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

#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

Support

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Thank you,