Need help with Counter/Timer application

[sayzer]

Hi Russ,

Something like below could work for you but it is just an example to show the idea.

Same concept could be applied to a Timer module of the PIC.

DEFINE OSC 20

TRISB = %00000000
PORTB = 0

Relay1     VAR PORTB.0  'A relay is driven through PORTB.0
Relay2     VAR PORTB.1
Relay3     VAR PORTB.2

RUSS_Timer var word     'A timer variable 
RUSS_Match var word     'A variable to match timer with stored variables in Lookdown Table.


Begin:

   Russ_Timer = 0
   RUSS_Match = 0


Start:

   PAUSE 100   'You need 100ms of time intervals.
   RUSS_Timer = Russ_Timer + 1
   
   LOOKDOWN RUSS_Timer ,[34,46,49,112,119,122,123,124,156,189,205,235],RUSS_Match     'Get an index value from the timer. Ad d more...

   BRANCHL  RUSS_Match, [Run_RED, Run_Green, Run_Blue, Run_last]     'Go run the matching set of instructions. Add more....
   

   goto start


Run_Red:

   high relay1
   goto start
   
Run_Green:

   high relay2
   low  relay1
   goto start

Run_Blue:

   TOGGLE relay3
   low relay2
   goto start
   
Run_Last:

   PORTB = 0
   goto begin  'Reset All.
   


END

[RussMartin]

Thanks. I wanted to try something like that, but the problem is the processor may have to do other things while the time is ticking away. Let me show it this way:

time 0.0 seconds -> We have an input, so we start counting.

time 0.1 seconds -> Is test1, test2, or test3 equal to 1? No? Let's keep counting.

. . .

time 12.3 seconds -> Is test1, test2, or test3 equal to 123? YES, test2 is! Let's quickly perform operation A while counting continues in the background. Is there any test value greater than 123? YES, test3 is, so let's just keep counting

. . .

time 45.6 seconds -> Is test1, test2, or test3 equal to 456? YES, test3 is! Let's quickly perform operation B while counting continues in the background. Is there any test value greater than 456? NO!--let's reset the counter to 0 and wait for another input.

[SteveB]

Russ,
Have a look at Darrel Taylor's Instant Interrupts. http://darreltaylor.com/DT_INTS-14/intro.html


From this (and Darrel's elapsed timer) you can get an interrupt driven timer to count out your .1sec intervals.

Then you can put the conditional tests and assosiated code either:
a) In the interrupt handler itself (OK if the code is short, but not very good for lots of code)
b) In your main loop, and poll the timer value for changes.

This should get you started in the right direction. There are otherways to do this, but Darrel Talyor has generously done all the hard work for you getting the interrupts working.

HTH,
Steve

[sayzer]

BTW - Since you are playing with time (which passes always and so quick and causes us to get older physically), how will you handle an incoming operation say B while the previous operation say A is still in progress?

Is there a possibility like that?

Here is another wish I should post to Wish list : A true Multitasking Processor – say four separate operations simultaneously.

[Melanie]

A PIC already multi-tasks...

It runs multiple Timers all independantly from each other or anything else that's happening...

It runs Multiple Comparators and Op-Amps (if fitted) all independantly from anything else...

It can Transmit and Receive on it's USART (if fitted) independantly from anything else...

It can do ADC conversion independantly from anything else...

It can do PWM Output independantly from anything else...

That's because it's got the HARDWARE to do it. However, until we get multi-core PICs, it can only execute one software instruction at a time. Even your desktop PC only executes one instruction at a time (ignoring the new dual-core CPU's), but it time-slices, so it appears like you are running multiple tasks. Time-Slicing is a kernel function of an OS which sits below any higher-level application program. PICs can time-slice too, but because until recently their Program Memory has been limited to only a few Kb, by the time you've added a true multi-tasking kernel, there's not been much room for anything else layered on top.

So until someone markets an embedded multitasking OS for the PICs, you're limited to writing clever programs that perform seemingly 'simultaneous' functions yourself.

[sayzer]

A PIC already multi-tasks...
That's because it's got the HARDWARE to do it. However, until we get multi-core PICs, it can only execute one software instruction at a time. ....

That is what I meant.

For example:

While PORTB.0 = 0 
  do a kind of loop here...
wend

While PORTA.0 = 1
  do another kind of loop here...
wend

These two while statements can not execute et the same time. This is just an example.

BTW; humans also multi-task albeit most of us do not even realize that we do.


---------------

[keithdoxey]

That is what I meant.

For example:

While PORTB.0 = 0 
  do a kind of loop here...
wend

While PORTA.0 = 1
  do another kind of loop here...
wend

These two while statements can not execute et the same time.

---------------

True... because of the way the program is written it will repeatedly service the PortB loop until such time as PORTB.0 = 1

If you want BOTH loops to be serviced then there is a way of doing that. Admittedly they wont be serviced simultaneously but each will be repeatedly serviced

ExampleLoop:

If PORTB.0 = 0 then
  do a kind of loop here...
Endif

If PORTA.0 = 1
  do another kind of loop here...
Endif

Goto ExampleLoop

I have a project where a PIC is decoding IR signals and also receiving short commands over a serial port. The main loop is basically

Main:
Gosub CheckForIR
Gosub CheckForSerial
Goto Main

The IR check takes the most time but that is the main activity that the PIC has to do. Serial data is received by the USART so will buffer upto two characters. Servicing the Serial data normally takes only 1ms so that it returns more or less immediately unless serial data is received at which point it waits in the serial loop a bit longer to receive any extra data as that now becomes the priority.

Its not true multi tasking but everything does get done OK

[keithdoxey]

true Multitasking Processor – say four separate operations simultaneously.

Which is fine until you want to do six things simultaneously.

As Melanie said

Even your desktop PC only executes one instruction at a time (ignoring the new dual-core CPU's), but it time-slices, so it appears like you are running multiple tasks.

My laptop is currently running many programs in the background and appears to be a speedy machine but when I first boot it up it takes forever due to the heavy processor demands for each of the applications starting up.

To achieve the appearance of effective multitasking you must prioritise each task and ensure that a routine to service that task is performed often enough for the program to work.

eg. Task levels "Critical", "Important", "Menial"

Main:

For MenialTasks = 0 to 5
   For ImportantTasks = 0 to 3
      Gosub CriticalTask
      Select Case ImportantTasks
          Case 0 
              Gosub MostImportantTask
          Case 1 
              Gosub LessImportantTask1
          Case 2 
              Gosub MostImportantTask
          Case 3 
              Gosub LessImportantTask2
      End Select
   Next ImportantTasks
   Select Case MenialTasks
          Case 0 
              Gosub MenialTask1
          Case 1 
              Gosub MenialTask2
          Case 2 
              Gosub MenialTask3
          Case 3 
              Gosub MenialTask4
          Case 4 
              Gosub MenialTask5
          Case 5 
              Gosub MenialTask6
      End Select
Next MenialTasks

Goto Main

To complete both the nested loops takes 24 circuits.
(6 MenialTasks * 4 ImportantTasks).

If you look you will see that the subroutines called are...

CriticalTask - 24 times (once every loop of the ImportantTasks)
MostImportantTask - 12 times (every other loop of ImportantTasks)
LessImportantTask 1 & 2 - 6 times each (once per ImportantTasks loop)

Each MenialTask gets called once for every complete cycle of both loops.

You just need to figure out the most important things to do and how to keep track of what you are doing

[RussMartin]

BTW - Since you are playing with time (which passes always and so quick and causes us to get older physically), how will you handle an incoming operation say B while the previous operation say A is still in progress?

Is there a possibility like that?

Sad to say, yes there is. That's why I'm having one PIC handling the user interface, inputs, and master timing, and other PICs performing the requisite operations.

Here is another wish I should post to Wish list : A true Multitasking Processor – say four separate operations simultaneously.

As you can see, I'm kind of approaching that with primitive "distributed (or parallel) processing".

All of my prior work over the years has involved the Z80, the 8051 family, and the 68HCxx line, always with "glue" in the form of support chips (RAM, PROM, EEPROM, SPIs and/or PPIs--you know), so it's kind of fun to look at "doing it all with PICs large and small".

PS: A lot of my practical PIC education is coming from reading Melanie's posts in this forum (and in the archives). Melanie, I'd like to nominate you for goddess.