progress on FAT16 support

OperatingSystem/software/include/fat16_file.s

@@ -0,0 +1,69 @@
+
+
+;1. find sector for given cluster
+;2. read sector
+;3. store first data sector to MEM_FAT_OF0_DATSEC
+;4. set MEM_FAT_OF0_DATREM to amount uf sectors per cluster
+;5. find next cluster in FAt and update MEM_FAT_OF0_CCLUST
+
+
+; gets sector in FAT table for the cluster stored in MEM_FAT_OF0_CCLUST
+; store result in MEM_FAT_OF0_FATSEC
+; stores next cluster in MEM_FAT_OF0_CCLUST
+fat_getfatsec:
+    ld HL,(MEM_FAT_OF0_CCLUST)  ;load cluster 
+    ;each sector contains 256 clusters
+    ;first 8bits are not needed (/256)
+
+    ld a,h  ;divide by 256
+    ld l,a
+    xor a
+    ld h,a
+
+    ld bc,(MEM_FAT_RESERVED)    ;add reserved sectors
+    add hl,bc
+    ld(MEM_FAT_OF0_FATSEC+0),hl;store sector to MEM_FAT_TMPPOINTER1
+    xor a
+    ld(MEM_FAT_OF0_FATSEC+2),a
+    ld(MEM_FAT_OF0_FATSEC+3),a
+
+    call ideif_get_drv_pointer
+    inc ix
+    inc ix
+    push ix
+    pop de  ;copy poiter to hl
+    ld bc,[MEM_FAT_OF0_FATSEC]
+    call _fat_math_add32    ;MEM_FAT_OF0_FATSEC now contains the correct sector
+                            ;in the FAT
+
+    call fat_print_dbg
+
+    ;read FAT sector
+    ld hl,MEM_FAT_OF0_FATSEC   ;read next sector
+    ld b,1
+    call read_lba_sector
+
+    ld hl, MEM_IDE_BUFFER
+    ld b,20
+    call dump_pretty
+
+    ;calculate offset address
+    ld a,(MEM_FAT_OF0_CCLUST)
+    RLA ;shift to left (x2)
+    ld l, a
+    ld a,0
+    RLA ;shift in carry flag
+    ld h,a
+    ld de,MEM_IDE_BUFFER
+    add hl,de
+    ;copy pointer
+    ld de,MEM_FAT_OF0_CCLUST
+    ldi ;copy byte for next cluster from FAT
+    ldi
+
+
+    call fat_print_dbg
+
+    ret
+    ;store data
+