From 88d3bc5df1933b2753f33e5436b49e37a193abe1 Mon Sep 17 00:00:00 2001
From: Niklas Halle <niklas@niklashalle.net>
Date: Tue, 5 May 2020 16:58:03 +0200
Subject: getc now waits for keys

---
 01_exercise/bootloader.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/01_exercise/bootloader.c b/01_exercise/bootloader.c
index e891116..bc7d807 100644
--- a/01_exercise/bootloader.c
+++ b/01_exercise/bootloader.c
@@ -6,7 +6,7 @@ asm(".code16gcc\njmp $0, $main");
 char WRITE_CHARACTER_TTY = 0x0E;
 
 // Syscall found here http://www.ctyme.com/intr/rb-0106.htm
-void put(char c) {
+void putc(char c) {
     short command = WRITE_CHARACTER_TTY << 8 | c;
     // volatile because there is no output, so the function might get optimized
     // away
@@ -20,16 +20,29 @@ void put(char c) {
 
 void print(char const *const str) {
     for (int i = 0; str[i] != '\0'; ++i) {
-        put(str[i]);
+        putc(str[i]);
     }
 }
 
 // Syscall found here http://www.ctyme.com/intr/rb-1754.htm
 char getc() {
     char ret;
-    asm("mov $0x00, %%ah;"
+    asm volatile(
+        ".no_key:"
+        "xor %%ax, %%ax;"
+        "mov $0x0100, %%ax;" // check for keystroke:
+        "int $0x16;"         // http://www.ctyme.com/intr/rb-1755.htm
+        "jz .no_key;"        // wait for a key
+        ".done:"
+        "xor %%ax, %%ax;"
+        "mov $0x1000, %%ax;" // get keystroke: http://www.ctyme.com/intr/rb-1754.htm
         "int $0x16;"
-        : "=a"(ret));
+        "mov %%al, %%bl;"  // temp store char in bl
+        "mov $0400, %%ax;" // clear keyboard buffer:
+        "int $0x16;"       // http://www.ctyme.com/intr/rb-1759.htm
+        : "=b"(ret)
+        :
+        : "ax");
     return ret;
 }
 
@@ -49,4 +62,7 @@ void sleep(short ms) {
 void main(void) {
     print("Hello!");
     print("\n\r > ");
+    while (1) {
+        putc(getc());
+    }
 }
\ No newline at end of file
-- 
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