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pascal@24476
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1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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2 ;; ;;
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pascal@24476
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3 ;; "BootProg" Loader v 1.5 by Alexey Frunze (c) 2000-2015 ;;
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pascal@24476
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4 ;; 2-clause BSD license. ;;
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pascal@24476
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5 ;; ;;
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pascal@24476
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6 ;; ;;
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pascal@24476
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7 ;; How to Compile: ;;
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pascal@24476
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8 ;; ~~~~~~~~~~~~~~~ ;;
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pascal@24476
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9 ;; nasm boot32.asm -f bin -o boot32.bin ;;
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pascal@24476
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10 ;; ;;
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pascal@24476
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11 ;; ;;
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pascal@24476
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12 ;; Features: ;;
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pascal@24476
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13 ;; ~~~~~~~~~ ;;
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pascal@24478
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14 ;; - FAT32 supported using BIOS int 13h function 42h (IOW, it will only ;;
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pascal@24478
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15 ;; work with modern BIOSes supporting HDDs bigger than 8 GB) ;;
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pascal@24476
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16 ;; ;;
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pascal@24476
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17 ;; - Loads a 16-bit executable file in the MS-DOS .COM or .EXE format ;;
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pascal@24476
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18 ;; from the root directory of a disk and transfers control to it ;;
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pascal@24476
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19 ;; (the "ProgramName" variable holds the name of the file to be loaded) ;;
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pascal@24476
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20 ;; ;;
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pascal@24476
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21 ;; - Prints an error if the file isn't found or couldn't be read ;;
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pascal@24476
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22 ;; ("File not found" or "Read error") ;;
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pascal@24476
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23 ;; and waits for a key to be pressed, then executes the Int 19h ;;
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pascal@24476
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24 ;; instruction and lets the BIOS continue bootstrap. ;;
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pascal@24476
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25 ;; ;;
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pascal@24476
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26 ;; ;;
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pascal@24476
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27 ;; Known Bugs: ;;
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pascal@24476
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28 ;; ~~~~~~~~~~~ ;;
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pascal@24476
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29 ;; - All bugs are fixed as far as I know. The boot sector has been tested ;;
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pascal@24476
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30 ;; on my HDD and an 8GB USB stick. ;;
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pascal@24476
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31 ;; ;;
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pascal@24476
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32 ;; ;;
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pascal@24476
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33 ;; Memory Layout: ;;
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pascal@24476
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34 ;; ~~~~~~~~~~~~~~ ;;
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pascal@24476
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35 ;; The diagram below shows the typical memory layout. The actual location ;;
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pascal@24476
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36 ;; of the boot sector and its stack may be lower than A0000H if the BIOS ;;
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pascal@24476
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37 ;; reserves memory for its Extended BIOS Data Area just below A0000H and ;;
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pascal@24476
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38 ;; reports less than 640 KB of RAM via its Int 12H function. ;;
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pascal@24476
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39 ;; ;;
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pascal@24476
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40 ;; physical address ;;
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pascal@24476
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41 ;; +------------------------+ 00000H ;;
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pascal@24476
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42 ;; | Interrupt Vector Table | ;;
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pascal@24476
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43 ;; +------------------------+ 00400H ;;
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pascal@24476
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44 ;; | BIOS Data Area | ;;
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pascal@24476
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45 ;; +------------------------+ 00500H ;;
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pascal@24476
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46 ;; | PrtScr Status / Unused | ;;
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pascal@24476
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47 ;; +------------------------+ 00600H ;;
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pascal@24476
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48 ;; | Loaded Image | ;;
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pascal@24476
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49 ;; +------------------------+ nnnnnH ;;
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pascal@24476
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50 ;; | Available Memory | ;;
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pascal@24478
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51 ;; +------------------------+ A0000H - 512 - 2KB ;;
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pascal@24478
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52 ;; | 2KB Boot Stack | ;;
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pascal@24478
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53 ;; +------------------------+ A0000H - 512 ;;
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pascal@24476
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54 ;; | Boot Sector | ;;
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pascal@24476
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55 ;; +------------------------+ A0000H ;;
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pascal@24476
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56 ;; | Video RAM | ;;
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pascal@24476
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57 ;; ;;
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pascal@24476
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58 ;; ;;
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pascal@24476
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59 ;; Boot Image Startup (register values): ;;
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pascal@24476
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60 ;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
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pascal@24476
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61 ;; dl = BIOS boot drive number (e.g. 80H) ;;
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pascal@24476
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62 ;; cs:ip = program entry point ;;
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pascal@24476
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63 ;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
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pascal@24476
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64 ;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
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pascal@24476
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65 ;; EXE program defaults: ds = es = EXE data - 10h (fake MS-DOS psp), ;;
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pascal@24476
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66 ;; ax = 0ffffh (both FCB in the PSP don't have a valid drive identifier), ;;
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pascal@24476
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67 ;; cs:ip and ss:sp depends on EXE header ;;
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pascal@24476
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68 ;; Magic numbers: ;;
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pascal@24476
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69 ;; si = 16381 (prime number 2**14-3) ;;
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pascal@24476
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70 ;; di = 32749 (prime number 2**15-19) ;;
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pascal@24476
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71 ;; bp = 65521 (prime number 2**16-15) ;;
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pascal@24476
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72 ;; The magic numbers let the program know whether it has been loaded by ;;
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pascal@24476
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73 ;; this boot sector or by MS-DOS, which may be handy for universal, bare- ;;
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pascal@24476
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74 ;; metal and MS-DOS programs. ;;
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pascal@24476
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75 ;; ;;
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pascal@24476
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76 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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77
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pascal@24491
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78 %define bx(label) bx+label-boot
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pascal@24491
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79
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pascal@24476
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80 [BITS 16]
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pascal@24476
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81
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pascal@24478
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82 ImageLoadSeg equ 60h ; <=07Fh because of "push byte ImageLoadSeg" instructions
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pascal@24476
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83
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pascal@24476
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84 [SECTION .text]
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pascal@24476
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85 [ORG 0]
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pascal@24476
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86
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pascal@24476
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87 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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88 ;; Boot sector starts here ;;
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pascal@24476
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89 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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90
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pascal@24491
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91 boot:
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pascal@24491
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92 HiLBA equ boot+0
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pascal@24476
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93 jmp short start ; MS-DOS/Windows checks for this jump
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pascal@24476
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94 nop
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pascal@24476
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95 bsOemName DB "BootProg" ; 0x03
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pascal@24476
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96
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pascal@24476
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97 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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98 ;; BPB1 starts here ;;
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pascal@24476
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99 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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100
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pascal@24479
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101 bpbBytesPerSector DW 0 ; 0x0B
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pascal@24479
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102 bpbSectorsPerCluster DB 0 ; 0x0D
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pascal@24479
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103 bpbReservedSectors DW 0 ; 0x0E
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pascal@24479
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104 bpbNumberOfFATs DB 0 ; 0x10
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pascal@24479
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105 bpbRootEntries DW 0 ; 0x11
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pascal@24479
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106 bpbTotalSectors DW 0 ; 0x13
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pascal@24479
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107 bpbMedia DB 0 ; 0x15
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pascal@24479
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108 bpbSectorsPerFAT DW 0 ; 0x16
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pascal@24479
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109 bpbSectorsPerTrack DW 0 ; 0x18
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pascal@24479
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110 bpbHeadsPerCylinder DW 0 ; 0x1A
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pascal@24479
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111 bpbHiddenSectors DD 0 ; 0x1C
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pascal@24479
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112 bpbTotalSectorsBig DD 0 ; 0x20
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pascal@24476
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113
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pascal@24476
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114 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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115 ;; BPB1 ends here ;;
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pascal@24476
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116 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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117
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pascal@24476
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118 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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119 ;; BPB2 starts here ;;
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pascal@24476
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120 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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121
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pascal@24479
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122 bsSectorsPerFAT32 DD 0 ; 0x24
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pascal@24479
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123 bsExtendedFlags DW 0 ; 0x28
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pascal@24479
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124 bsFSVersion DW 0 ; 0x2A
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pascal@24479
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125 bsRootDirectoryClusterNo DD 0 ; 0x2C
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pascal@24479
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126 bsFSInfoSectorNo DW 0 ; 0x30
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pascal@24479
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127 bsBackupBootSectorNo DW 0 ; 0x32
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pascal@24479
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128 bsreserved times 12 DB 0 ; 0x34
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pascal@24479
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129 bsDriveNumber DB 0 ; 0x40
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pascal@24479
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130 bsreserved1 DB 0 ; 0x41
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pascal@24479
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131 bsExtendedBootSignature DB 0 ; 0x42
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pascal@24479
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132 bsVolumeSerialNumber DD 0 ; 0x43
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pascal@24476
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133 bsVolumeLabel DB "NO NAME " ; 0x47
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pascal@24476
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134 bsFileSystemName DB "FAT32 " ; 0x52
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pascal@24476
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135
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pascal@24476
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136 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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137 ;; BPB2 ends here ;;
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pascal@24476
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138 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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139
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pascal@24476
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140 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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141 ;; Boot sector code starts here ;;
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pascal@24476
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142 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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143
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pascal@24476
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144 start:
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pascal@24476
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145 cld
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pascal@24476
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146
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pascal@24476
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147 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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148 ;; How much RAM is there? ;;
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pascal@24476
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149 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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150
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pascal@24476
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151 int 12h ; get conventional memory size (in KBs)
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pascal@24478
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152 shl ax, 6 ; and convert it to 16-byte paragraphs
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pascal@24476
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153
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pascal@24476
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154 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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155 ;; Reserve memory for the boot sector and its stack ;;
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pascal@24476
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156 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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157
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pascal@24478
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158 sub ax, 512 / 16 ; reserve 512 bytes for the boot sector code
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pascal@24478
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159 mov es, ax ; es:0 -> top - 512
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pascal@24478
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160
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pascal@24478
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161 sub ax, 2048 / 16 ; reserve 2048 bytes for the stack
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pascal@24478
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162 mov ss, ax ; ss:0 -> top - 512 - 2048
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pascal@24478
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163 mov sp, 2048 ; 2048 bytes for the stack
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pascal@24476
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164
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pascal@24476
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165 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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166 ;; Copy ourselves to top of memory ;;
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pascal@24476
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167 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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168
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pascal@24478
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169 mov cx, 256
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pascal@24476
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170 mov si, 7C00h
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pascal@24476
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171 xor di, di
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pascal@24476
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172 mov ds, di
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pascal@24478
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173 rep movsw
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pascal@24476
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174
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pascal@24476
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175 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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176 ;; Jump to the copy ;;
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pascal@24476
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177 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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178
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pascal@24476
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179 push es
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pascal@24478
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180 push byte main
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pascal@24476
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181 retf
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pascal@24476
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182
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pascal@24476
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183 main:
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pascal@24476
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184 push cs
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pascal@24476
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185 pop ds
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pascal@24476
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186
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pascal@24491
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187 xor bx, bx
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pascal@24491
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188 mov [bx(bsDriveNumber)], dx ; store BIOS boot drive number
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pascal@24476
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189
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pascal@24491
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190 and byte [bx(bsRootDirectoryClusterNo+3)], 0Fh ; mask cluster value
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pascal@24491
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191 mov esi, [bx(bsRootDirectoryClusterNo)] ; esi=cluster # of root dir
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pascal@24476
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192
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pascal@24476
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193 RootDirReadContinue:
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pascal@24478
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194 push byte ImageLoadSeg
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pascal@24478
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195 pop es
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pascal@24478
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196 push es
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pascal@24478
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197 call ReadCluster ; read one cluster of root dir
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pascal@24478
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198 pop es
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pascal@24478
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199 pushad ; save esi=next cluster # of root dir
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pascal@24478
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200 ; save eax=next sector # of root dir
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pascal@24478
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201 pushf ; save carry="not last cluster" flag
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pascal@24476
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202
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pascal@24476
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203 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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204 ;; Look for the COM/EXE file to load and run ;;
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pascal@24476
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205 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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206
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pascal@24476
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207 xor di, di ; es:di -> root entries array
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pascal@24478
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208 mov si, ProgramName ; ds:si -> program name
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pascal@24476
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209
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pascal@24476
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210 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24478
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211 ;; Looks for a file/dir by its name ;;
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pascal@24476
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212 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24478
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213 ;; Input: DS:SI -> file name (11 chars) ;;
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pascal@24478
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214 ;; ES:DI -> root directory array ;;
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pascal@24478
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215 ;; DX = number of root entries ;;
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pascal@24476
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216 ;; Output: ESI = cluster number ;;
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pascal@24476
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217 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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218
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pascal@24478
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219 FindName:
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pascal@24478
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220 mov cx, 11
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pascal@24476
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221 FindNameCycle:
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pascal@24478
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222 cmp byte [es:di], ch
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pascal@24478
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223 je ErrFind ; end of root directory (NULL entry found)
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pascal@24478
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224 FindNameNotEnd:
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pascal@24478
|
225 pusha
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pascal@24476
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226 repe cmpsb
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pascal@24478
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227 popa
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pascal@24476
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228 je FindNameFound
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pascal@24478
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229 add di, 32
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pascal@24476
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230 dec bp
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pascal@24476
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231 dec bp
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pascal@24476
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232 jnz FindNameCycle ; next root entry
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pascal@24478
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233 popf ; restore carry="not last cluster" flag
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pascal@24478
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234 ; restore eax=next sector # of root dir
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pascal@24478
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235 popad ; restore esi=next cluster # of root dir
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pascal@24476
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236 jc RootDirReadContinue ; continue to the next root dir cluster
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pascal@24478
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237 ErrFind:
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pascal@24478
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238 call Error ; end of root directory (dir end reached)
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pascal@24476
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239 db "File not found."
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pascal@24476
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240 FindNameFound:
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pascal@24478
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241 push word [es:di+14h]
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pascal@24478
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242 push word [es:di+1Ah]
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pascal@24478
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243 pop esi ; esi = cluster no. cx = 0
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pascal@24476
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244
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pascal@24476
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245 dec dword [es:di+1Ch] ; load ((n - 1)/256)*16 +1 paragraphs
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pascal@24478
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246 imul di, [es:di+1Ch+1], 16 ; file size in paragraphs (full pages)
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pascal@24478
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247 xor cx, cx
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pascal@24476
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248
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pascal@24476
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249 ;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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250 ;; Load the entire file ;;
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pascal@24476
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251 ;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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252
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pascal@24476
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253 push es
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pascal@24476
|
254 FileReadContinue:
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pascal@24476
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255 push di
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pascal@24478
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256 call ReadCluster ; read one cluster of root dir
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pascal@24476
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257 mov di, es
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pascal@24478
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258 add di, bp
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pascal@24478
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259 mov es, di ; es:bx updated
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pascal@24476
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260 pop di
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pascal@24478
|
261
|
pascal@24476
|
262 sub di, bp
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pascal@24476
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263 jae FileReadContinue
|
pascal@24476
|
264 pop bp
|
pascal@24476
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265
|
pascal@24476
|
266 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
|
267 ;; Type detection, .COM or .EXE? ;;
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pascal@24476
|
268 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
|
269
|
pascal@24476
|
270 mov ds, bp ; bp=ds=seg the file is loaded to
|
pascal@24476
|
271 add bp, [bx+08h] ; bp = image base
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pascal@24476
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272 mov ax, [bx+06h] ; ax = reloc items
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pascal@24476
|
273 mov di, [bx+18h] ; di = reloc table pointer
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pascal@24476
|
274
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pascal@24476
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275 cmp word [bx], 5A4Dh ; "MZ" signature?
|
pascal@24478
|
276
|
pascal@24476
|
277 je RelocateEXE ; yes, it's an EXE program
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pascal@24476
|
278
|
pascal@24476
|
279 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
280 ;; Setup and run a .COM program ;;
|
pascal@24478
|
281 ;; Set CS=DS=ES=SP SP=0 IP=100h ;;
|
pascal@24476
|
282 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
283
|
pascal@24476
|
284 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
|
pascal@24476
|
285 mov ss, bp
|
pascal@24476
|
286 xor sp, sp
|
pascal@24476
|
287 push bp ; cs, ds and es
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pascal@24476
|
288 mov bh, 1 ; ip
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pascal@24476
|
289 jmp short Run
|
pascal@24476
|
290
|
pascal@24476
|
291 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
292 ;; Relocate, setup and run a .EXE program ;;
|
pascal@24476
|
293 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
|
pascal@24476
|
294 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
|
pascal@24476
|
295 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
296
|
pascal@24476
|
297 ReloCycle:
|
pascal@24476
|
298 add [di+2], bp ; item seg (abs)
|
pascal@24476
|
299 les si, [di] ; si = item ofs, es = item seg
|
pascal@24476
|
300 add [es:si], bp ; fixup
|
pascal@24478
|
301 add di, 4 ; point to next entry
|
pascal@24476
|
302
|
pascal@24476
|
303 RelocateEXE:
|
pascal@24476
|
304 dec ax ; 32768 max (128KB table)
|
pascal@24476
|
305 jns ReloCycle ; leave with ax=0ffffh: both FCB in the
|
pascal@24476
|
306 ; PSP don't have a valid drive identifier
|
pascal@24476
|
307 les si, [bx+0Eh]
|
pascal@24476
|
308 add si, bp
|
pascal@24476
|
309 mov ss, si ; ss for EXE
|
pascal@24476
|
310 mov sp, es ; sp for EXE
|
pascal@24476
|
311
|
pascal@24476
|
312 lea si, [bp-10h] ; ds and es both point to the segment
|
pascal@24476
|
313 push si ; containing the PSP structure
|
pascal@24476
|
314
|
pascal@24476
|
315 add bp, [bx+16h] ; cs for EXE
|
pascal@24476
|
316 mov bx, [bx+14h] ; ip for EXE
|
pascal@24476
|
317 Run:
|
pascal@24476
|
318 pop ds
|
pascal@24476
|
319 push bp
|
pascal@24476
|
320 push bx
|
pascal@24476
|
321 push ds
|
pascal@24476
|
322 pop es
|
pascal@24476
|
323
|
pascal@24476
|
324 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
325 ;; Set the magic numbers so the program knows that it ;;
|
pascal@24476
|
326 ;; has been loaded by this bootsector and not by MS-DOS ;;
|
pascal@24476
|
327 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
328 mov si, 16381 ; prime number 2**14-3
|
pascal@24476
|
329 mov di, 32749 ; prime number 2**15-19
|
pascal@24476
|
330 mov bp, 65521 ; prime number 2**16-15
|
pascal@24476
|
331
|
pascal@24476
|
332 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
333 ;; All done, transfer control to the program now ;;
|
pascal@24476
|
334 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
335 retf
|
pascal@24476
|
336
|
pascal@24478
|
337 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24478
|
338 ;; Reads a FAT32 cluster ;;
|
pascal@24478
|
339 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
340 ;; Inout: ES:BX -> buffer ;;
|
pascal@24478
|
341 ;; ESI = cluster no ;;
|
pascal@24478
|
342 ;; Output: ESI = next cluster ;;
|
pascal@24478
|
343 ;; ES:BX -> next addr ;;
|
pascal@24478
|
344 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
345
|
pascal@24476
|
346 ReadCluster:
|
pascal@24476
|
347 inc cx
|
pascal@24478
|
348 loop ReadSectorLBA
|
pascal@24476
|
349
|
pascal@24478
|
350 mov ax, [bpbBytesPerSector]
|
pascal@24478
|
351 push ax
|
pascal@24478
|
352 shr ax, 2 ; ax=# of FAT32 entries per sector
|
pascal@24478
|
353 cwde
|
pascal@24478
|
354 lea ebp, [esi-2] ; esi=cluster #
|
pascal@24476
|
355 xchg eax, esi
|
pascal@24476
|
356 cdq
|
pascal@24478
|
357 div esi ; eax=FAT sector #, edx=entry # in sector
|
pascal@24476
|
358
|
pascal@24478
|
359 imul si, dx, 4 ; si=entry # in sector
|
pascal@24491
|
360 mov word [bx(HiLBA)], bx
|
pascal@24478
|
361 call ReadSectorLBAabsolute ; read 1 FAT32 sector
|
pascal@24476
|
362
|
pascal@24478
|
363 and byte [es:si+3], 0Fh ; mask cluster value
|
pascal@24478
|
364 mov esi, [es:si] ; esi=next cluster #
|
pascal@24476
|
365
|
pascal@24478
|
366 xchg eax, ebp
|
pascal@24491
|
367 movzx ecx, byte [bx(bpbSectorsPerCluster)]
|
pascal@24491
|
368 mul ecx ; edx:eax=sector number in data area
|
pascal@24478
|
369 xchg eax, ebp
|
pascal@24491
|
370 mov word [bx(HiLBA)], dx
|
pascal@24476
|
371
|
pascal@24491
|
372 movzx eax, byte [bx(bpbNumberOfFATs)]
|
pascal@24491
|
373 mul dword [bx(bsSectorsPerFAT32)]
|
pascal@24476
|
374
|
pascal@24478
|
375 add eax, ebp
|
pascal@24491
|
376 adc word [bx(HiLBA)], dx
|
pascal@24476
|
377
|
pascal@24478
|
378 pop bp ; [bpbBytesPerSector]
|
pascal@24478
|
379 shr bp, 4 ; bp = paragraphs per sector
|
pascal@24476
|
380
|
pascal@24478
|
381 ReadSectorLBAabsolute:
|
pascal@24491
|
382 movzx edx, word [bx(bpbReservedSectors)]
|
pascal@24478
|
383 add eax, edx
|
pascal@24491
|
384 adc word [bx(HiLBA)], bx
|
pascal@24491
|
385 add eax, [bx(bpbHiddenSectors)]
|
pascal@24491
|
386 adc word [bx(HiLBA)], bx
|
pascal@24476
|
387
|
pascal@24478
|
388 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
389 ;; Reads a sector using BIOS Int 13h fn 42h ;;
|
pascal@24478
|
390 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
391 ;; Input: EAX = LBA ;;
|
pascal@24478
|
392 ;; CX = sector count ;;
|
pascal@24478
|
393 ;; ES:BX -> buffer address ;;
|
pascal@24478
|
394 ;; Output: CF = 0 if no more sectors ;;
|
pascal@24478
|
395 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
396
|
pascal@24476
|
397 ReadSectorLBA:
|
pascal@24491
|
398 mov dx, [bx(bsDriveNumber)] ; restore BIOS boot drive number
|
pascal@24476
|
399 pusha
|
pascal@24476
|
400
|
pascal@24478
|
401 push bx
|
pascal@24491
|
402 push word [bx(HiLBA)] ; 48-bit LBA
|
pascal@24478
|
403 push eax
|
pascal@24476
|
404 push es
|
pascal@24476
|
405 push bx
|
pascal@24478
|
406 push byte 1 ; sector count word = 1
|
pascal@24478
|
407 mov cx, 16 ; retry count
|
pascal@24478
|
408 push cx ; packet size byte = 16, reserved byte = 0
|
pascal@24476
|
409
|
pascal@24478
|
410 ReadSectorRetry:
|
pascal@24478
|
411 mov ah, 42h ; ah = 42h = extended read function no.
|
pascal@24478
|
412 mov si, sp
|
pascal@24478
|
413 push ss
|
pascal@24478
|
414 pop ds
|
pascal@24478
|
415 int 13h ; extended read sectors (DL, DS:SI)
|
pascal@24478
|
416 push cs
|
pascal@24478
|
417 pop ds
|
pascal@24478
|
418 jnc ReadSuccess ; CF = 0 if no error
|
pascal@24476
|
419
|
pascal@24478
|
420 xor ax, ax ; ah = 0 = reset function
|
pascal@24476
|
421 int 13h ; reset drive (DL)
|
pascal@24476
|
422
|
pascal@24478
|
423 loop ReadSectorRetry ; extra attempt
|
pascal@24476
|
424 call Error
|
pascal@24476
|
425 db "Read error."
|
pascal@24476
|
426
|
pascal@24478
|
427 ReadSuccess:
|
pascal@24476
|
428
|
pascal@24476
|
429 popa ; sp += 16
|
pascal@24478
|
430
|
pascal@24478
|
431 popa
|
pascal@24478
|
432
|
pascal@24491
|
433 add eax, byte 1 ; adjust LBA for next sector
|
pascal@24491
|
434 adc word [bx(HiLBA)], bx
|
pascal@24478
|
435
|
pascal@24476
|
436 stc
|
pascal@24478
|
437 loop ReadSectorNext
|
pascal@24476
|
438
|
pascal@24478
|
439 cmp esi, 0FFFFFF8h ; carry=0 if last cluster, and carry=1 otherwise
|
pascal@24476
|
440
|
pascal@24478
|
441 ReadSectorNext:
|
pascal@24476
|
442 ret
|
pascal@24476
|
443
|
pascal@24476
|
444 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
445 ;; Error Messaging Code ;;
|
pascal@24476
|
446 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
447
|
pascal@24476
|
448 Error:
|
pascal@24476
|
449 pop si
|
pascal@24478
|
450 puts:
|
pascal@24476
|
451 mov ah, 0Eh
|
pascal@24476
|
452 mov bl, 7
|
pascal@24476
|
453 lodsb
|
pascal@24476
|
454 int 10h
|
pascal@24478
|
455 cmp al, '.'
|
pascal@24478
|
456 jne puts
|
pascal@24476
|
457 cbw
|
pascal@24476
|
458 int 16h ; wait for a key...
|
pascal@24476
|
459 int 19h ; bootstrap
|
pascal@24476
|
460
|
pascal@24476
|
461 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
462 ;; Fill free space with zeroes ;;
|
pascal@24476
|
463 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
464
|
pascal@24476
|
465 times (512-13-($-$$)) db 0
|
pascal@24476
|
466
|
pascal@24476
|
467 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
468 ;; Name of the file to load and run ;;
|
pascal@24476
|
469 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
470
|
pascal@24476
|
471 ProgramName db "STARTUP BIN" ; name and extension each must be
|
pascal@24476
|
472 ; padded with spaces (11 bytes total)
|
pascal@24476
|
473
|
pascal@24476
|
474 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
475 ;; End of the sector ID ;;
|
pascal@24476
|
476 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
477
|
pascal@24476
|
478 dw 0AA55h ; BIOS checks for this ID
|