Posted on May 17, 2011 at 13:03 Hi,
I'm recently in a project using a cortex where I need to build-in a FIR filter to make a LP filter on my captured ADC signal. I downloaded the DSP lib files from the ST site. ( FIR , IIR , ... )
I only use the following function which is in fact implemented in assembler for optimization reasons in T2:
typedef struct {
u16 *h;
u32 nh;
} COEFS;
void fir_16by16_stm32(int *a,short *x,struct COEFS *p,unsigned int N)
It's implementation is based on the well known book ''ARM System Developer's Guide'' page (I'm using Ride7/gcc as IDE)
When I write this:
int y[4];
short x[7] = {1,1,1,1,1,1,1};
short hc[4]= {1,1,1,1};
COEFS c;
int main(void)
{
c.h = hc;
c.nh = 4;
fir_16by16_stm32(y, x, c, M);
}
This does not work as it should be why ? Well I will try to explain here what I saw using the Ride simulator:
Out of the filter assembler code the load of the first coefficients (fir_stms)
...
LDRSH r3, [r2], 2 /* Load c_0 */
LDRSH r12, [r2], 2 /* Load c_1 */
...
The LDRSH instruction loads the value at address [R2] but this is not correctly filled as the first 4 bytes point to the the array's address but not to the actual coeff data.
When I change the snippet into:
int y[M];
short x[7] = {1,1,1,1,1,1,1};
short hc[M+1]= {1,1,1,1,4}; --> simulated the struct holder
int main(void)
{
fir_16by16_stm32(y, x, (COEFS *)hc, M);
}
The LDRSH instructions takes the pointer value as it should be now because it's address is not indirectly set and point straight to the array elements.
My questions:
- Is that due to compiler settings because I call assembler form C ?
- Or is this maybe a small bug in the assembler code ?
( where to post that kind of bugs ?)
( attached to this post:
- the FIR assembler code
- PDF description of the lib)
Thanks
Guy
address mailto:null
Code:
Code:
