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Hi Dave,</div>
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Thats a really good tip to use the I2C decoding feature on the Tek. I imagine by now its standard feature on the uhhh, clone Rigol scopes.</div>
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A look at basic circular buffer interrupt structure may help:</div>
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Buffer of length x is assigned;</div>
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head and tail pointers to buffer are equal;<br>
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Interrupt driven code is input from serial to buffer, moving head buffer and tail pointer +1 and storing new data;</div>
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application reads from tail buffer pointer, non interrupt driven, at its own speed, decrements tail pointer;</div>
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Modulo buffer len math on the pointers, these two buffer pointers chase each other as interrupts and application run.</div>
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Randy<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Dave Brown <davebr@modularsynthesis.com><br>
<b>Sent:</b> Thursday, March 19, 2020 11:13 PM<br>
<b>To:</b> synth-diy@synth-diy.org <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] MIDI I/O c code..</font>
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<span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">In 2005 I wrote a MIDI processing program to do minor manipulation such as transposing notes, changing CC messages, etc. I did it in assembly in an 8 MHZ ATTINY2313. Receive and
transmit are interrupt driven out of 32 byte buffers each. It handles running status and can filter out some of the real time messages. It will take everything I can throw at it with two hands on the keyboard. It is highly optimized assembly but I suspect
your issue is not emptying the buffers fast enough.</span></p>
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<span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
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<span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">I also run this same code on a 16 MHz Basic Stamp which does have I2C D/As which do take some time so care has to be taken. The same code on an Arduino runs about 4.5X faster
because the I2C is handled in hardware whereas on the Basic Stamp it is done in software.</span></p>
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<span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">I found my Tektronix scope with I2C decoding capability invaluable in seeing where my bottlenecks were in all the communications. Even without that capability I would often use
an external pin to create timing signals so I could accurately measure code execution. But I’m a hw guy by nature.</span></p>
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<span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">FYI</span></p>
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<span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"><br>
Dave</span></p>
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<b><span style="font-size:10.0pt; font-family:"Tahoma","sans-serif"" lang="FR">De :</span></b><span style="font-size:10.0pt; font-family:"Tahoma","sans-serif"" lang="FR"> dougall [mailto:<a href="mailto:dougalli@gmail.com" target="_blank">dougalli@gmail.com</a>]
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<b>Envoyé :</b> 19 mars 2020 21:06<br>
<b>À :</b> <a href="mailto:eidorian@aladan.net" target="_blank">eidorian@aladan.net</a><br>
<b>Cc :</b> Jean-Pierre Desrochers; <a href="mailto:Synth-diy@synth-diy.org" target="_blank">
Synth-diy@synth-diy.org</a><br>
<b>Objet :</b> Re: [sdiy] MIDI I/O c code..</span><span lang="FR-CA"></span></p>
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<span lang="FR-CA"> Are you handling running status and note off sent as zero velocity note on?</span></p>
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<span lang="FR-CA"> -d</span></p>
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<span lang="FR-CA"> On Fri, 20 Mar 2020 at 11:55, <<a href="mailto:eidorian@aladan.net" target="_blank">eidorian@aladan.net</a>> wrote:</span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">Sorry, I don't have example code for you, but here is some analysis that I hope might help point you in the right direction:</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">20MHz / 31,250Hz => ~640 instructions per MIDI data bit, or 6,400 instructions per MIDI data byte. That's quite a lot of instruction execution time between notes, so I'd be checking
the efficiency/optimisation of the code.</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">How long is it taking to update the analog outputs and do other processing? If it's updating all 8 CVs via a "slow" protocol like I2C every time it loops then that might be taking
a while, and maybe you need a different approach (i.e. only update a CV output when it changes).</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">How have you implemented the FIFO? Do you have locking to ensure the interrupt isn't writing to it while the main loop is updating it?</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">Create a debug version that has checks on the FIFO size in the interrupt, and sets an LED on if it overflows, so you can confirm for certainly whether or not that's the problem.</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">What I do (with 30+ years of programming experience) is pretend I'm the CPU, and "execute" the code in my head (or on paper if complex) in order to try to work out what unplanned
or unexpected things might be happening to cause the problematic behaviour.</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">Cheers,<br>
A.</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">---</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA"> </span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">On 20-03-2020 11:14, Jean-Pierre Desrochers wrote:</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">I’m working on a new polyphonic MIDI to CV module (8 voices).</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">So far I did my tests with an old PIC16F887 @ 20Mhz micro I had on hand.</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">I use a USART interrupt driven c function to ‘catch’ all the incoming MIDI bytes.</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">My code is pretty fast, but still, since I only read one MIDI channel (1-16) at the time
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when I play very fast chords on an external keyboard</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">all the notes are read in the incoming queue but sometimes</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">I get stuck notes or unread ones..</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">Same thing happens when playing MIDI files on Cakewalk SONAR
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feeding my prototype with a MIDI cable.<br>
The interrupt function grabs each incoming byte and put them</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">In a receive buffer of 32 bytes and the main () reads and treats them in a FIFO manner</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">Later in the main loop.</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA"> </span><span lang="FR-CA"></span></p>
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<em><span style="font-family:"Verdana","sans-serif"" lang="FR-CA">-Would a 32Mhz micro do a difference in the USART interrupt reading speed ?</span></em><span lang="FR-CA"></span></p>
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<em><span style="font-family:"Verdana","sans-serif"" lang="FR-CA">-And is 32 bytes long enough for the RxBuffer to handle a 6 voices chords ?</span></em><span lang="FR-CA"></span></p>
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<em><span style="font-family:"Verdana","sans-serif"" lang="FR-CA">-And finaly I checked the web for a ‘decent’ C code examples</span></em><span lang="FR-CA"></span></p>
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<em><span style="font-family:"Verdana","sans-serif"" lang="FR-CA"> for MIDI reception (MIDI Tx is much easier to implement) with no success..</span></em><i><span style="font-family:"Verdana","sans-serif"" lang="FR-CA"><br>
<em><span style="font-family:"Verdana","sans-serif""> ‘Obscure’ Arduino libraries all around with no explainations of its inner code.</span></em></span></i><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA"> </span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">Did anybody use good C code available ?</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA">JP</span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA"> </span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA"><a href="mailto:Synth-diy@synth-diy.org" target="_blank">Synth-diy@synth-diy.org</a></span><span lang="FR-CA"></span></p>
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<span style="font-size:10.0pt; font-family:"Verdana","sans-serif"" lang="FR-CA"> </span><span lang="FR-CA"></span></p>
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