more optimizations and typo fixes

Author: Joshua-Riek

makefile

@@ -136,5 +136,5 @@ debug: image
 	qemu-system-i386 -serial stdio -rtc base=localtime -S -s -drive file=bin/boot12.img,format=raw,if=floppy
 
 gdb: image
-	-gdb -q -ex "exec-file bin/boot12.elf" -ex "add-symbol-file bin/boot12.elf 0x9FA00 -readnow" -ex "b reallocatedEntry"
+	-gdb -q -ex "exec-file bin/boot12.elf" -ex "add-symbol-file bin/boot12.elf 0x9FA00 -readnow" -ex "break reallocatedEntry"
 endif

src/boot12.asm

@@ -122,8 +122,8 @@ reallocatedEntry:
 ;---------------------------------------------------
 
 allocDiskbuffer:
-    xor ax, ax
-    mov dx, ax                                  ; Calculate the size of fat in sectors
+    xor ah, ah
+    xor dx, dx                                  ; Calculate the size of fat in sectors
     mov al, byte [fats]                         ; Take the number of fats
     mul word [fatSectors]                       ; And multiply that by the number of sectors per fat
 
@@ -166,7 +166,7 @@ loadRoot:
 ;---------------------------------------------------
 
 findFile:
-    mov dx, word [rootDirEntries]               ; Search through all of the root dir entrys for the kernel
+    mov dx, word [rootDirEntries]               ; Search through all of the root dir entries for the kernel
     push di
 
   .searchRoot:
@@ -251,8 +251,7 @@ readClusters:
     mul bx                                      ; Multiply the cluster by the sectors per cluster
     add ax, word [cs:startOfData]               ; Finally add the first data sector
 
-    xor ch, ch
-    mov cl, byte [sectorsPerCluster]            ; Sectors to read
+    mov cx, bx                                  ; Sectors to read
     call readSectors                            ; Read the sectors
 
     pop ax
@@ -261,14 +260,14 @@ readClusters:
     push ds
     push si
 
-    xor dx, dx                                  ; Get the next cluster for FAT
-    mov bx, 3                                   ; We want to multiply by 1.5 so divide by 3/2 
+    xor dx, dx                                  ; Get the next cluster for fat
+    mov bl, 3                                   ; We want to multiply by 1.5 so divide by 3/2 
     mul bx                                      ; Multiply the cluster by the numerator
-    mov bl, 2                                   ; Return value in ax and remainder in dx
+    dec bx                                      ; Return value in ax and remainder in dx
     div bx                                      ; Divide the cluster by the denominator
 
-    add si, ax                                  ; Point to the next cluster in the FAT entry
-    mov ax, word [ds:si]                        ; Load ax to the next cluster in FAT
+    add si, ax                                  ; Point to the next cluster in the fat entry
+    mov ax, word [ds:si]                        ; Load ax to the next cluster in fat
 
     pop si
     pop ds
@@ -301,8 +300,8 @@ readClusters:
     add ch, dl                                  ; Then add the lower half to the segment
     mov es, cx
 
-    clc
-    add di, bx                                  ; Add to the pointer offset
+    clc                                         ; Add to the pointer offset
+    add di, bx
     jnc .clusterLoop 
 
   .fixBuffer:                                   ; An error will occur if the buffer in memory
@@ -342,7 +341,7 @@ readSectors:
     push cx
     push dx
 
-    div word [sectorsPerTrack]                  ; Divide the lba (value in ax:dx) by sectorsPerTrack
+    div word [sectorsPerTrack]                  ; Divide lba by the sectors per track
     mov cx, dx                                  ; Save the absolute sector value 
     inc cx
 
@@ -382,7 +381,9 @@ readSectors:
     pop cx
     pop ax
 
-    inc ax                                      ; Increase the next sector to read
+    clc
+    add ax, 1                                   ; Add one for the the next lba value
+    adc dx, 0                                   ; Make sure to adjust dx for carry
 
     clc
     add bx, word [bytesPerSector]               ; Add to the buffer address for the next sector

src/boot16.asm

@@ -119,8 +119,8 @@ reallocatedEntry:
 ;---------------------------------------------------
 
 allocDiskbuffer:
-    xor ax, ax
-    mov dx, ax                                  ; Calculate the size of fat in sectors
+    xor ah, ah
+    mov dx, dx                                  ; Calculate the size of fat in sectors
     mov al, byte [fats]                         ; Take the number of fats
     mul word [fatSectors]                       ; And multiply that by the number of sectors per fat
 
@@ -163,7 +163,7 @@ loadRoot:
 ;---------------------------------------------------
 
 findFile:
-    mov dx, word [rootDirEntries]               ; Search through all of the root dir entrys for the kernel
+    mov dx, word [rootDirEntries]               ; Search through all of the root dir entries for the kernel
     push di
 
   .searchRoot:
@@ -248,8 +248,7 @@ readClusters:
     mul bx                                      ; Multiply the cluster by the sectors per cluster
     add ax, word [cs:startOfData]               ; Finally add the first data sector
 
-    xor ch, ch
-    mov cl, byte [sectorsPerCluster]            ; Sectors to read
+    mov cx, bx                                  ; Sectors to read
     call readSectors                            ; Read the sectors
 
     pop ax
@@ -259,20 +258,20 @@ readClusters:
     push si
 
     xor dx, dx
-    mov cx, 2                                   ; Get the next cluster for FAT16 
+    mov cx, 2                                   ; Get the next cluster for fat 
     mul cx                                      ; Multiply the cluster by 2
 
     xor bx, bx
-    add si, ax                                  ; Add the offset into the FAT16 table
+    add si, ax                                  ; Add the offset into the fat table
     adc bx, dx                                  ; Make sure to adjust for carry 
 
     mov cl, 4
-    shl bl, cl                                  ; Correct the segment based on the offset into the FAT16 table
+    shl bl, cl                                  ; Correct the segment based on the offset into the fat table
     mov dx, ds                                  ; Shift left by 4 bits
     add dh, bl                                  ; Then add the higher half to the segment
     mov ds, dx
 
-    mov ax, word [ds:si]                        ; Load ax to the next cluster in the FAT16 table
+    mov ax, word [ds:si]                        ; Load ax to the next cluster in the fat table
 
     pop si
     pop ds
@@ -335,7 +334,7 @@ readSectors:
     push cx
     push dx
 
-    div word [sectorsPerTrack]                  ; Divide the lba (value in ax:dx) by sectorsPerTrack
+    div word [sectorsPerTrack]                  ; Divide lba by the sectors per track
     mov cx, dx                                  ; Save the absolute sector value 
     inc cx