fix ps2 link

Add BootMine boot sector game

README.adoc

@@ -16,6 +16,16 @@ link:{logo}[image:{logo}[]]
 
 toc::[]
 
+== China
+
+Before <<getting-started>>, read this important pre-requisite: https://github.com/cirosantilli/china-dictatorship
+
+Because human rights is more important than profit and technology.
+
+image::https://raw.githubusercontent.com/cirosantilli/china-dictatorship-media/master/Hao_Haidong_kick.jpg[width=600]
+
+image::https://raw.githubusercontent.com/cirosantilli/china-dictatorship-media/master/Xi_sadomasochist.jpg[width=600]
+
 == Getting started
 
 First read this introduction: https://stackoverflow.com/questions/22054578/how-to-run-a-program-without-an-operating-system/32483545#32483545
@@ -1277,7 +1287,7 @@ Without segment manipulation, the output would be just: TODO
 
 ===== Segmentation introduction
 
-First read the paging tutorial, and in particular: http://www.cirosantilli.com/x86-paging/#segmentation to get a feel for the type of register and data structure manipulation required to configure the CPU, and how segmentation compares to paging.
+First read the paging tutorial, and in particular: https://cirosantilli.com/x86-paging#segmentation to get a feel for the type of register and data structure manipulation required to configure the CPU, and how segmentation compares to paging.
 
 Segmentation modifies every memory access of a given segment by:
 
@@ -1485,7 +1495,7 @@ Try commenting out waking up the second processor and see it not get printed.
 
 ==== Paging
 
-Verbose beginner's tutorial: http://www.cirosantilli.com/x86-paging/
+Verbose beginner's tutorial: https://cirosantilli.com/x86-paging
 
 Change page tables and observe how that affects memory accesses:
 
@@ -2311,6 +2321,7 @@ Almost entirely in C `-nostdlib`, with very few inline `asm` commands, and a sma
 * https://github.com/nanochess/fbird Flappy bird in the 512-byte boot sector.
 * https://github.com/Overv/MineAssemble Minecraft
 * https://github.com/tsoding/pinpog Pong / Breakout
+* https://github.com/io12/bootmine Minesweeper game in a 512-byte boot sector.
 
 === Tutorials
 
@@ -2423,7 +2434,7 @@ A list of ARM bare metal resources can be found at: https://github.com/cirosanti
 
 == LICENSE
 
-Copyright Ciro Santilli http://www.cirosantilli.com/
+Copyright Ciro Santilli https://cirosantilli.com
 
 https://www.gnu.org/licenses/gpl-3.0.txt[GPL v3] for executable computer program usage.
 

common.h

@@ -212,8 +212,9 @@ protected_mode:
     mov %ebp, %esp
 .endm
 
-/* Setup a single page directory, which give us 2^10 * 2^12 == 4MiB
- * of identity memory starting at address 0.
+/* Setup the first Page Directory entry, which gives us a 4MB(2^10 * 2^12) memory region.
+ * The memory region starts at 0, and the virtual address and physical address are identical.
+ * 
  * The currently executing code is inside that range, or else we'd jump somewhere and die.
  */
 .equ page_directory, __end_align_4k
@@ -222,15 +223,15 @@ protected_mode:
     LOCAL page_setup_start page_setup_end
     PUSH_EADX
 
-    /* Page directory steup. */
+    /* Page Directory setup. */
     /* Set the top 20 address bits. */
     mov $page_table, %eax
-    /* Zero out the 4 low flag bits of the second byte (top 20 are address). */
+    /* Clear the low 12 bits of the first Page Directory entry. */
     and $0xF000, %ax
-    mov %eax, page_directory
-    /* Set flags for the first byte. */
+    /* Set the P, R/W, U/S, and A bits of the first Page Directory entry. */
     mov $0b00100111, %al
-    mov %al, page_directory
+    /* Setup the first Page Directory entry. */
+    mov %eax, page_directory
 
     /* Page table setup. */
     mov $0, %eax
@@ -241,14 +242,15 @@ page_setup_start:
     /* Top 20 address bits. */
     mov %eax, %edx
     shl $12, %edx
-    /* Set flag bits 0-7. We only set to 1:
-     * * bit 0: Page present
-     * * bit 1: Page is writable.
+    /* For flag bits 0-7. We only set bit 0 and bit 1:
+     * - bit 0: Page present
+     * - bit 1: Page is writable.
      *  Might work without this as the permission also depends on CR0.WP.
      */
     mov $0b00000011, %dl
     /* Zero flag bits 8-11 */
     and $0xF0, %dh
+    /* Setup the PTE(Page Table Entry). */
     mov %edx, (%ebx)
     inc %eax
     add $4, %ebx

interrupt_keyboard.S

@@ -1,4 +1,4 @@
-/* https://github.com/cirosantilli/x86-bare-metal-examples#ps-2-keyboard */
+/* https://github.com/cirosantilli/x86-bare-metal-examples#ps2-keyboard */
 
 #include "common.h"
 BEGIN

paging.S

@@ -1,4 +1,4 @@
-/* https://github.com/cirosantilli/x86-bare-metal-examples#paging.S */
+/* https://github.com/cirosantilli/x86-bare-metal-examples#paging */
 
 #include "common.h"
 
@@ -14,8 +14,15 @@ BEGIN
     /* Print the canary to make sure it is really there. */
     VGA_PRINT_HEX_4 0x1000
 
-    /* Make page 0 point to 4KiB. */
-    orb $0x10, page_table + 1
+    /* Make page 0 point to page frame 1(i.e. virtual address 0 points to physical address 4KB)
+     * by setting bit 12 of the Page Table Entry structure.
+     *
+     * At SETUP_PAGING_4M, page_table has been setup to
+     * point page frame 0(i.e. page 0 point to page frame 0).
+     * Bit 12 is the lowest bit of the "Address of 4KB page frame" field,
+     * By setting it, can relocate page 0 point to page frame 1.
+     */
+    orw $0x1000, page_table
 
     PAGING_ON