Changing mux2.0.sel values every X time.

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01 Feb 2013 20:06 #29433 by casetero
Hello everyone, i´m trying to learn some HAL code, and i don´t know if its possible to do that creating a thread or something.

The thing i want to do is that the PIN mux2.0.sel changes its values from 0 to 1 every 0.2 seconds for example.

I don´t have any idea to do it, maybe with a thread like base-thread or servo-thread, or something different. I´m starting to use the HAL code and i´m very lost.

Sorry for my english.

Thank you very much.

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02 Feb 2013 01:44 #29450 by ArcEye
Hi

Just trying to clarify the question

Do you want a component to link to mux2.sel pin to switch it on and off at preset intervals OR

do you just want to re-write mux2 so that it oscillates output between in1 and in0 at preset intervals without an external connection?

The latter seems the easiest, the code for mux2 is extremely simple, you would just need to add a counter to match the speed of the thread for the elapsed 0.2 seconds and reset the sel pin.

Something like this
component mux-toggle " toggles between two input values at preset rate";

pin out float out       "Follows the value of in0 if timer > period or in1 if timer < period";
pin in float in1        "if no period set will default to this;
pin in float in0;
param rw s32 period = 0     "number of thread periods between toggles";

variable s32 timer = 0;
function _;
author "ArcEye arceye@mgware.co.uk";
license "GPL";
;;
FUNCTION(_) 
{
    if(timer < period) 
        {
        out = in0;
        timer++;
        }
    else 
        {
        out = in1;
        timer = 0;
        }
}

regards
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02 Feb 2013 02:25 #29452 by PCW
Thats not quite right as it will only select in1 for 1 thread period...
you probably want something dealing with timer < and > period over 2

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02 Feb 2013 05:29 - 02 Feb 2013 06:32 #29454 by casetero
Hi,

PCW, i think what i want to do is what ArcEye has post, i can´t fully understand you, sorry for my english. I want that a PIN be excited by mux2.0.in0 and mux2.0.in1, changing between both every 0.2 seconds.

Thinking of it, will this charge much the processor and give me more latency??

Arceye doing this i will change the mux2 component in general, if i rename it as mux2_period.c and compile it like the shuttlexpress will work too??

I say this because maybe i need to use mux2 with his normal behaviour in other place. EDIT = Sorry i see now you have renamed to mux2-toggle.

Thank you!
Last edit: 02 Feb 2013 06:32 by casetero.

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02 Feb 2013 05:35 #29456 by PCW
Running such a simple component will not take much processor time at all

Yes compile it with a different name so you dont break the existing components

My previous post just mentions that there is a little bug in the code that needs to be fixed before it will do what you expect
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02 Feb 2013 06:43 #29458 by casetero
Ok, so i have to put a file like it is as a file.c in /build/src/hal/user_components/ compile it and copy to the real path of linuxcnc or can i make a file.comp and compile it with comp--??

Can i compile it with nothing more code?? dependencies?

What is the little bug? it will change one time and will stay with the in1 value?

Thank you!

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02 Feb 2013 07:17 #29460 by PCW
This should be closer to equal time on both in0 and in1
component mux-toggle " toggles between two input values at preset rate";

pin out float out       "Follows the value of in0 if timer > period or in1 if timer < period";
pin in float in1        "if no period set will default to this;
pin in float in0;
param rw s32 period = 0     "number of thread periods between toggles";

variable s32 timer = 0;
function _;
author "ArcEye arceye@mgware.co.uk";
license "GPL";

FUNCTION(_) 
{
    if(timer < period) 
        {
        out = in0;
        timer++;
        }
    else 
        {
        out = in1;
        timer++;
        }
	if(timer =period*2)
       {
       timer = 0;
      }
}
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02 Feb 2013 15:12 - 02 Feb 2013 19:37 #29470 by ArcEye
Thank you Peter

I had realised the error after I shut down the computer, but had other things to do
Your fix is exactly the same one I thought of :)

Regards compiling, it is a component, name the file mux-toggle.comp
and run sudo comp --install mux-toggle.comp

It won't build in the source tree under that name unless you change the makefile

regards
Last edit: 02 Feb 2013 19:37 by ArcEye.
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02 Feb 2013 17:10 #29473 by casetero
Ok, so i do create a file called mux-toggle.comp with the code and run sudo comp --install mux-toggle.comp.

But in what directory do i do all this??

Do i have to link the component after to any servo-thread or base-thread??

How do i fix the timer to 0.2 seconds?

Thank you!

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02 Feb 2013 18:55 #29477 by andypugh

The thing i want to do is that the PIN mux2.0.sel changes its values from 0 to 1 every 0.2 seconds for example.


You could do this with existing components, if you preferred.
www.linuxcnc.org/docs/html/man/man9/siggen.9.html

loadrt siggen num_chans=1

addf siggen.0 servo-thread

setp siggen.0.frequency 5

net toggle siggen.0.clock => mux2.0.sel

(I am not 100% certain that the "clock" output is a square wave, it might be necessary to use a conv_float_bit function on the square-wave output instead.)

However, learning how to write custom components in the comp preprocessor is a good thing to do, as you can see from mux2 it is much simpler than the C-code required for something like shuttlexpress.
Docs here:
www.linuxcnc.org/docs/html/hal/comp.html
(don't confuse the "comp" preprocessor with the "comp" HAL component)
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