x86_64/debug: implement debug port detection

1 files changed, 6 insertions, 4 deletions

diff --git a/arch/x86_64/include/x86_64/debug/qemu_output.hpp b/arch/x86_64/include/x86_64/debug/qemu_output.hpp
index 6ff4da6..61b47d6 100644
--- a/arch/x86_64/include/x86_64/debug/qemu_output.hpp
+++ b/arch/x86_64/include/x86_64/debug/qemu_output.hpp
@@ -15,13 +15,13 @@ namespace teachos::debug::x86_64
   //! This device implements output to the port 0xE9 debug console present in QEMU in Bochs. It is designed to wrap a
   //! different output device (e.g. a VGA text output device) and forwards the written data accordingly.
   //!
-  //! @note Support for the device has to be enabled when the emulator is started. Since there is no reliable way to
-  //! detect the presence of the port, writes will still happen even if the device is not enabled in the emulator. It is
-  //! thus possible that the output is simply lost.
+  //! @note Support for the device has to be enabled when the emulator is started. The device will try to detect if the
+  //! port is available. If the port is detected, any output to the device will be written to port before being
+  //! forwarded to the lower device.
   struct qemu_output : cio::output_device
   {
     //! The port to write to.
-    using dbg = io::x86_64::port<0xE9, char, io::x86_64::port_write>;
+    using port = io::x86_64::port<0xE9, unsigned char, io::x86_64::port_write, io::x86_64::port_read>;
 
     //! Construct a new debug device wrapper for the given output device.
     //!
@@ -34,6 +34,8 @@ namespace teachos::debug::x86_64
   private:
     //! The device to forward the output to.
     output_device & m_lower;
+    //! Whether the device has been detected.
+    bool m_present;
   };
 
 }  // namespace teachos::debug::x86_64