Add folder structure documentation for i386

As the project grows, it's a good idea to have an overview of the
project as a big picture. The newly added file will provide that big
picture for when the project is too big to read through for making a
small change. It contains unimplemented things in the described
folder structure (AHCI) as well as a documentation folder, which also
doesn't exist yet.

i386/folder-structure.md

@@ -0,0 +1,45 @@
+# i386 Nightloader | Folder Structure
+
+## Legacy BIOS bootsector (bootsector/)
+
+Contains one file, the source of the bootsector. This assembly program
+must span the first 512 byte of a legacy Nightloader-booted Partition.
+
+## Legacy BIOS Edition (legacy-boot/)
+
+This edition of the Nightloader is made for older devices that predate
+UEFI (or potentially for devices that have unreliable UEFI-support).
+
+This folder contains the assembly sources to create the loader
+partition which contains raw machine code that is loaded by the
+bootsector and to which the control is handed thereafter.
+
+### Source Folder Structure
+
+#### drivers/
+
+- acpi  
+  Driver for the Avanced Control and Power Interface.
+- pci  
+  Driver for the Peripheral Component Interconnect. This is used to
+  first find and then interact with the builtin devices in a computer,
+  mostly storage devices, but also network cards, USB keyboards, etc..
+- ahci  
+  Driver for AHCI, the ATA Host Controller Interface (ATA meaning 
+  (IBM PC) AT Attachment), storage interface. This is used to interact
+  with practically every modern consumer SSD and HDD. Older HDDs might
+  use another interface, but that's not of elevated relevance.
+
+
+#### memory/
+
+Memory Management functions, A20 line check, GDT setup and, some day
+in the future, paging for add-ons execution. This also contains utils
+like the allocators (arena, pool) used throughout the bootloader.
+
+#### utility/
+
+Helper functions that make it easier to write the other functionality
+but don't fall into any of the other categories on their own.
+
+## Documentation (docs/)

i386/legacy-boot/src-asm/drivers/acpi/utility.asm

@@ -53,7 +53,7 @@ acpi_enumerate_tables:
     mov ebx, [esi + 8]
     add ebx, eax
 
-    mov eax, [ebx]Z
+    mov eax, [ebx]
 
     inc ecx
     jmp .enumeration_loop
@@ -97,7 +97,7 @@ acpi_search_rsdt:
     pop         ebp
 
     cmp         ax,                     0
-    jne         .rsdp_found
+    jne         .resolve_rsdp
 
     add         ecx,                    16
     cmp         ecx,                    0x100000
@@ -105,6 +105,7 @@ acpi_search_rsdt:
     
     ; If no "RSD PTR "-signature could be found
     xor         ecx,                    ecx
+    jmp .epilog
 
 .resolve_rsdp:
     ; The 4-byte RSDT-pointer is at byte-offset 4 into the RSDP strucfture.

i386/legacy-boot/src-asm/drivers/pci/driver.asm

@@ -34,7 +34,7 @@ initialize_pci_driver:
 
     push ebp
     mov ebp, esp
-    push ebx
+    push dword PCI_DEVICE_COUNT_OFFSET
     push dword 2
     push dword 0
     push dword 0

i386/legacy-boot/src-asm/drivers/pci/enumerate.asm

@@ -190,11 +190,12 @@ pci_enumerate_bus:
 
     mov         [esi + (64 - 8)],       ebx
     mov         [esi + (64 - 12)],      ecx
+    mov         [esi + (64 - 16)],      edx
     mov         [esi + (64 - 20)],      edi
     ; [esi]:        Device-in-bus Index
     ; [esi + 4]:    Number of existing devices
     ; [esi + 8]:    Bus number
-    ; [esi + 12]:   
+    ; [esi + 12]:   PCI driver area pointer
     mov         [esi],                  dword 0
     mov         [esi + 4],              dword 0
     mov         eax,                    [ebp - 8]
@@ -259,6 +260,7 @@ pci_enumerate_bus:
 .epilog:
     mov         ebx,                    [esi + (64 - 8)]
     mov         ecx,                    [esi + (64 - 12)]
+    mov         edx,                    [esi + (64 - 16)]
     mov         edi,                    [esi + (64 - 20)]
 
     mov         eax,                    [esi + 4]
@@ -313,7 +315,6 @@ pci_enumerate:
     cmp         edx,                    [ebp - 8]
     jae         .epilog
 
-
 .call_bus_enumerator:
     push        ebp
     mov         ebp,                    esp

i386/legacy-boot/src-asm/entry.asm

@@ -54,6 +54,12 @@ stage_2_setup_entry:
 bits 32
 stage2_protected_entry:
 
+    push ebp
+    mov ebp, esp
+    call setup_drivers
+    mov esp, ebp
+    pop ebp
+    
     cli
     hlt