From 6f7633cf682c42984a9f12e1cf16c7123599f77e Mon Sep 17 00:00:00 2001
From: Niklas Halle <niklas@niklashalle.net>
Date: Tue, 5 May 2020 20:16:24 +0200
Subject: color!

---
 01_exercise/bootloader.c | 99 ++++++++++++++++++++++++++++++------------------
 1 file changed, 63 insertions(+), 36 deletions(-)

diff --git a/01_exercise/bootloader.c b/01_exercise/bootloader.c
index 07b3dcc..0500ce4 100644
--- a/01_exercise/bootloader.c
+++ b/01_exercise/bootloader.c
@@ -1,30 +1,60 @@
 /* needs to stay the first line */
-asm(".code16gcc\njmp $0, $main");
+asm(".code16gcc;"
+    "jmp $0, $main");
 
-/* space for additional code */
+/*
+ * 0 black
+ * 1 blue
+ * 2 green
+ * 3 cyan
+ * 4 red
+ * 5 magenta
+ * 6 brown
+ * 7 light gray
+ * 8 dark gray
+ * 9 light blue
+ * A light green
+ * B light cyan
+ * C light red
+ * D light magenta
+ * E yellow
+ * F white
+ */
 
-char WRITE_CHARACTER_TTY = 0x0E;
+#define BG_COLOR 0x0
+#define FG_COLOR 0x4
+#define TEXT_COLOR (BG_COLOR << 4 | FG_COLOR)
 
-// Syscall found here http://www.ctyme.com/intr/rb-0106.htm
 void putc(char c) {
-    short command = WRITE_CHARACTER_TTY << 8 | c;
-    // volatile because there is no output, so the function might get optimized
-    // away
-    // clang-format off
-    asm volatile(
-        "int $0x10;"
-        ::"a"(command)
-    );
-    // clang-format on
+    asm volatile("mov $0x0E, %%ah;"
+                 "int $0x10;" ::"al"(c));
+}
+
+void putc_color(char c, char color) {
+    asm volatile("mov $0x09, %%ah;"    // using Int 10h AH=09 for attributes
+                 "and $0x00FF, %%bx;"  // erase higher bits of bx
+                 "mov $0x0001, %%cx;"  // write the char once
+                 "int $0x10;"          // we need to manually move the cursor
+                 "mov $0x0300, %%eax;" // get cursor position
+                 "int $0x10;"
+                 "add $0x1, %%dl;"     // raise column by one
+                 "mov $0x0200, %%eax;" // set cursor position
+                 "int $0x10;" ::"al"(c),
+                 "bl"(color)
+                 : "cx", "dx");
 }
 
 void print(char const *const str) {
     for (int i = 0; str[i] != '\0'; ++i) {
-        putc(str[i]);
+        putc_color(str[i], TEXT_COLOR);
     }
 }
 
-// Syscall found here http://www.ctyme.com/intr/rb-1754.htm
+void new_line() {
+    putc('\n');
+    putc('\r');
+}
+
 char getc() {
     char ret;
     asm volatile(
@@ -48,21 +78,20 @@ char getc() {
     return ret;
 }
 
-void sleep(short ms) {
-    long ys = ms * 1000;
-    short cx = ys >> 16;
-    short dx = ys;
-
+void sleep(long ys) {
     // http://www.ctyme.com/intr/rb-1525.htm : Int 15/AH=86h bios wait
-    char ah = 0x86;
-    char al = 0x00;
-    short command = ah << 8 | al;
-
-    asm volatile("int $0x15;" : : "a"(command), "cx"(cx), "dx"(dx));
+    asm volatile("mov $0x8600, %%ax;"
+                 "int $0x15;" ::"cx"((ys >> 16)),
+                 "dx"(ys));
 }
 
 void main(void) {
-    print("Hello!\n\r");
+    print("Hello!");
+    new_line();
+
+    asm volatile("mov $0x00A2, %%ax;" // switch to video mode
+                 "int $0x10" ::
+                     : "ax");
 
     while (1) {
         char buf[9];
@@ -70,8 +99,9 @@ void main(void) {
             char c = getc();
             if (c == '\r') {
                 if (i == 0) { // empty entry
-                    print("Reboot!\n\r");
-                    sleep(250); // too see the reboot print out, even if short
+                    print("Reboot!");
+                    sleep(500000); // sleep 500ms, to see the reboot print out, even if
+                                   // short
                     asm volatile(
                         "cli;"              // disable interrupts
                         "mov $0x0FE, %%al;" // tell the keyboard controller to...
@@ -80,21 +110,18 @@ void main(void) {
                         "hlt;"          // some motherboards require this
                         "jmp .halt;" :: // and again, just to be sure
                         : "al");
-                    return;
                 } else {
                     break;
                 }
             }
             buf[i] = c;
             buf[i + 1] = 0;
-            putc('*');
-        }
-        while (1) {
-            if (getc() == '\r')
-                break;
+            putc_color('*', 0x02); // hard coded green on black
         }
-        print("\n\r");
+        while (getc() != '\r')
+            ;
+        new_line();
         print(buf);
-        print("\n\r");
+        new_line();
     }
 }
\ No newline at end of file
-- 
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