Cordic trig assembly code for PIC18f


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  1. #1
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    Default Cordic trig assembly code for PIC18f

    I have been trying to use cordic code that was originally written for a PIC18F device. I have made some changes to it to try to make it compatible with PicBasic Pro, but I am getting some unexpected results. I am compiling it to a PIC18F4620 device using 2.50b. It compiles without any errors, and prints the values to an LCD, but the results vary, and are unexpected. Any ideas would be greatly appreciated.

    Here is the original code:
    http://www.chiefdelphi.com/media/papers/2016


    Here is my stab at making it compatible:
    Code:
    ;*******************************************************************************
    ; --- CORDIC TRIG LIBRARY ---
    ;http://www.chiefdelphi.com/media/papers/2016
    ; FILE NAME:        trig.asm
    ; AUTHOR:           Patrick Fairbank
    ; LAST MODIFIED:    Jan. 16, 2008
    ;
    ; DESCRIPTION:      This file contains functions implementing the COORDIC
    ;                   algorithm.
    ;
    ; USAGE:            Add this file to your project.
    ;
    ; LICENSE:          Users are free to use, modify, and distribute this code
    ;                   as they see fit.
    ;
    ;    sin_cos: input ang, output x = sin and y = cos     
    ;
    ;         
    ;     atan2_sqrt: input x and y coordinates
    ;     Output the calculated angle and hypotenuse values
    ;     as output:    ang = angle x = hypotenuse
    ;
    ;******************************************************************************/
    
    
    
    
    
    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
    
    ; Calculates the sine and cosine of the given angle
    sin_cos:
    
      ; Set up the stack
      movff FSR2L, POSTINC1
      movff FSR1L, FSR2L
    
      ; Initialize _x to 18218
      movlw 0x2a
      movwf _x
      movlw 0x47
      movwf _x+1
    
      ; Initialize _y to 0
      clrf _y
      clrf _y+1
    
      ; Initialize _ang to passed parameter
      movlw 0xfd
      movff PLUSW2, _ang
      movlw 0xfe
      movff PLUSW2, _ang+1
    
      ; Initialize _quad to 0
      clrf _quad
    
      ; Check if the angle is greater than 16383 (90)
    sc_check_greaterthan:
      btfss _ang+1, 7
      btfss _ang+1, 6
      bra sc_check_lessthan
      bra sc_adjust_quad2
      
      ; Check if the angle is less than -16384 (-90)
    sc_check_lessthan:
      btfsc _ang+1, 7
      btfsc _ang+1, 6
      bra sc_setup_end
    
      ; If the angle is in quadrant 3, adjust it to quadrant 4
    sc_adjust_quad3:
      negf _ang
      bc sc_negate_quad3
      comf _ang+1
      bra sc_adjust_end
    
      ; If the low byte negation causes a carry, negate the upper byte
    sc_negate_quad3:
      negf _ang+1
      bra sc_adjust_end
    
      ; If the angle is in quadrant 2, adjust it to quadrant 1
    sc_adjust_quad2:
      comf _ang
      comf _ang+1
    
      ; Toggle the sign bit and set the '_quad' flag
    sc_adjust_end:
      btg _ang+1, 7
      setf _quad
    
      ; Multiply the angle by 2 to get better resolution
    sc_setup_end:
      bcf STATUS, 0
      rlcf _ang
      rlcf _ang+1
    
      ; Set up the main loop
    sc_loop_start:
      clrf _i
      banksel atans
      lfsr FSR0, atans
    
        ; The main loop label
    sc_loop:
        movff _x, _dy
        movff _x+1, _dy+1
        movff _i, _j
        movf _j
        bz sc_bs_x_done
    
          ; Loop to shift _dy right
    sc_bs_x_loop:
          bcf STATUS, 0
          rrcf _dy+1
          rrcf _dy
          btfsc _x+1, 7
          bsf _dy+1, 7
          decfsz _j
          bra sc_bs_x_loop
    
        ; Calculate what needs to be added to _x
    sc_bs_x_done:
        movff _y, _dx
        movff _y+1, _dx+1
        movff _i, _j
        movf _j
        bz sc_do_rotation
    
          ; Loop to shift _dx right
    sc_bs_y_loop:
          bcf STATUS, 0
          rrcf _dx+1
          rrcf _dx
          btfsc _y+1, 7
          bsf _dx+1, 7
          decfsz _j
          bra sc_bs_y_loop
    
        ; Perform adding operations on _x, _y and _ang
    sc_do_rotation:
        btfss _ang+1, 7
        bra sc_sub_angle
    
        ; If _ang is negative
        movf POSTINC0, W
        addwf _ang
        movf POSTINC0, W
        addwfc _ang+1
        movf _dx, W
        addwf _x
        movf _dx+1, W
        addwfc _x+1
        movf _dy, W
        subwf _y
        movf _dy+1, W
        subwfb _y+1
        bra sc_loop_bottom
    
        ; If _ang is positive
    sc_sub_angle:
        movf POSTINC0, W
        subwf _ang
        movf POSTINC0, W
        subwfb _ang+1
        movf _dx, W
        subwf _x
        movf _dx+1, W
        subwfb _x+1
        movf _dy, W
        addwf _y
        movf _dy+1, W
        addwfc _y+1
    
        ; Increment the counter and exit the loop if done
    sc_loop_bottom:
        incf _i
        movlw 0x0f
        cpfseq _i
        bra sc_loop
    
      ; Negate _x if it was initially in quadrant 2 or 3
    sc_finished:
      btfss _quad, 7
      bra sc_output
      negf _x
      bc sc_negate_x
      comf _x+1
      bra sc_output
    
      ; If the low byte negation causes a carry, negate the upper byte
    sc_negate_x:
      negf _x+1
    
      ; 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
    
      ; Restore the stack to its previous state
      movf POSTDEC1
      movff INDF1, FSR2L
    
      return
    
    
    ; Calculates the magnitude and direction of the given ordered pair
    atan2_sqrt:
    
      ; Set up the stack
      movff FSR2L, POSTINC1
      movff FSR1L, FSR2L
    
      ; Initialize _x to passed parameter
      movlw 0xfb
      movff PLUSW2, _x
      movlw 0xfc
      movff PLUSW2, _x+1
    ;  movff POSTINC2, _x
    ;  movff POSTDEC2, _x+1
    
      ; Initialize _y to passed parameter
      movlw 0xfd
      movff PLUSW2, _y
      movlw 0xfe
      movff PLUSW2, _y+1
    ;  movlw 0x03
    ;  movff PLUSW2, _y+1
    ;  movlw 0x02
    ;  movff PLUSW2, _y
    
      ; Initialize _ang to 0
      clrf _ang
      clrf _ang+1
    
      ; Initialize _quad to 0
      clrf _quad
    
      ; If the point is in quadrant 2 or 3, make _x positive and set flag
    as_check_negative:
      btfss _x+1, 7
      bra as_shift_x
      setf _quad
      negf _x
      bc as_negate_x
      comf _x+1
      bra as_shift_x
    
      ; If the low byte negation causes a carry, negate the upper byte
    as_negate_x:
      negf _x+1
    
      ; Divide the _x coordinate by 2 to prevent overflowing
    as_shift_x:
      bcf STATUS, 0
      rrcf _x+1
      rrcf _x
    
      ; Divide the _y coordinate by 2 to prevent overflowing
    as_shift_y:
      bcf STATUS, 0
      rrcf _y+1
      rrcf _y
      btfsc _y+1, 6
      bsf _y+1, 7
    
      ; Set up the main loop
    as_loop_start:
      clrf _i
      banksel atans
      lfsr FSR0, atans
    
        ; The main loop label
    as_loop:
        movff _x, _dy
        movff _x+1, _dy+1
        movff _i, _j
        movf _j
        bz as_bs_x_done
    
          ; Loop to shift _dy right
    as_bs_x_loop:
          bcf STATUS, 0
          rrcf _dy+1
          rrcf _dy
          btfsc _x+1, 7
          bsf _dy+1, 7
          decfsz _j
          bra as_bs_x_loop
    
        ; Calculate what needs to be added to _x
    as_bs_x_done:
        movff _y, _dx
        movff _y+1, _dx+1
        movff _i, _j
        movf _j
        bz as_do_rotation
    
          ; Loop to shift _dx right
    as_bs_y_loop:
          bcf STATUS, 0
          rrcf _dx+1
          rrcf _dx
          btfsc _y+1, 7
          bsf _dx+1, 7
          decfsz _j
          bra as_bs_y_loop
    
        ; Perform adding operations on _x, _y and _ang, shifting the atans right one
    as_do_rotation:
        movff POSTINC0, PRODL
        movff POSTINC0, PRODH
        bcf STATUS, 0
        rrcf PRODH
        rrcf PRODL
        btfsc  _y+1, 7
        bra as_sub_angle
    
        ; If _y is positive
        movf PRODL, W
        addwf _ang
        movf PRODH, W
        addwfc _ang+1
        movf _dx, W
        addwf _x
        movf _dx+1, W
        addwfc _x+1
        movf _dy, W
        subwf _y
        movf _dy+1, W
        subwfb _y+1
        bra as_loop_bottom
    
        ; If _y is negative
    as_sub_angle:
        movf PRODL, W
        subwf _ang
        movf PRODH, W
        subwfb _ang+1
        movf _dx, W
        subwf _x
        movf _dx+1, W
        subwfb _x+1
        movf _dy, W
        addwf _y
        movf _dy+1, W
        addwfc _y+1
    
        ; Increment the counter and exit the loop if done
    as_loop_bottom:
        incf _i
        movlw 0x0e
        cpfseq _i
        bra as_loop
    
      ; Multiply the _x value by 19898 and divide by 2^14 to scale it
    as_scale_x:
      movff _x, _dx
      movff _x+1, _dx+1
      movlw 0xba
      mulwf _dx
      movff PRODH, _x
      movlw 0x4d
      mulwf _dx+1
      movff PRODH, _dy
      movff PRODL, _x+1
      movlw 0xba
      mulwf _dx+1
      movf PRODL, W
      addwf _x, F
      movf PRODH, W
      addwfc _x+1, F
      clrf WREG
      addwfc _dy, F
      movlw 0x4d
      mulwf _dx
      movf PRODL, W
      addwf _x, F
      movf PRODH, W
      addwfc _x+1, F
      clrf WREG
      addwfc _dy, F
      movlw 0x06
      movwf _j
    as_scale_bs_loop:
        bcf STATUS, 0
        rrcf _dy
        rrcf _x+1
        rrcf _x
        decfsz _j
        bra as_scale_bs_loop
    
      ; Check if the quadrant was originally changed
    as_check_quad:
      btfss _quad, 7
      bra as_output
      btfss _ang+1,7
      bra as_adjust_quad1
    
      ; If the angle is in quadrant 4, adjust it to quadrant 3
    as_adjust_quad4:
      negf _ang
      bc as_negate_quad4
      comf _ang+1
      bra as_adjust_end
    
      ; If the low byte negation causes a carry, negate the upper byte
    as_negate_quad4:
      negf _ang+1
      bra as_adjust_end
    
      ; If the angle is in quadrant 1, adjust it to quadrant 2
    as_adjust_quad1:
      comf _ang
      comf _ang+1
    
      ; Toggle the sign bit
    as_adjust_end:
      btg _ang+1, 7
    
      ; 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
    I am using this as an includes file, but I am getting values so far from expected, that I can't figure out what is going on.

    Any help would be greatly appreciated.
    Last edited by ScaleRobotics; - 6th February 2009 at 22:21.

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