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user_firmware_mode.txt
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user_firmware_mode.txt
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LinnStrument User Firmware Mode
===============================
The intention of user mode is to provide a low level API to access calibrated and normalized LinnStrument sensor data
over MIDI so that custom applications can be written without requiring firmware changes. Obviously, since MIDI, even
over USB, is a slower transport than direct CPU access, certain features can't be developed that would need very quick
access to the data (like for instance velocity detection). User mode is complemented by the already available MIDI CC
API to control LEDs for user feedback of the custom functionalities through MIDI CC numbers 20, 21, and 22.
Activating User Firmware Mode
=============================
User Mode can be activated by sending LinnStrument the value 1 for MIDI NRPN 245 on any MIDI channel, sending value 0
will turn it off. When User Mode is active, all standard firmware features will be disabled and all LEDs will be turned
off, except for the Global Settings panel. This panel will only have settings available for Velocity Sensitivity,
Pressure Sensitivity, MIDI I/O and Actions, the others will be disabled. When the Global Settings panel is active, no
User Mode nor LED control features will be active. When User Mode is active, the Global Settings switch will be lit
yellow.
By default only Cell Presses will be active in User Firmware mode, 3D Touch Data data can be activated for each axis and
for each row individually (see below).
By holding OS Update in Global Settings for half a second when User Mode is active, the user can manually turn off User
Mode and return to the standard firmware mode. When this happens, LinnStrument will send out MIDI NRPN 245 on channel 9
with value 0 to notify the external application that user mode is now disabled. OS Update can also be held down in
standard firmware mode to manually re-enable User Mode, LinnStrument will then send out MIDI NRPN 245 on channel 9 with
value 1 to notify the external application that user mode is now enabled.
Each time User Mode is activated, it starts from a clean slate, so it's the responsibility of the application to set up
the appropriate lights and the configure X-axis slide mode if that's required.
Cell Presses
============
In User Mode, cell presses are tied to a coordinate system using MIDI channels and notes. The rows correspond to
channels 1 to 8 with the bottom row being 1, and the columns correspond to the MIDI notes 0 to 25 with the control
switches being 0. When a cell is pressed, the corresponding MIDI Note On message is sent with the velocity that is
configured in Global Settings. The velocity is needed since it will not be possible to do any meaningful velocity
calculation from the Z data sent over MIDI. When a cell is released the corresponding MIDI Note Off message is sent with
velocity 0.
3D Touch Data
=============
The X, Y and Z data are sent out over MIDI CC messages. X data is global in range, meaning that 0 starts at the left
edge of LinnStrument and the maximum value is at the right edge. Y and Z data have their own 0-max range for each cell.
The scheme below has been selected to provide direct access to the expression data of each individual cell, but also to
make user mode somewhat useful as a plain MIDI device with 200 expressive 3D controllers. The X data is sent out in 14
bit by using standard MSB/LSB pairs.
To enable X data, send MIDI CC message 10 with value 1 to Channels 1 to 8, corresponding to the rows.
Sending value 0 instead will disable X data for a row. The same applies to Y and Z data, using MIDI CC messages 11 and 12
respectively.
Z data is sent as Polyphonic Pressure message over channels 1 to 8, which again correspond to the rows. Similarly to the
note on message, the Polyphonic Pressure notes 0 to 25, correspond to the columns. The values range from 0 to 127, with
0 being a cell's lightest possible touch and 127 being the hardest one.
X data is sent over channels 1 to 8, mapped to rows 1 to 8 on the LinnStrument. MIDI CC messages 0 to 25 correspond to
the columns and contain the 14 bit MSB part. MIDI CC messages 32 to 57 can be used as the LSB counterparts of messages 0
to 25 to receive more precise X data. The 14-bit range from the left edge to the right edge is 0 to 4265.
Y data is sent over channels 1 to 8, corresponding to the rows. The columns correspond to MIDI CC messages 64 to 89. The
values range from 0 to 127, from the bottom edge to the top edge of a cell. X-axis Slide Mode
Data decimation
===============
Given the amount of data that LinnStrument sends out, it's possible to overload low powered or older receiving devices.
Turning on MIDI data decimation will increase the time interval between data updates, by default this feature is
disabled. Data decimation can be enabled by sending MIDI CC message 13 to LinnStrument, the value corresponds to the
number of milliseconds between data updates.
Slide Mode
==========
A unique feature of LinnStrument is to be able to smoothly slide across cells in the same row. It's impossible to
achieve this level of smoothness by combining received User Mode MIDI messages, so there's a special mode that can be
enabled for each row so that it tracks pitch slides across cells like the low row in the standard firmware mode.
When this mode is active and a slide transition occurs, MIDI CC 119 will be sent with as value the column of the cell
that is transitioning to another cell, the channel containing the row of the transitioning cell. The Note On message of
the cell to which the slide transitions will have the same velocity as the first cell in the slide. The Note Off message
of the cell that is released during a slide transition will have the slide target cell's column as velocity value. The
slide transition Note Off message will always occur after the Note On message. The combination of these messages allows
software to perfectly track slides as they occur.
To enable per-row slide mode, send MIDI CC message 9 with value 1 to Channels 1 to 8, corresponding to the rows.
Sending value 0 instead will disable slide mode for a row.
MIDI Message Summary
====================
Outgoing MIDI messages:
-----------------------
Note On Cell Down, Note Number: Column, Channel: Row, Velocity: Strike Velocity
Note Off Cell Up, Note Number: Column, Channel: Row, Velocity: Release Velocity
Polyphonic Pressure Z data, Note Number: Column, Channel: Row, Data: Per Cell Z Position
CC 0-25 X data, CC Number: Column, Channel: Row, Data: Global X Position MSB
CC 32-57 X data, CC Number-32: Column, Channel: Row, Data: Global X Position LSB
CC 64-89 Y data, CC Number-64: Column, Channel: Row, Data: Per Cell Y Position
CC 119 Cell Slide, Channel: Row, Data: Transitioning Column
- After CC 119 Note On Target Cell, Note Number: Column, Channel: Row, Velocity: First Slide Cell's Velocity
- After CC 119 Note Off Source Cell, Note Number: Column, Channel: Row, Velocity: Slide Target Column
Configuration MIDI messages:
----------------------------
NRPN 245 Enabling/disabling User Firmware mode (0: disable, 1: enable)
CC 9 Configure User Firmware X-axis row slide, the channel specifies the row (0: disable, 1: enable)
CC 10 Configure User Firmware X-axis data, the channel specifies the row, default is off (0: disable, 1: enable)
CC 11 Configure User Firmware Y-axis data, the channel specifies the row, default is off (0: disable, 1: enable)
CC 12 Configure User Firmware Z-axis data, the channel specifies the row, default is off (0: disable, 1: enable)
CC 13 Configure User Firmware MIDI decimation rate in milliseconds (minimum 12 ms in low power mode)
CC 20 Column coordinate for cell color change with CC 22 (starts from 0)
CC 21 Row coordinate for cell color change with CC 22 (starts from 0)
CC 22 Change the color of the cell with the provided column and row coordinates
see color value table in midi.txt, 7+: default color
Examples
========
In practice a single cell press could result in messages like this in non-slide mode:
Ch3 Note On 12 Velocity 120
Ch3 PolyPressure Key 12 Value Z
Ch3 CC 12 Value X MSB
Ch3 CC 44 Value X LSB
Ch3 CC 76 Value Y
Ch3 Note Off 12 Velocity 0
In practice a cell transition could result in messages like this in slide mode:
Ch3 Note On 12 Velocity 120
Ch3 PolyPressure Key 12 Value Z
Ch3 CC 12 Value X MSB
Ch3 CC 44 Value X LSB
Ch3 CC 76 Value Y
Ch3 CC 119 Value 12
Ch3 Note On 13 Velocity 120
Ch3 Note Off 12 Velocity 13
Ch3 PolyPressure Key 13 Value Z
Ch3 CC 13 Value X MSB
Ch3 CC 45 Value X LSB
Ch3 CC 77 Value Y
Ch3 Note Off 13 Velocity 0