Add support for reading from CD74HC165 shift-in register

[reznet]

This adds support for reading from the digital inputs on a CD74HC165 shift-in register. I based this on the multiplexer code and tested it in my own Arduino code. I'm on a Mac, so some of the build commands did not work and I added Mac equivalents to tasks.json. However, the arduino-example-builder exe does not run on Mac and I could not find a Mac equivalent.

the implementation uses bitRead and shiftIn from the Arduino library and compiles fine, but when trying to add tests, these are not defined. should they be? or do we need our own implementation of these methods?

as is, the test class is not useful - it's a placeholder. I'm happy to flesh it out when the missing Arduino methods are solved.

[tttapa]

Thank you for your contribution!

I cannot merge this pull request here, the Arduino-Helpers code is maintained separately, so I would have to merge that upstream.

I've added some comments, but don't feel obligated to fix them, I have an old local shift register input class stashed somewhere that's still waiting for me to order some hardware to test it, so I could always push that.

[tttapa]

These tasks should use operating system specific options within a single task rather than having multiple tasks for different operating systems.

[tttapa]

This function doesn't have a definition.

[tttapa]

This buffer should have enough space to store N bits, not just 8. It should probably be an AH::BitArray<N>, like the ShiftRegisterOut class.

[tttapa]

bitRead cannot address N bits, this should be a read from the AH::BitArray<N>.

[tttapa]

When do you have to change the mode of the data pin? AFAIK, shift registers have push/pull data outputs, so INPUT_PULLUP should never be necessary. Even if INPUT_PULLUP were necessary, it would have to be in a different method, the pinMode() method should change the modes of the input of the IO extender, not the data pins.

[tttapa]

Ideally, this would use an ExtIO version of shiftIn(), similar to

Control-Surface/src/AH/Hardware/ExtendedInputOutput/ExtendedInputOutput.cpp

Lines 176 to 209 in a061a3a

	void shiftOut(pin_t dataPin, pin_t clockPin, BitOrder_t bitOrder, uint8_t val) {
	// Native version
	if (isNativePin(dataPin) && isNativePin(clockPin)) {
	::shiftOut((int)dataPin, (int)clockPin, bitOrder, val);
	}
	// ExtIO version
	else if (!isNativePin(dataPin) && !isNativePin(clockPin)) {
	auto dataEl = getIOElementOfPin(dataPin);
	auto dataPinN = dataPin - dataEl->getStart();
	auto clockEl = getIOElementOfPin(clockPin);
	auto clockPinN = clockPin - clockEl->getStart();
	for (uint8_t i = 0; i < 8; i++) {
	uint8_t mask = bitOrder == LSBFIRST ? (1 << i) : (1 << (7 - i));
	dataEl->digitalWrite(dataPinN, (val & mask) ? HIGH : LOW);
	clockEl->digitalWrite(clockPinN, HIGH);
	clockEl->digitalWrite(clockPinN, LOW);
	}
	}
	// Mixed version (slow)
	else {
	for (uint8_t i = 0; i < 8; i++) {
	uint8_t mask = bitOrder == LSBFIRST ? (1 << i) : (1 << (7 - i));
	digitalWrite(dataPin, (val & mask) ? HIGH : LOW);
	digitalWrite(clockPin, HIGH);
	digitalWrite(clockPin, LOW);
	}
	}
	}
	void shiftOut(int dataPin, int clockPin, BitOrder_t bitOrder, uint8_t val) {
	::shiftOut(arduino_pin_cast(dataPin), arduino_pin_cast(clockPin), bitOrder,
	val);
	}

I'll see if I can add one.

I believe the bit order should be a parameter, similar to ShiftRegisterOut.

[tttapa]

From the datasheet:

For predictable operation the LOW-to-HIGH transition of CE should only take place while CP is HIGH. Also, CP and CE should be LOW before the LOW-to-HIGH transition of PL to prevent shifting the data when PL goes HIGH.

I don't believe this is satisfied here.