Rewrite on libavr

Same controller: thermistor on ADC0 averaged over 1000 free-running
conversions, 50 kHz fan PWM on OC0B, 115200 Bd console with the full
command set, EEPROM temperature histogram, watchdog-reset path into the
boot section. The Steinhart-Hart math and the libm log are gone — the
Beta equation and the cubic fan curve are consteval-evaluated into
flash tables; the firmware never does floating point. Byte-identical
.text in both libavr modes. Legacy stays on master.

Co-Authored-By: Claude <noreply@anthropic.com>

src/terminal.hpp

@@ -0,0 +1,173 @@
+#pragma once
+
+#include <cstdint>
+#include <string_view>
+
+#include <libavr/libavr.hpp>
+
+#include "board.hpp"
+#include "bootloader.hpp"
+#include "controller.hpp"
+#include "curve.hpp"
+#include "statistics.hpp"
+
+// The serial console: line-buffered commands over the hardware UART.
+// `help` lists everything; `monitor` streams until any key.
+namespace app {
+
+class terminal {
+	static constexpr std::uint8_t line_max = 24;
+	static inline char line[line_max]{};
+	static inline std::uint8_t at = 0;
+	static inline bool monitoring = false;
+	static inline std::uint64_t last_monitor = 0;
+
+	static void prompt()
+	{
+		serial << "> "_P;
+	}
+
+	static void show()
+	{
+		serial << "temperature "_P << controller::temperature_quarters() / 4 << '.'
+		       << (controller::temperature_quarters() % 4) * 25 << " C, adc "_P << controller::last_adc() << ", fan "_P
+		       << controller::fan_percent() << " %, "_P;
+		if (controller::automatic())
+			serial << "auto"_P;
+		else
+			serial << "manual"_P;
+		serial << "\r\n"_P;
+	}
+
+	static void print_curve()
+	{
+		for (std::int8_t t = 15; t <= 60; t += 5)
+			serial << t << " C -> "_P << curve::duty(t) << " %\r\n"_P;
+	}
+
+	static void print_uptime()
+	{
+		auto seconds = static_cast<std::uint32_t>(uptime::millis() / 1000);
+		serial << seconds / 86400 << "d "_P << (seconds / 3600) % 24 << "h "_P << (seconds / 60) % 60 << "m "_P
+		       << seconds % 60 << "s\r\n"_P;
+	}
+
+	static void print_statistics()
+	{
+		serial << "min "_P << statistics::min_temperature() << " C, max "_P << statistics::max_temperature()
+		       << " C, samples "_P << static_cast<std::uint32_t>(statistics::total_samples()) << "\r\n"_P;
+	}
+
+	static void print_histogram()
+	{
+		auto highest = statistics::highest_bucket();
+		if (highest == 0) {
+			serial << "empty\r\n"_P;
+			return;
+		}
+		for (std::uint8_t t = statistics::min_temperature(); t <= statistics::max_temperature(); ++t) {
+			serial << t << " C |"_P;
+			auto width = static_cast<std::uint8_t>((statistics::bucket(t) * 40) / highest);
+			for (std::uint8_t i = 0; i < width; ++i)
+				serial << '#';
+			serial << ' ' << statistics::bucket(t) << "\r\n"_P;
+		}
+	}
+
+	static void help()
+	{
+		serial << "help show curve monitor uptime statistics histogram reset set <0-100> auto version bootloader\r\n"_P;
+	}
+
+	static void dispatch(std::string_view cmd)
+	{
+		if (cmd.empty()) {
+		} else if (cmd == "help") {
+			help();
+		} else if (cmd == "show") {
+			show();
+		} else if (cmd == "curve") {
+			print_curve();
+		} else if (cmd == "monitor") {
+			monitoring = true;
+		} else if (cmd == "uptime") {
+			print_uptime();
+		} else if (cmd == "statistics") {
+			print_statistics();
+		} else if (cmd == "histogram") {
+			print_histogram();
+		} else if (cmd == "reset") {
+			statistics::reset();
+			serial << "statistics cleared\r\n"_P;
+		} else if (cmd == "auto") {
+			controller::set_automatic();
+			serial << "auto\r\n"_P;
+		} else if (cmd == "version") {
+			serial << "fantemp on libavr\r\n"_P;
+		} else if (cmd == "bootloader") {
+			serial << "entering bootloader\r\n"_P;
+			statistics::save();
+			bootloader::enter();
+		} else if (cmd.starts_with("set ")) {
+			std::uint8_t percent = 0;
+			bool valid = cmd.size() > 4;
+			for (std::size_t i = 4; i < cmd.size(); ++i) {
+				if (cmd[i] < '0' || cmd[i] > '9') {
+					valid = false;
+					break;
+				}
+				percent = static_cast<std::uint8_t>(percent * 10 + (cmd[i] - '0'));
+			}
+			if (valid && percent <= 100) {
+				controller::set_manual(percent);
+				serial << "fan "_P << percent << " %\r\n"_P;
+			} else {
+				serial << "set 0..100\r\n"_P;
+			}
+		} else {
+			serial << "? (help)\r\n"_P;
+		}
+	}
+
+  public:
+	static void init()
+	{
+		serial << "\r\nfantemp on libavr — help for commands\r\n"_P;
+		prompt();
+	}
+
+	static void poll()
+	{
+		if (monitoring) {
+			if (uptime::millis() >= last_monitor + 1000) {
+				show();
+				last_monitor = uptime::millis();
+			}
+			if (serial_t::read()) { // any key stops
+				monitoring = false;
+				prompt();
+			}
+			return;
+		}
+		while (auto in = serial_t::read()) {
+			char c = static_cast<char>(*in);
+			if (c == '\r' || c == '\n') {
+				serial << "\r\n"_P;
+				dispatch(std::string_view{line, at});
+				at = 0;
+				if (!monitoring)
+					prompt();
+			} else if (c == 0x7f || c == 0x08) {
+				if (at) {
+					--at;
+					serial << "\b \b"_P;
+				}
+			} else if (at < line_max && c >= ' ') {
+				line[at++] = c;
+				serial << c; // echo
+			}
+		}
+	}
+};
+
+} // namespace app