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valemike
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| question for "PCM Programmer" and your median_filt |
 Posted: Thu May 26, 2005 11:26 am |
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Hi PCMProg,
A few weeks ago, i decided to use your median_filter() code that you put on this forum in the past. Basically, i'm reading my A/D continuously in my main()'s while(1) loop. There are occasions though where i have a sub-loop that may run for a 1-2 seconds, and will starve the median_filter() from running. The next time i do call the median_filter() function, I then have a few stale values in my array.
Is there a way to "flush" this array?
I figure maybe i can just invoke the function 7 times to flush out any stale data. Or should I just re-initialize the static variables inbuf_index and num_elements to zero?
Thanks,
Mike
Your original code below...
| Code: |
int16 median_filter(int16 latest_element)
{
static int16 input_buffer[MEDIAN_FILTER_WIDTH];
static char inbuf_index = 0;
static char num_elements = 0;
int16 sorted_data[MEDIAN_FILTER_WIDTH];
int16 median;
// Insert incoming data element into circular input buffer.
input_buffer[inbuf_index] = latest_element;
inbuf_index++;
if(inbuf_index >= MEDIAN_FILTER_WIDTH) // If index went past buffer end
inbuf_index = 0; // then reset it to start of buffer
if(num_elements < MEDIAN_FILTER_WIDTH)
num_elements++;
// THIS LINE MAY NOT BE NEEDED IF SORTED DATA IS STATIC.
memset(sorted_data, 0, MEDIAN_FILTER_WIDTH * 2);
// Copy input data buffer to the (to be) sorted data array.
memcpy(sorted_data, input_buffer, num_elements * 2); // memcpy works on bytes
// Then sort the data.
Insertion_Sort_16(sorted_data, MEDIAN_FILTER_WIDTH);
// During the first few calls to this function, we have fewer
// elements in the sorted data array than the filter width.
// So to compensate for that, we pick the median from the number
// of elements that are available. ie, if we have 3 elements,
// we pick the middle one of those as the median.
// Also, because the sort function sorts the data from low to high,
// we have to calculate the index from the high end of the array.
median = sorted_data[MEDIAN_FILTER_WIDTH - 1 - num_elements/2];
return(median);
} |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu May 26, 2005 3:10 pm |
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You could add some code near the start of the routine,
and add a 2nd parameter to force an init if it's = TRUE,
and then just exit.
| Code: | int16 median_filter(int16 latest_element, int8 init)
{
static int16 input_buffer[MEDIAN_FILTER_WIDTH];
static char inbuf_index = 0;
static char num_elements = 0;
int16 sorted_data[MEDIAN_FILTER_WIDTH];
int16 median;
if(init == TRUE)
{
inbuf_index = 0;
num_elements = 0;
return(0);
}
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Call it with the 2nd parameter = TRUE to do the init.
| Code: | | median_filter(0, TRUE); |
Call it normally like this:
| Code: | | median_filter(value, FALSE); |
Or, you can do it whatever way you want. |
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valemike
Guest
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| Posted: Thu May 26, 2005 3:20 pm |
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| ok thanks. i think i'll do that. |
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