How to make this code more fast?

[p_chusak]

Hi i'am a new pic user;
I try to make servo control By Pic 18f4431
I have some problem

for this code

output_bit(PIN_B1,1);

compen_s=(kp_servo*new_error_pos/100)+ Kd_servo*diff_error_pos/100);

output_bit(PIN_B1,0);


all variable are 32bit signed

I use oscillloscope display output of PIN_B1
it show B1 high about 0.235ms or 235us i use 10Mz in H4 mode so
this process use 2350 Cycle (approximate) it use 35-40% cpu bandwidth
for one line code ( servo loop call every .5ms )

In datasheet of pic18f4431 i see hard ware multiply for fast mul
How i use it for this problem? or How to make this code line faster?


Thank.

[Ttelmah]

Division is the real 'killer' here. Do you need to use /100?. If you can change the scaling of your numbers, so you can use a _binary_ division (/128, or even better /256), then you can easily reduce the times by perhaps a factor of 3*. Division is the slowest arithmetic operation in general.
In general, servo algorithms in the PIC, use *256, as the 'factor', then you can declare a union somthing like:

[p_chusak]

Wow""ThanK:)......A lot>>.

now speed up >60% by shift>>8 and get 24bit signed"""

[Guest]

[Guest]

noticed that 1/100 ~ 1/128 + 1/512 + 1/4096

so, instead of using y = x/(int32)100, try this

int32 x, y, a;

y = (a=x>>7);
y+= (a>>=2);
y+= (a>>=3);

should be less than 7 usec at 40 MHz, I guess