Using EXT Interrupt with a goto.

[Username]

I'm pretty new at programming PIC MCUs, so don't be like "wow, duh". My question is how can I use the preprocessor command #INT EXT with a goto command. It will need to be Pin x sees high input>stops program where its at currently>adds 1 to a variable> then goto start of program (main). It does not need to return to where it was after the interrupt was completed, just go to main. This is actually being used to change modes with a switch command.

I just don't really know the syntax for using preprocessor commands. I need someone who has experience to help me out with this. I hope this makes sense. Thanks.

[PCM programmer]

See this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=45101

Also this one may help:
http://www.ccsinfo.com/forum/viewtopic.php?t=19704

[Username]

So do you think this would work?:

#int ext
{
set_tris_A0(1)
input_state_A0(x)
If (x==0)
goto start
}

Would this function correctly? Do you see what im trying to do? (Sorry, Im not sure how to put it into the code box thing) Thanks.

[dyeatman]

[Username]

Thats why I am asking how to write it correctly. I need the program to stop what it is doing when it sees a certain pin is recieving input, and go to the begging of the main section of code. It was not meant to be syntax correct, it is more sudocode.

[John P]

I can think of three ways to do this.

1 When you're in the interrupt, make the value change and go into an endless loop, which will make the watchdog reset the processor (watchdog must be enabled). Obviously your value mustn't get reset as part of the startup process.

2 Don't use an interrupt, just poll the interrupt flag. When found, go to Start.

3 Do use an interrupt, but have it set a flag explicitly in software. After returning from the interrupt, when the flag is found it causes the jump to Start.

None of these ideas would give you an instantaneous result. I don't know if a delay would be acceptable. But really, must you "restart" the program? Can't you go through a loop with a new value?

[Username]

What I am trying to do is have a button being pushed (it would cause the pin to go high) instantly switch modes of the program, even if the program is in the middle of a loop or another action. Since this has to be instant, I can't just have the program check for input, there are lots of loops and the user would have to know when to try to switch modes. I'm sure there are easier ways to do this, I'm just new at this so I thought an interrupt would be the easiest way to do it. (I can see that it isn't now).

[RF_Developer]

[Username]

Okay, thanks for your response RF_Developer. I realized that what I was saying was pretty stupid. I had thought about having the program structered like you say I should, I thought using an interrupt made more sense. But I get now that it doesn't. I'll change the layout so it cycles through the loops, instead of having to jump around. I haven't written in any high level language before, thats why I didn't really understand what I was doing wrong. So you are saying to structure the program in the way that would a lot of examples like this to govern the way it functions and where it goes?
I know its not syntax correct, im just talking about structure:

main()
{
if (c==d)
subroutine()
else
subroutine2()
}

subroutine
{
if (a==b)
ouput pin A0 high
else
break
}

This is a very basic form of what you are saying, right?

By instant I meant it would appear instant to the user, so like .1s like you said. Sorry, I should have clearer about that.

[temtronic]

umm RF D..
GOTOs not being used today ????

Have a look at any disassembled CCS code, it's full of GOTOs.First instruction in every program... GOTO !

While you may not think you're using them, they are a basic instruction to every micro and mini that I've cut code for.

sorry to digress but whether you like them or not, you are using them.

GOTO exit();

[bkamen]

[temtronic]

Gee, I thought I was being nice... at least in showing that GOTO is used by all of us, even if it's buried in the machine code.

What I find interesting is that if GOTO is 'bad form' WHY does the CCS C compiler have it as a valid statement? It is a very clear , precise statement of telling anyone reading the source code exactly where the program is going.

The bottom line is that as long as the program does what is expected it really doesn't matter how it's coded.One of the 'joys' of cutting code is seeing how others accomplish the same task. Some go for tight( low memory) code, others for speed,some neatly comment every line of source(great for future reference),some use really_long_variable_names_ that_describe_what_they_are_for, some just use 2 or 3 characters.

[bkamen]

[RF_Developer]

Unfortunately you're over 40 years too late to have that argument! its all been said before, many times!

The programming language world has more or less followed Dijkstra's idea. As languages have tended to higher levels of abstraction so the goto has become more difficult to use and more and more deprecated. Many more modern languages lack anything like it altogether. Exception handling is used instead to provide a structured mechanism for doing the only sort of thing that goto was useful for.

I've done my share of assembly over the years; in a lot of different assemblers, some real, some for pseudo-machines. Of course they use jumps, branches and other related mechanisms to implement program sequence control. All are gotos of one form or another. Sure. That's really not the point.

Its precisely because the presence of goto in languages like C (actually he was primarily referring to Fortran) enables, arguably positively encourages such things as jumping out of an interrupt service routine (no there was no native support for ISRs in Fortran, neither is there in C. Its provided to us as an compiler specific extension to support embedded programming) to any arbitrary code vector that Dijkstra famously wrote his letter "Go To Statement Considered Harmful". Well, actually he didn't. He wrote the letter, but it was Nicklaus Wirth, the father of Pascal, that actually wrote that famous tagline when the letter was first published in 1968. But as I say people far more clued up than I have argued over this since. I just happen to get what Dijkstra wrote. Yes, C# has a goto. Yes, it is occasionally useful, one blog article by Steve Wellens I've just pulled up says, "You can program for years and never use a goto. However, there are times when a goto can make the code simpler and that…is a very good thing." Well, there you go, the argument continues: its already in its fifth decade.

RF Developer.

[temtronic]

yeesh,....reminds me I'm almost in my 6th decade ! 4 of them in front of screens....yikes !!
time flies when you're having fun...drags when you're not !