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113 lines
3.7 KiB
Markdown
113 lines
3.7 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/FastShiftIn/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/FastShiftIn/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/FastShiftIn/blob/master/LICENSE)
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[](https://github.com/RobTillaart/FastShiftIn/releases)
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# FastShiftIn
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Arduino library for **AVR** optimized shiftIn - e.g. for 74HC165.
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Related libraries
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- https://github.com/RobTillaart/FastShiftOut
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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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FastShiftIn is a class that has optimized code (AVR only) to shift in data faster
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than the normal **shiftIn()** 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 FastShiftIn 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 shiftIn() implementation.
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Since 0.3.2 read16(), read24() and read32() are added.
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These are experimental and not fully tested yet.
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## Performance
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The performance of **read()** is substantially faster than the default Arduino
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**shiftIn()**, 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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Time in microseconds, Arduino UNO
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| function | 0.2.3 | 0.3.2 |
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|:---------------------|---------:|---------:|
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| read() | 19.30 | 20.49 |
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| read16() | | 41.04 |
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| read24() | | 62.91 |
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| read32() | | 83.95 |
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| readLSBFIRST() | 19.04 | 19.92 |
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| readMSBFIRST() | 19.04 | 19.92 |
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| reference shiftIn() | 107.82 | 108.20 |
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0.3.2 is a bit slower (incl. reference) than 0.2.3 but still much
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faster than the reference.
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## Interface
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```cpp
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#include "FastShiftIn.h"
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```
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#### Functions
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- **FastShiftIn(uint8_t dataIn, uint8_t clockPin, uint8_t bitOrder = LSBFIRST)** Constructor
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- **uint16_t read(void)** reads a new value, 8 bit.
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- **uint16_t read16(void)** reads a new value, 16 bit.
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- **uint32_t read24(void)** reads a new value, 24 bit.
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- **uint32_t read32(void)** reads a new value, 32 bit.
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- **uint32_t lastRead()** returns last value read.
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- **bool setBitOrder(uint8_t bitOrder)** set LSBFIRST or MSBFIRST.
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Returns false for other values.
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- **uint8_t getBitOrder(void)** returns LSBFIRST or MSBFIRST.
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- **uint16_t readLSBFIRST(void)** optimized LSB read(), 8 bit.
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- **uint16_t readMSBFIRST(void)** optimized MSB read(), 8 bit.
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#### Byte order
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It might be that **read16/24/32** has bytes not in the right order.
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Then you should use multiple calls to **read()** and merge these
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bytes in the order you want them.
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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 74HC165 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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## Future
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#### Must
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#### Should
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- extend unit tests
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#### Could
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- esp32 optimization readLSBFIRST readMSBFIRST
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- **read(uint8_t \* arr, uint8_t nr)** ??
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- example schema
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- would it be interesting to make a fastShiftIn16() etc?
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- squeeze performance but more maintenance.?
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#### Wont
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