir_instance_f32 * S,
float32_t * pSrc,
float32_t * pDst,
uint32_t blockSize)
{
float32_t *pState = S->pState; /* State pointer */
float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
float32_t *pStateCurnt; /* Points to the current sample of the state */
float32_t *px, *pb; /* Temporary pointers for state and coefficient buffers */
float32_t acc0, acc1, acc2, acc3, acc4, acc5, acc6, acc7; /* Accumulators */
float32_t x0, x1, x2, x3, x4, x5, x6, x7, c0; /* Temporary variables to hold state and coefficient values */
uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
uint32_t i, tapCnt, blkCnt; /* Loop counters */
float32_t p0,p1,p2,p3,p4,p5,p6,p7; /* Temporary product values */
/* S->pState points to state array which contains previous frame (numTaps - 1) samples */
/* pStateCurnt points to the location where the new input data should be written */
pStateCurnt = &(S->pState[(numTaps - 1u)]);
/* Apply loop unrolling and compute 8 output values simultaneously.
* The variables acc0 ... acc7 hold output values that are being computed:
*
* acc0 = b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]
* acc1 = b[numTaps-1] * x[n-numTaps] + b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]
* acc2 = b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] + b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]
* acc3 = b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps] +...+ b[0] * x[3]
*/
blkCnt = blockSize >> 3;
/* First part of the processing with loop unrolling. Compute 8 outputs at a time.
** a second loop below computes the remaining 1 to 7 samples. */
while(blkCnt > 0u)
{
/* Copy four new input samples into the state buffer */
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
/* Set all accumulators to zero */
acc0 = 0.0f;
acc1 = 0.0f;
acc2 = 0.0f;
acc3 = 0.0f;
acc4 = 0.0f;
acc5 = 0.0f;
acc6 = 0.0f;
acc7 = 0.0f;
/* Initialize state pointer */
px = pState;
/* Initialize coeff pointer */
pb = (pCoeffs);
/* This is separated from the others to avoid
* a call to __aeabi_memmove which would be slower
*/
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
/* Read the first seven samples from the state buffer: x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
x0 = *px++;
x1 = *px++;
x2 = *px++;
x3 = *px++;
x4 = *px++;
x5 = *px++;
x6 = *px++;
/* Loop unrolling. Process 8 taps at a time. */
tapCnt = numTaps >> 3u;
/* Loop over the number of taps. Unroll by a factor of 8.
** Repeat until we've computed numTaps-8 coefficients. */
while(tapCnt > 0u)
{
/* Read the b[numTaps-1] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-3] sample */
x7 = *(px++);
/* acc0 += b[numTaps-1] * x[n-numTaps] */
p0 = x0 * c0;
/* acc1 += b[numTaps-1] * x[n-numTaps-1] */
p1 = x1 * c0;
/* acc2 += b[numTaps-1] * x[n-numTaps-2] */
p2 = x2 * c0;
/* acc3 += b[numTaps-1] * x[n-numTaps-3] */
p3 = x3 * c0;
/* acc4 += b[numTaps-1] * x[n-numTaps-4] */
p4 = x4 * c0;
/* acc1 += b[numTaps-1] * x[n-numTaps-5] */
p5 = x5 * c0;
/* acc2 += b[numTaps-1] * x[n-numTaps-6] */
p6 = x6 * c0;
/* acc3 += b[numTaps-1] * x[n-numTaps-7] */
p7 = x7 * c0;
/* Read the b[numTaps-2] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-4] sample */
x0 = *(px++);
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Perform the multiply-accumulate */
p0 = x1 * c0;
p1 = x2 * c0;
p2 = x3 * c0;
p3 = x4 * c0;
p4 = x5 * c0;
p5 = x6 * c0;
p6 = x7 * c0;
p7 = x0 * c0;
/* Read the b[numTaps-3] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-5] sample */
x1 = *(px++);
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Perform the multiply-accumulates */
p0 = x2 * c0;
p1 = x3 * c0;
p2 = x4 * c0;
p3 = x5 * c0;
p4 = x6 * c0;
p5 = x7 * c0;
p6 = x0 * c0;
p7 = x1 * c0;
/* Read the b[numTaps-4] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-6] sample */
x2 = *(px++);
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Perform the multiply-accumulates */
p0 = x3 * c0;
p1 = x4 * c0;
p2 = x5 * c0;
p3 = x6 * c0;
p4 = x7 * c0;
p5 = x0 * c0;
p6 = x1 * c0;
p7 = x2 * c0;
/* Read the b[numTaps-4] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-6] sample */
x3 = *(px++);
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Perform the multiply-accumulates */
p0 = x4 * c0;
p1 = x5 * c0;
p2 = x6 * c0;
p3 = x7 * c0;
p4 = x0 * c0;
p5 = x1 * c0;
p6 = x2 * c0;
p7 = x3 * c0;
/* Read the b[numTaps-4] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-6] sample */
x4 = *(px++);
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Perform the multiply-accumulates */
p0 = x5 * c0;
p1 = x6 * c0;
p2 = x7 * c0;
p3 = x0 * c0;
p4 = x1 * c0;
p5 = x2 * c0;
p6 = x3 * c0;
p7 = x4 * c0;
/* Read the b[numTaps-4] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-6] sample */
x5 = *(px++);
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Perform the multiply-accumulates */
p0 = x6 * c0;
p1 = x7 * c0;
p2 = x0 * c0;
p3 = x1 * c0;
p4 = x2 * c0;
p5 = x3 * c0;
p6 = x4 * c0;
p7 = x5 * c0;
/* Read the b[numTaps-4] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-6] sample */
x6 = *(px++);
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Perform the multiply-accumulates */
p0 = x7 * c0;
p1 = x0 * c0;
p2 = x1 * c0;
p3 = x2 * c0;
p4 = x3 * c0;
p5 = x4 * c0;
p6 = x5 * c0;
p7 = x6 * c0;
tapCnt--;
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
}
/* If the filter length is not a multiple of 8, compute the remaining filter taps */
tapCnt = numTaps % 0x8u;
while(tapCnt > 0u)
{
/* Read coefficients */
c0 = *(pb++);
/* Fetch 1 state variable */
x7 = *(px++);
/* Perform the multiply-accumulates */
p0 = x0 * c0;
p1 = x1 * c0;
p2 = x2 * c0;
p3 = x3 * c0;
p4 = x4 * c0;
p5 = x5 * c0;
p6 = x6 * c0;
p7 = x7 * c0;
/* Reuse the present sample states for next sample */
x0 = x1;
x1 = x2;
x2 = x3;
x3 = x4;
x4 = x5;
x5 = x6;
x6 = x7;
acc0 += p0;
acc1 += p1;
acc2 += p2;
acc3 += p3;
acc4 += p4;
acc5 += p5;
acc6 += p6;
acc7 += p7;
/* Decrement the loop counter */
tapCnt--;
}
/* Advance the state pointer by 8 to process the next group of 8 samples */
pState = pState + 8;
/* The results in the 8 accumulators, store in the destination buffer. */
*pDst++ = acc0;
*pDst++ = acc1;
*pDst++ = acc2;
*pDst++ = acc3;
*pDst++ = acc4;
*pDst++ = acc5;
*pDst++ = acc6;
*pDst++ = acc7;
blkCnt--;
}
/* If the blockSize is not a multiple of 8, compute any remaining output samples here.
** No loop unrolling is used. */
blkCnt = blockSize % 0x8u;
while(blkCnt > 0u)
{
/* Copy one sample at a time into state buffer */
*pStateCurnt++ = *pSrc++;
/* Set the accumulator to zero */
acc0 = 0.0f;
/* Initialize state pointer */
px = pState;
/* Initialize Coefficient pointer */
pb = (pCoeffs);
i = numTaps;
/* Perform the multiply-accumulates */
do
{
acc0 += *px++ * *pb++;
i--;
} while(i > 0u);
/* The result is store in the destination buffer. */
*pDst++ = acc0;
/* Advance state pointer by 1 for the next sample */
pState = pState + 1;
blkCnt--;
}
/* Processing is complete.
** Now copy the last numTaps - 1 samples to the start of the state buffer.
** This prepares the state buffer for the next function call. */
/* Points to the start of the state buffer */
pStateCurnt = S->pState;
tapCnt = (numTaps - 1u) >> 2u;
/* copy data */
while(tapCnt > 0u)
{
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
tapCnt--;
}
/* Calculate remaining number of copies */
tapCnt = (numTaps - 1u) % 0x4u;
/* Copy the remaining q31_t data */
while(tapCnt > 0u)
{
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
tapCnt--;
}
}