FastShiftOut

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

Related libraries

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.

test 0.2.4 Arduino UNO

function	time (us)
write()	21.66
writeLSBFIRST()	22.94
writeMSBFIRST()	20.30
reference shiftOut()	89.74

Interface

The interface exists of the following functions:

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").

Operation

See examples

Future

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

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