// Test-fixture application for the pureboot protocol tests: prints "APP" on
// the chip's serial link (the same link the loader uses) — the proof that
// the loader's hand-over, and on the tinies the host's reset-vector
// surgery, actually launched it. Linked normally (crt, vectors at 0); on
// the tinies its reset vector is the rjmp the host re-homes.
//
// On the mega it then listens, and an 'L' makes it jump into the resident
// loader — the application-owned loader entry a BOOTRST-unprogrammed mega
// relies on (reset always boots the application there), exercised by the
// self-update tests. The tinies idle: reset reaches their loader through
// the patched vector, so the application owes it nothing.
#include <libavr/libavr.hpp>

using namespace avr::literals;

namespace {

consteval avr::hertz_t clock()
{
	if (avr::hw::db.name == "ATtiny13A")
		return 9.6_MHz;
	if (avr::hw::db.name == "ATtiny85")
		return 8_MHz;
	return 16_MHz;
}

using dev = avr::device<{.clock = clock()}>;

template <avr::hertz_t C,
          bool Hardware = avr::hw::db.has_instance("USART0") || avr::hw::db.has_instance("USART")>
struct link {
	using tx_t = avr::uart::usart0<C, {.baud = 115200_Bd, .max_baud_error = 2.5_pct}>;
	static void tx(char c)
	{
		tx_t::write(static_cast<std::uint8_t>(c));
	}
	[[noreturn]] static void idle()
	{
		// 'L' hands back to the loader at the top slot — 512 bytes, or the
		// 1 KiB the >64 KiB chips use.
		constexpr std::uint32_t slot = avr::hw::db.mem.flash_size > 65536 ? 1024 : 512;
		for (;;)
			if (tx_t::read_blocking() == 'L')
				reinterpret_cast<void (*)()>(static_cast<std::uint16_t>((avr::hw::db.mem.flash_size - slot) / 2))();
	}
};

template <avr::hertz_t C>
struct link<C, false> {
	using tx_t = avr::uart::software_tx<C, avr::pb1, 57600_Bd>;
	static void tx(char c)
	{
		tx_t::write(static_cast<std::uint8_t>(c));
	}
	[[noreturn]] static void idle()
	{
		while (true) {
		}
	}
};

} // namespace

int main()
{
	avr::init<typename link<dev::clock>::tx_t>();
	link<dev::clock>::tx('A');
	link<dev::clock>::tx('P');
	link<dev::clock>::tx('P');
	link<dev::clock>::idle();
}