Merge upstream changes from branch 'trunk' into fat32_sys_rewrite

include/fat32/FAT32_SYS.inc

@@ -40,16 +40,14 @@ InitFATDriver:
     sub sp, 0x6
 
 .calc_active_part:
-    mov bx, [partition_offset]                     
-    mov ax, partition_table
-    add ax, cx
-    mov si, ax                                  ; si = offset to active partition
-    
-    mov ax, fat32_state
-    mov di, ax
+    mov ax, word [partition_offset]            
 
-    mov eax, dword [si + PartEntry_t.lba_start]
-    mov dword [di + FAT32_State_t.curr_drive_lba_32], eax
+    mov dx, partition_table
+    add dx, ax                                                           ; dx points to the partition that was booted from
+    mov bx, dx                                                           ; set bx, should point at our partition
+
+    mov eax, dword [bx + PartEntry_t.lba_start]
+    mov dword [fat32_state + FAT32_State_t.active_drive_lba_32], eax
 
     mov ax, fat32_bpb
     mov si, ax
@@ -138,7 +136,7 @@ SearchFATDIR:
         add sp, 0x4
 
         cmp eax, 0x0fff_fff7
-        ;je SearchFATDIR.bad_cluster
+        ;je SearchFATDIR.bad_cluster            ; TODO: Implement Bad cluster checks
         jb SearchFATDIR.load_next_dir_next_OK
         ERROR STAGE2_FAT32_END_OF_CHAIN
 
@@ -245,7 +243,8 @@ NextCluster:
     add eax, ecx        ; fat_sector + first_fat_sector
     mov dword [si + FAT32_NextClusterData_t.fat_sector], eax
 .load_fat_table:
-    mov ax, word [boot_drive]
+    xor ax, ax
+    mov al, byte [boot_drive]
     push ax
 
     mov ax, 0x1
@@ -260,20 +259,6 @@ NextCluster:
 
     xor ax, ax
     push ax
-    ; BUG: something about this function causes this BIOS call to come back wrong
-    ; somehow the drive number is being read in wrong, but I can't find evidence of it being modified or writen
-    ; to memory incorrectly.
-    ; 00007109574i[BIOS  ] Booting from 0000:7c00
-    ; 00007123227i[CPU0  ] [7123227] Stopped on MAGIC BREAKPOINT
-    ; (0) Magic breakpoint
-    ; Next at t=7123227
-    ; (0) [0x000000000502] 0000:0502 (unk. ctxt): cli                       ; fa
-    ; <bochs:2> c
-    ; 00007252963i[BIOS  ] int13_diskette: unsupported AH=42
-    ; 00007253071i[CPU0  ] [7253071] Stopped on MAGIC BREAKPOINT
-    ; (0) Magic breakpoint
-    ; Next at t=7253071
-    ; (0) [0x00000000095c] 0000:095c (unk. ctxt): mov al, 0x47              ; b047
     call read_disk_raw  
     add sp, 0xC
     ; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, 
@@ -317,7 +302,8 @@ ReadFATCluster:
 .func:
     print_string ReadFATCluster_info
 
-    mov ax, word [boot_drive]
+    xor ax, ax
+    mov al, byte [boot_drive]
     push ax
 
     mov ax, 0x1                         ; count = 1