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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.
Custom Row classes
------------------
Row classes are central to the keybrd library.
Row is an abstract base class that allows flexibility in designing derived Row classes:
* Row functions can be overridden in a derived class
* choice of Debouncers
* choice of Scanners
This example illustrates the custom Row classes for a fictional keybrd_Ext extension library.
The keybrd_Ext library is for a split keyboard with a matrix on each hand and sticky keys.
Row_Ext::keyWasPressed() overrides Row::keyWasPressed() which is used to unstick sticky keys.
Row_Ext_uC and Row_Ext_ShiftRegisters are a custom classes composed of stock keybrd library classes.<br>
Row_Ext_uC uses Scanner_uC to scan the primary matrix.<br>
Row_Ext_ShiftRegisters uses Scanner_ShiftRegs74HC165 to scan the peripheral matrix.
Class inheritance diagram
```
Row
|
Row_Ext (override Row::keyWasPressed() )
/ \
Row_Ext_uC Row_Ext_ShiftRegisters (inherit Row_Ext::keyWasPressed() )
Scanner_uC Scanner_ShiftRegs74HC165
```
Dependency diagram
```
________ Row_Ext_uC[1] ______________
/ | \
Scanner_uC[1] Debouncer_Samples[1] Key[1..*]
/ |
strobePin[1] Code[1..*]
_________ Row_Ext_ShiftRegisters[1] ________
/ \ \
Scanner_ShiftRegs74HC165[1] Debouncer_Samples[1] Key[1..*]
| |
strobePin[1] Code[1..*]
```
Class inheritance diagrams
--------------------------
Keybrd library class inheritance diagram
```
________ Row ___________
/ | \
Row_uC Row_ShiftRegisters Row_IOE (todo to be added)
Scanner_uC Scanner_Port Scanner_ShiftRegs74HC165
PortIOE
PortWrite
|
PortWrite_PCA9655E (one PortWrite class for each IOE type)
PortRead
|
PortRead_PCA9655E (one PortRead class for each IOE type)
_ LED _
/ \
LED_uC LED_PCA9655E
DebouncerInterface
|
Debouncer_Samples
ScanDelay
LayerStateInterface
|
LayerState
Key __
| \
| Key_LayeredKeysArray
|
Code
|_____________________
| \ \
| Code_LayerLock Code_LayerHold
|
|___________________________
| \ \
| Code_LayeredScScBase Code_LayeredCodeScBase
| | |
| Code_LayeredScSc Code_LayeredCodeSc
|
|_________________________________________________________
\ \ \ \ \
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_uC[1..*] _
/ | \
Scanner_uC Debouncer Keys[1..*] __
| \
Code[1..*] Code_LEDLock[1..*]
|
LED_PinNumber[1]
```
Dependency diagram of example multi-layer keyboard with layer LEDs
```
LayerStates[1..*]
________ Row_uC[1..*] ___________/__ | \
/ | \ / \ | \
Scanner_uC[1] Debouncer[1] Keys[1..*] / Code_Layer[1..*] LED_PinNumber[0..*]
| /
Code[1..*]
```
Dependency diagram of example peripheral matrix with shift registers
```
Row_ShiftRegisters[1..*]
/ \ \
RowScanner_ShiftRegisters Debouncer Keys[1..*]
|
Code[1..*]
```
Dependency diagram of example peripheral matrix with I/O Expander and LEDs
```
_____ Row_IOE[1..*] _________
/ \ \
__ Scanner_Port[1] __ Debouncer[1] Keys[1..*] __
/ | \ | \
PortWrite[1] strobePin[1] PortRead[1] Code[1..*] Code_LEDLock[1..*]
\ / \ |
\ / ColPins[1..*] LED[1]
\ /
PortIOE[0..*]
```
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".
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
*Code_Layered* class names start with "Code_Layered" and end with a descriptive name.
Example Code_Layered class names:
* Code_LayeredScSc
* Key_LayeredKeysArray
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.
Refer to it like a table of contents while reading the keybrd library.
```
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>
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