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 Forum index » DIY Hardware and Software » Microcontrollers and Programmable Logic
Assembler Code, help needed (ATTiny85 midi to CV&GATE)
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beep



Joined: May 05, 2013
Posts: 105
Location: Germany

PostPosted: Thu Apr 12, 2018 10:52 am    Post subject: Assembler Code, help needed (ATTiny85 midi to CV&GATE)
Subject description: "Mitxela MidiMonotron" need advice how to modify the code for the CV out to stay.
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Hello,

on my search for the ultimatively simple midi to CV interface,
I stepped across this https://github.com/mitxela/MidiMonotron

Built the circuit and programmed the chip with the .hex file, it worked. YAAY!
But when you release the keys, the CV output jumps back to zero.

So I figured out how to compile the .asm file to hex with AVR Studio 4, got it.

Spent the whole day on modifying the code by trial and error.
(I have no clue about Assembler or barely about coding in general)
disabling the "setNote" call in the "noteOffMove" sub resulted in a a stuck CV, which stayed but didn't change
when playing legato. And the Gate stayed HIGH. undo.

Then I tried by disabling and re-enabling single lines in all subroutines that
had something to do with notes, including the outputtOff subroutine at the end.

When I removed the line "out OCR1A.r16" in the outputOff sub
and the last two "ldi" and "out" lines before the "ret" command,
the CV out behaved as I wanted, but then the gate output got stuck.

After six hours I decided to give up the trial&error thing and ask in the
forums.

I'd aprecciate your advice.

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Grumble



Joined: Nov 23, 2015
Posts: 827
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PostPosted: Fri Apr 13, 2018 11:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

My guess is:

Almost at the bottom of the code you find:
Code:

outputOff:
   clr r16
   out OCR1A,r16

   cbi PORTB,3
   cbi PORTB,0
   ldi r16, 0b00000000
   out DDRB,r16

   ret

Here the cv for notes is set to 0 where it says: clr r16 (cleares r16) and out OCR1A, r16 (output r16 to OCR1A) effectively stopping the pwm that causes the cv for notes. So just remove these two statements while keeping the rest of the code and try again.

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beep



Joined: May 05, 2013
Posts: 105
Location: Germany

PostPosted: Sun Apr 15, 2018 12:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Your guess was right, but that' only half of the enemy killed.
The last two commands turn off the PWM outputs, so they have to go.
CV works like a charm then but the GATE output cannot retrigger unless
you change the note.

That was the point where I got stuck before I decided to ask people out there.
Got help in the SDIY facebook group. Someone found out that those lines:


in r16,OCR1A
cp r16,r19
breq setNoteEnd

in the SetNote: sub cause the retriggering problem. just delete them too.
voila.

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beep



Joined: May 05, 2013
Posts: 105
Location: Germany

PostPosted: Sun Apr 15, 2018 12:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Next things I want to find out is how to restrict the whole thing either to
high note or to low note priority. I think of two ATTinys being triggered
from the same midi signal, but outputting high and low note CV -> duophony!

And it should be possible to change the MIDI channel for each chip.

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