Added basic GDT and (very) basic IDT. And serial output.

targets/_any/include/os/serial.hpp

@@ -0,0 +1,76 @@
+
+#pragma once
+
+#if !defined(BAD_APPLE_OS_SERIAL_HPP_INCLUDED)
+#define BAD_APPLE_OS_SERIAL_HPP_INCLUDED
+
+#include <cstdint>
+
+inline constexpr std::uint16_t PORT_COM1 = 0x3F8;
+inline constexpr std::uint16_t PORT_COM2 = 0x2F8;
+inline constexpr std::uint16_t PORT_COM3 = 0x3E8;
+inline constexpr std::uint16_t PORT_COM4 = 0x2E8;
+inline constexpr std::uint16_t PORT_COM5 = 0x5F8;
+inline constexpr std::uint16_t PORT_COM6 = 0x4F8;
+inline constexpr std::uint16_t PORT_COM7 = 0x5E8;
+inline constexpr std::uint16_t PORT_COM8 = 0x4E8;
+
+inline void writePortByte(std::uint16_t port, std::uint8_t value) noexcept
+{
+    __asm__ __volatile__(
+          "outb %0, %1"
+        :
+        : "a"(value), "Nd"(port)
+    );
+}
+
+inline std::uint8_t readPortByte(std::uint16_t port) noexcept
+{
+    std::uint8_t value = 0;
+    __asm__ __volatile__(
+          "inb %1, %0"
+        : "=a"(value)
+        : "Nd"(port)
+    );
+    return value;
+}
+
+[[nodiscard]] inline bool initSerialPort(std::uint16_t port) noexcept
+{
+    writePortByte(port + 1, 0x00);    // Disable all interrupts
+    writePortByte(port + 3, 0x80);    // Enable DLAB (set baud rate divisor)
+    writePortByte(port + 0, 0x03);    // Set divisor to 3 (lo byte) 38400 baud
+    writePortByte(port + 1, 0x00);    //                  (hi byte)
+    writePortByte(port + 3, 0x03);    // 8 bits, no parity, one stop bit
+    writePortByte(port + 2, 0xC7);    // Enable FIFO, clear them, with 14-byte threshold
+    writePortByte(port + 4, 0x0B);    // IRQs enabled, RTS/DSR set
+    writePortByte(port + 4, 0x1E);    // Set in loopback mode, test the serial chip
+    writePortByte(port + 0, 0xAE);    // Test serial chip (send byte 0xAE and check if serial returns same byte)
+
+    // Check if serial is faulty (i.e: not same byte as sent)
+    if(readPortByte(port + 0) != 0xAE) {
+        return false;
+    }
+
+    // If serial is not faulty set it in normal operation mode
+    // (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
+    writePortByte(port + 4, 0x0F);
+    return true;
+}
+
+inline void serialWrite(std::uint16_t port, std::uint8_t data) noexcept
+{
+    while ((readPortByte(port + 5) & 0x20) == 0);
+    writePortByte(port, data);
+}
+
+inline void serialWriteString(std::uint16_t port, const char* str) noexcept
+{
+    while (*str)
+    {
+        serialWrite(port, *str);
+        ++str;
+    }
+}
+
+#endif // !defined(BAD_APPLE_OS_SERIAL_HPP_INCLUDED)