Cordic trig assembly code for PIC18f

[ScaleRobotics]

Here are the changes I have made to the assembly code to try to get it to work with PicBasic:


commented out EXTERN AARGB3, UDATA_ACS, IDATA, CODE, edited variable descriptions so that variables are declared in PicBasic.

Original Code:

  ; Import the address the compiler uses to store 32-bit return values
    EXTERN AARGB3


    UDATA_ACS

; Variable declarations
i       RES 1
j       RES 1
quad    RES 1
x       RES 2
y       RES 2
ang     RES 2
dy      RES 2
dx      RES 2


    IDATA

; Table of arctan values
atans   DW D'16384', D'9672', D'5110', D'2594', D'1302', D'652', D'326', D'163'
        DW D'81', D'41', D'20', D'10', D'5', D'3', D'1'


    CODE

I edited out where the result is moved to AARGB3, and just use the word variables _x, _y, and _ang to store the results. Commented out Globals and End. And of course added ASM and ENDASM.

My code:

i       var byte    
j       Var byte
quad    var byte
x       var word
y       var word
ang     var word  
dy      var word
dx      var word

goto main

asm
    ;IDATA

; Table of arctan values
atans   DW D'16384', D'9672', D'5110', D'2594', D'1302', D'652', D'326', D'163'
        DW D'81', D'41', D'20', D'10', D'5', D'3', D'1'


    ;CODE


-snip

  ; Output the calculated _x and _y values
sc_output:
  ;movff _y, AARGB3
  ;movff _y+1, AARGB3+1
  ;movff _x, AARGB3+2
  ;movff _x+1, AARGB3+3

-snip

  ; Output the calculated angle and hypotenuse values
as_output:
  ;movff _ang, AARGB3
  ;movff _ang+1, AARGB3+1
  ;movff _x, AARGB3+2
  ;movff _x+1, AARGB3+3

  ; Restore the stack to its previous state
  movf POSTDEC1
  movff INDF1, FSR2L

  return

endasm
    ; Export the functions to the linker
    'GLOBAL sin_cos
    'GLOBAL atan2_sqrt

    'END

Please let me know if you have any suggestions. It does compile without errors, but I do not get useful data out. When I input 5461 as the angle, I get the sin=29998, and cos=405. The result should be 15000, and 25980. But then if I run it again, a different value pops up for cos, that still does not get close to expected values.

Thanks,

Walter