How to use a "Timer"
 

How to include the Timer to the program.

P.S how many 1/x bits per Sec.



Thx alot "Hamosad" team. :yikes:

Re: How to use a "Timer"
 

one loop of the controller is 26.2 millis - approx 38 loops per second. just add a variable to count till 38 and then reset it to zero

good luck/behatzla'ha

Re: How to use a "Timer"
 

A word of caution--I learned the hard way that this is not always true.

The loop executes at a minimum of 26.6ms, but it most certainly can take much longer than 26.6ms!
The BLROD doesn't trigger until the code takes a whopping 1/4 to 1/2 second per loop! :ahh:

EDIT:
If you want an example of this behavior, try the 2005 default camera code.
The code slows dramatically as soon as the camera is hooked up, and as far as I can tell, takes more on the order of 1/4-second per loop.

Re: How to use a "Timer"
 

Do not depend on loop timings! They are highly variable!

Use timer interrupts. Kevin has code on his website.

Re: How to use a "Timer"
 

I'm a little unclear of what the actual question is. Are you asking how to use the PIC's internal timers? How to use the timers would vary based on your application. The PIC's timer modules can be configured as either timers or counters based on a few different internal sources (at varying speeds) as well as external sources.

If you are interested in using the timer modules I would suggest you start by reading the data sheet on the PIC micro timer modules and then reviewing Kevin's interrupt/timer code from 2005 (he hasn't posted 2006 code yet).

Once you've reviewed the above items you should have a better idea of what you are looking for, or where you may need some assistance.

Re: How to use a "Timer"
 

We did read the PDF files and we dont know the specific code to operate the Timer.

( AKA. we dont know how to use the code thats in the "H" files ) .


Thx again : ) :ahh: :) :ahh:

Re: How to use a "Timer"
 

Hmm...i wouldn't recommend using the "approx 38 loops per second" method.

If you're looking for greater precision i recommend using the interrupt-driven timers. Our team is currently using Timer1 of the five PIC timers. Perhaps i'm not the best person to explain you exactly how they work but let me see if i can help...

First off, we created a function known as Init_timers(); (inside a .c file of our choice), which is called from inside User_Initialization() under user_routines.c.

Inside Init_timers we wrote the following code (to initialize and configure Timer1):

void Init_timers(void)
{
T1CONbits.T1CKPS0 = 1; // 1:8 Prescale (clock=1.25MHz/each tick=800ns)
T1CONbits.T1CKPS1 = 1;

TMR1H = 0x85; // sets Timer1's most significant byte
TMRIL = 0xED; // sets Timer1's least significant byte

T1CONbits.TMR1CS = 0; // Uses Internal clock

T1CONbits.T1OSCEN = 0; // Internal oscillator off

T1CONbits.RD16 = 1; // Timer1 operations done in 16-bit accesses

IPR1bits.TMR1IP = 0; // Sets interrupt as low priority

PIR1bits.TMR1IF = 0; // Overflow flag

PIE1bits.TMR1IE = 1; // Timer1 interrupt OK

INTCONbits.GIEL = 1; // Low priority interrupts OK

T1CONbits.TMR1ON = 1; // Timer1 set as on

}

Next you'll need to add a few things inside InterruptHandlerLow() inside user_routines_fast. This is a system function; I.E. when an interrupt is set, this function is immediately called by IFI's interrupt handler. You do not need to call it from anywhere in your code, however, you will need to include the following lines of code inside it. You'll notice this function already has several "IF" loops so all you have to do is add one more...

void InterruptHandlerLow ()
{
if[...]

else if (PIR1bits.TMR1IF && PIE1bits.TMR1IE) // checks to see if overflow has occured
{
PIR1bits.TMR1IF = 0; // resets Timer1 overflow
TMR1L = 0xED;
TMR1H = 0x85;
timer1_count++; // Timer1 counter incremented every 25ms
}

[...]

} // end of InterruptHandlerLow() function

Since I'm assuming you'll be working with timers inside your Autonomous code (as are we), all you'd have to do next is use "IF"s to compare the timer1_count variable. As was explained, the timer increments every 25ms, so if for example you wanted to have your robot execute a specific part of your code for 1s (=1000 ms), simple!: check if timer1_count is equivalent to 40...! For 2 seconds, 80, for 10 seconds, 400, etc etc etc...

This may not perhaps be the most accurate method but from our experiences it suited our specific needs...

Hope this helps...
any questions whatsoever, pm me...

Re: How to use a "Timer"
 

oops...rather small yet important detail....don't forget to include the "timers.h" header file inside any .c files that work with Timers... ;)

Re: How to use a "Timer"
 

Thx all !!!! (for the help :) )

....

:ahh: 21' is comming soon :ahh: ;)

Re: How to use a "Timer"
 

thanks a ton. this is very useful. I think.

Re: How to use a "Timer"
 

Do you think you could provide more details on interrupt driven timers? Does it use up one of the six interrupts your robot has? Oh, and the 25 ms timing loop, why is it 25 ms? It seems to me that the calculation is:

2 bytes*8 bits/byte = 16 bits

largest possible 2-byte integer = 2^16 - 1 = 65535

And 800 ns*65535 =52.428 ms

You seem to get half of that...

I'm not doubting the correctness of 25 ms, I just wonder as to why it is 25 ms...

Re: How to use a "Timer"
 

TMR1H = 0x85; // sets Timer1's most significant byte
TMRIL = 0xED; // sets Timer1's least significant byte

Rather small detail...on my posts above i made a typo mistake ... TMRIL should be TMR1L...so don't panic if you're getting any "symbol undefined" errors!! Sorry about that...:yikes:

Now a few comments on the 25 ms loop...:

OK up to that point that's correct... according to the Timers White Paper found here:(http://www.ifirobotics.com/docs/time...004-jan-14.pdf) the following formula should give you what you want:

# of ticks = (time elapsed) * 10^7s / (prescale factor)

As you said above, with a 16 bit timer, counting to 65535, we can measure 6.5535 ms (considering the fact that the internal clock is 10MHz). What happens is that this duration is far too small to use for real applications, so then we used a prescale factor. In this case, we're using one of 8. This means that the timer will only increment once every eight ticks, therefore it will overflow after 52.428 ms. So that is where and how you got this value.

OK up to that point i think we can agree on. Now, we use the formula above to find the # of ticks we need to get a nice even interval of 25 ms (= 0.025 s):

# of ticks = (time elapsed) * 10^7s / (prescale factor)
# of ticks = (0.025) * 10^7s /(8)





Therefore we get 65535 (timer's max value of ticks) - 31250 (number of ticks we need) = 34285 (preload value).



TMR1H = 0x85; // sets Timer1's most significant byte
TMR1L = 0xED; // sets Timer1's least significant byte


So, if for example you wanted to work a different time interval (50 ms, let's suppose) use the formula to find out the number of ticks you will need, subtract that value from 65535 and convert the result of that into hexadecimal. That will get you your preload value.

Hope this helps...

Re: How to use a "Timer"
 

Oh alright. I somehow overlooked the preload values.

So, how do I set a sclaing factor? In your code there seems to be a line that sets it to one yet it's 8...

Re: How to use a "Timer"
 

There is one problem with this

the timer link you have is for the 8520 controller the new controller is the 8720 and I can't get the code that was given in this thread to work has any one else???
also does any one have the code/"white papers" for the 8720 timers???
or is it the same and we just messed with it too much???

Re: How to use a "Timer"
 

Check out the OpenTimer#() functions in this PDF:
http://www.kevin.org/frc/C18_libraries.pdf

It's very useful.

Re: How to use a "Timer"
 

The new PIC is 8722 not 8720 and the processor runs at 40 MHz but the prescaler examples are assuming the procesor is running at 10 MHz.

This is the actual Pic18F8722 data sheet:http://www.kevin.org/frc/PIC18F8722_ds.pdf

That is just he C18 complier library to help with timers and stuff but not the actual Pic data sheet.

Re: How to use a "Timer"
 

How do I use another timer? The way I'm having things work right now, I'm already using Timer 1 to do something. Now I want another timer to do something else? How can I do that? And if there are two timers firing interrupts at the same time, is that going to mess things up? I heard that the five timers in the FRC are all different, so how do I use another timer?

Re: How to use a "Timer"
 

It wasn't meant to be a link to the datasheet, and yes it is in fact a 10MHz clock. I'm using those to generate a 4ms overflow timer, and I've verified its speed by having a printf every 250 overflows (one second) and timing it with my watch, as well as a few other people who concur, its definitely 10MHz.

Make sure to include timers.h

Re: How to use a "Timer"
 

Sorry I ment the clock speed is 40 MHz but the timer incriments one every 4 of them. Same with the processor instructions cycle. It is 1/4 the speed of the clock.

The example has a 10MHz clock but but the acutal ticks on the timer are only 2.5 MHz so per second(assuming 1 to 1 prescale). So on the robot controller you have to multiply that number by 4 to get the real number of ticks per second( If you are going by the example in Kevin Watson's interrupt code or the data sheets).

Re: How to use a "Timer"
 

Huh?

I've never heard of it running a 40MHz clock and none the tests I've run support that, they do however support a 10MHz clock.

For example, the code example I posted previously is a 4ms clock.
I preloaded the timer with 60535 so it would overflow 5000 ticks later (65535).
4ms / 5000 = 800 ns per tick
1 second / 800 ns = 1,250,000 ticks = 1.25 MHz
1.25MHz * 8 (1 to 8 prescale) = 10MHz

If I missed something, can you point out where I can find it? I'm genuinely confused and I don't understand where you got your numbers from.

Hopefully helping,
Matt

Re: How to use a "Timer"
 

I am now confused too. This is what I know:

The PIC's have an internal hardware PLL(Phase Loop Lock hardware multiplier). I can't find the setup of this of RC but if you connect a 10MHz crystal to a pic and turn on hardware PLL, its like running 40 MHz crystal.(Don't ask me how it does it, I have no clue, try the data sheet) But they might have just hooked it up directly to a 40MHz clock, I guess you can do it.

I see this everywhere Foso/4, I am guessing but I think it means frequency of the oscillator(clock). I might be screwing up the technical terms.

In the Data Sheet I found this "One instruction cycle consists of four oscillator periods...".

So 10 MIPS * 4 = 40MHz

oscillator is just a crystal or resonator that oscillates or resonates at a particular frequency.

Don't worry about it. All you need to know is that the processor executes at 10 MIPS

Re: How to use a "Timer"
 

Ahhhh. Thanks for clarifying that, I wonder what the deal is with that....

However you're right, basing the timers and ticks on 10 million a second works. Perhaps after ship you and I should take up a research project to demystify this? :)

Re: How to use a "Timer"
 

Perhaps, I have already started working with an individual PIC form Microchip.
I ordered a sample pack for free. I am currently working on 18F458.
10MIPS
32k code spack
1.5k RAM
256bytes EEPROM

A free chip with similar processing power as the RC!! Though I took a little while to get it to work. I can run a servo directly off a pin on the chip!!!

Where do you want to start?

Re: How to use a "Timer"
 

Are you using a breadboard? A programmer? Would you mind detailing your setup? I'm interested in playing with something like this outside of FIRST.

Thanks,

Re: How to use a "Timer"
 

I am using a breadboard and a very cheap programmer(took me 20 hours of websurfing to find one that I could buy all the parts at radioshack).
http://www.picbasic.co.uk/forum/arch...php/t-703.html

You will need a data sheet for your particular pic.
PGD = data
PGC = clock
Vss = ground
Vpp/Vdd = power
All you need is a serial plug and some wire and registers.

Software is http://www.ic-prog.com/

I prefer the 18F series chips because the C18 compiler is readily available. Unless you want to program in assembly, then you can get any pic.

Just order a sample pack(up to 15 chips) umm....chips

To date I have only ordered one sample pack with 12 16f series chip and 3 18f series. A good free compiler for the 16f series has been hard to find.
Another big plus for 18F series is that you can easily use the code written by Kevin Watson, with a few modifications.

In fact, I looked through the IFI default code to understand the structure and impliment it into my pic.

Re: How to use a "Timer"
 

It sounds like you're still a little unclear on how this stuff works.

The PIC18F8720 (and presumably others) has a PLL as an option. This allows you to multiply the frequency of the oscillator that is used as the clock source. Whether IFI impliments this or not, I don't know (their website only quotes 10MIPS). So, if we have a 10MHz crystal and take advantage of the PLL, the PIC sees a 40MHz crystal. The datasheet mentions that this would be good to do of you are worried about having external high frequency signals.

The Foso/4 you see refers to what the PIC does with the clock. Each instruction cycle is 4 clock cycles. If you connect a 40MHz crystal, instructions are 10MHz. The details should be in the datasheet, but in essence, it takes the processor 4 clock cycles to process an instruction.

What you need to take away from this: The PIC in the RC is 10MIPS.