Hello world over serial

kernel/amd64/debug.c

@@ -0,0 +1,46 @@
+#include <libk/std.h>
+#include <libk/string.h>
+#include <libk/printf.h>
+#include <sys/debug.h>
+#include <amd64/debug.h>
+#include <amd64/io.h>
+
+#define PORT_COM1   0x03F8
+#define BUFFER_SIZE 1024
+
+static bool amd64_debug_serial_tx_empty(void) {
+  return (bool)(amd64_io_inb(PORT_COM1 + 5) & 0x20);
+}
+
+static void amd64_debug_serial_write(char x) {
+  while (!amd64_debug_serial_tx_empty());
+  amd64_io_outb(PORT_COM1, (uint8_t)x);
+}
+
+void debugprintf(const char *fmt, ...) {
+  char buffer[BUFFER_SIZE];
+  memset(buffer, 0, sizeof(buffer));
+
+  va_list ap;
+  va_start(ap, fmt);
+  vsnprintf(buffer, sizeof(buffer), fmt, ap);
+  va_end(ap);
+
+  buffer[sizeof(buffer) - 1] = '\0';
+
+  const char *p = buffer;
+  while (*p) {
+    amd64_debug_serial_write(*p);
+    p++;
+  }
+}
+
+void amd64_debug_init(void) {
+  amd64_io_outb(PORT_COM1 + 1, 0x00);
+  amd64_io_outb(PORT_COM1 + 3, 0x80);
+  amd64_io_outb(PORT_COM1 + 0, 0x03);
+  amd64_io_outb(PORT_COM1 + 1, 0x00);
+  amd64_io_outb(PORT_COM1 + 3, 0x03);
+  amd64_io_outb(PORT_COM1 + 2, 0xC7);
+  amd64_io_outb(PORT_COM1 + 4, 0x0B);
+}