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- Опубліковано 30 вер 2024
- First steps towards coding sketches in a multi-tasking manner. Simple & Easy.
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We really need to code differently if we are to ever create a responsive program. Sequential execution is sometimes necessary, but often we need to do more than one thing at a time. Here I show the absolute basics in how to get two functions running simultaneously.
As this video is aimed at beginners, each step is carefully explained - no skipping ahead 😁
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I would prefer redMillis += 500; and grnMillis += 100; in the if () statements. If the processor gets busy enough, millis() can count a few times before the assignment and these missed counts will accumulate. By adding a fixed amount, one loop might go long, but the next will be short and restore the timing.
Yes, what you say will ensure it is self regulating, good call 😁
Hiding timers inside functions is a bad idea. It is better to calculate timers explicitly in a loop.
When you say "hiding timers", can you just elaborate on that as I don't follow where this is in the video?
@@RalphBacon 10:27 Inside the blinkRedLed() function, there is a calculation when the LED flashes. It seems to me that it's a bad idea to do this inside a function. It is better to calculate it from the outside, and then call the blinkRedLed() function if the time has come.
I do this in one of two ways.
One, as you describe above, I calculate whether a routine should run or not from within that routine. This means that I can call that routine from within the loop each time and the function determines whether it will run or not. Keeps the loop clean.
The second way is, as you suggest, calculate whether I _should_ call a function in the loop, and the function "just runs" when it is called. Makes the function slightly cleaner but adds "noise" to the loop.
Unless the timing is dependent on something I can only determine from within the main loop function I prefer the first way, to keep things as clean as possible in the main loop function. Personal preference, not really a right or wrong way to do this.
@@RalphBacon ok
@@RalphBacon it's more efficient and preferable from a design and maintenance clarity standpoint to implement this in main.
A state mahine demo would be wonderful. Great video as always, thank you!
Noted!
Thank Ralph. I've used millis() before but your explanation of "Static" was helpful. When I first saw the subroutine code I said wait, that's not going to work the timer is constantly being reset. Nope! For some reason I only thought static was when you didn't want the program to ever change the value. I can think of several projects I've done where timer and other declarations are littered throughout the program, when they can be neatly stored as a local variable in the subroutine.
Yes, keep things tidy and your program will be more maintainable, for sure.
The shortest Blink sketch I know:
void setup(){
pinMode(LED_BUILTIN,OUTPUT);
}
void loop(){
digitalWrite(LED_BUILTIN,millis() % 500 < 250);
}
Yes, I use that too! 👍
Me, after reading some of the comments: Man, some of these people need to relax - he made it clear that this is just the first video, etc.
Also me: BUT WHAT ABOUT WHEN MILLIS() ROLLS OVER TO ZERO AFTER ~49 DAYS??????
Nothing happens. It all "just works". I'll have to explain why in another video.
@@RalphBacon Well, that was kinda the whole point of my post, innit bruv? 😊I'm sure that the state machine code will handle the rollover case with aplomb and literally zero flashes will be missed when it does roll over.
Quite so, you have understood it all very well. 👍 Hang on, "innit bruv"? 🙄
@@RalphBacon I like to pretend I'm a West Brom ultra, even though I'm a Chelsea supporter living on the US.
Great video today Ralph. Thanks for your explanation of "static" in the situation, could you also please contrast that to "const", I would love to see more of the state machine, concepts, and practices. I'm an "old or rather very old" assembly language programmer in multiple flavors, so just now getting my feet wet with C++ and object-oriented ideas, certainly a lot to learn!
const means constant meaning once defined it cannot be changed, static means you can access it from any function, like a global variable but defined in a local scope (memory is "static" and kept after function executes) but you can also change the value.
A "const" value still requires a memory location just like any other variable. Except you can't change it. You can declare it inside a function (to constrain the scope) or make it global (grrr).
A #define allows a literal to be substituted by the precompiler and no extra memory is used. It's just becomes part of the code.
@@RalphBacon yes, and static constexpr is better still: no memory overhead, ability to use an explicit type and the static forces the compiler to evaluate at compile time.
I've done similar things, but being self-taught I didn't realize that the static variable declaration would only be evaluated the first time the function is called and not subsequent calls. I knew about the concept of scope, but not that run once concept. Thanx for clearing that up. 😀
Glad it helped, Christopher! 👍
a normal variable inside a function will lose its life. a static variable inside a function doesn't and remember its state. and that's why that line "only runs once". that line is a declaration of a variable with initial value from millis() and a static variable that is already existing won't be "re-declared" in the next function call.
Very good video, calm and patient explanation. Please follow up with a real state machine video - I barely can wait!
Regards
Soon. All things come to those who wait. And wait. And... you get the idea.
State machines are fun! Show transition diagrams. Pass on UML. Maybe show how easy to add states in a table-based machine.
I will probably show a quick and simple transition diagram but will concentrate on getting the states written and read. Noobs, remember. KISS as they say.
Hi Mr Ralph, although I’ve been programming for a number of years I’ve actually forgotten about the static variable declaration indeed of a function. Very informative always something new to learn.
Excellent! Always worth getting a refresher!
Really well explained Mr Bacon. Yes, please, I'd like to see more on State Machines.
Yes, I'll expand on this in the future, no problemo.
A problem of using millis() without any type o case protection is when millis() overflows, the LEDs are not going to blink anymore
I thought with unsigned long it will just going to start over from 0 and count up again ?
Wouldnt using the "millis() - variable" technique be overflow proof though? Whereas "millis() > variable" would be troublesome.
@@jestr1845 When millis() goes back to zero, the variable (redMillis) is going to still be really big, which is going to result in a negative number and the difference never pass the 500ms again. This can be a bigger issue when you use the micros(), that reset every 70min
If millis( ) overflows, it will have NO EFFECT on these sketches. Trust me, I'm a doctor, er, programmer 😆
@@FelipeLenschow It should still work. Lets use bytes for numeric simplicity:
255 - 250 = 5 // as expected
256 - 250 // is in reality...
1 - 250 // which simplifies to...
-249 // which as a byte would be...
6 // as expected. Or am I wrong?
Lots of computation repeated unnecessarily... The test does subtraction every time. Set redMillis to millis()+500 to the time when the pin should next be toggled and compare to millis().
There is only so much time to do stuff... the less you do (unnecessarily), the more time you have for useful stuff.
Doing less in each compute loop, reduces the granularity of response, something very important when one has real-time considerations.
Sorry, I disagree. In this instance, subtracting a stored value from millis works well and also caters for the millis( ) overflow - you still get the right answer.
I'm more interesting in getting people to code better than worrying about a few nanoseconds "optimising" the efficiency to the detriment of the robustness of the code.
Just sayin' 😉
@@RalphBacon I agree that the rollover of millis() would require special handling.
Generally not a problem if you know about it.
Those nanoseconds get chewed up rapidly, even with unsigned long arithmetic and comparisons. And the time can vary depending on the processor type, even within 8-bit AVR.
It's better to be able to burn idle cycles than to run out of cycles doing something useful.
Using more of the hardware to blink lights, without CPU utilisation would be instructive... Learning how a timer-counters can be used instead.
Looking forward to more "short" state machine videos. 😀
I'll try and make the next one shorter - or I'll record it at 1.5x speed.
@@RalphBacon 🤣🚀🚀🚀
I can see a major problem with this. Its not preemptive. A subtask has the possibility of locking up the whole thing.
I wrote a preemtive task manager in assembler that I use as a pseudo o/s. If i need something done when a condition occurs, I add a task to a Que that is prioritized based upon a priority number. What I put into the Que is a priority, condition, and task to run when condition is true. This condition can be a timer, semaphore, port change, etc. The task in the Que is passed control upon condition being true. The task does get interrupted by a timer interrupt, so a task can not hang the system. Before returning control to the interrupted task, it will place on the Que the interrupted task with the same priority as the original task wjth a condition of true. The task manager will rescan the Que and if no other higher priority task needs to run, the original task will get back control. Easy peasy
I use this all the time when coding on micro processors like the arduino, PIC, and TI
Correct, it's not pre-emptive - as I mentioned in the video it's important to prevent one task from monopolising the μController processor. That is, it's important the developer deals with this!
However, in the next step towards a State Machine, we can simply exit the function at a particular state and allow other things to run. A pseudo-yield, if you will.
It's certainly nothing as sophisticated as what you have described and written, but does work well enough for non-critical tasks. Have you published your task scheduler?
I've been made aware of FreeRTOS (optimised for Arduino) which I hope to try out soon, especially if it runs on the Nano Every (AtMega4809 chip which as 6K SRAM). github.com/feilipu/Arduino_FreeRTOS_Library
@@RalphBacon hey Ralph. No I did not publish it as it is written in assembler for each processor type i use. Its not ready for prime-time :)
Ralph very well explained example for multitasking the Arduino. I think you hit a very well deserved explanation for using global variables sparingly. I think that would be a great topic for an Arduino subject.
Glad it was helpful!
Yes please to a state machine follow on. Do you use any timer libraries ?
It's a _simple_ state machine, I don't want to scare the noobs. I don't use any timer libraries as such; you mean to trigger functions or something else?
@@RalphBacon Thanks Ralph, loving you posts! Yes, timer libraries for doing the 'have x millis passed' type functions
@@georgeboydratcliff1036 please, which would such library be?
@@alvarobyrne I like Eventually - makes timers almost like an event (hence the name!)
@@georgeboydratcliff1036 Thank you will check
I use Finite State Machine Library, FSM. Very easy yo use.
Thanks for the tip!
Greetings from Canada, Ralph. PLEASE delve deeper into State Machines, as I have been trying to grasp this concept, and how to implement it, for quite some time, now. Been scouring the internet for good explanations.
I agree, the archer video dude helped (here on YT) but I'd like to see more.
Will do! Next video on this subject (soon... ish) will delve into actual "states" so we can skip to the correct bit of code in a longer, single-responsibility function.
I use case statements to code state machines something like:
uchar8 abcReceived = FALSE;
uchar8 state = 0;
while ( abcReceived == FALSE )
switch ( state )
{
case 0:
if ( inputChar = ='A' ) state = 1;
break;
case 1:
if ( inputChar == 'B' )
state = 2;
else
state = 0;
break
case 2:
if ( inputChar == 'C' )
{
state = 0;
abcReceived = TRUE;
}
else
state = 0;
break;
default:
// an error condition or expected state
break;
}
@@RalphBacon Thank you, Ralph. Looking forward to your next lesson.
I understand that you are starting from the beginning but putting state machine in the title may be a little confusing / misleading, it is essentially a timed function loop.
It's the first step towards ensuring a State Machine can even run. Or do you propose we have a State Machine in a monolithic structure? We've got to get more things running _first_ and that we did!
@@RalphBacon I am not proposing anything, but reading the comments some think that this is a state machine when it is not.
Very good instruction !!! Three thumbs up !
My question is, what happens on day 50....when the "static unsigned long" variable is as high as it can go...but the time counter starts over .....Does everything stop ?
Have I missed something?
Yes, everything stops and the universe implodes. It's a well-known Arduino side effect. 😉
On the other hand, nothing happens because the counter (and millis) is an UNsigned long integer, it tries to take away a larger number (the old value of millis) from a tiny number (the new millis) and gets the correct value! Magic! Arduino have thought of everything.
As an example, let's pretend that millis was stored in a single byte, unsigned integer so could only count to 255 before overflowing (going back to zero). When that happened, we might suddenly be faced with a calculation such as 2 - 200 which normally could not be done (or would go negative, ie -198). But the value you get is 58 (ie the number of milliseconds that has passed since the count was 200 and is now 2.
If you don't believe me, write a simple sketch to prove it to yourself!
@@RalphBacon I've no reason not to believe you.
I'm just trying to understand.....
time now = 2 Millis()
time then was 4 million +/- redmillis
so, if(now (2) - then (4 million) > 500)
{
do stuff...
redMillis = millis(); //
Write that simple demo sketch! It's an eye opener! Nothing to do with millis, really, more to do with maths and unsigned integers.
@@RalphBacon Thank you , Sir.
Thanks Ralph,
You have presented a well though out video, covering the subject matter very well. It would be great if you would create another video on this subject, I look forward to it. You are a great teacher, your library of videos are a great resource!!!🙂🙃🙂
I found part 2. Thank you for putting in the time and sharing you knowledge with us.🙂😀🙂
I'm glad you found part 2 as that leveraged part 1 but then used a true 'state' too. Your projects now have guaranteed success 🤔
Good explanation. Thank you
You are welcome!
Great, i finally understand what the mean for static statement. Thanks
Glad it helped!
Hello Ralph, I would like to see a follow up to this video, I enjoyed your informative and educational video. I'm somewhat of a neophyte to Arduino sketch coding and would like if the sketch you presented will work with a Larson Scanner sketch using millis()? Looking forward to viewing your other related videos. Thanks again for your instructional video.
Neophytes are more than welcome to my channel; it's why I created it!
When you say "will [it] work with a Larson Scanner", do you mean you want to write a sketch that does a Knight Rider/Battlestar Galactica sweep of LEDs from left-to-right and back again?
If so, there are easier ways of doing that with NeoPixels and I demoed that (in passing) when I did recent video on NeoPixels (see video #239 ua-cam.com/video/SStRG-_1wXc/v-deo.html ).
If you really want to build a Larson Scanner (or have one) with a number of LEDs then a State Machine (my next video in this series, coming "soon") would certainly work (each LED is a State).
@@RalphBacon Hello Ralph. Thank you for welcoming this newbie and helping this old dog learn a new trick. I apologize for not being clear in my wording of my question to you. What I was trying to convey is I have a Larson Scanner (LS) using millis(), which I would like to incorporate with your sketch/code. When I wrote will [it] work with a Larson Scanner, I neglected to write I am planning to add the #define LEDs from the LS code at below your #define grnLED 8 of your sketch. The void from the LS below your void blinkGrnLed() and will place the LS void loop() below the void BlinkGrnLed() of your sketch and was wondering if you thought combining your code/sketch and the LS code work? Or is this combining of codes/actions require a “state machine” sketch type code? Thank you for your thoughts and I will let you know what comes of my attempts to combine these sketches.
If you can describe your Larson Scanner (or give me a link to it) I can help further.
For example, is your LS just a string of LEDs that you can control however you want or has it got electronics in there too? Have you got any code that already works with it?
@@RalphBacon Hello, Ralph, thank you again for responding back to me, it's kind of you. Just a quick FYI to let you know I was able to combine your sketch with the LS sketch I found it made for a interested time. Thank you for the link (video #239 ua-cam.com/video/SStRG-_1wXc/v-deo.html ) to your video on NeoPixels it will be a help in learning to control these as well. I am looking forward to viewing your other videos and hope you don't mind me dropping you a question from time to time. :-D
to prevent slowly introducing lag, instead of doing: grnMillis = millis(), you should do: grnMillis += 100. This ensures that regardless of hickups and delays in other functions, the interval will remain (or correct itself to) 100ms.
I'm just trying to work out where the lag is, that you refer to. Just so that others are aware, the timing here is anything but critical but even so...
I think I understand your concern: on each invocation we check the millis() and if true grab a new value from the millis(). That new value could be more than 100 + the original millis() (because we started late and/or have done some work). So we slowly drift further and further away from a true 100mS flash - it might be 100, 102, 103, 104... etc since the first flash.
Yes, your suggestion would ensure that only 100mS would have passed until we ran the code inside the "if" statement. Good call. 👍
@@RalphBacon I should have called it drift, but that indeed is the issue: scheduling the next action 100ms from now, instead of from the previous action. Keep in mind that the millis-overflow edge-case could be tricky here, so it'd be best to extract it from the two functions and write it as a separate function that handles all the miserable edge cases :)
Oh, man, I came here to say this!
And for exactly the same reason you could initialize the static variable with 0, Ensuring that the first event happens 'exactly' on the set interval after startup
@@sdr9682 Doesn't that timer counter start at 0 when first turned on? Oh... I just thought of something. I don't think it resets the timer counter when you =reset= the AVR.
So initializing it with 0 at startup, you do have a set interval each time, even if you reset rather than power up.
I'm not sure "short video" means what you think it means, Ralph! 😂 Very useful info, thank you!
Less than an hour, in my book. In fact this was less than half an hour. Hardly worth making, it was so short. 🤣😁
😁😁😁
Brilliant video, for getting started on non-blocking coding.
I am assuming that reading (and especially de-bouncing) buttons - without the use of delay() - will also be one of the upcoming examples on the state-machine list.
Sometimes I need to have buttons de-bounced, both when they are pressed and released. I find that is a good job to define via a state-machine.
Well, I'd probably be more inclined to have a "readButton" function that does all the debouncing but we will see.
@@RalphBacon I did think to put the state-machine into the function "readButton", so the main loop, can still consist of a list of function calls.
One of the cleraest way of explanation I've ever heard and not just this video, but all of them. Thank you Ralph!
Wish we had teachers like you in school - would have gotten much better grades for sure. :)
Glad it was helpful!
What would happen when millis() is called after 60 days? Edit - I discovered becuase it's unsigned it'll just overflow to 0 and the subtraction method will still work just fine
Exactly so!
The timing would not likely be 500ms though. It should use a signed variable to maintain timing.
Cool video, IMO using object oriented code can make this sort of program much cleaner, as you wouldn't need to repeat the state machine logic code for every instance you want to create
If you are using C rather than C++ then classes and such doesn't exist so it depends what your compiler is.
No beginner understands OOP so I'll be giving that a miss for now. This is still very clean _and maintainable_ code. Also, this demo flashed LEDs but in the Real World I hope we do more than that!
Great Video !! Well explained!! I hope there are more parts to come. Up to a real State Machine.
That's the plan!
Great stuff Ralph! For 5 bonus points code how you deal with the millis() rolling over...
It already deals with the rollover just as it stands. That was an easy 5 points.
@@RalphBacon yes, but here is a fuller explanation ... The question often comes up in conversations about signed Vs unsigned integer calculations: what happens when the max value is reached and goes negative if incremented. As any assembly programmer should know, the compiler generates the same code for both signed and unsigned. Let that sink in and you will realise the it MUST still work.This is the beauty of twos-complement!
A wonderful video, Ralph. The comments demonstrate its efficacy by the fact that viewers have started thinking out of the blink sketch box. The important thing to take away from the loop you showed is that other tasks can be added to the loop by adding another function into the loop. Of course, just as with intercepts, one can't use too much time in that function. However, the added task could be broken up into smaller bits. An example: say you have an LCD and a real time clock (RTC) chip and you want to change the display of time once a second; but you find that each time that function 'activates' the procedure, the pattern of the LEDs stutters. In that case, you would have the function read the RTC and save the value in a static variable and sets a static flag. The nest time the function is called by the loop it checks the flag (in truth, the function checks the flag every time it is called) and ignores the millis count but changes the display to reflect the value that was saved last time and clears the flag. Thus, the two blink functions get their chance to check the millis count in the middle of your task.
Wouldn't an interrupt be far more superior yo implement that scenario? One that either frequently reads from the RTC or even better if wired properly uses the RTC as the interrupt source.
Of course, the more "work" we do in (or call from) the loop the less time there is to go around. But the next stage of this multi-tasking approach is to do "bits" of each function for a short time but return to the same point on the next invocation - hence the 'state' of each function must be known.
But there is nothing to stop us calling functions like this:
A ⬅
B
C
A ⬅
D
E
A ⬅
F
G
where function A is time-critical and must run more often.
Ultimately, a true multitasking system will only ever allow each function a maximum of (say) 1mS of run-time before switching context to the next function (round-robin approach). But that has its drawbacks too which you alluded to. And running a critical function at a higher priority just starves lower priority tasks.
I had to take into account all this with my ESP32 Web Radio that streams the audio from the Internet, buffers that data, passes the data to the MP3 decoder, updates the screen, gets user input... the list goes on!
Coding, ain't it wonderful?
Cool as always. You need to take advantage of the pcbway perks and design a custom uno board that people can buy and populate themselves. I would love to have that.
I love the proper practices scope, encapsulation, millis.
I rarely write my code in the loop. It's usually a series of function calls. I love your videos though as I don't code as much as I used to and you're sharp. No one else introduces this stuff to people. Thank you.
Thanks for your kind words. I have ideas for a couple more videos that might help people write better code. Stay tuned!
Always have trouble getting a grip of this ....thanks...look forward to next installment.
I hope that after this video, at least the first (multitasking) step should be pretty easy, Jorgo?
Thanks for the lesson. I'm new to Arduino and I haven't written any C/C++ code since the 90s! So, I'm really finding this a great help to get up to speed on some recommended tricks and techniques. Right now I'm keen to see how much can be done with a single Arduino. Seems like we could control many devices with this technique. Cheers!
You're very welcome!
Great video! I've been using pseudo multitasking on Arduino's, ESP8266's and ESP32's for years but learned a few things from this video (Ie. the use of Static). I'm glad you pointed out that this is not true multi-tasking as that is often mistaken when discussing this with the Arduino/C++ coded devices. It would be interested to have a discussion of true multi-tasking with the dual processor ESP32 but that probably would be a fairly advanced topic?
I'm not sure what the fascination is with "true multitasking" versus pseudo-multitasking using time-slicing.
Yes, using both cores on the ESP32 is a possibility for true multi-tasking but then you run the risk of crashing Wi-Fi or BT or something on Core 0. We're not running NASA here, so why the fascination?
That all said, I did a video on simple dual core multitasking on an ESP32 here in video #149: ua-cam.com/video/jpVcCmh8sig/v-deo.html and on passing values between tasks in video #151: ua-cam.com/video/ywbq1qR-fY0/v-deo.html
But none of my Real World ESP32 projects use both cores as application cores.
Timer interrupts... 😀
That's in the next video #BB6 using the RTOS for Arduino.
great video and a very good explaination of static and global commands in a program I think 😄
Glad you liked it!
@@RalphBacon I did like it of course understanding it is another thing😁
My choice of words was deliberate! 🤭
Another Great video. I've seen static mentioned in some sample programs but never understood it. Thanks, it will be very useful. State Machine lecture Please.
Glad it was helpful!
This is primitive enought to be very applicable to an ATtiny... The ATmega328 is capable of running freeRTOS which is worth the investment in the learning curve. As long as your project does not need a huge amount of code. I finally got freeRTOS running on the 32MHz LGT8F328 which is nice - the extra MHz more than make up for the overhead of the RTOS. A state machine is also a great idea on the ESP8266 which does not have freeRTOS support, although the "TICKER" library offers a simpler solution for simple projects. The ESP32 family has freeRTOS built-in and it should be used for projects of any complexity. Especially the dual-core models like the 32 and the 32-S3.
still looking for someone who knows how to run ESP-NOW and WiFi Webclient on the same MCU.... works on the ESP8266 but not on the 32s, strangely enough.
Keep up the good work, Ralph, you stimulate beginners to go on to bigger and better as I discussed above.
Greetings from Canada.
Hello to Canada! I'm very glad I inspire you to do more, after watching my videos. My work here is done!
As a retired ex HW engineer I have decided to play with Arduino and after the first exercise I was stuck as I could not “accept” an infinite loop. I started to look for resources till I found your video. It is great, it has answered in a very clear way to all my doubts. Thank you for your clarity. This should become something that the Arduino team should explain to all beginners.
Glad I could help!
Hello. I really like your videos. I'm really new to Arduino but not in programming. I have a question. Is calling the functions many many times "for nothing" in the loop using more power? I'm thinking of battery powered projects. Would it be better if we put a delay of 100 ms in the loop? Thanks for your great channel.
Whether the loop is called thousands of times a second, or you put in a "delay" (which is an even tighter loop) uses the same power.
If you _know_ you have nothing to do for a while, the best approach is to put the microcontroller to sleep; essential in battery powered projects.
I've done a few videos on Deep Sleep and the Arduino, have a look!
@@RalphBacon Thank you. I will surely watch them.
A "state machine" does not multi-task. A state machine has "states", a transition function, and an implicit "clock." I think what you're doing is "polling."
OH NO. I was just fed a YT link to another RSB vid, which seems to acknowledge what I said. So shame on me for having responded to this 24-min vid without having watched the next one.
Well, yes, the first vid, was as the title stated, "moving _towards_ an FSM" and was indeed polling. Sometimes this is all you need. But it is a logical step towards an FSM which is also, sometimes, what you need too!
Excellent content, thank you! In times of inflation, 15 minutes can become 24, no problem 😊
Very true! When I say "15" that's _Arduino_ minutes which, as everyone knows, is longer than a Real World minute 🤣
My first HW state machine was an prom and a latch (back in the TTL days). Clicked on this video to see if you had something easier to read than: switch (current State) {
Waiting to see your next video😊
That is awesome!
So you used the floating MOSFETs in a PROM for a counter, or something?
Let's see now. 16-bit PROMs with 16 address lines (64K words of storage, I presume). Bring the PROM data lines out to a 16-bit latch, then connect the sixteen latch outputs back to the PROM address lines.
But what's coming out of the PROM data lines? I guess we would need to "burn fuses" there first. Each location would contain the next memory location to be accessed. First location (zero) put 0001, next location (one) put 0002 and so on. A programmable counter.
As a State Machine. 🎇✨🌟
@@RalphBacon not so complicated. The latch holds the current state. Feed the outputs of the latch to the prom's address lines along with the inputs to the state machine. Wrap the outputs of the prom back to the inputs to the latch (this represents the next state number). Program the prom so that at the address of the current state, with the inputs to the state machine the prom holds the next state number. Each time you strobe the latch it will move from the current state to the next. Speed is only limited to the speed of the prom, sub microseconds. Pre FPGA's and cheap microcontrollers it worked.
Awesome. The good old days. Well, maybe not, in this case. 😁
Thank you! Seems silly NOW to move the millis() value into the "current time" as most do , where you just utilizing the mills() in the IF statement to compare it to the last time the IF statement was executed. Every one teaching on UA-cam has created the extra variable "current time". I will be following you. Thank you Sir! I will be studying the "static" and how the compiler does stuff with it during optimization.
Glad it helped!
@@RalphBacon
I like this simple use of comparing millis but, what about when the clock rolls back to zero? If the capture of the millis is at the end of the clock and rolls over to zero shortly after, the “if” statement will never execute again because the millis compare will never be greater than 500, or whatever value you have.
I seem to remember this type of thing was called "timeslicing" back in the distant past.
Pretty much!
It was a lifesaver when I found the millis function, I have been using it for years but now I am more into timer interrupts.
Timer interrupts are good for the Arduino. Tasks are (much) better for the ESP32, though.
Ralph, I've been struggling with sorting out this technique for several projects. You have clarified a programming concept I've been looking for a long time. Thanks! thanks! thanks!
You are welcome! I'll expand on this topic in a future video.
@@RalphBacon I'm looking forward to more on this.
very helpful, but please keep the videos to the point, it will make it easier to watch.
Sorry, I was distract------- squirrel!!!
Quite good training indeed. Thank you for the time and effort you put into this.
Glad you enjoyed it!
Nice video, this is how i started with arduino 10 years ago. after that i made my own library that can increase or decrease value(s) without blocking. this way i can easly use PWM or servo's with Scene time and fadetime. and 3 years ago i also added sin to it to make it more smooth.
Cool. Sounds great Emile 👍
What about digitalWrite and read taking some ms to complete in both functions, they will take it from 500/200 ms check. Isnt it?
digitalWrite/Read are relatively slow as they carry out several checks (safety checks for beginner coders). You can speed them up by setting the relevant registers (eg PORTC). That will hardly take any time at all.
@@RalphBacon Even doing such checks digitalWrite is faaar faster than that... Assembly for them should not have more than 30 instructions... Most uC do one instruction in 1-3 CPU cycles, so even 1MHz CPU can do about 500 instructions in ONE ms. Notice that slowest uC has at least 8 MHz - so it should do at least houdred digitalWrite() per millisecond. For blinking it's overkill.
you need almost 300 digitalWrite to waste one millisecond
I get the heebie-jeebies whenever I read code that has an implicit reliance on time or the specific hardware. We're dealing with C++. Functions can be overwritten by, for example, a function that invokes an actuator ("Open the door, Hal") that operates in realworld time, not in CPU cycles. If we rely on the speed of the processor, we're not doing a good job at abstraction.
Ralph, You almost have a state machine, you have two independent loops, my understanding of a state machine, is nothing moves to the next state until a condition is met, something like this;
//Define the states of the machine
#define LED_OFF 0
#define LED_ON 1
uint8_t fsm_state;
void setup() {
fsm_state = LED_OFF;// beginning state
}
void loop(){
//state machine
switch (fsm_state)
{
case LED_OFF: //Statements to execute every time LED_OFF is reached
digitalWrite(13, LOW);
if (digitalRead(13)==LOW) { // verify output is low
fsm_state = LED_ON;// the state condition is met, change state
break;
}else{
fsm_state = LED_OFF;//continue waiting for condition to change
break;
}
case LED_ON: //Statements to execute every time LED_ON is reached
digitalWrite(13, HIGH);
if(digitalRead(13)==HIGH) { // verify output is high
fsm_state = LED_OFF;// the state condition is met, change state
break;
}else{
fsm_state = LED_ON;//continue waiting for condition to change state
break;
}
default:
break;
}
delay(1000); // wait for a second
}
Now stop skipping ahead, Jeff 😜 I'll be doing a _simple_ State Machine in the same vein as what you say but wait!
@@RalphBacon Sorry Ralph
I thought it was about RTOS.
Well, in a way this leads up to that. But we're some way off at the moment.
@@RalphBacon As close to a rtos your going to get on a uno : )
Pro code right here! Thanks for the lesson!
You're welcome!
Ooo that's interesting, I can use this on my boat automation project.
Quite possibly. If you need to do more than one thing at a time this is the way to do it (on an Arduino).
@@RalphBacon I'll be using esp32
Do a proper state machine. please...
All in the plan.
I've just found your channel and I'm enjoying your videos very much indeed!
My first introduction to Arduino-esque non-blocking code was the example sketch 'BlinkWthoutDelay' that's bundled in with the IDE.
Welcome aboard! Yes, the Blink-Without-Delay is a good intro to only carrying out tasks after a predetermined time. Not quite multi-tasking but getting there, and could be "enough" for many projects.
Wow ! I self taught myself in C+ and didn’t know about static variable or the ! ‘trick’. Most of my Esp8266s use Blynk which requires keeping the loop clean, thus the extensive use of timers. Looking forward to the next video. Is that push button going to be used as an interrupt ?
The push button (and yellow LED) will be used to further develop the State Machine code. Stay tuned! Or subscribe!
I know you stated "no bit manipulation", but the first solution I thought was:
Leds on PD0 and PD3:
void setup(){
DDRD=255;
}
void loop(){
PORTD ++;
delay(300);
}
Well, you've broken the rules (admittedly, my own rules) but if it works then it works!
Genius! I'd love to know more.
All in good time more will be forthcoming.
Dear Ralph, I installed VS code and the paltfomIO extension. I was able to run this code and even make some modifications for views in the thermonal. However, after closing the project and VS code and reopening VS code, the PlatformIO icon no longer appears.
I've done everything, reinstalled, PlatIO and VSC and nothing. I made a thousand queries in Git and found that there are dozens of cases opening with the same problems. Please do you have any tips so I can reset PlatIO in VSC? I found your explanation very interesting, saying that the compiler only uses the static variable once inside the if() loop. Congratulations!
My PlatformIO (alien head) icon appears several (long) seconds after opening Visual Studio Code. It's an add-in, after all. Click on the extensions icon (4 square boxes) and ensure that "Platformio IDE" is enabled globally and running.
After that let me know if it's working or not.
Good sensible explanations.
Glad you think so!
Hi, just found your channel, this video is really useful for my projects since I'm always seeing projects using millis() but didn't know exactly how it worked. Thanks!
Glad it was helpful! Feel free to subscribe so you don't miss the next video (end of shameful plug) 😁
Good video, I can do wonders with plc ladder logic, program blocks,register manipulation etc but when it comes to C+ and words and punctuation I'm lost, it's taken 10 years to flash an LED 😂
Just 10 years? Well, maybe your next sketch will be completed a bit sooner 😁
Nice job Ralph. This is probably one of most useful thing newcomers to embedded programming can learn.
Glad it was helpful!
Paused: I did this on a project a few years ago; you create a loop, save the current millis() in a seperate variable for each timed activity and then go round the loop subtracting the saved value from the current value of millis() until the difference is the time required. You then reset the saved millis to the current, and go on to check the next variable. Using this technique I was able to get a single arduino to take timed photos with a jpeg camera, and send them off to a phobe via a GSM modem, using the timer to time the pictures, handle the serial communication with the GSM modem, and read various sensors and battery monitors. It would have been quicker to use a raspberry pi, but the friend I was doing the software for wanted to make a dozen, and the cost would have been too high! It worked fine in the end.
I'm glad it worked well (in the end). Without this simple technique I could not have written my ESP32 Web Radio, although admittedly that uses a more developed state machine concept and even a couple of extra tasks.
Not having blocking functions and in this case, using a timer, is good programming practice and you have explained it well. I have never used static before and used global variables as counters triggered from a timer, it works but not ideal. Look forward to your next video and implementing states machines as never really understood them.
Using timer-driven tasks is another concept (let's face it, using FreeRTOS to run tasks is exactly that) but not just yet, Crawl before we walk, right?
Ralph is this part of the code explicitly necessary for this to code to work? static unsigned long redMillis = millis(); Couldn't one just declare the variable in the beginning equal to zero. unsigned long redMillis = 0; this would be done in the setup loop or when declaring the variable. Then the redMillis = millis(); in the if function would update it properly? I liked the introduction of the static modifier but don't really see a benefit. Unless the main benefit is for readability. Being able to set a variable once within another part of code looks great from readability standpoint.
If the variable were declared as a _global_ variable and initialised in the setup() and then modified in the function, that would work. But!
But I dislike global variables because their scope is, well, global! By using the _static_ keyword from within the function that it is being used in, it means that the scope is restricted to that function - and it's "just a snapshot", not an important, global variable (like the time), after all.
I would like to debate what the static does in a compiler ;) Because it sure makes it just as "bad" as globals in that sense :) ... static just makes sure the compiler doesn't optimize it out AND destroy it after it leaves context because you indicate it will be referenced and or update outside of the compilers scope ( like a bit of inline assembly in ISR s) ps: or reentry but defining static would only upset linters in scopes but effectively it creates a global. I would need to check though.. But else there would be conditional branching in the function to check if the function is called the first time :D
It can't be "as bad as globals" because you can't reference the variable anywhere except in the function in which it was declared.
You are correct inasmuch that the compiler does not include it in the scope of the function it was declared in, so it is available, untouched, the next time the function is called. Technically, the scope of the variable is as long as the executable runs for; but access to the variable is restricted to the instantiating function.
The compiler tries to initialise static variables at compile time; but if it cannot it initialises them at run time before the main() function runs. It would make sense to initialise the static oldMillis variable with zero so the compiler can initialise it.
Thank you for the millis inclusion for pseudo state operation on an Arduino. I have to think about an LDR to start the millis counter to flash LEDs for a period of time then stop until the LDR detects nightfall again. (Two red LEDs hanging in a tree at Halloween to simulate a critter looking down on you.)
Sounds scary 👀
Rather than repeating the code snippet over and over again, I think I would just create a class called "IntervalTimer" that has a constructor which takes the interval time. The class has a Poll() method that you call in the loop and returns true when the timer has expired (and resets internally when that occurs). Then create two instances of that class, one called "redIntervalTimer" and one called "greenIntervalTimer". Better yet, I would create an additional constructor that accepts a lambda that is the action.
As soon as you mentioned the word "class" it told me this video was way below your pay grade. Beginners have no idea what a class is or how to use one.
@@RalphBacon And then I mentioned "lambda" :). Fair point, although judging from the comments, your followers seem to have a fairly wide range of experience. Well then, I suppose we can view my comment as "an exercise for the interested reader" then! :)
A very good answer. A bit like a teacher saying "I'll leave it to you to read more about OOP in your own time, class!" Yeah, like that's ever going to happen.
@@RalphBacon Seriously though, and judging by the comments, I do think many of your followers are more sophisticated than you might think. In addition, I would hope that beginners who mainly use libraries ought to learn at some point that they are making an "instance" of something based on a "class" definition (BTW, I may have "reinvented" the "PollingTimer" library so I might suggest that beginners examine that library after watching your video).
After all a "sketch" is C++ so why not take advantage of the "++"? I gather that you will eventually get to discussing the notion of a "class" and "instance" at some point. At least I hope so! :)
BTW, I really enjoy your videos and the way you approach things, wish we lived in the same neighborhood! :)
Hi Ralph, another seasoned coder here. I’m glad you are showing these techniques (and I love how you saved yourself a variable by reading the state of the LED rather than drive it from a Boolean). At some point down the road it could be an interesting construct to introduce power management techniques. Eg if the next required state change is not due for x millis then either shut down the main core while pwm runs, or adjust the clock speed to match the requirements of the states that are in the set of states that are under current consideration.
Power management techniques could be included, if there is "nothing to do", so in effect we are just idling. Yes, in a battery-powered device every millisecond asleep is another millisecond we can run on power.
Very good video! I think the next step into a state machine is to use a state variable instead of digitalRead. After that, show how to make the on and off-times different for a LED.
I want to show some Real World use of a State Machine; using one to record the state of the LED is not necessarily the best use as we can do _that_ the way I've already done it.
Better use would be to be able to exit (and re-enter at the same point) the function between states (assuming there are some, not yet in the demo I showed).
I'm an experience developer, and I've used C++ for years in the past, and have used to state machines in the past to solve various problems, but it took me more than 10 minutes to solve my state machine problem. Mostly because of complications of C++ compared to Python and general debugging issues, as well as figuring out my state machine!
I think most developers (pro or bedroom) would be happy to solve a coding issue in just 10 minutes! So go for the small wins!
I very much like those "shorts" not like the others in youtube... 24 minutes is short in that kind of videos (for me)...
This video overran. But I think it was worth the extra time.
learnt about usage of static variables
Yes, always useful to know about them.
Me too.
Static local variable tip was really important and I think should help resolve an issue in some code I was looking at a while back, thanks.
Anything that makes your code better means my work here is done!
Nice. I am intrigued by the button and yellow led. Interrupt example?
No spoilers but it's still to do with moving to a State Machine.
Thanks Ralph - very informative ..you are the Champ!
Ooh, I like that: champ Ralph 😁
Could you make a video where you can make a button function as a switch and a second button to change which device it enables/disabled? I can’t seem to find a good tutorial on something like that yet it seem like a simple task. Thanks
Remember that the button doesn't do the actual switching; it's your microcontroller that decides what "thing" to switch. So if you detect a button push, then decide from the second button (state) which "thing" to switch all will be well.
My next video on State Machines is due in a couple of weeks or so, and uses a button, so you may get some ideas from that.
This looks like an example of cooperative multi-tasking to me. I'd say you are not adding a state machine until part 2.
Yes, it's step 1 in getting to (and supporting) what a FSM can do.
Some techniques I haven't used in many years, now that I am a java programmer. You always explain things so well.
Glad it helped. My most recent project uses FSM methodology.
Very rudimentary. Would hardly call it a state-machine yet.
Your explanation deals more with *multi tasking* than with *state machines* . They are different concepts.
In the example you have *2 tasks* (two objects) and each task (object) has *2 states* (LED-ON/LED-OFF)
You are kinda hiding the state machine concept by writing :
digitalWrite(RedLED, !digitalRead(RedLED) ) ;
it obfusactes the fact that
when STATE-RedLED == ON... -> switch it OFF (and it becomes state ON)
when STATE-RedLED == OFF -> switch it ON (and it becomes state OFF ... again)
Yep.. @21:00 🙂
The "state" of the system is held, in this case, by the millis timer/counter AND the two io pins.
"Very rudimentary". Excellent, just what I was aiming for. Beginners should be able to grasp the simple concept without any problems. 😁
This is something i've been trying to do off and on for 2 months ! this is going to help massively thanks for the content!
Great to hear!
Im still wondering how arduino manage to drive 3 steppers plus display plus hot plate and nozzle at the same time in Marlin or smilar 3d codes?
Because it is a fast processor! 16MHz clock, one or two clock cycles per instructions... it can get through quite a bit of work in a millisecond! Oh, and some really, really tight aka efficient programming, of course.
Variabels - you're making words up again.
British English is the best. Vary-Abbles. Sounds fine to me.
Of course, once you're done with this State Machine mini-series you will revisit this setup with the Timers->Interrupts->ISR approach, won't you?
Interesting you should say that...
@@RalphBacon ... or maybe not, since you've done it already not so long ago. My bad for not paying attention!
ua-cam.com/video/fFrL5Vh8Dis/v-deo.html
Hmm, for some reason I cannot see your reply to my response but you mentioned that I'd already done it and I forgot to paste in the link to the video in my first reply... TL;DR here's the missing link:
video #209 Arduino Timer Interrupts ua-cam.com/video/fFrL5Vh8Dis/v-deo.html
BTW did you notice the bit manipulation we had to do in that video? No easy Arduino-speak and no-one has invented a library for it yet - although *Norman Dunbar* has *AVRAssist* which at least does all the hard work for you:
github.com/normandunbar/avrassist
@@RalphBacon Yeah, my reply had a link to the exact same video you pointed out. Maybe UA-cam has a thing against linking. However I can see the one you posted just fine (probably because you're the OP, therefore more trustworthy in YT's eyes).
I just re-watched that video and frankly that bit-magic is not that scary once you know what's behind it. I went through all that 30 years ago in college when I had my first programming courses (general C / C++ and also some microcontroller stuff).
Anyway, I really like the way you handle the educational approach compared to other resources that tell you the WHAT but not the WHY.
Your name is a great component of second breakfast! Much appreciate all your hard work to help teach those of us whom hobby our hobbies.
Thank you very much!
Just found your video series. Thank you. I need all the help you offer
Happy to help!
"short video"...is almost half an hour =D lmao, but I love it
Glad you enjoyed! Sorry it overran!
For my conclusion, we can use time flow rather than work flow to make an arduino run multiple task simultaneously 😅
"...to make an arduino APPEAR to run multiple tasks simultaneously".
Great Video Ralph - Reinforces use of Functions
Well, we don't want huge big monolithic loops, do we?
12:30 Could you elaborate a bit more what the problem is with defining those global variables? That is the way I always work and to be honest I don't understand why that is such a problem. I'm only an amateur but keen to lean :)
I've ranted before about global variables but here goes.
Although I (tongue-in-cheek) call them the Spawn of the Devil, that's not strictly true. I sometimes use global variables IF they are being used globally; that is, by more than one function.
But variables, in general, should be restricted in their visibility (and, hence, use) by defining them in the function (or, better still, namespace) to which they belong. That way, they are not arbitrarily changed by functions which have no business using them, let alone updating them.
It's to ensure your code is "cleaner". For example, if you were to refactor (refine, rewrite) one of your functions by removing it and adding it to a different namespace, would the rest of your code throw a hissy fit at not finding a variable any more?
So, put logically connected functions into one file. Include that file into the main sketch with the use of the #include statement. Ensure that file has a namespace so that you can't just access its functions or variables without also specifying the namespace. See my simple videos on namespaces if this is not clear to you!
Real World Example: you are reading a temperature sensor. Chances are, that you want other functions to be able to know what the current temperature is (eg, to display it, or take action when it reaches a certain level). So should this variable (let's call it "currTemperature") be visible to all functions in your sketch?
Not if you want to do a good job. The functions that are to do with the temperature sensor might be in a namespace call "sensor". So that variable is now referred to, by the rest of the sketch, as "sensor::currTemperature". But it is not global, and it should be very clear in the code that you are referring to the variable in the "sensor" namespace.
TL;DR I covered all this in various videos before! Grab the pdf file of all my videos and search for ones that cover this topic. Worth understanding the concept, at least!
@@RalphBacon Thanks so much, this provides a good starting point for understanding the namespace concept better. I will definitely check out your other video's for this topic!
Thanks very informative leaves me wanting more information
So you'll be back then? See you in the next video (not about State Machines).
“Get on your bike” I love Britishisms 😁
"Sling your hook" is another one (with the same meaning).