Go Down

### Topic: Calculate the Root Mean Sqaure (Read 1 time)previous topic - next topic

#### pedrolopes746

##### Sep 01, 2013, 10:37 am
hello,

I'm using the library (... \ Arduino \ hardware \ arduino \ sam \ system \ CMSIS \ CMSIS \ DSP_Lib \ Source \ StatisticsFunctions) to calculate the RMS value  of the elements in the input vector. but the value I get is 0.0.

code used:
Code: [Select]
`#define ARM_MATH_CM3#include <arm_math.h>float32_t data[5] = {1, 2, 3, 4, 5};float32_t *d = data;float32_t *pResult;void setup() {Serial.begin(9600); }void loop() {arm_rms_f32(d, 5, pResult);Serial.println(*pResult);while(1){}}`

Quote

output

0.0

#### pedrolopes746

#1
##### Sep 01, 2013, 01:48 pm
after a detailed analysis found that the problem is in the following line of code library arm_rms_f32.c:
Code: [Select]
`/ * Compute Rms and store the result in the destination * /   arm_sqrt_f32 (sum / (float32_t) blockSize, pResult);`

if we have:
Quote

arm_sqrt_f32 (7.5 pResult);

pResult = 2.74

if we have:
Quote

float32_t sum = 30

uint32_t blockSize = 4

arm_sqrt_f32 (sum / (float32_t) blockSize, pResult);

pResult = 0.0

any solution?

#### Palliser

#2
##### Sep 01, 2013, 03:51 pm
Hello pedrolopes746,

Try this:

Code: [Select]
`#define ARM_MATH_CM3#include <arm_math.h>float32_t data[5] = {1, 2, 3, 4, 5};float32_t *d = data;float32_t *pResult;void setup() {Serial.begin(9600); }void loop() {arm_rms_f32(d, 5, pResult);while(1){}}void arm_rms_f32(  float32_t * pSrc,  uint32_t blockSize,  float32_t * pResult){  float32_t sum = 0.0f;                          /* Accumulator */  float32_t in;                                  /* Tempoprary variable to store input value */  uint32_t blkCnt;                               /* loop counter */#ifndef ARM_MATH_CM0  /* Run the below code for Cortex-M4 and Cortex-M3 */  /* loop Unrolling */  blkCnt = blockSize >> 2u;  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.      ** a second loop below computes the remaining 1 to 3 samples. */  while(blkCnt > 0u)  {    /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */    /* Compute sum of the squares and then store the result in a temporary variable, sum  */    in = *pSrc++;    sum += in * in;    in = *pSrc++;    sum += in * in;    in = *pSrc++;    sum += in * in;    in = *pSrc++;    sum += in * in;    /* Decrement the loop counter */    blkCnt--;  }  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.      ** No loop unrolling is used. */  blkCnt = blockSize % 0x4u;#else  /* Run the below code for Cortex-M0 */  /* Loop over blockSize number of values */  blkCnt = blockSize;#endif /* #ifndef ARM_MATH_CM0 */  while(blkCnt > 0u)  {    /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */    /* Compute sum of the squares and then store the results in a temporary variable, sum  */    in = *pSrc++;    sum += in * in;    /* Decrement the loop counter */    blkCnt--;  }  /* Compute Rms, store the result in the destination and print it */  Serial.println(sqrt(sum / (float32_t) blockSize));}`

Output:

Quote
3.32

Regards!

#### pedrolopes746

#3
##### Sep 01, 2013, 04:34 pm
thanks Palliser

Go Up

Please enter a valid email to subscribe