A couple of questions regarding global variables

[deckingman]

Short version.

Q1 This guide https://duet3d.dozuki.com/Wiki/GCode_Meta_Commands talks about how to declare global variables but it doesn't say where to put that declaration. Would I be correct in assuming that I could add the relevant commands to the end of my config.g file for example?

Q2 The same guide states "Within a macro file, parameters that were passed to the macro (typically in the M98 command) can be retrieved using the syntax....." But the description of M98 https://duet3d.dozuki.com/Wiki/Gcode#Section_M98_Call_Macro_Subprogram makes no mention of how to pass parameters to a macro. Would I be correct in assuming that if I declare a global variable in config.g, then it will be automatically available within any macro or do I need to do something to pass the variable to the macro (and if so, what and how)?

Longer version

I have a number of macros (nozzle heat, purge, wipe and sections of my homing files) which move a number of gantries (XY, UV and AB) to the same fixed set of XY co-ordinates. But those XY co-ordinates might need to be "tweaked". Changing every co-ordinate, for every macro is a little tiresome (and prone to "fat finger syndrome") so I'd like to set those co-ordinates in one place. I.e. use global variables which be used by all gantries and all macros (e.g "left_pos" and "rear_pos" or some such names).

[jay_s_uk]

@deckingman said in A couple of questions regarding global variables:

that I could add the relevant commands to the end of my config.g file for example?

yes or in any other file. you could call another file that just allocates global variables (which would be tidier) but really they can be created from anywhere as long as its from before they are called.

@deckingman said in A couple of questions regarding global variables:

Within a macro file, parameters that were passed to the macro (typically in the M98 command) can be retrieved using the syntax

this is different to a global variable and allows a value to be passed to a macro without the need to populate a variable. e.g. G1 X1 passes the value 1 for axis X to the G1 command. I've not tried any yet so can't elaborate further but from your long description, a global variable sounds most appropriate for your use case

[deckingman]

@jay_s_uk Thanks. I like your idea of using a separate file to declare variables. I'll appreciate that in 6 months time when I need to change something but can't remember where I put it.

[OwenD]

As has been pointed out, you can declare the globals wherever you like, but of course you must ensure that you do so before you try to use them anywhere.
I always check if the global has already been created as I don't like seeing the errors if I run M98 P"0:/sys/config.g" for example.
It also ensures the global is reset in case I changed it in code somewhere.
In some cases I check for a null value, but in most cases that's probably not necessary.

if !exists(global.InputStart) || global.InputStart=null
	global InputStart=0
else 
	set global.InputStart=0
 
if !exists(global.InputEnd) || global.InputEnd=null
	global InputEnd=1
else
	set global.InputEnd=1

With regards to sending parameters using M98, it's pretty straight forward.
For example you might use it when there is a value you want to use from your slicer.
Here I pass an "S" and a "D" parameter taken from the slicer

M98 P"0:/macros/print/doPrimeLine" S[extrusion_multiplier] D[nozzle_diameter] F[filament_diameter] ; does prime line with calculated extrusion amount

In my macro I use the values passed thus
This macro also uses local variables which are freed once the macro has run.
It's a fair bit of overkill to do a prime line, but it was mainly a test bed for various methods

; 0:/macros/print/doPrimeLine
 
if state.currentTool = -1
	abort "No tool selected"
var ThisHeater = tools[state.currentTool].heaters[0] ; create local variable
if {heat.heaters[var.ThisHeater].state != "active"}
	abort "Heater " ^ var.ThisHeater ^ " on " ^ tools[state.currentTool].name ^ " not active"
if  {heat.heaters[var.ThisHeater].active < heat.coldExtrudeTemperature}
	abort "Heater " ^ var.ThisHeater ^ " on " ^ tools[state.currentTool].name ^ " set below min extrude temp"
if !exists(param.S)
	abort "no ""S"" (extrusion factor) parameter sent to macro in M98"
if !exists(param.D)
	abort "no ""D"" (nozzle diameter) parameter sent to macro in M98"
if !exists(param.F)
	abort "no ""F"" (filament diameter) parameter sent to macro in M98"
 
M116 ; wait for heaters to settle
 
var height = 0.2 ; create a variable then set it depending on slicer commanded position prior to calling this macro
if move.axes[2].machinePosition <= 0.4
	set var.height = move.axes[2].machinePosition
else
	set var.height = 0.3
 
var SF = 100
if param.S <=1 ; check if slicer sends percentage of 1 or 100
	set var.SF = param.S   ; extrusion multiplier as a percentage of 1
else
	set var.SF = param.S / 100
 
var FD = 1.75 ; set default filament diameter
set var.FD = param.F  ; but over write with slicer setting
 
; set start and end of move	in Y direction - X position will be set manually
var start = {move.axes[1].max -10 } ; extrude line start position
var end = {move.axes[1].min +10} ; extrude line end position
var l = var.start -  var.end ; calculated line length
var d = param.D ; nozzle diameter that is passed to macro as paramater
var amount = ((var.d*var.height*var.l) + (pi*((var.height/2)*(var.height/2))*var.l)) / (pi*((var.FD/2)*(var.FD/2))) * var.SF ; calculate how many mm of filament to extrude - Owen's calculation
echo "flow rate value " ^ var.SF ^ " with " ^ var.d ^ "mm nozzle, " ^  var.FD ^ "mm filament dia over " ^ var.l ^ "mm length = E" ^ var.amount ^ "mm"
M83 ; set relative extrusion
G1 X0 Y{var.start} Z{var.height} F1200 ; move to edge to wipe any oozed filament
G1 X0 Y{var.end}  F600 E{var.amount}; move and extrude
G1 X{var.d} ; move by one nozle width
G1  Y{var.start}  F600 E{var.amount}; move and extrude
G10 ; retract

[deckingman]

@owend Thanks. I always appreciate your replies. You have a good way of explaining things in a way that an old retired mechanical engineer can understand.

[OwenD]

@deckingman said in A couple of questions regarding global variables:

@owend Thanks. I always appreciate your replies. You have a good way of explaining things in a way that an old retired mechanical engineer can understand.

Ah well, I'm a welder by trade, so we're used to telling engineers how it "should have been done"
Sorry, couldn't help myself

[deckingman]

For the sake of completeness and for anyone stumbling on this thread in the future, and thanks to those who helped, I have created a macro called "declareGlobals". This macro contains:-

global left=64 ; 64mm from left hand edge
global rear=366; equal to Y max

I call this macro from my config.g file with :-

M98 P"0:/macros/declareGlobals.g"

In my "user macros", I then use commands such as:-

G1 X{global.left} U{global.left} A{global.left} F12000
G1 Y{global.rear} V{global.rear} B{global.rear} F12000

Which all works a treat. So if the position of my nozzle relative to my wiping strip changes (as it is apt to do when I modify things or swap hot ends), then all I have to do is set the variables "left" and "rear" to some other value and all gantries will move to the new position for any of the multiple macros which are affected.

Thanks again @jay_s_uk & @OwenD

[deckingman]

Just a quick update on this. Having slept on it, I'm not sure if putting the variable declarations into a separate file is quite such a good idea. The reason being that if I make changes to those global variables (i.e edit the macro and save it) I must remember to run that macro again because the changes only get applied when the macro is run and not when it's saved. The same thing applies if the variables are set in config.g but at least I get a prompt and config.g will get run "automatically" again if any changes are made to it, whereas this doesn't happen when changes are made to any other macro.

I'll leave it for now and I've put a comment in the macro in big bold letters to remind me to always run it if any changes are made. But I suspect it might come back to bite me at some point in the future.

[o_lampe]

@deckingman you could also add a trigger event to the end of the macro which asks you to rerun it or not.

[deckingman]

@o_lampe said in A couple of questions regarding global variables:

@deckingman you could also add a trigger event to the end of the macro which asks you to rerun it or not.

Now that's a brilliant idea!. How would I go about adding such a trigger?

[o_lampe]

@deckingman there's an option to add external trigger or use the touchpad of a PanelDue

[jay_s_uk]

@o_lampe i suppose the only issue there is remembering to run the macro once you've edited it.
You'd also have to include the checks that @OwenD mentioned so you don't get errors

[o_lampe]

@jay_s_uk
I'm struggling to find the right command which pops up a question and asks you to confirm or cancel.

[jay_s_uk]

@o_lampe M291

[OwenD]

@deckingman
I'm going to have a bit of a rant, but it's not aimed at you specifically, it's more an observation given the embryonic state of people using conditional code on printers.

I still feel the best way is have a section in config.g where you put all your global variables.
I also feel checking if the global exists is important not just from the point of view of avoiding console errors.
It is equally important to ensure that any temporary alteration to that global is returned to the default on a restart.
Putting the code in config.g handles that most completely and easily.
As you've deducted, using a macro called from config only works if you then have a mechanism to ensure changes apply.
I guess you could check the file hash value from daemon.g, but why?
Some people feel doing such checks is "too much work", but the fact is that if you want to start using code, then you'd better start getting used to ensuring YOUR code handles unexpected events.
If YOUR code will except something to be in a certain state, then it's YOUR responsibility to ensure that is the case before your code executes.

I wonder if the guy that programmed the plc in your microwave said "meh - too much work to check the doors closed before starting... we know they're going to close it right?"

[deckingman]

@owend Fair comments I suppose. It's the mechanical engineer mentality thing vs software engineer thing again. If I adjust something mechanically, I tend to accept that the adjusting screw that I know I fitted earlier exists. I don't say to myself, "every time I want to turn this adjusting screw, I must check that I fitted this adjusting screw and if I didn't, then fit one and turn it, else just turn it".

[fcwilt]

@deckingman

To give you an opinion from a retired programmer:

• if we had a command to remove all existing global vars I would create them all in a file which I called from config.g
• since we don't I create them all in config.g
• I do not check for their existence when I use them - I verify my code works and leave it at that

Frederick

[o_lampe]

@owend
Some macros can get several pages long, so I agree it's best practice to check for existing variable names. Especially when more than one person develops or changes this macro over time.
Additional to your post, I'd propose NOT to use standard variable names (X,Y, I,J etc) but 'speaking' names, but that's common sense I guess.

[deckingman]

Playing Devils advocate here, but going back to my original use case, the reason I wanted to use global variables in a number of macros, was so that I could set the values in one place and any macro that needed to use those values would do so. The alternative (which I used before) is to use a fixed value which involves editing numerous files if that value needed to be changed. This could mean that "fat finger syndrome" might mean that one or more macros could use the wrong value. If I check that the global variable exists and that it is set to a certain value at the start of every macro, then I'm back to editing every file which uses those global variables every time I make a change. Which negates the advantages of using global variables instead of fixed values does it not?

[OwenD]

@deckingman
I think you misunderstand my reasoning.
The only place I definitely check for the existence of the global is in config.g
If you don't do so and run say M98 P"config.g" then you'll get error messages saying the global already exists.
Maybe not a big deal, but apart from the aesthetic annoyance it also also means you can't reset your globals to "default" without a full restart.

When you run M98 P"config.g" and it gets to your global creation directive it does not process the value if it already exists. It (correctly) gives an error and moves on.
So any changes to your values require a full restart of they won't apply!

So... if it doesn't exist, I create it and apply a value.
If it DOES exist I reset the value because I can be pretty sure it's been changed in code somewhere.

With the calls to allow globals to be freed, it will become more important to check for existence in all macros.

Personally I think there's less chance of drama the way it is now.
If you don't want a persistent variable use a var instead of a global.
That said there are probably cases where it might be handy to free individual globals, so I'm not fussed either way there.