x86_64: implement very simple VGA text output

4 files changed, 46 insertions, 5 deletions

diff --git a/source/kernel/arch/x86_64/CMakeLists.txt b/source/kernel/arch/x86_64/CMakeLists.txt
index 99fafe7..ffce50c 100644
--- a/source/kernel/arch/x86_64/CMakeLists.txt
+++ b/source/kernel/arch/x86_64/CMakeLists.txt
@@ -7,6 +7,7 @@ mark_as_advanced(TEACHOS_KERNEL_LINKER_SCRIPT)
 
 target_sources("kernel" PRIVATE
   "src/entry.cpp"
+  "src/vga.cpp"
 )
 
 target_include_directories("kernel" PRIVATE
diff --git a/source/kernel/arch/x86_64/include/kernel/vga.hpp b/source/kernel/arch/x86_64/include/kernel/vga.hpp
new file mode 100644
index 0000000..ee5a808
--- /dev/null
+++ b/source/kernel/arch/x86_64/include/kernel/vga.hpp
@@ -0,0 +1,11 @@
+#ifndef TEACHOS_KERNEL_VGA_HPP
+#define TEACHOS_KERNEL_VGA_HPP
+
+#include <string_view>
+
+namespace teachos::kernel::vga
+{
+    auto write(std::string_view text, std::byte color) -> void;
+}
+
+#endif
\ No newline at end of file
diff --git a/source/kernel/arch/x86_64/src/entry.cpp b/source/kernel/arch/x86_64/src/entry.cpp
index 2d4e7fb..fd9d9d0 100644
--- a/source/kernel/arch/x86_64/src/entry.cpp
+++ b/source/kernel/arch/x86_64/src/entry.cpp
@@ -1,10 +1,9 @@
-namespace teachos
+#include "kernel/vga.hpp"
+
+namespace teachos::kernel
 {
   extern "C" auto kernel_main() -> void
   {
-    while (true)
-    {
-      asm volatile("nop");
-    }
+    vga::write("TeachOS is starting up...", static_cast<std::byte>(0x4f));
   }
 }  // namespace teachos
diff --git a/source/kernel/arch/x86_64/src/vga.cpp b/source/kernel/arch/x86_64/src/vga.cpp
new file mode 100644
index 0000000..d25eaa5
--- /dev/null
+++ b/source/kernel/arch/x86_64/src/vga.cpp
@@ -0,0 +1,30 @@
+#include "kernel/vga.hpp"
+
+#include "boot/asm_pointer.hpp"
+#include "boot/pointers.hpp"
+
+#include <string_view>
+#include <algorithm>
+
+namespace teachos::kernel::vga
+{
+
+  namespace
+  {
+    auto constinit text_buffer_pointer = boot::asm_pointer{boot::vga_buffer_pointer};
+
+    auto write(char character, std::byte color) -> void
+    {
+      auto & p = *text_buffer_pointer;
+      (*p++) = static_cast<std::byte>(character);
+      (*p++) = color;
+    };
+  }  // namespace
+
+  auto write(std::string_view text, std::byte color) -> void {
+    std::ranges::for_each(text, [&](auto character) {
+        write(character, color);
+    });
+  }
+
+}  // namespace teachos::kernel
\ No newline at end of file