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Forum Index : Microcontroller and PC projects : Memory issues
| Author | Message | ||||
karlelch Senior Member  Joined: 30/10/2014 Location: GermanyPosts: 172 |
Hi, I am getting the `Too many global variables` error and to solve that, I am wondering what counts as global variable? Identifiers declared with `Dim` and `Const` only? Or also `Static`? Thanks! Memory after the error: Program: 49K (36%) Program (1672 lines) 83K (64%) Free Library: 3K ( 2%) Library 129K (98%) Free Saved Variables: 16K (100%) Free RAM: 40K (24%) 272 Variables 5K ( 2%) General 115K (74%) Free My options: PicoMite MMBasic Version 5.08.00 OPTION AUTORUN ON OPTION LIBRARY_FLASH_SIZE 21000 OPTION COLOURCODE ON OPTION HEARTBEAT OFF OPTION CPUSPEED 252000 'KHz OPTION DISPLAY 64, 80 |
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Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
AFAIK all variables are global unless used as local. So, in a SUB: SUB something '(you can do the same in a FUNCTION) LOCAL a,b,c$ STATIC d e = 5 ... END SUB a,b and c$ are created with null values at the start of the sub and destroyed on leaving it. d is also created on first entering the SUB or FUNCTION but it's value is retained and is reloaded next time the SUB or FUNCTION is re-entered. It isn't a global variable and isn't available outside the sub or function. I assume it is stored in the variables area though. e is a global variable and it's value is changed. If you had used DIM or CONST to create a, b and c$ at the beginning of the program then those are global and are not affected by the LOCAL ones. Global variables exist until the program ends or CLEAR is used to get rid of them, or ERASE is used to get rid of arrays. Local variables are always transitory. It slows the program a little while they are created and destroyed, but it's a very efficient way to use the variable space. Edited 2024-02-04 06:59 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
Does a array count as one variable or many? If it counts as one group related variables in an array. eg. replace:- Dim Volts, Amps, Power.factor With Dim VAP(2) 'base 0 |
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| karlelch Senior Member Joined: 30/10/2014 Location: GermanyPosts: 172 |
Thank you for the detailed reply. Somehow I did not consider the static variables - I guess I thought they were not counted at global, but your explanation makes sense. I like static variables because they allow subs to “remember”, while being hidden from the global context. But the downside is that the program reaches the total number of global variables only when all subs and functions that use static variables at least once … In often called subs I sometimes make variables static instead of local to speed things up. But the gain in speed seems mostly marginal. |
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| karlelch Senior Member Joined: 30/10/2014 Location: GermanyPosts: 172 |
Yes, true. But then good programming style would call for constants to address the elements, e.g., const ID_VOLTS = 0 and VAP(ID_VOLTS) = 5.6, ending up with more global variables/constants then before  |
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| flip Senior Member Joined: 18/07/2016 Location: AustraliaPosts: 114 |
My 2c worth (not confident as haven't tested recently) STATIC (as they are permanent) have to occupy space for the life of the program, I guess first time the procedure is called. I remember for the Micromite and Geoff's MM for Windows(DOS/text), the STATIC modifier prefixes the varname with the procname,(and can be seen globally) which can be useful.(occupies permanent space)...maybe can free up with ERASE {procname}{varname} ?? I think DIM can be assigned in a procedure, but CONST had some issue when the same one exists in two procedures. But in any case ERASE can free up variable-namespace. (which makes me wonder does ERASE work with CONSTs...) Maybe needs testing to prove some of these things? Regards Phil |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
I doubt if there's much difference in speed between LOCAL and STATIC. For LOCAL: enter routine create variable with null value ... destroy variable exit For STATIC: enter routine look up name of static variable load static variable ... update static variable value exit STATIC may even be slower. Not tested this. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| karlelch Senior Member Joined: 30/10/2014 Location: GermanyPosts: 172 |
Interesting - thanks for the hint. I’ll have a look. In my programs I tend to use many constants to make the code readable and adaptable. So a great solution would be constants that ”don’t eat bread”. Like #define in C. But that’s not compatible with the interpreter approach. Best Thomas |
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| karlelch Senior Member Joined: 30/10/2014 Location: GermanyPosts: 172 |
I measured it for a few cases. In my experience, local for arrays seems a bit slower, but as I said, the difference is marginal. Static instead of local for simple variables does not seem to make a difference. |
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| flip Senior Member Joined: 18/07/2016 Location: AustraliaPosts: 114 |
Sorry got ideas stuck in my head and have to continue probing the edge Bear in mind all this is using it at boundary cases / dodgily and WILL reduce readability / maintainability, I'm just playing to get understanding what does / does not cause problems..checking a couple of things at once as follows: CONST foo="Initial Value" Output:Sub RedefConstInProcDoesntWork 'But ERASE does, also Static Var can become visible Static Integer Var=1 ?"Var (in proc)=";var ERASE foo CONST foo="FOO" End Sub ? "foo=";foo '? RedefConstInProcDoesntWorkVar 'if you look at variable BEFORE running procedure, it breaks your procedure, i.e. this is BAD outside USE OF STATIC Var RedefConstInProcDoesntWork ? "Proc Erases foo but doesn't set to new value, referencing foo returns value of default type:";foo ERASE foo CONST foo="foo" ?"foo=";foo ? "Globally visible local var =";RedefConstInProcDoesntWorkVar;" works!" foo=Initial Value Var (in proc)= 1 Proc Erases foo but doesn't set to new value, referencing foo returns value of default type: 0 foo=foo Globally visible local var = 1 works! (Geoff's MMBASIC for DOS/Windows (Text-based) EDIT - In terms of speed I'd have thought that STATIC only defines the variable once, and doesn't need to create/erase every invocation of procedure.But maybe number of variables becomes a slowing factor at runtime Regards Phil Edited 2024-02-04 08:52 by flip |
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thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4039 |
IIRC from my work on MMB4L: - If you use CONST inside a fun/sub then it is local to that fun/sub. - You cannot declare a global CONST within a fun/sub. - You can DIM a global variable within a fun/sub. - Declaring a STATIC within a fun/sub creates both a global with the variable name prefixed by the fun/sub name AND also a local with the un-prefixed variable name. Every time you exit the fun/sub the value of the local is copied into the corresponding global (I'm guessing here). Every time you re-enter the fun/sub that local is again created with the value taken from the corresponding global, hence the "static" behaviour. Given the above I believe "globals" are: - all DIM variables - all CONST declared outside of fun/sub - all STATIC variables Best wishes, Tom Edited 2024-02-04 10:26 by thwill Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
Why guess ' DIM var0,var1,var2,var3,var4,var5,var6,var7,var8,var9,var10,var11,var12,var13,var14,var15 DIM var16,var17,var18,var19,var20,var21,var22,var23,var24,var25,var26,var27,var28,var29,var30,var31 DIM var32,var33,var34,var35,var36,var37,var38,var39,var40,var41,var42,var43,var44,var45,var46,var47 DIM var48,var49,var50,var51,var52,var53,var54,var55,var56,var57,var58,var59,var60,var61,var62,var63 DIM var64,var65,var66,var67,var68,var69,var70,var71,var72,var73,var74,var75,var76,var77,var78,var79 DIM var80,var81,var82,var83,var84,var85,var86,var87,var88,var89,var90,var91,var92,var93,var94,var95 DIM var96,var97,var98,var99,var100,var101,var102,var103,var104,var105,var106,var107,var108,var109,var110,var111 DIM var112,var113,var114,var115,var116,var117,var118,var119,var120,var121,var122,var123,var124,var125,var126,var127 DIM var128,var129,var130,var131,var132,var133,var134,var135,var136,var137,var138,var139,var140,var141,var142,var143 DIM var144,var145,var146,var147,var148,var149,var150,var151,var152,var153,var154,var155,var156,var157,var158,var159 DIM var160,var161,var162,var163,var164,var165,var166,var167,var168,var169,var170,var171,var172,var173,var174,var175 DIM var176,var177,var178,var179,var180,var181,var182,var183,var184,var185,var186,var187,var188,var189,var190,var191 DIM var192,var193,var194,var195,var196,var197,var198,var199,var200,var201,var202,var203,var204,var205,var206,var207 DIM var208,var209,var210,var211,var212,var213,var214,var215,var216,var217,var218,var219,var220,var221,var222,var223 DIM var224,var225,var226,var227,var228,var229,var230,var231,var232,var233,var234,var235,var236,var237,var238,var239 DIM var240,var241,var242,var243,var244,var245,var246,var247,var248,var249,var250 MEMORY testit MEMORY SUB testit LOCAL varx1,varx2,varx3,varx4,varx5, varx6 STATIC Svar1, Svar2 ', Svar3,Svar4 PRINT "sub run" END SUB Compare the two MEMORY results. The static variables get counted after the sub is run. Remove the comment in the static declarations and run again = error. edit: sorry about the wordwrap... Jim Edited 2024-02-04 11:51 by TassyJim VK7JH MMedit MMBasic Help |
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| karlelch Senior Member Joined: 30/10/2014 Location: GermanyPosts: 172 |
So true  Thanks for all of your input! That was very helpful. I already managed to change my code to free up some global variable slots. It was also interesting to learn that statics can be accessed globally ... Cheers Thomas |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
Very interesting. The manual describes STATIC variables as only being visible inside the SUB or FUNCTION, like a LOCAL. Obviously, they have to be stored somewhere so storing them in the variables area with a prefix makes sense. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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