Cordic trig assembly code for PIC18f

[ScaleRobotics]

For instance

x = 25980
y = 15000

.....and that is 30 degrees

My perspective was all wrong in the above post. I was supposed to be lying down and facing East, that is the radian way.

to convert to degrees ......

Imagine a circle with degree headings, but instead of starting at the top, and going clockwise, as the numbers get higher, we are going to do something completely different. Starting at 90 degrees, we are going to go counterclockwise while our radians rise. From zero to 32,767 is the arc from 90 degrees (through 0) to 270 degrees. To complete the circle, our arc continues from 32,768 to 65,535 as it travels from 270 degrees to 90 degrees in a counter clockwise rotation.

So, as you can see there is just a little bit of manipulation to get the result in angle, but it really isn't too bad.

Thanks Joe.

[ScaleRobotics]

For anyone else like me that forgot all they learned about radians.... This should help. These go from 0 to 65,535.

[Archangel]

Thank You Walter,
It is definitely going to take some time to get my head around this, unfortunate side effect of growing up during the Vietnam war, where we were expected to become soldiers who got shipped there and returned in a nicely bagged and boxed container. My algebra teacher was a retired navel captain, who taught spit about the subject but spoke extensively about his career and travels in Tahiti. That notwithstanding I will get this. I am sure nobody who participates in this forum is going to point at me in the store and say "hey there is the dummy who couldn't understand that code Walter wrote . . . " <b>So Anyway</b> the numbers you plugged in represent . . .Units, of my choosing . . .and to use this

include"trig.inc"
main:
ang=5461
x=0
y=0

asm
    call sin_cos
endasm
    
Lcdout $fe, 1   ' Clear LCD screen

lcdout $FE,1,#x,",",#y
lcdout $FE,$C0,#ang

Correct? Figure I do not need to know how to build a truck to drive one.

[ScaleRobotics]

Hey Joe,

No you definitely do not need to know how it works. But if you find out, please let me know. The assembly code only seems to put me to sleep when I read it. Something about rotating angle, shifting bits zzzzz.....

Your code will work, but it can be even simpler since it has the includes file in it. You don't have to get in to the asm endasm, as the sincos function is already there.

include"trig.inc"
main:
ang=5461
x=0
y=0

call sincos
    
Lcdout $fe, 1   ' Clear LCD screen

lcdout $FE,1,#x,",",#y
lcdout $FE,$C0,#ang

It is that easy. Only a little bit harder if you want to do anything with the data returned in x and y (or ang and x for atan function)

[Archangel]

You don't have to get in to the asm endasm, as the sincos function is already there.

Funny, that was a copy paste, I don't know where the asm / endasm went, glad to know it can be omitted ( call sincos ). Just 1 (I hope) more question: Where does the number ang=5461 come from ? I apologize if I seem tedious, I really haven't a clue. Thanks.

[ScaleRobotics]

That is the hardest part. Darn radians are 90 degrees off from the start.

For example

0 = 90 degrees
5461 = 60 degrees
10922 = 30 degrees
16383 = 0 degrees (or North)
21844 = 330 degrees
32767 = 270 degrees
38228 = 240 degrees

and so on.....

You definitely do not have to know this, but I think it is interesting:
In the time it takes for a regular Sin, or Cos 16 bit function on a PIC18 to give a result, light travels 3000 kilometers
The time it takes for this cordic 16 bit result, light travels 33.3 kilometers.
How do you say "Your mileage may vary" when you use kilometers?

[Archangel]

That is the hardest part. Darn radians are 90 degrees off from the start.

For example

0 = 90 degrees
5461 = 60 degrees
10922 = 30 degrees
16383 = 0 degrees (or North)
21844 = 330 degrees
32767 = 270 degrees
38228 = 240 degrees

and so on.....

You definitely do not have to know this, but I think it is interesting:
In the time it takes for a regular Sin, or Cos 16 bit function on a PIC18 to give a result, light travels 3000 kilometers
The time it takes for this cordic 16 bit result, light travels 33.3 kilometers.
How do you say "Your mileage may vary" when you use kilometers?

Moving counter clockwise from the 3 o'clock position . . .I see for every 30 degrees the numbers change 5461 or 182.03333333333333333333333333333 per degree or 65532 for a full circle which is a number that fits nicely in a word variable.