quick question: TIMERS

[Xufer]

The code below works but i need just a few more loops in the code in order to get it to go exactly where i need it to any one know how i can make it start a new count after it gets past 254 so it doesnt loop, and i can add a few more steps to it, or does some one have a better way of doing this ? I got this way to work it just needs to run for a little bit longer.

void User_Autonomous_Code(void)
{
 int count;
 count = 1;
 while (autonomous_mode)   /* DO NOT CHANGE! */
 {  
     if (statusflag.NEW_SPI_DATA)      /* 26.2ms loop area */
     {
         Getdata(&rxdata);   /* DO NOT DELETE, or you will be stuck here forever! */
   /*40ticks = 1 sec 20ticks = .5 secs 10ticks=.25 secs */ //increse counter by 1 /* DO NOT DELETE, or you will get no PWM outputs! *//*40ticks = 1 sec 20ticks = .5 secs 10ticks=.25 secs */
   
   if ( count >= 124 ) {
   }   

   if (count > 0 && count < 34 )
   { 
    pwm05 = 60;
       }
   if (count > 35 )
   { 
    pwm05 = 127;
       }
   if (count > 0 && count < 30 )
   { 
    pwm04 = 0;
       }
   if (count > 32 )
   { 
    pwm04 = 127;
       }
   if (count > 35 && count < 90 )
   { 
    pwm01 = 190;
       }
   if (count > 35 && count < 90 )
   { 
    pwm02 = 190;
       }
   if (count > 92  && count <= 122)
   {
    pwm01 = 190;
   }
   if (count > 92 && count <= 122)
   {
    pwm02 = 53;
   }
   if (count > 130 && count < 160 )
   { 
    pwm01 = 190;
       }
   if (count > 130 && count < 160 )
   { 
    pwm02 = 190;
      }
   if (count > 163  && count <= 183)
   {
    pwm01 = 190;
   }
   if (count > 163 && count <= 183)
   {
    pwm02 = 53;
   }
   if (count > 223 && count < 250 )
   { 
    pwm01 = 190;
       }
   if (count > 223 && count < 250 )
   { 
    pwm02 = 190;
      }
   if (count > 255  && count <= 275)
   {
    pwm01 = 190;
   }
   if (count > 255 && count <= 275)
   {
    pwm02 = 53;
   }

   ++count;  
      Putdata(&txdata);   
  }
 }
}

any help would be greatly appreciated.

[Tom Bottiglieri]

you could just do an if of when it goes above the time.

if(timer>40)
{}
else if(timer>80)
{}

[Daniel]

Your code is begging to become a state machine. It is a codeing techinque that uses a switch statement and where each case is an independant state. This works well because of the 26.3 ms looping process. The benefit of state machines is that it can be written so that some states are re-entrant where they look for some event like time or distance to trigger the program into the next state.

switch (state) {
case 1 :
// start motors
t = time + SomeDiration
break;

case 2 :
if (time < t) // This is re-entrant.
state = 2;
else
state = 3;
break;

case 3 :
// stop motors and start next manuever...
...

Get the picture? It's not hard. It does require some thought. But this is how most very complex programs start out. There are other ways of doing this with pointers and trillions of function - but this is just so simple and readable.
If you are at the Great Lakes Competition look me up and I'll show you more.

[Xufer]

huh ? dun quite get it, too tired maybe ...

[10intheCrunch]

A few things:

At the most basic level, you don't need to worry about the int looping over. Ints in C are two byte variables; an unsigned one will store up to 32000+. If you need more than that, you can use long, which is a four byte variable.

Second, you don't need two seperate if statements when you are setting pwm01 and pwm02--they do the same thing, so put all the code you need in one! You'll save processing power and increase readability.

State machines can be a little confusing at first, but they will make your code much more readable in the end, and much faster. A state machine uses the switch command, which will look at one variable, and jump to the "case" that the variable number points to. So you would have an int variable to count another int variable that would be the state.

int count;
int state = 0;

void InitAuto(void){
count = 0;
//any other variables that you need to reset
}

void User_Auto_Code(void){
switch(state){ //look at the state variable for code to jump to

case 0:
//do some stuff
if(count > 100){
state++; //move to state 1
InitAuto();
}
break;

case 1:
//do some other stuff
if(count > 50){
state++; //move to state 2
InitAuto();
}
break;

etc etc etc....
}//close switch
count++;

As you can see, its really easy to make readable code this way, and you know exactly how many program counts are in each state without having to do any math =). This is also a much lighter load on your processor; your program will execute a lot faster and be cleaner in memory.

A couple symantic things: the break; statement is needed at the end of every case, to tell the compiler that you are done with the case. Just set up your cases in order, and tell your motors what to do =).

If you can implement real timers, it will make the program that much better (254 uses a millisecond timer), but you should be fine with the program counts.

Good luck!

[Ryan M.]

Originally Posted by Xufer

huh ? dun quite get it, too tired maybe ...

Instead of stead of what you currently have, you'd put in something like his example. The basic idea is laid out below: (in semi-pseudo-code)

Static state variable starting at 0

switch(state variable)
{
    case 0:
        perform actions set 1
        check if this state is complete
             if it is, increment the state variable

     case 1:
        perform actions set 2
        check if this state is complete
             if it is, increment the state variable

    case 2:
        perform actions set 3
        check if this state is complete
             if it is, increment the state variable

    ...

     case X:
        don't do anything
}

By repeatedly calling this switch statement, it will work its way through all the states. You can, of course, also have statements in there that reset the statee variable, or put it to where ever you want.

Hope that clarifies it some.

[Xufer]

Originally Posted by Texan

Instead of stead of what you currently have, you'd put in something like his example. The basic idea is laid out below: (in semi-pseudo-code)

Static state variable starting at 0

switch(state variable)
{
    case 0:
        perform actions set 1
        check if this state is complete
             if it is, increment the state variable

     case 1:
        perform actions set 2
        check if this state is complete
             if it is, increment the state variable

    case 2:
        perform actions set 3
        check if this state is complete
             if it is, increment the state variable

    ...

     case X:
        don't do anything
}

By repeatedly calling this switch statement, it will work its way through all the states. You can, of course, also have statements in there that reset the statee variable, or put it to where ever you want.

Hope that clarifies it some.

yea kind of but what tells it when a state is complete ? how would i say
case 1 is to happen for 2 seconds and case 2 is supposed to happen for 3 seconds?
pseudo of what im talking about :

case 1 for 2 seconds
pwm01= 200
pwm02= 200
pwm03= 150
pwm04= 200

then go to case 2

case 2 for 3 seconds
pwm01= 200
pwm02= 100

then go to case 3

case 3
pwm01= 200
pwm02= 200

etc . what keeps it with in time constraints and what cuases it to go to the next case statement.

[10intheCrunch]

That's all up in my post...

Make a "StateInit" function that runs everytime you move to a new state, that at the very least resets your count to 0. Put a count++; statement after the switch. Then, inside each case, say

if(count > someNumber){
StateInit();
state++;
}

That will move it to the next case when the count is above the number you want. Since you don't have a real timer you'll have to do the math yourself for how long to stay in each one but it shouldn't be that bad.

[Xufer]

Originally Posted by 10intheCrunch

That's all up in my post...

Make a "StateInit" function that runs everytime you move to a new state, that at the very least resets your count to 0. Put a count++; statement after the switch. Then, inside each case, say

if(count > someNumber){
StateInit();
state++;
}

That will move it to the next case when the count is above the number you want. Since you don't have a real timer you'll have to do the math yourself for how long to stay in each one but it shouldn't be that bad.

If you do that wont the count everflow after it reaches 254 ? whats to keep it from doing that ? Im still kind of missing it i guess. Or how would i make a real timer i mean i treid experimenting with one but i failed.

[10intheCrunch]

Again...read my post...

If you use an int for your counter variable, you will have more than enough space. An int in C is a two byte variable, meaning the signed version can store from -32000 to 32000.

What you're thinking about is a char, a one byte variable. That will turn over at 254 (or 128 if it is signed).

Have you tested your code yet?

[Xufer]

Originally Posted by 10intheCrunch

Again...read my post...

If you use an int for your counter variable, you will have more than enough space. An int in C is a two byte variable, meaning the signed version can store from -32000 to 32000.

What you're thinking about is a char, a one byte variable. That will turn over at 254 (or 128 if it is signed).

Have you tested your code yet?

so what if i use my orrigianl code and just change char to int then i wont have to eorry about the overflow problem right ?

[Ryan M.]

Originally Posted by Xufer

yea kind of but what tells it when a state is complete ? how would i say
case 1 is to happen for 2 seconds and case 2 is supposed to happen for 3 seconds?
pseudo of what im talking about :

case 1 for 2 seconds
pwm01= 200
pwm02= 200
pwm03= 150
pwm04= 200

then go to case 2

case 2 for 3 seconds
pwm01= 200
pwm02= 100

then go to case 3

case 3
pwm01= 200
pwm02= 200

etc . what keeps it with in time constraints and what cuases it to go to the next case statement.

You could have a variable that gets increment every 26.2ms. If this functions is getting called that often, it could be static to it. If not, it could be a global variable that is incremented in something that is. Then, for the tests, you would check if the variable was greater than, say, 78. This would make it run for approzimately 2 second ((1000ms/26.2ms)*x seconds). Or, if you need more accuracy than that, and that's not bad, you can have an external clock attched to pin 1/2 and have an interrunpt that increments it.

[10intheCrunch]

Originally Posted by Xufer

so what if i use my orrigianl code and just change char to int then i wont have to eorry about the overflow problem right ?

Your original code does use int instead of char, but yes. You shouldn't have any overflow problem.

[jacob_dilles]

Originally Posted by Texan

you can have an external clock attched to pin 1/2 and have an interrunpt that increments it.

doesnt the pic have like 3 built in timers?

[Astronouth7303]

5: 0-4. 0 is used by FRC_library.lib and is slowest of all, 1&3 are faster than 2&4.
Range: (Prescaler Range|Postscaler Range)
0: 1:2-1:256|1:1
1: 1:1-1:8|1:1
2: 1:1-1:16|1:1-1:16
3: 1:1-1:8|1:1
4: 1:1-1:16|1:1-1:16
The prescalers are powers of 2 (*2), and postscalers are integers (+1). The base frequincies of all the timers is the same: w/o scaling they are 10MHz clocks and a 100ns tick.

This all out of Kevin's interupt.c file. WELL commented