begin working on LBA to CHS conversion in assembly

Makefile

@@ -102,7 +102,7 @@ $(OBJ_DIR)/%.o: $(SRC_DIR)/%.s
 $(OBJ_DIR)/%.o: $(SRC_DIR)/%.c
 	$(CC) $(CFLAGS) -c -o $@ $<
 
-MBR_TEST_OBJ		=	obj/mbr_test.o obj/serial.o obj/itoa.o obj/util.o obj/test_disk_target.o
+MBR_TEST_OBJ		=	obj/mbr_test.o obj/serial.o obj/itoa.o obj/util.o obj/test_disk_target.o obj/test_disk_read.o
 
 mbr_test: $(MBR_TEST_OBJ) $(DISK)
 	$(LD) -T src/mbr_test.ld -o $(BIN_DIR)/mbr_test.bin $(MBR_TEST_OBJ)

src/mbr_test.s

@@ -36,7 +36,7 @@ entry:
 .bootloader:
     call serial_init
 
-    mov $0x01, %al # disk 1
-    call test_disk_params
+    mov $73728, %eax
+    call lba_to_chs
 .halt:
     jmp .halt

src/test_disk_read.s

@@ -1,8 +1,72 @@
 .section .text
 .code16
 
+.globl lba_to_chs
 .globl test_disk_read
 
+# eax - LBA
+# dh - head, ch - cylinder low 8 bits, cl - high 2 cylinder bits, 6 low bits is sector
+lba_to_chs:
+    # we actually gonna need stack frame for that one lol
+    push %bp
+    mov %sp, %bp
+    sub $10, %sp
+    # -4(%bp)   dword   LBA
+    # -6(%bp)   word    cylinder
+    # -8(%bp)   word    head
+    # -10(%bp)  word    sector
+    mov %eax, -4(%bp) # save LBA
+
+    # chs->head = lba / (conf->num_heads * conf->num_sectors);
+    # (conf->num_heads * conf->num_sectors)
+    movw disk_heads, %ax
+    mulw disk_sectors
+    mov %ax, %bx
+    # lba /
+    xor %dx, %dx
+    mov -4(%bp), %eax
+    div %ebx
+    # ax - head
+    mov %ax, -8(%bp)
+
+    # chs->cylinder = (lba / conf->num_sectors) % conf->num_heads;
+    # (lba / conf->num_sectors)
+    xor %dx, %dx
+    movw disk_sectors, %bx
+    mov -4(%bp), %eax
+    div %ebx
+    # % conf->num_heads
+    xor %dx, %dx
+    divw disk_heads
+    # dx, as remainder, now has cylinder
+    mov %dx, -6(%bp)
+
+    # chs->sector = (lba % conf->num_sectors) + 1;
+    xor %dx, %dx
+    mov -4(%bp), %eax
+    divw disk_sectors
+    # dx now has sector num, but we need to increment it
+    inc %dx
+    # dx - sector
+    mov %dx, -10(%bp)
+
+    # now lets print C H S values
+    mov -6(%bp), %ax
+    mov $str_cylinder, %si
+    call prints_number
+
+    mov -8(%bp), %ax
+    mov $str_head, %si
+    call prints_number
+
+    mov -10(%bp), %ax
+    mov $str_sector, %si
+    call prints_number
+
+    mov %bp, %sp
+    pop %bp
+    ret
+
 # eax   - LBA address
 # cx    - number of sectors
 # es:di - destination
@@ -14,11 +78,14 @@ test_disk_read:
 test_disk_taste_sector:
     # test pattern partition - each sector has 32 bit integer in beginning
     # so we read this integer and output it, it must increment as well as LBA address
-    lodsd # load 32 bit into eax
+    mov (%esi), %eax
     mov $str_taste, %si
     call prints_number
 
     ret
 
 .section .rodata
+str_cylinder:   .asciz  "Cylinder: "
+str_head:       .asciz  "Head: "
+str_sector:     .asciz  "Sector: "
 str_taste:      .asciz  "Sector test pattern: "

src/test_disk_target.s

@@ -1,6 +1,11 @@
 # template file for disk parameters
 # this will target disk 1
 
+.globl disk_id
+.globl disk_heads
+.globl disk_cylinders
+.globl disk_sectors
+
 .section .rodata
 disk_id:        .word 1
 disk_heads:     .word 16