From 1c0fe61eb340d0b5f59fb81517f468fbd4fe1208 Mon Sep 17 00:00:00 2001
From: Niklas Halle <niklas@niklashalle.net>
Date: Tue, 5 May 2020 18:25:29 +0200
Subject: better reboot

---
 01_exercise/bootloader.c | 32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/01_exercise/bootloader.c b/01_exercise/bootloader.c
index afd4d96..50a6b0e 100644
--- a/01_exercise/bootloader.c
+++ b/01_exercise/bootloader.c
@@ -29,20 +29,22 @@ char getc() {
     char ret;
     asm volatile(
         ".no_key:"
-        "xor %%ax, %%ax;"
+        "xor %%eax, %%eax;"
         "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;"
+
+        "xor %%eax, %%eax;"
         "mov $0x1000, %%ax;" // get keystroke: http://www.ctyme.com/intr/rb-1754.htm
         "int $0x16;"
+
         "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");
+        : "eax");
     return ret;
 }
 
@@ -67,20 +69,16 @@ void main(void) {
             char c = getc();
             if (c == '\r') {
                 if (i == 0) { // empty entry
-                    print("Reboot!");
-                    /*asm volatile(
-                        "mov $0x5307, %%ax;" // TURN OFF SYSTEM:
-                                             // http://www.ctyme.com/intr/rb-1356.htm
-                        "mov $0x0001, %%bx;"
-                        "mov $0x0003, %%cx;"
-                        "int $0x15" ::
-                            : "ax", "bx", "cx");*/
-                    asm volatile("xor %%eax, %%eax\n"
-                                 "push %%eax\n"
-                                 "push %%ax\n"
-                                 "lidt (%%esp)\n"
-                                 "mov %%ss, %%eax" ::
-                                     : "eax");
+                    print("Reboot!\n\r");
+                    sleep(250); // too see the reboot print out, even if short
+                    asm volatile(
+                        "cli;"              // disable interrupts
+                        "mov $0x0FE, %%al;" // tell the keyboard controller to...
+                        "out %%al, $0x64;"  // ...activate the CPU reset line
+                        ".halt:"
+                        "hlt;"          // some motherboards require this
+                        "jmp .halt;" :: // and again, just to be sure
+                        : "al");
                     return;
                 } else {
                     break;
-- 
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