Subject:
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RE: IC Pointer Questions
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sun, 15 Mar 1998 21:03:44 GMT
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Original-From:
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Jaron Paludanus <j.paludanus@tip%StopSpammers%.nl>
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Viewed:
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1502 times
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Hi, thanks for your reply ...
Why don't I use the encoder0_counts variable ?
I want to create a multi-tasked environment with seperate processes for
each wheel to calculate wheel speeds. The same code will be used to
calculate speed for 4 wheels. What I realize now is that I can dereference
the velocity variable when using it. I was (am) very focussed on creating a
- simple - uniform structure describing the robot, without pointer
references to simplify coding and prevent errors. So what I thought up was;
A memory location XXXX with contents AAAA is named "encoder0_velocity" when
using the compiler / interpreter. It would be very convieniant if I could
create a variable named "CurrentSpeed" using memory location XXXX as well.
Then I could use both names in the compiler/interpreter - to create clean
code - while actually describing one memory location containing AAAA.
Maybe I could change the MC routines to use a structure to return their
value and recompile them to icb files? Just to clean up the code ? Or is
this extreme knit picking?
struct drivewheel wheel[4];
void launch () {
int i;
for (i=0;i<4;i++)
start_process( calculate_speed( i ) );
}
void calculate_speed( int index ) {
wheel[i].motor.speed.average = ( wheel[i].motor.speed.average * 9 +
wheel[i].motor.speed.current ) / 10;
wheel[i].wheel.speed.current = *wheel[i].encoder.velocity * 1000 /
64;
wheel[i].wheel.speed.average = ( wheel[i].wheel.speed.average * 9 +
wheel[i].wheel.speed.current ) / 10;
}
-----Original Message-----
From: Anthony Oren Loeppert [SMTP:oren@mail.utexas.edu]
Sent: Sunday, March 15, 1998 7:55 PM
To: Jaron Paludanus; handyboard@media.mit.edu
Subject: Re: IC Pointer Questions
> struct _wheel {int radius;int ticks;};
> struct _encoder {int port;int *velocity ;int *count;};
> struct drivewheel {struct _encoder encoder;struct _wheel wheel;}
> wheel[4];
>
> wheel[0].encoder.count= &encoder0_counts;
> *wheel[0].encoder.count= 0; /*I want to get rid
> of that dereferencing
> asterix ...*/
>
> Is there a way I can declare "wheel.encoder.count" so that it exists as an
> integer pointing to the same memory location as "encoder0_counts"?
> "wheel[0].encoder.count= 0;" Would then be the same as "encoder0_counts=
> 0;"
If I am understanding you right... I haven't looked at the encoder
routines yet, but I am assuming encoder0_counts is global. Why not, just
omit the pointer count from the _encoder struct and just use the global,
since you already have it? That aside, I'm don't know what you have
against '*' in having the statement *wheel[0].encoder.count = 0; It
accomplishes what you want and that's going to be your only solution I
think. I'm not too familiar with IC, but I am guessing it adhears fairly
closely to standard C in it's implementation. You are wanting to use a
feature of C++, pass by reference. Standard C doesn't support it.
void change_count(int& iamTheSaveVar)
{
iamTheSaveVar=0;
}
int main()
{
int somevar=1;
change_count(somevar);
return somevar;
}
in C++, this would effectively set somevar to 0, but I don't think that it
would work in IC, but I haven't tried it. I would but I am online and I
only have on RS232 serial cable and it is connected to my modem right now
:) The passing by reference is not any different that passing a pointer
and deferencing it.
> Can I change the pointer of an existing integer?
I'm not quite sure what you mean by that.
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