Docs : loader/cpu

ChangeLog

@@ -23,7 +23,7 @@
 #=----------------------------------------------------------------------------=#
 
 2018-10-00  @os-k-team <os-k-team@os-k.eu>
-Adrien Bourmault and Julian Barathie started talking about making their own OS
+Adrien Bourmault and Julian Barathieu started talking about making their own OS
 
 2018-11-00  @os-k-team <os-k-team@os-k.eu>
 Name decided & creation of os-k.eu

docs/boot/grub/grub.desc

@@ -12,7 +12,17 @@
 #   Foundation; with no Invariant Sections, no Front-Cover Texts, and          #
 #   no Back-Cover Texts.  A copy of the license is included in the             #
 #   file entitled "COPYING.GFDL"                                               #
-#=-----------------------------------------------------------------------------#
+#=----------------------------------------------------------------------------=#
 
 
-WIP
+    This folder contains the GRUB configuration file, `boot/grub/grub.cfg`,
+used by GRUB to know which OS to boot and how to boot it.
+
+    The GRUB configuration is pretty simple. We choose to use a 0 timeout, a
+single entry that starts OS/K.
+
+Because OS/K is a multiboot compliant kernel, we launch it with the multiboot
+command.
+
+For instance, we ask vbe and vga modules to be provided, but OS/K doesn't use
+these modules. 

docs/boot/loader/cpu

@@ -0,0 +1,51 @@
+#=----------------------------------------------------------------------------=#
+#                        GNU GPL OS/K Documentation                            #
+#                                                                              #
+#   Desc:   OS/K Loader : CPU Management functions                             #
+#                                                                              #
+#                                                                              #
+#   Copyright © 2018-2020 The OS/K Team                                        #
+#                                                                              #
+#   Permission is granted to copy, distribute and/or modify this               #
+#   document under the terms of the GNU Free Documentation License,            #
+#   Version 1.3 or any later version published by the Free Software            #
+#   Foundation; with no Invariant Sections, no Front-Cover Texts, and          #
+#   no Back-Cover Texts.  A copy of the license is included in the             #
+#   file entitled "COPYING.GFDL"                                               #
+#=----------------------------------------------------------------------------=#
+
+
+    This folder contains two files, `boot/loader/cpu/cpu.inc` and
+boot/loader/cpu/cpu32.inc`.
+
+The `boot/loader/cpu/cpu32.inc` is intented to provide 32 bits protected mode
+function that can control wether the CPU is qualified to run the OS/K code.
+
+The `boot/loader/cpu/cpu3.inc` provides 64 bits long mode temporization function
+used by the loader when necessary.
+
+
+    There is two functions in `cpu32.inc` :
+    - Is64Bits(), intented to check if the CPU is "ok" with 64 bit code,
+if it supports long mode and will not burn if we ask it to execute OS/K
+(i.e trigger a #UD fault).
+
+For this check, we use first the 0x80000000 function of the CPUID instruction
+that returns the highest CPUID function available. It must return at least
+0x80000001, otherwise we can't check the long mode presence and it is most
+likely absent. We pass the function number in the eax register.
+
+As soon as 0x80000001 is available, we use it and verify it flips to 1 the bit
+29 in edx.
+
+
+    - Check_cpuid(), that check if the CPUID instruction is supported by the CPU
+before use it (don't want #UD).
+
+For this, we use the FLAGS register and check if we can flip (overwrite with
+a 1 persistantly) the bit 21. If it is possible, then CPUID is supported.
+
+
+    The temporize(), bitemporize() and tritemporize() functions in `cpu.inc`
+are juste loops that make the cpu busy to wait. These temporization are not
+precise at all, and are not intented to wait for a determined time lapse. 

docs/boot/loader/loader.desc

@@ -12,7 +12,7 @@
 #   Foundation; with no Invariant Sections, no Front-Cover Texts, and          #
 #   no Back-Cover Texts.  A copy of the license is included in the             #
 #   file entitled "COPYING.GFDL"                                               #
-#=-----------------------------------------------------------------------------#
+#=----------------------------------------------------------------------------=#
 
 
     This folder contains the source for OS/K's early loader.
@@ -30,4 +30,8 @@ specified address and prepare it for the hard work it have to do :
     - Send a structure for it with memory map, cpu infos, and other devices
 infos, prepared by GRUB.
     - Switch into long mode.
-    - Jump to Kaleid kernel.
+    - Jump to Kaleid kernel.
+
+    Our loader contains the multiboot header used by GRUB to check if the kernel
+can be started with the multiboot method. We use an ELF multiboot format, because
+it is more convenient.