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# FastShiftIn

Arduino library for **AVR** optimized shiftIn - e.g. for 74HC165.

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


## Description

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

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


## Performance

The performance of **read()** is substantially faster than the default Arduino 
**shiftIn()**, 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.

test 0.2.3  Arduino UNO

|  function            | time (us) |
|:---------------------|----------:|
|  read()              |    19.30  |
|  readLSBFIRST()      |    19.04  |
|  readMSBFIRST()      |    19.04  |
|  reference shiftIn() |   107.82  |


## Interface

The interface exists of the following functions:

- **int read(void)** reads a new value.
- **int lastRead()** returns last value read.
- **bool setBitOrder(uint8_t bitOrder)** set LSBFIRST or MSBFIRST. Returns false for other values.
- **uint8_t getBitOrder(void)** returns LSBFIRST or MSBFIRST
- **int readLSBFIRST(void)**  optimized LSB read().
- **int readMSBFIRST(void)**  optimized MSB read().


## Notes

- The optimizations are AVR only for now, other platforms may follow.
- The 74HC165 needs 0.1uF caps and the data and clock lines may need  
pull up resistors, especially if wires are exceeding 10 cm (4").


## Operation

See examples


## Future

- esp32 optimization readLSBFIRST readMSBFIRST
- read8() read16(), read24(), read32() 
- **read(uint8_t \* arr, uint8_t nr)** ??
- example schema