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It's easy to run one-time code leaving a state, but not during the entrance of the state. It's counter-intuitive to me and I think it can be made clearer by adding two more states, each that only wait. A toggler that uses an additional state to wait for the counter. Timing and accuracy side note: The counter has been modified to to account for the extra state, but it doesn't help much. We're getting farther off the faster we run the clock.
We see that the extra states have become extra cases in the switch statement.
Characteristics of Upward Lightning Flashes
States that always move on simply assign the next state to the state variable. The delay states check the counts before assigning a new state, thus retaining the state they were in. Meanwhile, loop the FSM as fast as possible. This will correct timing. Keep in mind that if the code execution time between ISR calls the state machine processing time is longer than the ISR call interval, the program will most likely lock up. Please consider an alarm clock's alarming functions.
What would its behavioral model look like? The alarm clock has several states it can exist in and has a couple of inputs that can be used to control it. There are a few more, like time set and alarm set inputs, but this example is limited to just the alarm operations. Try mentally walking through the operation of the state machine. I see that I can't get from 'idle' to 'ringing' if the alarm clock is not armed. Also I can't get back to 'idle' by pressing the snooze button, I have to disarm the alarm.
This meets my internal definition of how an alarm clock acts, so I proceed. There isn't a way of actually tracking time yet, even if just for the experiment. Rather than keeping track of days, hours, etc. I want to only keep track of seconds. So I'll need to count seconds. Well, the LED toggling state machine does that already! I'll just change it to keep track and add the whole darn state machine in. Re-using the blink state machine to count seconds. As a benefit, I can block the blinking of the LED unless the alarm is going off, and use that as the debug output.
Next, the alarm state machine states and variables. The alarm time is set to 15 seconds from reboot actually about 20 with error , and the snooze cycle is set for 5 seconds. In my experience, any coder who can diagram a program before writing it will succeed at the program. I've written one too many programs that ended up as a wad of nested 'if' statements because I didn't plan ahead. Inevitably, I needed to add one little thing that horribly broke the program and I was forced to re-evaluate my life choices. Using tools like state machine diagrams, flowcharts, class diagrams and unit tests have allowed me to write more complex yet maintainable code while staying relatively sane.
The state machine is just another idea to have in the toolbox and I hope that it will help you in the future! I also come from a hardware background and when I began programming state machines the most difficult part was how to actually draw the state machines.
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However, once I figured out that the state transitions should be some sort or event button press, timer tick, message received, etc it made things a lot easier. After that I was constructing state machines using the good 'ol switch statement. Then I came across this interesting post and my whole paradigm shifted forever. It is so much easier to read, easier to edit, easier to debug.
With more then just a few states the switch statement quickly gets out of control and unmanageable.
With the 'table-driven' method everything is much cleaner. Sometimes a switch statement is just great especially where the processing is simple and needs to be very fast, but for more complex application level state machines the 'table-driven' method is king!faziwifeqy.tk/map3.php
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Table driven state machines are great but to get the most benefit from them you also need a state monitoring function for each state. You can already see the event function in the example shown in the link. It gets called when a particular event occurs for a given state. On the other hand the state monitoring function gets called repeatedly by the state machine "engine" when no events have occurred.
In this function you might call a function that looks for "key presses" and generates an event when a key press is detected. This means that you only check for things within certain states. In some states you might want to check for key presses while in others you might want to check for key releases. This greatly simplifies code and reduces the monitoring overhead on the MCU. There is nothing to stop you sharing a state monitoring function between different states.
Nice link! Oh man, big switch statements All the child state classes will define a Run method, which will return the next state, or itself.
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That way, each class only has to deal with the state changes it will change to next. Run ; My C is really rusty, but I'm sure the pro's on here can make it work function pointers in structs? I'm no object oriented pro but I've been coding exercises to get better. Recently I wrote a linked list of objects that is dynamically allocated to the heap with no leaks!
Later, the thought dawned on my that the states could be connected in the way you describe, and I contemplated changing my 'snippet' implementation to be more object oriented. With 10 to 20 foreseeable states in a personal project, I weighed the benefit of flexibility vs. I think the art of engineering is the decision of what solution to use for a particular problem. I was chatting with Byron in the office when the model-view-controller idea came up. There's an application where a switch statement most likely the wrong thing to use unless maybe the controller had a subsystem implementing radio-like selects, for instance.
Before that I was typing up how to implement a bit-banged synchronous serial interface for microcontrollers, and I couldn't come up with a decision on whether that should be switch statements or objects. I don't want to control low-level hardware from an included. I think object orientation makes the machine tidy in code at the cost of hierarchical clutter, and it's the engineer's job to step in and proclaims "I think things!
Having said that, you've got my curiosity piqued and so I have to do it now. Perhaps I'll come up with something I like better.
Thanks for reading and making me think! Hi MTaylor, I'm also a big fan of state machines and would really like to encourage people to use them where appropriate which seems to be in a great many circumstances. I did however feel that your post was too detailed for the majority of amateur programmers and hobbyist makers and probably for the average professional programmer to see what the underlying benefits really are.
I would have lead with: In programming terms a state machine is a way of telling a program what to do when something happens and what to do until that thing happens. Because these things can happen at different times and in different orders trying to write pure code can often obscure the relationship between what can happen and when. A greatly simplified way of describing the relationship is with the use of state diagrams. A quick look at a state diagram can quickly show where you have overlooked a relationship or where a relationship does not make sense.