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'[EE]: Multiple values accelerating at different ra'
2001\10\13@122303
by
TH

I've got this application were multiple RAM values in an array are given a
target value which can be above or below their current value and must reach
this target within a given time.
For example :
ORIGINAL VALUES A=010 B=020 C=055 D=255 E= 000 etc ...
TARGET VALUES A'=020 B'=010 C'=055 D'=000 E'=255 etc ...
time required = 1,000,000 processor cycles (50 Hz refresh rate with a 20MHz
processor)
Given these conditions :
A must increase by 10 in 1,000,000 cycles
B must decrease by 10 in 1,000,000 cycles
C must not change in 1,000,000 cycles
D must decrease by 255 in 1,000,000 cycles
E must increase by 255 in 1,000,000 cycles
etc ...
The first obvious way to do this is :
(A'A)/1,000,000 = RateA = 0.00001 per cycle
(B'B)/1,000,000 = RateB = 0.00001 per cycle
(C'C)/1,000,000 = RateC = 0 per cycle
(D'D)/1,000,000 = RateD = 0.000255 per cycle
(E'E)/1,000,000 = RateE = 0.000255 per cycle
and continuously multiply the values in memory by these constants until
we're done counting 1,000,000 cycles, phew!
Since I don't need such a high resolution (1 cycle) and couldn't possibly
calculate all these values fast enough (with a PIC)I could simplfy these
operations by updating the values only every 20,000 cycles (50 Hz refresh
rate with a 20MHz clock) his still gives some rather hefty fractional values
to handle with a PIC. Besides, this method requires twice the amount of
memory to store the Rate constants ...
Any thoughts ?
regards,
Tobie Horswill
Le Projet Ex Machina, QC, CAN.
spam_OUTthorswilTakeThisOuTexmachina.qc.ca

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2001\10\13@163844
by
Olin Lathrop
> Since I don't need such a high resolution (1 cycle) and couldn't possibly
> calculate all these values fast enough (with a PIC)I could simplfy these
> operations by updating the values only every 20,000 cycles (50 Hz refresh
> rate with a 20MHz clock) his still gives some rather hefty fractional
values
> to handle with a PIC. Besides, this method requires twice the amount of
> memory to store the Rate constants ...
>
> Any thoughts ?
How about a Bresenham algorithm?
********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 7429014, olinKILLspamembedinc.com, http://www.embedinc.com

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2001\10\14@171351
by
TH
Olin, I did a quick search on the net for "Brensenhams Algorithm" and
quickly found several explanations of this Computer Graphics method for
selecting which pixel should be illuminated when drawing a line onscreen.
It fits nicely with my objective, it's simply a matter of replacing the X
displacement by the number of processor cycles and the Y displacement by the
difference between the target and the original values =) I also found an
Integer version of the algorithm which I think can be adapted quite easily
to PIC assembly. =)) For those interested, here is one of the best documents
I've found :
graphics.cs.ucdavis.edu/GraphicsNotes/BresenhamsAlgorithm/Bresenhams
Algorithm.html
Have you worked in computer graphics before or is this algorithm considered
common knowledge ?
Anyway, many thanks!
Tobie Horswill
Le Projet Ex Machina, QC. CAN.
EraseMEthorswilspam_OUTTakeThisOuTexmachina.qc.ca
{Original Message removed}
2001\10\14@185858
by
Bob Ammerman
On this discussion list Bresenham is considered common knowledge by now 
and we've keep finding new uses for it, too.
Bob Ammerman
RAm Systems
(contract development of high performance, high function, lowlevel
software)
{Original Message removed}
2001\10\15@100744
by
Olin Lathrop
> Have you worked in computer graphics before or is this algorithm
considered
> common knowledge ?
I used to design display controllers and first ran into Bresenham's
algorithm there, however it's widely used in other applications. Jack
Bresenham's original problem was to make a pen plotter driven by stepper
motors follow an arbitrary straight line. I wrote a paper once about how
Bresenham's algorithm can be extended to start and stop at fractional end
points (subpixel addressing) and still maintain the same integer algorithm
after setup.
********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 7429014, olinspam_OUTembedinc.com, http://www.embedinc.com

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2001\10\17@071315
by
TH
Well huuhhhh? Sorry, I'm not an EE so I'll have to look that up before I can
answer your question =)
Thx!
Tobie Horswill
Le Projet Ex Machina,QC, CAN.
@spam@thorswilKILLspamexmachina.qc.ca
{Original Message removed}
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