GY-63_MS5611/libraries/FastShiftOut/README.md

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# FastShiftOut

Arduino library for **AVR** optimized shiftOut - e.g. 74HC595.

Related libraries
- https://github.com/RobTillaart/FastShiftIn
- https://github.com/RobTillaart/FastShiftInOut
- https://github.com/RobTillaart/ShiftInSlow
- https://github.com/RobTillaart/ShiftOutSlow


## Description

FastShiftOut is a class that has optimized code for AVR to shift out data faster 
than the normal **shiftOut()** function.
It speeds up the shift using low level ports and masks. These are predetermined
in the constructor of the FastShiftOut object.

If not an **ARDUINO_ARCH_AVR** or **ARDUINO_ARCH_MEGAAVR** the class falls back 
to the default shiftOut() implementation. 


## Performance

The performance of **write()** is substantially faster than the default Arduino 
**shiftOut()**, but not as fast as HW SPI. 
Exact how big the performance gain is can be seen with the example sketch.
It does a comparison and shows how the class is to be used.

Time in microseconds, Arduino UNO

|  function                |  0.2.4  |   0.3.1  |
|:-------------------------|--------:|---------:|
|  write()                 |  21.66  |   22.48  |
|  writeLSBFIRST()         |  22.94  |   23.37  |
|  writeMSBFIRST()         |  20.30  |   21.86  |
|  reference shiftOut()    |  89.74  |   89.74  |
|  println("Hello world")  |         |  328.92  |
|  println(1357)           |         |  313.56  |
|  println(3.14159265, 4)  |         |  717.36  |


## Interface

```cpp
#include "FastShiftOut.h"
```

#### Functions

- **FastShiftOut(uint8_t dataOut, uint8_t clockPin, uint8_t bitOrder = LSBFIRST)** Constructor.
- **size_t write(const uint8_t data)** send a byte, also the workhorse of the **Print** interface.
- **uint8_t lastWritten()** returns last byte written.
- **bool setBitOrder(uint8_t bitOrder)** set LSBFIRST or MSBFIRST. Returns false for other values.
- **uint8_t getBitOrder(void)** returns LSBFIRST or MSBFIRST.
- **size_t writeLSBFIRST(const uint8_t data);**  most optimized.
- **size_t writeMSBFIRST(const uint8_t data);**  most optimized.


As a FastShiftOut object implements the Print interface, one can also call

- **FSO.print(any type);** or 
- **FSO.println(any type);** 

to send e.g. a float with 4 digits over the line, or some text string. 

Note: **FSO.print()** returns the number of characters printed, including an optional \\r or \\n.


## Notes

- The optimizations are AVR only for now, other platforms may follow.
- The 74HC595 needs 0.1uF caps and the data and clock lines may need  
pull up resistors, especially if wires are exceeding 10 cm (4").


## Future


#### Must

#### Should

- extend unit tests

#### Could

- performance ESP32
- check optimized ESP32
- add **size_t write(const uint8_t \*buffer, size_t size)**
- example schema

#### Wont