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87 lines
3.1 KiB
Markdown
87 lines
3.1 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/FastShiftOut/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/FastShiftOut/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/FastShiftOut/blob/master/LICENSE)
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[](https://github.com/RobTillaart/FastShiftOut/releases)
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# FastShiftOut
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Arduino library for **AVR** optimized shiftOut - e.g. 74HC595.
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Related libraries
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- https://github.com/RobTillaart/FastShiftIn
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- https://github.com/RobTillaart/FastShiftInOut
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- https://github.com/RobTillaart/ShiftInSlow
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- https://github.com/RobTillaart/ShiftOutSlow
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## Description
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FastShiftOut is a class that has optimized code for AVR to shift out data faster
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than the normal **shiftOut()** function.
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It speeds up the shift using low level ports and masks. These are predetermined
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in the constructor of the FastShiftOut object.
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If not an **ARDUINO_ARCH_AVR** or **ARDUINO_ARCH_MEGAAVR** the class falls back
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to the default shiftOut() implementation.
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## Performance
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The performance of **write()** is substantially faster than the default Arduino
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**shiftOut()**, but not as fast as HW SPI.
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Exact how big the performance gain is can be seen with the example sketch.
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It does a comparison and shows how the class is to be used.
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test 0.2.4 Arduino UNO
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| function | time (us) |
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|:----------------------|----------:|
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| write() | 21.66 |
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| writeLSBFIRST() | 22.94 |
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| writeMSBFIRST() | 20.30 |
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| reference shiftOut() | 89.74 |
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## Interface
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The interface exists of the following functions:
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- **size_t write(const uint8_t data)** send a byte, also the workhorse of the **Print** interface.
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- **uint8_t lastWritten()** returns last byte written.
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- **bool setBitOrder(uint8_t bitOrder)** set LSBFIRST or MSBFIRST. Returns false for other values.
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- **uint8_t getBitOrder(void)** returns LSBFIRST or MSBFIRST.
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- **size_t writeLSBFIRST(const uint8_t data);** most optimized.
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- **size_t writeMSBFIRST(const uint8_t data);** most optimized.
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As a FastShiftOut object implements the Print interface, one can also call
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- **FSO.print(any type);** or
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- **FSO.println(any type);**
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to send e.g. a float with 4 digits over the line, or some text string.
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Note: **FSO.print()** returns the number of characters printed, including an optional \\r or \\n.
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## Notes
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- The optimizations are AVR only for now, other platforms may follow.
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- The 74HC595 needs 0.1uF caps and the data and clock lines may need
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pull up resistors, especially if wires are exceeding 10 cm (4").
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## Operation
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See examples
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## Future
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- performance ESP32
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- check optimized ESP32
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- add **size_t write(const uint8_t \*buffer, size_t size)**
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- example schema
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