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Forum Index : Microcontroller and PC projects : Possible bug in CONST operation.
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| Andy-g0poy Regular Member  Joined: 07/03/2023 Location: United KingdomPosts: 59 |
I seem to have run into a buggette with the use of CONST I have been converting a state machine version of a rotary encoder program to mmbasic, which is working fine. (I just did not use the const type) To keep things tidy, I decided to put the various setups and inits in a subroutine, and just call that subroutine from the main program. This keeps the clutter in the main program down, and showed up the problem. A short test program running mmbasic V5.0707 on pico start: init_enc print " in start dt is " dt% print " clk start is " clk% print " state% is" ,state% end sub init_enc const dt% = 19 'gp14 const clk% = 20 'gp15 SetPin clk%, DIN SetPin dt%, Din print "in sub dt is ",dt% print "in sub clk is ",clk% state% = port(dt%,2) end sub output is: RUN in sub dt is 19 in sub clk is 20 in start dt is 0 clk start is 0 state% is 0 The value of the constants clk and dt have NOT been passed back to the main program. Remove the const declaration and the output is as expected. in sub dt is 19 in sub clk is 20 in start dt is 19 clk start is 20 state% is 0 it's as if the const is acting as a local variable within the subroutine. I don't think I am doing anything silly... Andy |
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| toml_12953 Guru  Joined: 13/02/2015 Location: United StatesPosts: 339 |
I would expect that if you define them in a sub, they're local to the sub, constants or not. If you want them to be global, you have to define them in the main program. Edited 2023-07-30 12:40 by toml_12953 |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2136 |
Edited 2023-07-30 15:09 by phil99 |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
If you are wanting to set CONST values conditionally then why not put them in a subroutine and use GOSUB? It may be considered old-fashioned but it works with globals. You can use labels: 'k% selects the set to use. It is only set once and cannot be changed within the program. const k%=1 if k%=0 then gosub cz1 else gosub cz2 main: DO ........ LOOP END '---------------------------- cz1: const speed = 45 const led = RGB(blue) return cz2: const speed = 33.33 const led = RGB(red) return . Edited 2023-07-30 17:00 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| flip Senior Member  Joined: 18/07/2016 Location: AustraliaPosts: 114 |
That's a neat idea Mick  .. a structured way of achieving multiple config settings within same file... excellent case for keeping GOSUB...RETURN.I will be using that idea a lot once I make it work OK - doesn't seem to work for me in MM for DOS - after RETURNing from Sub, it loses the CONST value...will keep trying EDIT: I could be dreaming but I recall that some change was done to GOSUB...RETURN that made it behave differently so this capability was lost...maybe Geoff or Peter can confirm...and (hopefully please) reinstate?...but I don't trust my memory on this Phil Edited 2023-07-30 18:48 by flip |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
I must admit that I didn't test it. I can't see why the CONST values should be lost though. That doesn't make sense - unless GOSUB is being simulated by the SUB mechanism of MMBasic. Tested: You're quite right. It doesn't work for setting CONST values, but it does work with globals. Nasty gotcha. Easy enough to put a conditional jump at the beginning of the prog with several sets of CONST statements, I suppose. Not as neat though. Edited 2023-07-30 19:00 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3150 |
This is what I did in a program I worked on with Paul_L. We wrote very different parts--he wrote the guts and I wrote the interface. The parts were very separable, and to keep from mixing our constants and variables, in the initialization phase I put a goto with a return to main. goto LBDefinitions ' can't gosub--definitions would be local; returns with goto Main: Main: '========================================================================= Otherwise I'm a pretty strict "Go-to statement considered harmful" guy. ~ Edited 2023-07-30 22:11 by lizby PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
I don't mind GOTO and GOSUB providing they are used sensibly. They can even be used in structured programming if not abused. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| toml_12953 Guru Joined: 13/02/2015 Location: United StatesPosts: 339 |
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| Andy-g0poy Regular Member Joined: 07/03/2023 Location: United KingdomPosts: 59 |
Thanks, did not spot that bit I was looking at page 24 Variables and expressions. Andy |
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| Andy-g0poy Regular Member Joined: 07/03/2023 Location: United KingdomPosts: 59 |
It threw me for a while, mainly because I did not spot that this was the way it worked in the detail of the CONST (p89) I assumed that anything not tagged with LOCAL would be global even if in a subroutine. Dangers of making an assumption. What I wanted to do was create a method that would hold the setup info for a particular module which would keep it out of the way. The next module will be for a Si5351 and that will have a load of setup to do. Keeping the setup in a sub works fine, I will just have to remember not to use CONSTs Andy |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9128 |
You can put constants in the library, then they will always be available when you run your program as the library is run before other commands in your program Edited 2023-08-01 21:47 by matherp |
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| Andy-g0poy Regular Member Joined: 07/03/2023 Location: United KingdomPosts: 59 |
Maybe, but not what I really want. I've not looked at libraries much, and so far I cannot see how to load things into them externally, apart for write a program then convert it too a library and it all happens. Some of the code I've developing may well be used by others (it's a VFO for Amateur Radio use. So it is likely that different users will need to make various modifications to cater for how they build things and so on. So having each module with it's own setup is a much easier way to work. I don't think the library system is built with that use in mind. This all started when someone on the GQRP (low power communications) group posted a link to the pico VGA, I then discovered that there was a standard type mmbasic for the pico. I've been trying it out as a possible development system, and so far it's proving to be very good for general projects. It's turning out to be fast and very easy. (I can't stand Python generally, it gets be cursing at it in minutes, mainly due to the tab delimited blocks system so mmbasic looks to be a much better bet). This CONST issue is the first real hiccup that caught me out. It's very minor. I was using TWO constants only. As pointed out earlier basic did not have CONSTS so it's no real problem just to avoid using them - it was just a safety feature to prevent unintentional changes. Andy |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
How about using a config file and loading the variables that you need from that? Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Andy-g0poy Regular Member Joined: 07/03/2023 Location: United KingdomPosts: 59 |
Messy, and asking for trouble I think. It's not just variables. It just so happened that I used a CONST to define the pins assuming that this would be global, and if anyone tried to use the same name that they would get an error. I then found that the constant was local to the subroutine, hence this thread... I would use a config file if it was a lot of data, something that you would edit with a text editor such as memory channels (radio stuff) and read them into the program from an SD card. Which will happen later, as will various things for the GUI when I get around to it. This is really about config for various bit's of hardware etc. I started with the rotary encoder - now got that running nicely as a finite state machine with the improved table method. See: (last example in article) https://www.best-microcontroller-projects.com/rotary-encoder.html That needs: pins defined and interrupts to use a couple of variables the state table Once set up that's it, you would not normally need to touch it again. However someone else may need to use different pins or even a different encoder (this one is a half step) So a little tweaking would be needed. I was just trying for something that would be pretty much self contained and easy to use. (I dislike cluttering up the start of programs with loads of setup which you then have to skip over to get to the actual program) Another option inspired by the conversation here would be to use a set of gotos: Would need careful management, but could be done then all things would work. However using a subroutine call is a lot easier to manage. So I'll stick with that and avoid using CONSTs in it :-) Andy |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
Idea? 'Initialisation at end of program GOTO INIT Main: Do everything Loop End '---------------------- INIT: 'change the following to the encoder pins used CONST EncPinA = 1 CONST EncPinB = 2 'if elephants fly change the following to INIT2 GOTO INIT1 INIT1: something special here GOTO MAIN INIT2: something alternative GOTO MAIN . Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4043 |
Untested, but if you were feeling crazy I believe you could read the CONST statements as strings from DATA and then EXECUTE them, something like: Const config$ = "init1" Dim cmd$ Restore config$ Do Read cmd$ If cmd$ = "" Then Exit Do Execute cmd$ Loop ... End init1: DATA "CONST EncPinA = 1" DATA "CONST EncPinB = 2" DATA "" Best wishes, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Andy-g0poy Regular Member Joined: 07/03/2023 Location: United KingdomPosts: 59 |
Yes I was thinking of something similar. goto init_thing1 init_thing1_done: goto init_thing2 init_thing2_done: Main: Do everything Loop End init_thing1: do this that and the other goto init_thing1_done init_thing2: do this that and the other goto init_thing2_done This way you don't have to chain the various inits in a specific order. Just goto the name and the next line has a label that they come back to. But yes deffo for some time when feeling crazy.. mind you the SI5351 datasheets is enough to make your head spin :-) Andy |
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