eink/eink_spi.hpp

#pragma once

#include "../clock.hpp"

#include <type_traits>

#include <cstdint>

#include <avr/interrupt.h>

#include "../io/io.hpp"
#include "../util/util.hpp"

namespace eink {

template <io::P SclPin, io::P SdaPin, io::P CsPin, io::P DcPin, std::uint32_t Freq = 100'000>
class Spi {
	template <std::uint32_t StaticClockCycles>
	static constexpr double calcClockDelay()
	{
		constexpr auto maxFrequency = F_CPU / StaticClockCycles;
		static_assert(Freq <= maxFrequency, "SPI frequency not achievable using selected clock speed");
		constexpr auto staticDelay = (1.0 * 1000 * 1000 / maxFrequency);
		const auto delayUs = ((1.0 * 1000 * 1000 / Freq) - staticDelay) / 2;
		return (delayUs > 0 ? delayUs : 0);
	}

	static constexpr double calcWriteClockDelay()
	{
		return calcClockDelay<8>();
	}

	static constexpr double calcReadClockDelay()
	{
		return calcClockDelay<5>();
	}

	static constexpr auto THREE_WIRE_SPI = (DcPin == io::P::NONE);

  public:
	using word_t = std::conditional_t<THREE_WIRE_SPI, std::uint16_t, std::uint8_t>;

	static void init()
	{
		sm_scl = false;
		sm_cs = true;

		sm_scl.dir(io::Dir::OUT);
		sm_sda.dir(io::Dir::OUT);
		sm_cs.dir(io::Dir::OUT);
		sm_dc.dir(io::Dir::OUT);
	}

	static void write(word_t data, const bool command = true)
	{
		constexpr auto numBits = THREE_WIRE_SPI ? 9 : 8;

		const auto oldInterruptState = disableInterrupts();

		sm_sda.dir(io::Dir::OUT);

		if constexpr (THREE_WIRE_SPI) {
			if (command) {
				data &= ~(1 << 8);
			} else {
				data |= 1 << 8;
			}
		}

		sm_dc = !command;

		util::for_constexpr(
		    [&](const auto idx) {
			    constexpr auto bitPos = numBits - idx.value - 1;

			    sm_sda = data >> bitPos & 1;

			    _delay_us(WRITE_DELAY_US);
			    sm_scl.toggle();

			    _delay_us(WRITE_DELAY_US);
			    sm_scl.toggle();
		    },
		    std::make_index_sequence<numBits>{});

		enableInterrupts(oldInterruptState);
	}

	static word_t read()
	{
		constexpr auto numBits = 8;

		const auto oldInterruptState = disableInterrupts();

		if constexpr (THREE_WIRE_SPI) {
			sm_sda = true;
			_delay_us(READ_DELAY_US);
			sm_scl.toggle();
			_delay_us(READ_DELAY_US);
			sm_scl.toggle();
		}

		sm_sda.pullup(false);
		sm_sda.dir(io::Dir::IN);

		sm_dc = true;

		auto res = word_t{};

		util::for_constexpr(
		    [&](const auto idx) {
			    constexpr auto bitPos = numBits - idx.value - 1;

			    _delay_us(READ_DELAY_US);
			    sm_scl.toggle();

			    const auto receivedBit = sm_sda.read();
			    res |= word_t{receivedBit} << bitPos;

			    _delay_us(READ_DELAY_US);
			    sm_scl.toggle();
		    },
		    std::make_index_sequence<numBits>{});

		enableInterrupts(oldInterruptState);

		return res;
	}

	static inline void select(const bool selectState)
	{
		sm_cs = !selectState;
	}

  private:
	static io::Pin<SclPin> sm_scl;
	static io::Pin<SdaPin> sm_sda;
	static io::Pin<CsPin> sm_cs;
	static io::Pin<DcPin> sm_dc;

	static constexpr auto WRITE_DELAY_US = calcWriteClockDelay();
	static constexpr auto READ_DELAY_US = calcReadClockDelay();

	static inline std::uint8_t disableInterrupts()
	{
		const auto oldInterruptState = SREG;
		cli();
		return oldInterruptState;
	}

	static inline void enableInterrupts(const std::uint8_t oldInterruptState)
	{
		SREG = oldInterruptState;
	}
};

} // namespace eink