167 lines
3.3 KiB
C++
167 lines
3.3 KiB
C++
// SoftwareSPI.cpp
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// Author: Chris Lapa (chris@lapa.com.au)
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// Copyright (C) 2014 Chris Lapa
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// Contributed by Chris Lapa
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#include <RHSoftwareSPI.h>
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RHSoftwareSPI::RHSoftwareSPI(Frequency frequency, BitOrder bitOrder, DataMode dataMode)
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:
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RHGenericSPI(frequency, bitOrder, dataMode)
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{
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setPins(12, 11, 13);
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}
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// Caution: on Arduino Uno and many other CPUs, digitalWrite is quite slow, taking about 4us
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// digitalWrite is also slow, taking about 3.5us
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// resulting in very slow SPI bus speeds using this technique, up to about 120us per octet of transfer
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uint8_t RHSoftwareSPI::transfer(uint8_t data)
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{
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uint8_t readData;
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uint8_t writeData;
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uint8_t builtReturn;
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uint8_t mask;
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if (_bitOrder == BitOrderMSBFirst)
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{
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mask = 0x80;
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}
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else
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{
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mask = 0x01;
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}
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builtReturn = 0;
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readData = 0;
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for (uint8_t count=0; count<8; count++)
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{
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if (data & mask)
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{
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writeData = HIGH;
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}
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else
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{
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writeData = LOW;
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}
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if (_clockPhase == 1)
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{
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// CPHA=1, miso/mosi changing state now
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digitalWrite(_mosi, writeData);
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digitalWrite(_sck, ~_clockPolarity);
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delayPeriod();
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// CPHA=1, miso/mosi stable now
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readData = digitalRead(_miso);
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digitalWrite(_sck, _clockPolarity);
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delayPeriod();
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}
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else
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{
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// CPHA=0, miso/mosi changing state now
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digitalWrite(_mosi, writeData);
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digitalWrite(_sck, _clockPolarity);
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delayPeriod();
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// CPHA=0, miso/mosi stable now
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readData = digitalRead(_miso);
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digitalWrite(_sck, ~_clockPolarity);
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delayPeriod();
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}
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if (_bitOrder == BitOrderMSBFirst)
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{
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mask >>= 1;
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builtReturn |= (readData << (7 - count));
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}
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else
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{
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mask <<= 1;
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builtReturn |= (readData << count);
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}
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}
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digitalWrite(_sck, _clockPolarity);
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return builtReturn;
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}
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/// Initialise the SPI library
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void RHSoftwareSPI::begin()
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{
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if (_dataMode == DataMode0 ||
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_dataMode == DataMode1)
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{
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_clockPolarity = LOW;
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}
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else
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{
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_clockPolarity = HIGH;
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}
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if (_dataMode == DataMode0 ||
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_dataMode == DataMode2)
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{
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_clockPhase = 0;
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}
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else
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{
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_clockPhase = 1;
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}
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digitalWrite(_sck, _clockPolarity);
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// Caution: these counts assume that digitalWrite is very fast, which is usually not true
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switch (_frequency)
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{
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case Frequency1MHz:
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_delayCounts = 8;
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break;
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case Frequency2MHz:
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_delayCounts = 4;
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break;
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case Frequency4MHz:
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_delayCounts = 2;
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break;
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case Frequency8MHz:
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_delayCounts = 1;
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break;
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case Frequency16MHz:
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_delayCounts = 0;
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break;
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}
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}
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/// Disables the SPI bus usually, in this case
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/// there is no hardware controller to disable.
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void RHSoftwareSPI::end() { }
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/// Sets the pins used by this SoftwareSPIClass instance.
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/// \param[in] miso master in slave out pin used
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/// \param[in] mosi master out slave in pin used
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/// \param[in] sck clock pin used
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void RHSoftwareSPI::setPins(uint8_t miso, uint8_t mosi, uint8_t sck)
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{
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_miso = miso;
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_mosi = mosi;
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_sck = sck;
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pinMode(_miso, INPUT);
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pinMode(_mosi, OUTPUT);
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pinMode(_sck, OUTPUT);
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digitalWrite(_sck, _clockPolarity);
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}
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void RHSoftwareSPI::delayPeriod()
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{
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for (uint8_t count = 0; count < _delayCounts; count++)
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{
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__asm__ __volatile__ ("nop");
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}
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}
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