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LinnStrument: 
the ultimate open-source hacker instrument 
Geert Bevin
Who am I? 
• Geert Bevin, Twitter @gbevin 
• XRebel Product Manager at ZeroTurnaround 
• Java Champion, Musician, Composer...
Musical instrument hacker
Software for Eigenharp
GECO for Leap Motion
LinnStrument firmware and tools
What is the LinnStrument?
Revolutionary Music Performance 
Controller with 3D Note Expression
DEMO
What’s inside LinnStrument?
Front-panel 
Chassis + circuit boards 
Translucent silicone sheet 
Final prototype before production - actual units are sl...
Metal chassis with wooden sides 
Sensor board 
Final prototype before production - actual units are slightly different
LEDs board 
Final prototype before production - actual units are slightly different
Connection between circuit boards 
Final prototype before production - actual units are slightly different
Arduino Due’s 
ARM chip Serial <-> USB MIDI Shield 
Final prototype before production - actual units are slightly differen...
What you need to know about 
the Arduino Due
ARM Cortex-M3 
32-bit 84MHz 
CPU 
SPI signals 
shared by 
LED/Sensor 
Digital 33-37 
Footpedals 
DIN <-> USB 
LED control ...
Arduino Due and LinnStrument 
• 32-bit core, 4 bytes wide operations within single CPU clock 
• CPU Clock at 84Mhz 
• 96 K...
Very simple Arduino program 
// the setup function runs once when you press reset or power the board 
void setup() { 
// i...
Arduino code 
• language based on C/C++ 
• concise reference with all language structures, values and functions 
• Arduino...
Only one execution thread 
• what happens in the ‘loop’ function is all that’s happening 
• if something takes too long, s...
How to use the Arduino IDE
Source code in editor
Select target board
Select serial port
Compile and Upload
I don’t like the Arduino IDE 
• non-HDPI fonts 
• extremely basic editor 
• bad OS integration 
• I use Sublime Text 3 wit...
How the LinnStrument hardware 
is accessed through software
Easy LED functions 
• Change the color and brightness of a single LED 
void setLed(byte col, // Column of LED to be change...
Details of LED control 
• LED control is done through SPI using pin 10, with mode 0, running at 21MHz 
SPI.begin(10); 
SPI...
Easy sensor functions 
• Send 16-bit word over SPI to touch sensor to set the analog switches 
void selectSensorCell(byte ...
Details of touch sensor control 
• Touch sensor control is done through SPI using pin 4, 
with mode 0, running at 21MHz 
S...
Read touch sensor data 
• Touch sensor A/D input is using SPI through pin 52, 
with mode 0, running at 21MHz 
SPI.begin(52...
Reading the foot pedals 
• Done in ls_switches.ino, modify this method to add custom behavior 
void handleFootSwitchState(...
Details of MIDI / Serial - USB / DIN 
• Setting digital switches changes the communication methods from the LinnStrument 
...
That’s all the hardware stuff!
Serial Monitor for debugging
Uncomment line in ls_debug.h 
Recompile and upload
Enable Update OS mode 
Which essentially turns on Serial instead of MIDI
Click on the Looking Glass icon 
To enable Serial Monitor and reset LinnStrument
Column 17 selects the debug level 
By default it’s -1, meaning that no debug info is printed
Row 2 selects debug level 0
Row 3 selects debug level 1
Row 4 selects debug level 2
This is printed in the Serial Console 
Along with the actual debug messages of corresponding levels
The relevant debug code 
if (sensorCol == 17 && sensorRow < 4) { 
debugLevel = sensorRow - 1; 
DEBUGPRINT((-1,"debugLevel ...
Overview of firmware files
Core Files 
• linnstrument-firmware.ino: global data structures, setup and main loop 
• ls_displayModes.ino: illuminate LE...
Low-level Files 
• ls_calibration.ino: calibration procedure and data conversion 
• ls_leds.ino: low-level communication w...
Auxilliary Features Files 
• ls_arpeggiator.ino: arpeggiator logic, tied to internal MIDI clock 
• ls_faders.ino: MIDI CC ...
Support Header Files 
• ls_bytebuffer.h: circular byte buffer with independent push and pop 
locations, used by ls_midi.in...
Useful global functionalities
Global variables 
• byte sensorCol: the column number of the current sensor cell 
• byte sensorRow: the row number of the ...
Global functions 
• TouchInfo &cell(): the last touch data for the current cell 
• TouchInfo &cell(byte col, byte row): th...
Some specific firmware 
examples
Per-finger touch-tracking 
• With a general purpose CPU, you’d model this as touch ‘sessions’ 
that are dynamically create...
Inside ls_handleTouches.ino 
void handleNewTouch(byte z) { 
// ... snip ... 
// check if the new touch could be an ongoing...
Check potential slide transfer 
boolean potentialSlideTransferCandidate(int col) { 
if (col < 1) return false; 
if (sensor...
Is the sibling cell ready for the transfer? 
boolean isReadyForSlideTransfer(int col) { 
// there's a pending release wait...
Perform the data transfer 1/3 
void transferFromSameRowCell(byte col) { 
cell().initialX = cell(col, sensorRow).initialX; ...
Perform the data transfer 2/3 
if (cell(col, sensorRow).touched != untouchedCell) { 
cell(col, sensorRow).touched = transf...
Perform the data transfer 3/3 
// transfer the focus if this was the focused cell 
byte channel = cell().channel; 
if (cha...
Finding the right MIDI channels 
• Note-per-channel distributes up to 16 MIDI channels across notes 
• Notes should reuse ...
Low-row functionalities 
• Intuitively you’d detect a touch on low-row cells when it’s active 
• Then evaluate state of ev...
Inside ls_handleTouches.ino 
void handleXYZupdate(byte z) { 
// ... snip ... 
handleLowRowState(z); 
if (isLowRow()) { 
if...
Inside ls_lowRow.ino 1/2 
void lowRowStart() { 
switch (Split[sensorSplit].lowRowMode) { 
case lowRowStrum: 
lowRowState[s...
Inside ls_lowRow.ino 2/2 
void handleLowRowState(byte z) { 
// this is a low-row cell 
if (isLowRow()) { 
// send out the ...
Sending MIDI bytes 
• MIDI was causing the LEDs to flicker 
• Too much time was spent at once (need more guerrilla!) 
• Cr...
Patched UARTClass 
--- UARTClass.cpp 2014-11-10 14:55:10.000000000 +0100 
+++ UARTClass.cpp 2014-10-10 19:39:43.000000000 ...
Queuing of messages 
ByteBuffer<4096> midiOutQueue; 
// called for each MIDI message that is sent 
void queueMidiMessage(M...
More information at 
http://www.rogerlinndesign.com 
Questions? 
@gbevin
LinnStrument : the ultimate open-source hacker instrument
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LinnStrument : the ultimate open-source hacker instrument

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The video recording of this presentation is available on YouTube: https://www.youtube.com/watch?v=iENVztlxWuk

LinnStrument is a new expressive electronic instrument that was invented by Grammy award winner, Roger Linn, creator of the MPC and the LinnDrum. It is built with open-source hardware, the Arduino Due and runs with firmware that is completely open-source as well. With its 3 dimensional touch sensor, 200 cells and multi-color LEDs, LinnStrument presents itself as an amazing playground to discover embedded Arduino development with concrete musical and visual results. This session will introduce the Arduino development concepts, tie them back to the actual hardware concerns, provide an overview of the main algorithms in the LinnStrument firmware and explain valuable lessons that were learned during the development.

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LinnStrument : the ultimate open-source hacker instrument

  1. 1. LinnStrument: the ultimate open-source hacker instrument Geert Bevin
  2. 2. Who am I? • Geert Bevin, Twitter @gbevin • XRebel Product Manager at ZeroTurnaround • Java Champion, Musician, Composer, Arranger, Producer, Singer, Guitarist, Gamer, Kung-Fu • Many open-source projects including Gentoo Linux, OpenLaszlo, RIFE, Juce, …
  3. 3. Musical instrument hacker
  4. 4. Software for Eigenharp
  5. 5. GECO for Leap Motion
  6. 6. LinnStrument firmware and tools
  7. 7. What is the LinnStrument?
  8. 8. Revolutionary Music Performance Controller with 3D Note Expression
  9. 9. DEMO
  10. 10. What’s inside LinnStrument?
  11. 11. Front-panel Chassis + circuit boards Translucent silicone sheet Final prototype before production - actual units are slightly different
  12. 12. Metal chassis with wooden sides Sensor board Final prototype before production - actual units are slightly different
  13. 13. LEDs board Final prototype before production - actual units are slightly different
  14. 14. Connection between circuit boards Final prototype before production - actual units are slightly different
  15. 15. Arduino Due’s ARM chip Serial <-> USB MIDI Shield Final prototype before production - actual units are slightly different
  16. 16. What you need to know about the Arduino Due
  17. 17. ARM Cortex-M3 32-bit 84MHz CPU SPI signals shared by LED/Sensor Digital 33-37 Footpedals DIN <-> USB LED control MIDI <-> Serial
  18. 18. Arduino Due and LinnStrument • 32-bit core, 4 bytes wide operations within single CPU clock • CPU Clock at 84Mhz • 96 KBytes of SRAM • 512 KBytes of Flash memory for code • Digital I/O pins • Serial Peripheral Interface (SPI) pins with Slave Select
  19. 19. Very simple Arduino program // the setup function runs once when you press reset or power the board void setup() { // initialize digital pin 13 as an output. pinMode(13, OUTPUT); } // the loop function runs over and over again forever void loop() { digitalWrite(13, HIGH); // turn the LED on (HIGH is the voltage level) delay(1000); // wait for a second digitalWrite(13, LOW); // turn the LED off by making the voltage LOW delay(1000); // wait for a second }
  20. 20. Arduino code • language based on C/C++ • concise reference with all language structures, values and functions • Arduino IDE to get started • the ‘setup’ function runs once, when the board starts up • the ‘loop’ function runs at 100% CPU, over and over again
  21. 21. Only one execution thread • what happens in the ‘loop’ function is all that’s happening • if something takes too long, something else isn’t happening • guerrilla coding tactics: powerful, short strikes and get out of there • design your algorithms to be sub-dividable • avoid dynamic memory allocation, it’s very slow
  22. 22. How to use the Arduino IDE
  23. 23. Source code in editor
  24. 24. Select target board
  25. 25. Select serial port
  26. 26. Compile and Upload
  27. 27. I don’t like the Arduino IDE • non-HDPI fonts • extremely basic editor • bad OS integration • I use Sublime Text 3 with the Stino plugin
  28. 28. How the LinnStrument hardware is accessed through software
  29. 29. Easy LED functions • Change the color and brightness of a single LED void setLed(byte col, // Column of LED to be changed byte row, // Row of LED to be changed byte color, // Color of LED to be changed byte brightness) // Brightness of LED (0, 1, 2 or 3) • Light up a single LED with the default color and brightness void lightLed(byte col, // Column of LED to be changed byte row ) // Row of LED to be changed • Clear a single LED void clearLed(byte col, // Column of LED to be changed byte row ) // Row of LED to be changed
  30. 30. Details of LED control • LED control is done through SPI using pin 10, with mode 0, running at 21MHz SPI.begin(10); SPI.setDataMode(10, SPI_MODE0); SPI.setClockDivider(10, 4); // 84MHz divided by 4 • Digital pin 37 is an output and connected to the LED driver chips pinMode(37, OUTPUT); • Write 32-bit data structure to SPI to control the LEDs, refreshed every 100μs digitalWrite(37, HIGH); // enable the outputs of the LED driver chips SPI.transfer(10, column, SPI_CONTINUE); // send column (left-shifted 2 bits + special bit 7) SPI.transfer(10, blue, SPI_CONTINUE); // send blue byte SPI.transfer(10, green, SPI_CONTINUE); // send green byte SPI.transfer(10, red); // send red byte digitalWrite(37, LOW); // disable the outputs of the LED driver chips
  31. 31. Easy sensor functions • Send 16-bit word over SPI to touch sensor to set the analog switches void selectSensorCell(byte col, // Column used by analog switches byte row, // Row used byte switch) // Switch to read X (0), Y (1) or Z (2) • Read stable raw X value at the current col and row (returns 0-4095) int readX() • Read stable raw Y value at the current col and row (returns 0-127) int readY() • Read stable raw Z value at the current col and row (returns 0-127, 255 feather) byte readZ()
  32. 32. Details of touch sensor control • Touch sensor control is done through SPI using pin 4, with mode 0, running at 21MHz SPI.begin(4); SPI.setDataMode(4, SPI_MODE0); SPI.setClockDivider(4, 4); // 84MHz divided by 4 • Write 16-bit data to SPI to set analog switches (see ls_sensor.ino) SPI.transfer(4, lsb, SPI_CONTINUE); // first byte of data structure SPI.transfer(4, msb); // second byte of data structure
  33. 33. Read touch sensor data • Touch sensor A/D input is using SPI through pin 52, with mode 0, running at 21MHz SPI.begin(52); SPI.setDataMode(52, SPI_MODE0); SPI.setClockDivider(52, 4); // 84MHz divided by 4 • Read sensor data delayUsec(7); // wait for stable current after sensor // control changes the analog switches // delay different for each analog switch byte msb = SPI.transfer(4, 0, SPI_CONTINUE); // first byte of sensor data byte lsb = SPI.transfer(4, 0); // second byte of sensor data int raw = (int(msb) << 8 | lsb) >> 2; // pack into int, shift from 16 to 14 bit
  34. 34. Reading the foot pedals • Done in ls_switches.ino, modify this method to add custom behavior void handleFootSwitchState(byte whichSwitch, boolean state) • Digital pin 33 and 34, respectively for left and right foot switches, configured as pull-up inputs (inverted inputs: high is off, low is on) pinMode(33, INPUT_PULLUP); pinMode(34, INPUT_PULLUP); • Read the digital value of foot pedal states (typically every 20ms) boolean leftPedalState = digitalRead(33); boolean rightPedalState = digitalRead(34);
  35. 35. Details of MIDI / Serial - USB / DIN • Setting digital switches changes the communication methods from the LinnStrument to the outside world • Digital pin 35 switches between Serial and MIDI pinMode(35, OUTPUT); digitalWrite(35, HIGH); // high switches to Serial input/output digitalWrite(35, LOW); // low switches to MIDI input/output • Digital pin 36 switches between USB and DIN connectors pinMode(36, OUTPUT); digitalWrite(36, HIGH); // high switches to USB input/output digitalWrite(36, LOW); // low switches to DIN input/output
  36. 36. That’s all the hardware stuff!
  37. 37. Serial Monitor for debugging
  38. 38. Uncomment line in ls_debug.h Recompile and upload
  39. 39. Enable Update OS mode Which essentially turns on Serial instead of MIDI
  40. 40. Click on the Looking Glass icon To enable Serial Monitor and reset LinnStrument
  41. 41. Column 17 selects the debug level By default it’s -1, meaning that no debug info is printed
  42. 42. Row 2 selects debug level 0
  43. 43. Row 3 selects debug level 1
  44. 44. Row 4 selects debug level 2
  45. 45. This is printed in the Serial Console Along with the actual debug messages of corresponding levels
  46. 46. The relevant debug code if (sensorCol == 17 && sensorRow < 4) { debugLevel = sensorRow - 1; DEBUGPRINT((-1,"debugLevel = ")); DEBUGPRINT((-1,debugLevel)); DEBUGPRINT((-1,"n")); } void handleNewTouch(byte z) { DEBUGPRINT((1,"handleNewTouch")); DEBUGPRINT((1," col="));DEBUGPRINT((1,(int)sensorCol)); DEBUGPRINT((1," row="));DEBUGPRINT((1,(int)sensorRow)); DEBUGPRINT((1," z="));DEBUGPRINT((1,(int)z)); DEBUGPRINT((1,"n")); void handleTouchRelease() { DEBUGPRINT((1,"handleTouchRelease")); DEBUGPRINT((1," col="));DEBUGPRINT((1,(int)sensorCol)); DEBUGPRINT((1," row="));DEBUGPRINT((1,(int)sensorRow)); DEBUGPRINT((1,"n"));
  47. 47. Overview of firmware files
  48. 48. Core Files • linnstrument-firmware.ino: global data structures, setup and main loop • ls_displayModes.ino: illuminate LEDs for the different display modes • ls_handleTouches.ino: driven by main loop, handles touch tracking • ls_rtos.ino: primitive scheduler calling continuous tasks during delay • ls_settings.ino: switch behavior from UI, store and recall settings • ls_touchInfo.ino: encapsulate sensor data into touched cells
  49. 49. Low-level Files • ls_calibration.ino: calibration procedure and data conversion • ls_leds.ino: low-level communication with the LEDs • ls_midi.ino: MIDI input, NRPN control, clock, output and queue • ls_sensor.ino: low-level touch sensing with bias and curve • ls_test.ino: debug functions and low-level reports
  50. 50. Auxilliary Features Files • ls_arpeggiator.ino: arpeggiator logic, tied to internal MIDI clock • ls_faders.ino: MIDI CC faders touch handling and data sending • ls_font.ino: tiny, small, and big font display, including scrolling • ls_lowRow.ino: continuous cell evaluation for low-row features, driven by the main touch tracking • ls_noteTouchMapping.ino: track MIDI notes to touched cells, mainly used by arpeggiator • ls_switches.ino: handles control switches and foot pedals
  51. 51. Support Header Files • ls_bytebuffer.h: circular byte buffer with independent push and pop locations, used by ls_midi.ino output queue • ls_channelbucket.h: hands out MIDI channels from a bucket of allowed channel numbers. • ls_debug.h: debug macros and defines • ls_midi.h: standard MIDI status codes, used by ls_midi.ino
  52. 52. Useful global functionalities
  53. 53. Global variables • byte sensorCol: the column number of the current sensor cell • byte sensorRow: the row number of the current sensor cell • byte sensorSplit: the split of the current sensor cell (0: left, 1: right) • DisplayMode displayMode: the active display mode (see DisplayMode enum in linnstrument-firmware.ino for the values)
  54. 54. Global functions • TouchInfo &cell(): the last touch data for the current cell • TouchInfo &cell(byte col, byte row): the last touch data for a cell • FocusCell &focus(byte split, byte channel): the current cell that has the focus for a particular split and channel (FocusCell is a structure that just contains col and row)
  55. 55. Some specific firmware examples
  56. 56. Per-finger touch-tracking • With a general purpose CPU, you’d model this as touch ‘sessions’ that are dynamically created and have a life of their own • Too much memory churn for Arduino, too much book-keeping also • Instead, have a touch state for each cell • Transfer data between cells since we don’t support two fingers touching the same cell
  57. 57. Inside ls_handleTouches.ino void handleNewTouch(byte z) { // ... snip ... // check if the new touch could be an ongoing slide to the right if (potentialSlideTransferCandidate(sensorCol-1)) { // if the pressure gets higher than adjacent cell, // the slide is transitioning over if (isReadyForSlideTransfer(sensorCol-1)) { transferFromSameRowCell(sensorCol-1); handleXYZupdate(z); } // otherwise act as if this new touch never happened else { cellTouched(transferCell); } } // similar for slide to the left
  58. 58. Check potential slide transfer boolean potentialSlideTransferCandidate(int col) { if (col < 1) return false; if (sensorSplit != getSplitOf(col)) return false; if (!isLowRow() && (!Split[sensorSplit].sendX || !isFocusedCell(col, sensorRow))) return false; if (isLowRow() && !lowRowRequiresSlideTracking()) return false; if (isStrummingSplit(sensorSplit)) return false; // the sibling cell has an active touch return cell(col, sensorRow).touched != untouchedCell && // either a release is pending to be performed, or (cell(col, sensorRow).pendingReleaseCount || // both cells are touched simultaneously on the edges abs(cell().calibratedX() - cell(col, sensorRow).calibratedX()) < TRANSFER_SLIDE_PROXIMITY); }
  59. 59. Is the sibling cell ready for the transfer? boolean isReadyForSlideTransfer(int col) { // there's a pending release waiting return cell(col, sensorRow).pendingReleaseCount || // the cell pressure is higher cell().rawZ > cell(col, sensorRow).rawZ; }
  60. 60. Perform the data transfer 1/3 void transferFromSameRowCell(byte col) { cell().initialX = cell(col, sensorRow).initialX; cell().initialReferenceX = cell(col, sensorRow).initialReferenceX; cell().lastMovedX = cell(col, sensorRow).lastMovedX; cell().fxdRateX = cell(col, sensorRow).fxdRateX; cell().rateCountX = cell(col, sensorRow).rateCountX; cell().initialY = cell(col, sensorRow).initialY; cell().note = cell(col, sensorRow).note; cell().channel = cell(col, sensorRow).channel; cell().fxdPrevPressure = cell(col, sensorRow).fxdPrevPressure; cell().fxdPrevTimbre = cell(col, sensorRow).fxdPrevTimbre; cell().velocity = cell(col, sensorRow).velocity; cell().vcount = cell(col, sensorRow).vcount; noteTouchMapping[sensorSplit] .changeCell(cell().note, cell().channel, sensorCol, sensorRow);
  61. 61. Perform the data transfer 2/3 if (cell(col, sensorRow).touched != untouchedCell) { cell(col, sensorRow).touched = transferCell; } cell(col, sensorRow).initialX = -1; cell(col, sensorRow).initialReferenceX = 0; cell(col, sensorRow).lastMovedX = 0; cell(col, sensorRow).fxdRateX = 0; cell(col, sensorRow).rateCountX = 0; cell(col, sensorRow).initialY = -1; cell(col, sensorRow).note = -1; cell(col, sensorRow).channel = -1; cell(col, sensorRow).fxdPrevPressure = 0; cell(col, sensorRow).fxdPrevTimbre = 0; cell(col, sensorRow).velocity = 0; cell(col, sensorRow).pendingReleaseCount = 0; // do not reset vcount!
  62. 62. Perform the data transfer 3/3 // transfer the focus if this was the focused cell byte channel = cell().channel; if (channel != -1 && col == focus(sensorSplit, channel).col && sensorRow == focus(sensorSplit, channel).row) { focus(sensorSplit, channel).col = sensorCol; focus(sensorSplit, channel).row = sensorRow; } }
  63. 63. Finding the right MIDI channels • Note-per-channel distributes up to 16 MIDI channels across notes • Notes should reuse same channel as late as possible (release trails) • Intuitively you’d scan all the active notes and determine which channel is available for a new note, which is again too much overhead • We use a bucket of available channels, channels bubble up or sink down • A new note merely has to take the next channel from the top • Fully encapsulated inside ls_channelbucket.h
  64. 64. Low-row functionalities • Intuitively you’d detect a touch on low-row cells when it’s active • Then evaluate state of every other cell and trigger behavior • This is again too much overhead • Instead keep track of low-row start/stop in a state machine • Piggy-back when processing each cell in the main loop to evaluate appropriate low-row behavior
  65. 65. Inside ls_handleTouches.ino void handleXYZupdate(byte z) { // ... snip ... handleLowRowState(z); if (isLowRow()) { if (newVelocity) { lowRowStart(); } return; } // ... snip ... } void handleTouchRelease() { // ... snip ... if (isLowRow()) { lowRowStop(); } // ... snip ... }
  66. 66. Inside ls_lowRow.ino 1/2 void lowRowStart() { switch (Split[sensorSplit].lowRowMode) { case lowRowStrum: lowRowState[sensorCol] = pressed; break; // ... snip, different for each low-row mode } } void lowRowStop() { switch (Split[sensorSplit].lowRowMode) { case lowRowStrum: lowRowState[sensorCol] = inactive; break; // ... snip, different for each low-row mode } }
  67. 67. Inside ls_lowRow.ino 2/2 void handleLowRowState(byte z) { // this is a low-row cell if (isLowRow()) { // send out the continuous data for low-row cells if (cell().velocity) { // ... snip, different for each low-row mode } } // this is a non low-row cell else { switch (Split[sensorSplit].lowRowMode) { case lowRowStrum: // uses lowRowState to correlate with column handleLowRowStrum(); break; // ... snip, other cases } } }
  68. 68. Sending MIDI bytes • MIDI was causing the LEDs to flicker • Too much time was spent at once (need more guerrilla!) • Created a MIDI queue to continuously send byte-by-byte from our RTOS • Arduino UART classes still caused problems: synchronous wait for readiness when sending
  69. 69. Patched UARTClass --- UARTClass.cpp 2014-11-10 14:55:10.000000000 +0100 +++ UARTClass.cpp 2014-10-10 19:39:43.000000000 +0200 @@ -109,9 +109,15 @@ size_t UARTClass::write( const uint8_t uc_data ) { + return write(uc_data, true); +} + +size_t UARTClass::write( const uint8_t uc_data, const bool wait ) +{ // Check if the transmitter is ready - while ((_pUart->UART_SR & UART_SR_TXRDY) != UART_SR_TXRDY) - ; + while ((_pUart->UART_SR & UART_SR_TXRDY) != UART_SR_TXRDY) { + if ( !wait ) return 0; + } // Send character _pUart->UART_THR = uc_data;
  70. 70. Queuing of messages ByteBuffer<4096> midiOutQueue; // called for each MIDI message that is sent void queueMidiMessage(MIDIStatus type, byte param1, byte param2, byte channel) { param1 &= 0x7F; param2 &= 0x7F; midiOutQueue.push((byte)type | (channel & 0x0F)); midiOutQueue.push(param1); if (type != MIDIProgramChange && type != MIDIChannelPressure) { midiOutQueue.push(param2); } } // continuously called by our RTOS void handlePendingMidi() { if (!midiOutQueue.empty()) { if (Serial.write(midiOutQueue.peek(), false) > 0) { // patched UART method midiOutQueue.pop(); } } }
  71. 71. More information at http://www.rogerlinndesign.com Questions? @gbevin

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