Need help with Counter/Timer application

[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.


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[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

[sayzer]

.....

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.....

I wanted to indicate that when a continious loop is in progress and you need that progress as long as your circuit is in operation, you will not be able to do other things.

In my example above, "While" statements have loops inside.
They are not a single line of instructions, they are loops.

One must be completed so that other can run. But, if you need an infinite loop, it will never exit that loop.

However, if we had a dual core PIC as Melanie mentioned or quad core, then you can do a simple thing as below. Say CORE1, CORE2, CORE3 etc. are new commands of PBP's 2010 version.

CORE1    'Separate Job Handler.

While PORTB.0 = 0 
   Do a loop here....
Wend

END CORE1

CORE2     'Separate Job Handler.

While PORTB.A = 1 
   Do a loop here....
Wend

END CORE2


CORE3      'Separate Job Handler.
...
END CORE3

..
...
....

etc...

they all work simultaneously.


Am I being too much imaginery here?

[Ioannis]

OK. Multi-core MCU I think is expensive. Using more than one chip also.

So why not use a bigger PIC with more memory to do the job of all others smaller PIC's?

How? Well I have never done it but for a long time I was thinking to do it like that:

1. All tasks even loops should execute only for a fraction of time, a slot.
2. An interrupt handler would share time slots to all loops or subs.
3. The interrupt handler might also grab the serial characters and buffer them as long as the serial transmission is slower than the handler execution time.
4. If a loop has to execute 10 times, then a counter and a flag could be used so that every time that loop is given time, it knows where it was and what to do.

In general I think these are the main rules to make an RTOS on a PIC. May be if we work together we can built an RTOS of our own for control applications. One man is difficult to accomplish this task.

Ioannis

[Acetronics2]

Hi,Sayzer

You're a bit complicated in your thoughts ...

just need to send keywords to other " slave" PICs to have them running or waiting ... WHILE your main program ( and CORE ...) is running. as you can write a full port at a time, that make 8 perfectly synchronized "slaves" ... for an 8 bits device.


Now, if TRUE multitasking is really needed, nothing keeps you away from two processors running on the same clock ... and sharing some of their inputs, even a full 8 bits bus.

BUT, a good analysis of the problem greatly simplifies the hardware ... say 999 times upon 1000... Humour.

A good peripheral use is also something to think at ... as we always overuse our CPU's ... for little stupid things ( i.e. translate in physical units instead of "counts" !!! )

assembler is a really good programming teacher ...

Alain

[sayzer]

You're a bit complicated in your thoughts ...

When I was 13 yrs old, in 1989, I was telling about my thoughts to some electronic engineers around me.

One thought was about having a wireless network card (1989 !).
I was playing with FM transmitters and was thinking how can I get rid of the wires of the LAN cards (old ones with BNC); could it be possible to adapt an FM transmitter to a LAN card etc.

The engineers that I mentioned this to told me "You're a bit complicated in your thoughts ..."

They said it would be useless, who would need a wireless LAN ? !!!!

Well...no comment there today!

A few yrs later, I was telling about having wireless earphones for cell phones.
Guess what? who would need it? Just put the phone on your ear!!!

Well, Bluetooth is kind of thing that people tend to use!

Alain, pls do not take it personal, it is not about you. I am sure you understand my point.

This is why my signature is like that.

But,

Now, if TRUE multitasking is really needed, nothing keeps you away from two processors running on the same clock ... and sharing some of their inputs, even a full 8 bits bus.

This is a good idea and I have seen some similar examples of it albeit not really true multi tasking.

Having say 12F508, cheap ones, as slaves to do small jobs etc. could be nice. I will have a drawing to see what I can do. But, ONE PIC with TRUE multitasking is not that.



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