FastShiftIn

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

Related libraries

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

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