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keybrd/doc/keybrd_library_developer_guide.md

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keybrd Library Developer's Guide
================================
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This guide if for maintaining and writing new classes for the keybrd library and its extension libraries.
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The most common reason for adding new classes are:
* I/O expander classes
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* custom layer schemes for multi-layer keyboards
* experimental features
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Who this guide is for
---------------------
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This guide is for the maintainers and developers of the keybrd library and it's extensions.
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It is assumed the reader is familiar with the C++ language including pointers, objects, classes, static class variables, composition, aggregation, inheritance, polymorphism, and enum.
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Row, Scanner, and Debouncer classes use bit manipulation.
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Class inheritance diagrams
--------------------------
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Keybrd library class inheritance diagram
```
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Row
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___ ScannerInterface ___
/ | \
Scanner_uC Scanner_IOE Scanner_ShiftRegsPISO
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PortInterface
/ \
Port_PCA9655E Port_MCP23S17 (one Port class for each IOE type)
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LEDInterface
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/ \
LED_uC LED_Port
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DebouncerInterface
|
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Debouncer_Samples
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ScanDelay
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LayerStateInterface
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|
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LayerState
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Key
|____
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| \
| Key_LayeredKeysBase
| \____________________
| / \
| Key_LayeredKeys Key_LayeredKeys1
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|
|___________________________
| \ \
| Key_LayeredScScBase Key_LayeredCodeScBase
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| | |
| Key_LayeredScSc Key_LayeredCodeSc
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|
Code
|_____________________
| \ \
| Code_LayerLock Code_LayerHold
|
\________________________________________________________
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\ \ \ \ \
Code_Sc Code_Shift Code_AutoShift Code_LEDLock Code_Null
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/ \
Code_ScS Code_ScNS
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```
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Dependency diagrams
-------------------
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Dependency diagram of example single-layer keyboard with LEDs
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```
____ Row ______
/ | \
Scanner_uC Debouncer Key ___
| | \
readPins Code Code_LEDLock
|
LED_PinNumber
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```
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Dependency diagram of example multi-layer keyboard with layer LEDs
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```
LayerStates
___________ Row ________________/__ | \
/ / \ / \ | \
Scanner_uC Debouncer Key_LayeredKeys / Code_Layer LED_PinNumber
| \ /
readPins Code
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```
Dependency diagram of example shift registers Row
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```
_______ Row _______
/ | \
RowScanner_ShiftRegsPISO Debouncer Key
|
Code
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```
Dependency diagram of example I/O expander matrix with LEDs
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```
_________ Row ________
/ \ \
__ Scanner_IOE __ Debouncer Key
/ | \ / \
strobePin PortWrite PortRead Code Code_LEDLock
| \ / \ |
| PortIOE readPins LED_Port
\___________________________/ \
pin
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```
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Class naming conventions
------------------------
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Class names start with upper case letter.
Most derived-class names start with the base class name followed by "_" and a name e.g.
```
Code
|
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Code_LayerLock
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```
This convention leads to class names that convey information about the classes inheritance.
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Underscore delineates base class name and sub-class name. Capital letters delineate words.
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Interface class names end with "Interface".
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Except for Key, to reduce clutter because sketches define so many Key[] arrays.
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Layer-class naming conventions
------------------------------
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Layer classes are explained in [tutorial_3a_multi-layer_keyboard.md](../tutorials/tutorial_3a_multi-layer_keyboard.md).
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*Code_Layer* class names are concatenations of "Code_", "Layer" or layer name, and persistence.
Example persistences are:
* "Lock" - layer remains active after the layer key is released
* "Hold" - layer is active for as long as layer key is held down
Example Code_Layer class names:
* Code_LayerHold
* Code_LayerLock
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*LayerState* class names start with "LayerState" and end with a descriptive name.
Example LayerState class names:
* LayerState - basic LayerState class in keybrd library
* LayerState_DH - main LayerState for the keybrd_DH library
* LayerState_MF - LayerState for Mouse Function sub-layers in the keybrd_DH library
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*Key_Layered* class names start with "Key_Layered" and end with a descriptive name.
Example Key_Layered class names:
* Key_LayeredScSc
* Key_LayeredKeys
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Style guide
-----------
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Following the style guide makes it easier for the next programmer to understand your code.
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* For class names, see above section "Class naming conventions".
* Member names use camelCase starting with lowercase letter.
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* Use constants rather than macros, except for header guards.
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* Global const names and static const names use ALL_CAPS_WITH_UNDERSCORE.
* Macros use ALL_CAPS_WITH_UNDERSCORE and have _MACRO suffix e.g. SAMPLE_COUNT_MACRO
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* Header guards have _H suffix e.g. #ifndef FILE_NAME_H
* Pointer names are prefixed with "ptr" e.g. ptrRow = &row;
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* Arrays names use the plural of the element name e.g. Row* const = ptrsRows { &row0, &row1 };
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* Pass arrays using array notation rather than pointer notation:
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```
void printArray(char[] array);
not
void printArray( char* array);
```
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* In constructor's initialization list, use same names for fields and constructor parameters.
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* Do not use new or malloc (make memory leaks impossible).
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* Document class interface in .h file, above the class declaration.
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* Code should be self-documenting. A simple function with a good name needs no comment.
* Code is automatically formatted before being pushed to the keybrd repository.
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The [astyle_cpp](astyle_cpp) file specifies the format:
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* Allman style indentation
* indent 4 spaces
* replace tabs with spaces
* maximum code width of 100 columns
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<!-- http://stackoverflow.com/questions/2198241/best-practice-for-c-function-commenting -->
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Trace of keybrd scan
--------------------
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Arduino does not have a debugger.
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So here is a list of functions in the order that they are called.
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The trace is of a one-row single-layer keybrd scan.
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```
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loop() for each row
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Row::process()
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Scanner_uC::scan() strobe row on
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for each readPin
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set readState bit
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strobe row off
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Debouncer_Samples::debounce() debounce
Row::send() for each key in row
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if falling edge
Key_*::release() scanCode->release()
Code_*::release() Keyboard.release(scancode)
if rising edge
Key_*::press() scanCode->press()
Code_*::press() Keyboard.press(scancode)
scanDelay.delay();
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```
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The Arduino libraries
---------------------
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The keybrd libraries compile on the Arduino IDE and make extensive use of the following [Arduino libraries](https://www.arduino.cc/en/Reference/Libraries):
#include <Arduino.h>
#include <Wire.h>
#include <Keyboard.h>
#include <Mouse.h>
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<a rel="license" href="https://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://licensebuttons.net/l/by/4.0/88x31.png" /></a><br /><span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">keybrd guide</span> by <a xmlns:cc="https://creativecommons.org/ns" href="https://github.com/wolfv6/keybrd" property="cc:attributionName" rel="cc:attributionURL">Wolfram Volpi</a> is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.<br />Permissions beyond the scope of this license may be available at <a xmlns:cc="https://creativecommons.org/ns" href="https://github.com/wolfv6/keybrd/issues/new" rel="cc:morePermissions">https://github.com/wolfv6/keybrd/issues/new</a>.