Interrupting a While Loop Playing a Song on Boot Alarm When Disarm Signal is Sent

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#1 21660547 02 Jan 2012 21:35

Joshua Bishop Joshua Bishop

Anonymous

Post #1
21660547 02 Jan 2012 21:35

Scenario: I'm updating my Boot Alarm and part of this process is turning the alarm into a song. Before, the alarm would do quick repeating cycles and it would check to see if it was disarmed after each cycle. However, with a song, the cycle becomes much, much longer. An interrupt is generated and the status is changed but I would like to break out of the song as soon as the disarm signal is sent, not after the entire song is done and it checks the status again.

Question: Is there a way to break out of the while loop as soon as the signal is sent? Currently, I just have for() loops placed throughout the song so that it only continues for a couple of seconds after disarming. It seems... inelegant - to use the words of someone else in these forums recently.

Thanks!

- Josh
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#2 21660548 02 Jan 2012 21:44

Eduardo Viramontes Eduardo Viramontes

Anonymous

Post #2
21660548 02 Jan 2012 21:44

Break statement:
http://www.cprogramming.com/reference/break.html
#3 21660549 02 Jan 2012 22:01

Joshua Bishop Joshua Bishop

Anonymous

Post #3
21660549 02 Jan 2012 22:01

The switch/break would work the same as the for() loop, but maybe a bit cleaner in code. It doesn't address the issue of cutting off at anytime in the code (being forced by an interrupt, perhaps?), not just when it does the regular checks. And saying that, I should have mentioned before that exactly what I'm looking for may not be possible without a significant rethinking and rewriting of my code.

Also, I don't see why someone would simply have a break statement in the middle of their code, without any sort of decision making involved, as shown as the first example on the page.

Appreciate the quick response, that was eerily fast.
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#4 21660550 02 Jan 2012 22:10

Eduardo Viramontes Eduardo Viramontes

Anonymous

Post #4
21660550 02 Jan 2012 22:10

I'm just making time to go to sleep early...I'm driving back home tomorrow ;)

As for the example...programming text book examples are usually like that, I don't like it either, it's not a practical example, and thus, not relatable.

Have you ever used software interrupts? That might also work.
#5 21660551 02 Jan 2012 22:20

Joshua Bishop Joshua Bishop

Anonymous

Post #5
21660551 02 Jan 2012 22:20

Vacation is over? Always disappointing, tomorrow is my first day back to the normal tempo at work and I'm not looking forward to it...

Unfortunately, the way I have the code setup, my software interrupt only changes my status. I have three statuses (stati?), disarmed, armed, and alarming. Disarmed and armed are just sitting there, looping while waiting for an interrupt to change the status. When the status changes, it notices on the next loop and switches over to the while loop that associates with the status.

Here, I'll attach the heart of my code for your perusal.

[code lang="c"]
while(1) {
while(status == 0xAA) { /* Disarmed */
NOP();
}
while(status == 0xBB) { /* Armed */
RD6 = 1;
for (y = 1; y
#6 21660552 03 Jan 2012 04:17

Bob Loy Bob Loy

Anonymous

Post #6
21660552 03 Jan 2012 04:17

It IS late, and my eyes are bleary from coding my own C tonight, so this may not make as much sense as I'd like:

There is not quite enough info for me to figure out which while loop you want to break out of.
It is the main while(1) loop, or the while that the siren() call is in, or is there some while within siren()?

I'm assuming that siren() is the call to what is now your song.
And I'm assuming that the for loops in siren() are also testing for the alarm status.

If the second assumption is correct, then does PIC allow siren() to return a value?
If so, then you could rewrite the call to be:

if ((returnvar = siren()) == 0xWhichever)
break;
}

You could then also immediately test returnvar below the siren() while loop:

if ((returnvar = siren()) == 0xWhichever)
break;
}
if (returnvar == 0xWhichever)
break;
} /* end of while(1) */

... and then you'd be out of all the whiles.

I have a LinkedIn connection to a PIC programmer, so ultimately we could bring in his clear head.

- Inelegant Bob
#7 21660553 03 Jan 2012 04:23

Bob Loy Bob Loy

Anonymous

Post #7
21660553 03 Jan 2012 04:23

Well, the eeweb comment server killed my line breaks in my C examples.
Also removed one of the double-equals signs for some reason even though I cut and pasted from notepad.

Still, I think you can get the idea.

You'll have to tell us how you got your code to format so nicely - eeweb didn't crush it like it did mine...
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#8 21660554 03 Jan 2012 04:46

Bob Loy Bob Loy

Anonymous

Post #8
21660554 03 Jan 2012 04:46

That is, removed ALL the equality tests in ONE of the lines is what I meant. Aargh.
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#9 21660555 03 Jan 2012 07:50

Pieter Kruger Pieter Kruger

Anonymous

Post #9
21660555 03 Jan 2012 07:50

It seems you have 2 options:

1. Check the status at regular intervals in siren() - assuming this is playing the song. Not a very elegant solution.
2. Change the program structure (a little?) so the song is played by a timer interrupt, i.e. the timer interrupt rolls over
at a convenient rate (maybe a note interval), plays the next note and checks the status. If the status has changed it
aborts the song immediately. (If you set this at a high constant rate, you can also use this for delays of course.)

Let us know what you decide and how it turns out...
#10 21660556 03 Jan 2012 08:38

Joshua Bishop Joshua Bishop

Anonymous

Post #10
21660556 03 Jan 2012 08:38

You are correct, within siren() is the while() loop that I would like to break out of. And I could have siren() return a value if I wanted it to. I think this still has the same issue that it is only checking the status at the end of the while() loop [i.e. siren() function] and then making a decision at the end of the function as to whether or not it should jump back in and execute the entire function over again.

I'm honestly thinking that exactly what I'm looking for is not possible, which is kinda what I thought in the first place, I just wanted to ask someone smarter than me.

Also, for the code formatting, at the top of the textbox where I'm typing this is a line of formatting options (headers, bold, italics, strikethrough, etc..) At the right end of the line there is what looks like a piece of paper with on it. Click on that and you'll be good to go!
#11 21660557 03 Jan 2012 08:45

Joshua Bishop Joshua Bishop

Anonymous

Post #11
21660557 03 Jan 2012 08:45

Pieter, I'm currently implementing the first option but the second option is interesting. I think I see how I could do it. In the twelve hours since I posted this question, though, I've already decided that the first option is good enough for this project. I'm still interested in the answer for future projects, but I'm done with this boot. I'll try and get some good documentation posted on this site when I finish with the second version, see if anyone else enjoys its ridiculousness.

Thanks for your help! I'm going to bed...
#12 21660558 03 Jan 2012 10:41

Ty Wangsness Ty Wangsness

Anonymous

Post #12
21660558 03 Jan 2012 10:41

The right-most button above the textarea (looks like a piece of paper with '' symbols on it) can be used to insert code blocks with highlighting for various languages. Relatively new feature.
#13 21660559 04 Jan 2012 23:58

Bob Loy Bob Loy

Anonymous

Post #13
21660559 04 Jan 2012 23:58

Josh - I know you said you were done with the boot code and that's fine, programmers are like sharks: gotta keep moving.
But Pieter's idea about single notes got my subconscious working on an "elegant" (hopefully) approach.

Besides, I wanted to try out the tag to format some code ;^)

So, say your song has 30 notes...

[code lang="c"]
/* somewhere inside siren() */

int pitch[30] = {440,660,300,440, blah...};
int duration[30] = {1,2,2,4, blah...};
int play_song = 1;

while (play_song) {
for (j=0; j
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Topic summary

✨ The discussion addresses the challenge of interrupting a long-running while loop that plays a song as part of a boot alarm system when a disarm signal is received. The original alarm used short repeating cycles with status checks after each cycle, allowing prompt disarm detection. Transitioning to a song playback extended the cycle duration, delaying response to disarm signals. Proposed solutions include inserting multiple for() loops within the song playback to periodically check the disarm status, though this is considered inelegant. Suggestions involve using break statements to exit loops, but these only work at predefined check points. Software interrupts were considered but currently only update status flags without immediate loop interruption. A more robust approach discussed is restructuring the program to use timer interrupts to play individual notes, allowing status checks between notes and immediate song abortion upon disarm. Returning status values from the siren() function to control loop exits was also proposed. Ultimately, the first approach of periodic status checks within the song was implemented for the current project, while the timer interrupt method remains a promising solution for future development. Code formatting tips for forum posts were also shared.
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FAQ

TL;DR: To stop a boot-alarm song instantly, drive playback from a timer interrupt that advances one note at a time in a 30-note array; "abort the song immediately" when the disarm flag flips. [Elektroda, Pieter Kruger, post #21660555]

Why it matters: You’ll cut mid-song latency from an entire loop to a single note interval, improving safety and UX for DIY alarm builds.

Status-driven design: 0xAA=Disarmed, 0xBB=Armed; main loop idles until status changes. [Elektroda, Joshua Bishop, post #21660551]
Interrupt method: Timer tick plays next note, checks status, and exits on change for immediate stop. [Elektroda, Pieter Kruger, post #21660555]
Nested-loop caveat: break exits only one loop; return a code from siren() to unwind further. [Elektroda, Bob Loy, post #21660552]
Loop-based fallback: Insert frequent status polls inside siren() to limit overrun after disarm. [Elektroda, Joshua Bishop, post #21660549]
Song data model: pitch[] and duration[] arrays (e.g., 30 notes) keep playback logic clean. [Elektroda, Bob Loy, post #21660559]

Quick Facts

Status-driven design: 0xAA=Disarmed, 0xBB=Armed; main loop idles until status changes. [Elektroda, Joshua Bishop, post #21660551]
Interrupt method: Timer tick plays next note, checks status, and exits on change for immediate stop. [Elektroda, Pieter Kruger, post #21660555]
Nested-loop caveat: break exits only one loop; return a code from siren() to unwind further. [Elektroda, Bob Loy, post #21660552]
Loop-based fallback: Insert frequent status polls inside siren() to limit overrun after disarm. [Elektroda, Joshua Bishop, post #21660549]
Song data model: pitch[] and duration[] arrays (e.g., 30 notes) keep playback logic clean. [Elektroda, Bob Loy, post #21660559]

How do I stop a song-playing while loop the moment a disarm signal arrives?

Move playback into a timer interrupt. On each tick, play the next note, read the disarm flag, and exit immediately on change. This limits latency to one note interval and avoids waiting for the full loop. As one expert put it, “abort the song immediately.” [Elektroda, Pieter Kruger, post #21660555]

Will a simple break statement solve nested loops in my alarm code?

No. break exits only the innermost loop. To leave multiple loops, make siren() return a status code, test it after the loop, and then break or return again to unwind higher levels. This pattern reliably propagates the stop condition. [Elektroda, Bob Loy, post #21660552]

How can siren() return a value to unwind multiple loops safely?

Have siren() return a code such as DISARMED. In the caller, check the return and break out of the enclosing while. Then test again at the next level, exiting the main loop if needed. This staged exit avoids hanging inside nested structures. [Elektroda, Bob Loy, post #21660552]

Can software interrupts help if my loop is busy?

Yes. A software interrupt can set a global status flag. Your main state machine branches when it next checks the flag. However, if siren() runs long without polling, response still delays until the next check. [Elektroda, Joshua Bishop, post #21660551]

What’s a simple interrupt-driven design to play notes and stop instantly?

Store the song as pitch[] and duration[] indices.
Configure a timer to tick at your smallest note unit.
On each ISR tick, advance timing, output the note, check disarm, and exit if set. This yields near-instant stops mid-song. [Elektroda, Pieter Kruger, post #21660555]

How often should I poll the status if I keep a loop-based song?

Poll at short, regular intervals inside siren(). Insert quick checks between note steps or partial delays. This reduces overrun after disarm without a full rewrite, though it remains less elegant than interrupts. The author used scattered for() checks for this. [Elektroda, Joshua Bishop, post #21660549]

What edge cases can still block an immediate stop?

If you only check the flag at the end of siren(), the system won’t stop mid-note. Long operations between polls will delay exit. Restructure loops or use timer-driven steps to avoid full-function waits before noticing disarm. [Elektroda, Joshua Bishop, post #21660556]

How do I store a song cleanly for microcontroller playback?

Use arrays for notes and durations, for example pitch[30] and duration[30]. Iterate with an index, not long blocking loops. This makes ISR-based stepping easy and keeps code readable and maintainable. [Elektroda, Bob Loy, post #21660559]

Why does my for-loop polling approach feel “inelegant,” and is it acceptable?

It spreads status checks across the song, which works but mixes control and timing logic. It’s acceptable for quick results, but interrupts or return-code unwinding are cleaner long-term designs. “It seems…inelegant,” noted the author. [Elektroda, Joshua Bishop, post #21660549]

How do I exit both the siren loop and the main loop after disarm?

Return a DISARMED code from siren(), check it immediately in the caller to break that loop, then test once more to break the main while(1). This two-stage check exits cleanly from nested loops. [Elektroda, Bob Loy, post #21660552]

What’s a minimal change if I’m done with this build but want faster stops?

Keep your current design and add tighter-granularity polls inside siren(). Check the status between short delay slices or note segments to cut post-disarm overrun without major refactoring. [Elektroda, Joshua Bishop, post #21660557]

How do I format code blocks correctly in this forum thread?

Use the right-most toolbar button above the editor that looks like a document with code symbols. It inserts language-highlighted code blocks for clearer sharing. [Elektroda, Ty Wangsness, post #21660558]

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