#349 stringy/DemoBurner

Burning a new demo mode for the Boldport Club Stringy, with a Ruby gem for MusicXML conversion to PIC assembler.

A quick video of the the new demo…

Notes

So, a long time after building the Boldport Club String, I decided to read the source .. and discovered I totally missed the fact that it has a demo mode;-)

I was reading the source to learn more about what tricks James Hutchby used to implement the Karplus-Strong algorithm, but now I am distracted and decided first to make some new demo tracks.

First Step - Building the Original Source

It’s great to see source code being released, thank you Boldport and MadLabs!

I’m using MPLAB X IDE v3.51 on MacOSX. NB: subsequently updated and recompiled with MPLAB X IDE v5.30.

After loading the source files in a new project CustomDemo.X, my first build failed with two errors:

Error[151]   LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X/stringy.asm 1426 : Operand contains unresolvable labels or is too complex
Error[151]   LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X/stringy.asm 469 : Operand contains unresolvable labels or is too complex

It seems this is to do with addressing, so I switch to absolute mode:

.. and now it builds

make -f nbproject/Makefile-default.mk SUBPROJECTS= .build-conf
make[1]: Entering directory 'LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X'
make  -f nbproject/Makefile-default.mk dist/default/production/CustomDemo.X.production.hex
make[2]: Entering directory 'LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X'
"/Applications/microchip/mplabx/v3.51/mpasmx/mpasmx" -q -p12f1840 -u \"LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X/stringy.asm\"
"/Applications/microchip/mplabx/v3.51/mpasmx/mplink"    -p12f1840  -w  -m"dist/default/production/CustomDemo.X.production.map"   -z__MPLAB_BUILD=1  -odist/default/production/CustomDemo.X.production.cof  build/default/production/stringy.o
MPLINK 5.08, LINKER
Device Database Version 1.34
Copyright (c) 1998-2011 Microchip Technology Inc.
Errors    : 0

MP2HEX 5.08, COFF to HEX File Converter
Copyright (c) 1998-2011 Microchip Technology Inc.
Errors    : 0

make[2]: Leaving directory 'LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X'
make[1]: Leaving directory 'LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X'

BUILD SUCCESSFUL (total time: 880ms)
Loading code from LittleArduinoProjects/BoldportClub/stringy/DemoBurner/CustomDemo.X/dist/default/production/CustomDemo.X.production.hex...
Loading completed

Step Two - Reprogramming the Stringy

The stringy board has pin sockets for all the PIC pins (even in the same order as exposed from a programmer), so I’m guessing I can program this in-circuit?

Here’s a PICkit 3 connected to the stringy, with some blu tack assist:

Connecting up the programmer, and I’m seeing the device OK..

And it programs without error..

*****************************************************

Connecting to MPLAB PICkit 3...

Currently loaded firmware on PICkit 3
Firmware Suite Version.....01.46.14
Firmware type..............Enhanced Midrange

Programmer to target power is enabled - VDD = 4.750000 volts.
Target device PIC12F1840 found.
Device ID Revision = 5

Device Erased...

Programming...

The following memory area(s) will be programmed:
program memory: start address = 0x0, end address = 0x49f
configuration memory
User Id Memory
Programming/Verify complete

Note that I’ve enabled powering the device, so I can test it without having to install a battery. Out of habit, I set the voltage at 4.75V instead of 5V, as the PICkit 3 is prone to errors otherwise.

Power up the stringy, and it works just fine. So far so good!

Burning a new Demo

So the final thing I want to do for now is burn new demo track.

.. but I don’t want to be transcribing/composing in assembler, so instead I “assembled” this workflow:

• score in Guitar Pro
• export to MusicXML
• convert to assembler for the stringy with a Ruby gem StringyFi
• compile with MPLAB X IDE
• program the stringy using a PICkit 3

Olé!

See the music sources in examples - *.gp is the Guitar Pro file, *.xml is the MusicXML export.

My first attempts were with some quite complex scores and I immediately ran into the major problem: the current stringy code only allows for 2-bits worth of note duration, which doesn’t cut it for anything ranging from half notes to 32nd’s, with dotted notes and ties!

So I limited myself and found a nice (appropriately named) candidate - the main riff from Deep Purple’s Burn. I still had to simplify the transcription somewhat to encourage the stringy to play it decently, and I think the result is “OK” .. see it on YouTube.

Here’s the simplified score:

MusicXML Conversion

I clobbered together some routines I’d used before into a simple converter packaged as the Ruby gem stringyfi. It has to make a whole lot of assumptions like: only covert 1 part, 1 voice, and choose the closest duration. It currently pays no attemption to original tempo, and doesn’t support many notation features (such as tied notes).

Installing the Coverter

There’s a Gemfile waiting to install in this directory. Assuming you have a working Ruby environment:

$ gem install bundler  # if not already installed
$ bundle install

Running a Conversion

Choose the XML to convert, and pipe the output into the demo.tun file

$ stringyfi ./examples/BurnIntro.xml > ./CustomDemo.X/demo.tun
converting ./examples/BurnIntro.xml..
  shortest_fractional_duration: 0.125
  octave_range: [3, 5]
.. done.

Recompiling

Now just recompile the CustomDemo.X project with MPLAB and program. Here’s BURN getting burned:

*****************************************************

Connecting to MPLAB PICkit 3...

Currently loaded firmware on PICkit 3
Firmware Suite Version.....01.46.14
Firmware type..............Enhanced Midrange

Programmer to target power is enabled - VDD = 4.750000 volts.
Target device PIC12F1840 found.
Device ID Revision = 5

Device Erased...

Programming...

The following memory area(s) will be programmed:
program memory: start address = 0x0, end address = 0x49f
configuration memory
User Id Memory
Programming/Verify complete

Reverting the Source

The freshen_source.sh script grabs the original sources files (including the original demo) and replaces the sources in CustomDemo.X project.

Useful to:

• put the original demo tune back in place
• undo any modifications to the firmware and revert to “factory” mode

Next Steps

After investigating the original source, I’ve seen a few areas that might be worth working on:

• finer-grained duration control. 2 bits isn’t enough for more complex scores
• running longer tracks. When I tried longer pieces, I suspect I ran into memory addressing limits or possibly timing bugs - not sure which yet, but 20 odd measures in, the stringy would go haywire.

Credits and References

• LEAP#323 stringy - my original stringy build and project info
• StringyFi - source for the MusicXML conversion gem
• Original String Source
• MPLAB X IDE
• Guitar Pro
• ..as mentioned on my blog