Cordic trig assembly code for PIC18f

[samuelaaronward]

Hey, nerds! I'm relatively new to PICs, and right now I'm using the PIC16F684.

I'm trying to write a program for a mobile robot with two stepper motors for differential steering - to navigate it along a predefined path (or function). In order to do this, I need to be able to calculate trig values using Assembly code (yikes!). Not only that, but due to the physical geometry of my robot, I need to calculate the sine and cosine of multiples of 0.72 (non-integers).

Will this TRIG.INC file work with non-integers? If not, is there a way to get around this (DP shifting)?

Thanks for your help!
Samuel Aaron Ward
[email protected]
(740) 357-8016 cell

[ScaleRobotics]

Hello Samuel,

Can you explain the significance of the .72, or maybe what you are calculating. I put on my nerd glasses, but it's not helping. There might not enough resolution in the PIC16 cordic version, but then, I do not have a grasp of what you are measuring, so maybe it would be fine.

The PIC16 cordic is here http://www.picbasic.co.uk/forum/showthread.php?t=7502

Thanks,
Walter

[Dave]

scalerobotics, the .72 probably represents 7.2 degrees per step for the motor... Stepper motors usually come in 1.8 and 7.2 degrees per step...

Dave Purola,
N8NTA

[ScaleRobotics]

Thanks Dave!

In that case, the PIC16 should work for you Samuel. But it does need some modification to enable you to find the angle throughout 360 degrees. The PIC16 cordic only does 0 to 90 degrees. But the rest can be done pretty easily with PicBasic. I think it handles around 2000 iterations per second, but I may have been doing a few more equations when I measured that.

Here is some code that works on a Pic16F877a:

'****************************************************************
'*  Name    : UNTITLED.BAS                                      *
'*  Author  : Walter Dunckel                                    *
'*  Notice  : Copyright (c) 2009 Scale Robotics Inc.            *
'*          : All Rights Reserved                               *
'*  Date    : 10/7/2009                                         *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************
DEFINE __16F877A 1				; list directive to define processor
DEFINE OSC 20                    ' Define Oscillator Speed                    
DEFINE LOADER_USED 0
include "trig-pic16.inc"   

' Shutdown comparators
ADCON1 = 7                        ; Turn of all A/D
CMCON  = 7
' Set the port directions
' 0=output 1=input
TRISA=%00000011                         ' Set PORTA  0-1-3 used for AD
TRISB=%11011100                         ' Set PortB
TRISC=%10000000  
TRISD=%00000000                       ' Set PortC USART RX as an input
porta.2 = 0 
porta.3 = 0

x           var     word
y           var     word
z           var     word
i           var     word
lon_dif     var     word
lat_dif     var     word
angle       var     word
angle_deg   var     word
distance    var     word
j           var     word

;---------[change these to match your hardware]------------------------------
DEFINE LCD_DREG PORTD             ; Set LCD Data port                B C   D
DEFINE LCD_DBIT 0                 ; Set starting Data bit (0 or 4)   4 0
DEFINE LCD_RSREG PORTA            ; Set LCD Register Select port     A A
DEFINE LCD_RSBIT 3                ; Set LCD Register Select bit      3 2
DEFINE LCD_EREG PORTA             ; Set LCD Enable port              A A
DEFINE LCD_EBIT 1                 ; Set LCD Enable bit               1 5
DEFINE LCD_BITS 4                 ; Set LCD bus size (4 or 8 bits)   4 4
DEFINE LCD_LINES 2                ; Set number of lines on LCD       2 2
'----------------------------------------------------------------------------
clear
lcdout $FE,1
' to convert degrees to radians Z_ * 256 / 90
' to convert radians to degrees Z_ * 90 / 256
Start:
x = 0
y = 0
z = 0  

Z_ = 90                    'put angle in Z_ in degrees
Z_ = (Z_ * 255)/90     'convert degrees to radians
Call sincos                 'perform sin and cos on Z_ value
                               'cos(Z_) = X_ :sin(Z_) = Y_

lcdout $FE,1,"cos Z=",#X_                                          
lcdout $FE,$C0,"sin Z=",#Y_ 
end

And the pic16 trig file: http://sites.picbasic.net/media/uhp2...trig_pic16.txt

[Art]

Nice work, but I am also challenged with maths.
Will this allow me to do point rotation?

Say I have an origin x=0 & y=0, and another point x=4, y=4.
Can I find out the angle of the second coordinates where the first set is the origin,
and then rotate the second point say 180 degrees around the origin ?
Art.

[Art]

Uh-oh.. just including the line:
include "trig-pic16.inc"
causes this:

Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 213 : [235] Opcode Expected Instead of 'dt'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 216 : [235] Opcode Expected Instead of 'dt'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 219 : [235] Opcode Expected Instead of 'dt'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 222 : [235] Opcode Expected Instead of 'dt'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 237 : [226] Numeric Constant or Symbol Name Expected
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 239 : [226] Numeric Constant or Symbol Name Expected
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 269 : [235] Opcode Expected Instead of 'movfw'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 283 : [235] Opcode Expected Instead of 'movfw'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 301 : [235] Opcode Expected Instead of 'movfw'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 306 : [235] Opcode Expected Instead of 'movfw'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 316 : [235] Opcode Expected Instead of 'movfw'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 321 : [235] Opcode Expected Instead of 'movfw'
Error C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 349 : [235] Opcode Expected Instead of 'movfw'
Warn C:\PROGRA~1\MPLAB\PROJECT\SCROLL.ASM 934 : [102] Code Crosses Boundary @ 800h

I'm using a 16F877 too.

[Darrel Taylor]

Use MPASM for the assembler.
<br>

[ScaleRobotics]

Nice work, but I am also challenged with maths.
Will this allow me to do point rotation?

Say I have an origin x=0 & y=0, and another point x=4, y=4.
Can I find out the angle of the second coordinates where the first set is the origin,
and then rotate the second point say 180 degrees around the origin ?
Art.

Hi Art,

You can definitely find the angle in the first part of your question. As far as rotation, I have to think a little more. Should be possible though.

Are you rotating one of your LED displays? If so, are we talking full rotation, or just 90, 180, 270 degrees?

[Art]

Ideally, to potentially be able to do full rotation of a pixel.
Yes, I have a matrix LED display in mind
I wouldn't care whether or not it is equally divided into 360 degrees.
I already have made routines that make it easy to draw to the screen.

I can do this in C on the Sony PSP like this

xx = 240;
yy = 30;
x = xx - 240;
y = yy - 136;

theta = rotation;
thetab = 360 - theta;
thetab = (3.141592 / 180) * theta;

xnew = cos(thetab)*x - sin(thetab)*y;
ynew = sin(thetab)*x + cos(thetab)*y;

xnew = xnew + 240;
ynew = ynew + 136;

Where x-240, y-136 are coordinates for the centre of the screen,
x-240,y-30 is the arbitrary point I want to rotate (the one given is a point directly above the centre of the screen),
rotation is the real angle 0-359 (0 can also be 360).
xnew and ynew are the new (rotated) coordinates.
I don't know if this works with microcontrollers even if you do use a C compiler.