Arduino library for AVR optimized shiftInOut (simultaneously).
Experimental
FastShiftInOut is a class that has optimized code (AVR only) to send and receive bytes simultaneously. In that sense it mimics a SPI bus. 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 a default non optimized implementation.
The library allows to set (and get) the bitOrder and apply this to multiple write() calls. It also provide access to writeLSBFIRST() and writeMSBFIRST() which are the low level workers and most optimized code (so far).
Note: the bitOrder of the byte read and the byte written are the same.
The 0.2.0 version has a flag to unroll the inner loop in writeLSBFIRST() and writeMSBFIRST(). The unrolled loop blocks the interrupts per byte.
Note: this optimization is new and thus experimental. Feedback, including improvements, is welcome.
Performance of write()
| version | UNO (us) | ESP32 (us) |
|---|---|---|
| 0.1.0 | 181.08 | 4.32 |
| 0.1.1 | 26.84 | 4.32 |
| 0.1.2 | 26.84 | no data |
| 0.1.3 | 25.52 | 4.32 |
(0.2.0)
Indicative time in microseconds, Arduino UNO, IDE 1.8.19, measured over 1000 calls.
(delta between 2 calls and 1 call to eliminate overhead)
| function | 0.1.3 | 0.2.0 | 0.2.0L |
|---|---|---|---|
| write() (reference) | no data | 158.24 | no data |
| write() | 25.52 | 17.61 | 12.26 |
| writeLSBFIRST() | 25.52 | 17.61 | 12.26 |
| writeMSBFIRST() | 25.52 | 17.60 | 12.20 |
- Note: 0.1.3 added from old table.
- Note: reference run on AVR by commenting all optimizations.
- Note: 0.2.0 measured with loop unroll flag disabled.
- Note: 0.2.0L measured with loop unrolled flag enabled.
- https://github.com/RobTillaart/FastShiftIn
- https://github.com/RobTillaart/FastShiftInOut
- https://github.com/RobTillaart/FastShiftOut
- https://github.com/RobTillaart/ShiftInSlow
- https://github.com/RobTillaart/ShiftOutSlow
#include "FastShiftInOut.h"bitOrder = { LSBFIRST, MSBFIRST };
- FastShiftInOut(uint8_t dataIn, uint8_t dataOut, uint8_t clockPin, uint8_t bitOrder = LSBFIRST) Constructor.
- uint8_t write(uint8_t data) reads and writes simultaneously.
- uint8_t lastWritten(void) returns last byte written.
- uint8_t lastRead(void) returns last byte read.
- uint8_t writeLSBFIRST(uint8_t data) lowest level function, optimized for LSB.
- uint8_t writeMSBFIRST(uint8_t data) lowest level function, optimized for MSB.
- bool setBitOrder(uint8_t bitOrder) bitOrder must be LSBFIRST or MSBFIRST.
- uint8_t getBitOrder(void) idem.
- Update documentation
- Follow FastShiftIn and FastShiftOut
- void ignoreRead() => would in effect be FastShiftIn()
- add Print interface?
- meaning of the return value is not defined.
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