Ultrasonic Sample Code Explanation

[guil]

Hi,
Can somebody explain to me the sample code here -> link.
Particularly in this line:

for(i = 0 ; i < BUFSIZE ; i++)  // for all samples in buffer
 {
       cm += buf[i] ;  // add to sum
 }
 cm /= BUFSIZE ;             // average samples

Why he divide it by 10? I am confused.

And also in this line:

buf[idx] = TMR1H ;              // build a 16 bit value from timer1
buf[idx] <<= 8 ;                // MSB
buf[idx] += TMR1L ;             // LSB

When TMR1H > 0, I am expecting TMR1L = 0xff always, since the timer counts from 0x0000 to 0xffff. Am I right?

thanks in advance.
Ilms

 

[btbass]

cm is the sum of 10 samples. Dividing by 10 would give you the average.

Timer 1 would count from 0x0100 to 0x01ff,
Then from 0x0200 to 0x2ff etc.
So TMR1L would not always be 0xff when TMR1H > 0.

 

[guil]

cm is the sum of 10 samples. Dividing by 10 would give you the average.

Thank you btbass. So quick!
Yes, I know it was the average of the 10 samples in .1sec period approximately. But he should not averaging it unless the buffer gets full (buf[0...9] filled up). Right?
And he will not displaying it until averaging is complete.
Although, 10ms is fast enough for human to noticed. The logic is somewhat confusing.

regards
guil