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