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keybrd/doc/keybrd_library_developer_guide.md

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keybrd Library Developer's Guide
================================
This guide if for maintaining and writing new classes for the keybrd library and its extension libraries.
The most common reason for adding new classes are:
* I/O expander classes
* custom layer schemes for multi-layer keyboards
* experimental features
Who this guide is for
---------------------
This guide is for the maintainers and developers of the keybrd library and it's extensions.
It is assumed the reader is familiar with the C++ language including pointers, objects, classes, static class variables, composition, aggregation, inheritance, polymorphism, and enum.
Row, Scanner, and Debouncer classes use bit manipulation.
Class inheritance diagrams
--------------------------
Keybrd library class inheritance diagram
```
Row
___ ScannerInterface ___
/ | \
Scanner_uC Scanner_IOE Scanner_ShiftRegsPISO
PortIOE
PortWriteInterface
/ \
PortWrite_PCA9655E PortWrite_MCP23S17 (one PortWrite class for each IOE type)
PortReadInterface
/ \
PortRead_PCA9655E PortRead_MCP23S17 (one PortRead class for each IOE type)
_ LED _
/ \
LED_uC LED_PCA9655E
DebouncerInterface
|
Debouncer_Samples
ScanDelay
LayerStateInterface
|
LayerState
Key
|____
| \
| Key_LayeredKeysBase
| \____________________
| / \
| Key_LayeredKeys Key_LayeredKeys1
|
|___________________________
| \ \
| Key_LayeredScScBase Key_LayeredCodeScBase
| | |
| Key_LayeredScSc Key_LayeredCodeSc
|
Code
|_____________________
| \ \
| Code_LayerLock Code_LayerHold
|
\________________________________________________________
\ \ \ \ \
Code_Sc Code_Shift Code_AutoShift Code_LEDLock Code_Null
/ \
Code_ScS Code_ScNS
```
Dependency diagrams
-------------------
Dependency diagram of example single-layer keyboard with LEDs
```
____ Row ______
/ | \
Scanner_uC Debouncer Key ___
| | \
readPins Code Code_LEDLock
|
LED_PinNumber
```
Dependency diagram of example multi-layer keyboard with layer LEDs
```
LayerStates
___________ Row ________________/__ | \
/ / \ / \ | \
Scanner_uC Debouncer Key_LayeredKeys / Code_Layer LED_PinNumber
| \ /
readPins Code
```
Dependency diagram of example shift registers Row
```
_______ Row _______
/ | \
RowScanner_ShiftRegsPISO Debouncer Key
|
Code
```
Dependency diagram of example I/O expander matrix with LEDs
```
_________ Row ________
/ \ \
__ Scanner_IOE __ Debouncer Key
/ | \ / \
strobePin PortWrite PortRead Code Code_LEDLock
| \ / \ |
| PortIOE readPins LED
\___________________________/ \
pin
```
Class naming conventions
------------------------
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
|
Code_LayerLock
```
This convention leads to class names that convey information about the classes inheritance.
Underscore delineates base class name and sub-class name. Capital letters delineate words.
Interface class names end with "Interface".
Except for Key, because sketches look nicer with short names defining Key[] arrays.
Layer-class naming conventions
------------------------------
Layer classes are explained in [tutorial_3a_multi-layer_keyboard.md](../tutorials/tutorial_3a_multi-layer_keyboard.md).
*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
*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
*Key_Layered* class names start with "Key_Layered" and end with a descriptive name.
Example Key_Layered class names:
* Key_LayeredScSc
* Key_LayeredKeys
Style guide
-----------
Following the style guide makes it easier for the next programmer to understand your code.
* For class names, see above section "Class naming conventions".
* Member names use camelCase starting with lowercase letter.
* Use constants rather than macros, except for header guards.
* 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
* Header guards have _H suffix e.g. #ifndef FILE_NAME_H
* Pointer names are prefixed with "ptr" e.g. ptrRow = &row;
* Arrays names use the plural of the element name e.g. Row* const = ptrsRows { &row0, &row1 };
* Pass arrays using array notation rather than pointer notation:
```
void printArray(char[] array);
not
void printArray( char* array);
```
* In constructor's initialization list, use same names for fields and constructor parameters.
* Do not use new or malloc (make memory leaks impossible).
* Document class interface in .h file, above the class declaration.
* 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.
The [astyle_cpp](astyle_cpp) file specifies the format:
* Allman style indentation
* indent 4 spaces
* replace tabs with spaces
* maximum code width of 100 columns
<!-- http://stackoverflow.com/questions/2198241/best-practice-for-c-function-commenting -->
Trace of keybrd scan
--------------------
Arduino does not have a debugger.
So here is a list of functions in the order that they are called.
The trace is of a one-row single-layer keybrd scan.
```
loop() for each row
Row::process()
Scanner_uC::scan() strobe row on
for each readPin
set readState bit
strobe row off
Debouncer_Samples::debounce() debounce
Row::send() for each key in row
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();
```
The Arduino libraries
---------------------
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>
<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>.