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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 boot16.asm -f bin -o boot16.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@24476
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14 ;; - FAT12 and FAT16 supported using BIOS int 13h function 42h or 02h. ;;
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pascal@24476
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15 ;; ;;
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pascal@24476
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16 ;; - Loads a 16-bit executable file in the MS-DOS .COM or .EXE format ;;
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pascal@24476
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17 ;; from the root directory of a disk and transfers control to it ;;
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pascal@24476
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18 ;; (the "ProgramName" variable holds the name of the file to be loaded) ;;
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pascal@24476
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19 ;; Its maximum size can be up to 635KB without Extended BIOS Data area. ;;
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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 ;; - cpu 8086 is supported ;;
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pascal@24476
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27 ;; ;;
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pascal@24476
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28 ;; ;;
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pascal@24476
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29 ;; Known Bugs: ;;
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pascal@24476
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30 ;; ~~~~~~~~~~~ ;;
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pascal@24476
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31 ;; - 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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32 ;; on the following types of diskettes (FAT12): ;;
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pascal@24476
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33 ;; - 360KB 5"25 ;;
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pascal@24476
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34 ;; - 1.2MB 5"25 ;;
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pascal@24476
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35 ;; - 1.44MB 3"5 ;;
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pascal@24476
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36 ;; on my HDD (FAT16). ;;
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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@24476
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57 ;; +------------------------+ A0000H - 512 - 3KB ;;
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pascal@24476
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58 ;; | Boot Sector | ;;
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pascal@24476
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59 ;; +------------------------+ A0000H - 3KB ;;
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pascal@24476
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60 ;; | 3KB Boot Stack | ;;
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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. 0, 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 %define bx(label) bx+label-boot
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pascal@24476
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85
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pascal@24476
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86 [BITS 16]
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pascal@24476
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87 [CPU 8086]
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pascal@24476
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88
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pascal@24476
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89 ImageLoadSeg equ 60h
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pascal@24476
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90 StackSize equ 3072 ; Stack + cluster list
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pascal@24476
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91
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pascal@24476
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92 [SECTION .text]
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pascal@24476
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93 [ORG 0]
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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 ;; Boot sector starts here ;;
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pascal@24476
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97 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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98
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pascal@24476
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99 boot:
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pascal@24476
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100 jmp short start ; MS-DOS/Windows checks for this jump
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pascal@24476
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101 nop
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pascal@24476
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102 bsOemName DB "BootProg" ; 0x03
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pascal@24476
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103
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pascal@24476
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104 ;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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105 ;; BPB starts here ;;
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pascal@24476
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106 ;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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107
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pascal@24479
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108 bpbBytesPerSector DW 0 ; 0x0B
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pascal@24479
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109 bpbSectorsPerCluster DB 0 ; 0x0D
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pascal@24479
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110 bpbReservedSectors DW 0 ; 0x0E
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pascal@24479
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111 bpbNumberOfFATs DB 0 ; 0x10
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pascal@24479
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112 bpbRootEntries DW 0 ; 0x11
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pascal@24479
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113 bpbTotalSectors DW 0 ; 0x13
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pascal@24479
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114 bpbMedia DB 0 ; 0x15
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pascal@24479
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115 bpbSectorsPerFAT DW 0 ; 0x16
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pascal@24479
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116 bpbSectorsPerTrack DW 0 ; 0x18
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pascal@24479
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117 bpbHeadsPerCylinder DW 0 ; 0x1A
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pascal@24479
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118 bpbHiddenSectors DD 0 ; 0x1C
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pascal@24479
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119 bpbTotalSectorsBig DD 0 ; 0x20
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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 ;; BPB ends 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@24479
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125 bsDriveNumber DB 0 ; 0x24
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pascal@24479
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126 bsUnused DB 0 ; 0x25
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pascal@24479
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127 bsExtBootSignature DB 0 ; 0x26
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pascal@24479
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128 bsSerialNumber DD 0 ; 0x27
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pascal@24476
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129 bsVolumeLabel DB "NO NAME " ; 0x2B
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pascal@24476
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130 bsFileSystem DB "FAT12 " ; 0x36
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pascal@24476
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131
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pascal@24476
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132 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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133 ;; Boot sector code starts here ;;
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pascal@24476
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134 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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135
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pascal@24476
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136 start:
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pascal@24476
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137 cld
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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 ;; How much RAM is there? ;;
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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 int 12h ; get conventional memory size (in KBs)
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pascal@24476
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144 mov cx, 106h
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pascal@24476
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145 shl ax, cl ; and convert it to 16-byte paragraphs
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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 ;; Reserve memory for the boot sector and its stack ;;
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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 sub ax, (512+StackSize) /16 ; reserve bytes for the code and the stack
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pascal@24476
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152 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
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pascal@24476
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153 mov ss, ax
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pascal@24476
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154 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
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pascal@24476
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155
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pascal@24476
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156 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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157 ;; Copy ourselves to top of memory ;;
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pascal@24476
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158 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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159
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pascal@24476
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160 mov si, 7C00h
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pascal@24476
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161 xor di, di
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pascal@24476
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162 mov ds, di
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pascal@24476
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163 mov [si], dx ; store BIOS boot drive number
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pascal@24476
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164 rep movsw ; move 512 bytes (+ 12)
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pascal@24476
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165
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pascal@24476
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166 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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167 ;; Jump to the copy ;;
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pascal@24476
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168 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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169
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pascal@24476
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170 push es
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pascal@24476
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171 mov cl, byte main
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pascal@24476
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172 push cx
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pascal@24476
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173 retf
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pascal@24476
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174
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pascal@24476
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175 main:
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pascal@24476
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176 %if ImageLoadSeg != main-boot
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pascal@24476
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177 %if ImageLoadSeg >= 100h
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pascal@24476
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178 mov cx, ImageLoadSeg
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pascal@24476
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179 %else
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pascal@24476
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180 mov cl, ImageLoadSeg
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pascal@24476
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181 %endif
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pascal@24476
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182 %endif
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pascal@24476
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183 push cx
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pascal@24476
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184
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pascal@24476
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185 ;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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186 ;; Get drive parameters ;;
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pascal@24476
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187 ;; Update heads count ;;
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pascal@24476
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188 ;; for current BIOS ;;
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pascal@24476
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189 ;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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190
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pascal@24476
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191 mov ah, 8
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pascal@24476
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192 int 13h ; may destroy SI,BP, and DS registers
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pascal@24476
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193 ; update AX,BL,CX,DX,DI, and ES registers
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pascal@24476
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194 push cs
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pascal@24476
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195 pop ds
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pascal@24476
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196 xor bx, bx
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pascal@24476
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197
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pascal@24479
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198 and cx, byte 3Fh
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pascal@24476
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199 cmp [bx(bpbSectorsPerTrack)], cx
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pascal@24476
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200 jne BadParams ; verify updated and validity
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pascal@24476
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201 mov al, dh
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pascal@24476
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202 inc ax
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pascal@24476
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203 mov [bpbHeadsPerCylinder], ax
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pascal@24476
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204 BadParams:
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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 ;; Load FAT (FAT12: 6KB max, FAT16: 128KB max) ;;
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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 pop es ; ImageLoadSeg
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pascal@24476
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211 push es
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pascal@24476
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212
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pascal@24476
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213 mul bx ; dx:ax = 0 = LBA (LBA are relative to FAT)
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pascal@24476
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214 mov cx, word [bx(bpbSectorsPerFAT)]
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pascal@24476
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215
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pascal@24942
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216 call ReadCXSectors ; read fat and clear ax & cx
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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@24476
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219 ;; load the root directory in ;;
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pascal@24476
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220 ;; its entirety (16KB max) ;;
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pascal@24476
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221 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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222
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pascal@24942
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223 mov al, 32
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pascal@24476
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224
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pascal@24476
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225 mul word [bx(bpbRootEntries)]
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pascal@24476
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226 div word [bx(bpbBytesPerSector)]
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pascal@24476
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227 xchg ax, cx ; cx = root directory size in sectors, clear ax
|
pascal@24476
|
228
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pascal@24476
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229 mov al, [bpbNumberOfFATs]
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pascal@24476
|
230 mul bp ; [bx(bpbSectorsPerFAT)], set by ReadCXSectors
|
pascal@24476
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231
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pascal@24476
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232 push es
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pascal@24942
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233 call ReadCXSectors ; read root directory; clear ax, cx and di
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pascal@24476
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234 pop es
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pascal@24476
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235
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pascal@24476
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236 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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237 ;; Look for the COM/EXE file to load and run ;;
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pascal@24476
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238 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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239
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pascal@24476
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240 ; es:di -> root entries array
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pascal@24476
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241
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pascal@24476
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242 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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243 ;; Looks for the file/dir ProgramName ;;
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pascal@24476
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244 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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245 ;; Input: ES:DI -> root directory array ;;
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pascal@24476
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246 ;; Output: SI = cluster number ;;
|
pascal@24476
|
247 ;; AX = file sector count ;;
|
pascal@24476
|
248 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
249
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pascal@24476
|
250 FindNameCycle:
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pascal@24476
|
251 push di
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pascal@24476
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252 mov cl, 11
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pascal@24476
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253 mov si, ProgramName ; ds:si -> program name
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pascal@24476
|
254 repe cmpsb
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pascal@24476
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255 pop di
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pascal@24476
|
256 je FindNameFound
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pascal@24942
|
257 scasb
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pascal@24942
|
258 je FindNameFailed ; end of root directory (NULL entry found)
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pascal@24942
|
259 add di, byte 31
|
pascal@24476
|
260 dec word [bx(bpbRootEntries)]
|
pascal@24476
|
261 jnz FindNameCycle ; next root entry
|
pascal@24476
|
262
|
pascal@24476
|
263 FindNameFailed:
|
pascal@24476
|
264 call Error
|
pascal@24476
|
265 db "File not found."
|
pascal@24476
|
266
|
pascal@24476
|
267 FindNameFound:
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pascal@24476
|
268 push si
|
pascal@24476
|
269 mov si, [es:di+1Ah] ; si = cluster no.
|
pascal@24476
|
270 les ax, [es:di+1Ch] ; file size
|
pascal@24476
|
271 mov dx, es
|
pascal@24476
|
272 div word [bx(bpbBytesPerSector)]
|
pascal@24476
|
273 cmp bx, dx ; sector aligned ?
|
pascal@24476
|
274 adc ax, bx ; file last sector
|
pascal@24476
|
275 pop di ; di = ClusterList
|
pascal@24476
|
276
|
pascal@24476
|
277 pop es ; ImageLoadSeg
|
pascal@24476
|
278 push ax
|
pascal@24476
|
279
|
pascal@24476
|
280 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
281 ;; build cluster list ;;
|
pascal@24476
|
282 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
283 ;; Input: ES:0 -> FAT ;;
|
pascal@24476
|
284 ;; SI = first cluster ;;
|
pascal@24476
|
285 ;; DI = cluster list :;
|
pascal@24476
|
286 ;; CH = 0 ;;
|
pascal@24476
|
287 ;; Output: SI = cluster list ;;
|
pascal@24476
|
288 ;; CH = 0 ;;
|
pascal@24476
|
289 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
290
|
pascal@24476
|
291 push di ; up to 2 * 635K / BytesPerCluster bytes
|
pascal@24476
|
292 mov cl, 12
|
pascal@24476
|
293 ClusterLoop:
|
pascal@24476
|
294 mov [di], si
|
pascal@24476
|
295
|
pascal@24476
|
296 mov ax, es ; ax = FAT segment = ImageLoadSeg
|
pascal@24476
|
297 add si, si ; si = cluster * 2
|
pascal@24476
|
298 jnc First64
|
pascal@24476
|
299 mov ah, (1000h+ImageLoadSeg)>>8 ; adjust segment for 2nd part of FAT16
|
pascal@24476
|
300 First64:
|
pascal@24942
|
301 mov dx, 0FFF8h
|
pascal@24942
|
302
|
pascal@24476
|
303 cmp [bx(bpbSectorsPerFAT)], cx ; 1..12 = FAT12, 16..256 = FAT16
|
pascal@24476
|
304 mov ds, ax
|
pascal@24942
|
305 ja ReadClusterFat16
|
pascal@24476
|
306
|
pascal@24942
|
307 mov dh, 0Fh
|
pascal@24476
|
308 add si, [cs:di]
|
pascal@24476
|
309 shr si, 1 ; si = cluster * 3 / 2
|
pascal@24476
|
310
|
pascal@24942
|
311 ReadClusterFat16:
|
pascal@24476
|
312 lodsw ; ax = next cluster
|
pascal@24476
|
313 jnc ReadClusterEven
|
pascal@24476
|
314
|
pascal@24476
|
315 rol ax, cl
|
pascal@24476
|
316
|
pascal@24476
|
317 ReadClusterEven:
|
pascal@24942
|
318 and ah, dh ; mask cluster value
|
pascal@24942
|
319 cmp ax, dx
|
pascal@24476
|
320
|
pascal@24476
|
321 push cs
|
pascal@24476
|
322 pop ds
|
pascal@24476
|
323 inc di
|
pascal@24476
|
324 inc di
|
pascal@24476
|
325 xchg ax, si
|
pascal@24476
|
326 jc ClusterLoop
|
pascal@24476
|
327 pop si
|
pascal@24476
|
328 pop di ; file size in sectors
|
pascal@24476
|
329
|
pascal@24476
|
330 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
331 ;; Load the entire file ;;
|
pascal@24476
|
332 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
333 ;; Input: ES:0 -> buffer ;;
|
pascal@24476
|
334 ;; SI = cluster list ;;
|
pascal@24476
|
335 ;; DI = file sectors ;;
|
pascal@24476
|
336 ;; CH = 0 ;;
|
pascal@24476
|
337 ;; Output: BP:0 -> buffer ;;
|
pascal@24476
|
338 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
339
|
pascal@24476
|
340 push es
|
pascal@24476
|
341
|
pascal@24476
|
342 ReadClusters:
|
pascal@24476
|
343 lodsw
|
pascal@24476
|
344 dec ax
|
pascal@24476
|
345 dec ax
|
pascal@24476
|
346
|
pascal@24476
|
347 mov cl, [bx(bpbSectorsPerCluster)]
|
pascal@24476
|
348 mul cx ; cx = sector count (ch = 0)
|
pascal@24476
|
349
|
pascal@24476
|
350 add ax, bp ; LBA for cluster data
|
pascal@24476
|
351 adc dx, bx ; dx:ax = LBA
|
pascal@24476
|
352
|
pascal@24942
|
353 call ReadSector ; clear ax & cx, restore dx
|
pascal@24476
|
354
|
pascal@24476
|
355 jne ReadClusters
|
pascal@24476
|
356
|
pascal@24476
|
357 pop bp ; ImageLoadSeg
|
pascal@24476
|
358
|
pascal@24476
|
359 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
360 ;; Type detection, .COM or .EXE? ;;
|
pascal@24476
|
361 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
362
|
pascal@24476
|
363 mov ds, bp ; bp=ds=seg the file is loaded to
|
pascal@24476
|
364
|
pascal@24476
|
365 add bp, [bx+08h] ; bp = image base
|
pascal@24476
|
366 mov di, [bx+18h] ; di = reloc table pointer
|
pascal@24476
|
367
|
pascal@24476
|
368 cmp word [bx], 5A4Dh ; "MZ" signature?
|
pascal@24476
|
369 je RelocateEXE ; yes, it's an EXE program
|
pascal@24476
|
370
|
pascal@24476
|
371 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
372 ;; Setup and run a .COM program ;;
|
pascal@24476
|
373 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
|
pascal@24942
|
374 ;; AX=0ffffh BX=0 CX=0 DX=drive ;;
|
pascal@24942
|
375 ;; and cmdline=void ;;
|
pascal@24476
|
376 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
377
|
pascal@24942
|
378 mov di, 100h ; ip
|
pascal@24476
|
379 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
|
pascal@24476
|
380 mov ss, bp
|
pascal@24476
|
381 xor sp, sp
|
pascal@24476
|
382 push bp ; cs, ds and es
|
pascal@24476
|
383 jmp short Run
|
pascal@24476
|
384
|
pascal@24476
|
385 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
386 ;; Relocate, setup and run a .EXE program ;;
|
pascal@24476
|
387 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
|
pascal@24476
|
388 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
|
pascal@24942
|
389 ;; AX=0ffffh BX=0 CX=0 DX=drive cmdline=void ;;
|
pascal@24476
|
390 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
391
|
pascal@24476
|
392 ReloCycle:
|
pascal@24476
|
393 add [di+2], bp ; item seg (abs)
|
pascal@24476
|
394 les si, [di] ; si = item ofs, es = item seg
|
pascal@24476
|
395 add [es:si], bp ; fixup
|
pascal@24476
|
396 scasw ; di += 2
|
pascal@24476
|
397 scasw ; point to next entry
|
pascal@24476
|
398
|
pascal@24476
|
399 RelocateEXE:
|
pascal@24942
|
400 dec word [bx+06h] ; reloc items, 32768 max (128KB table)
|
pascal@24942
|
401 jns ReloCycle
|
pascal@24476
|
402 ; PSP don't have a valid drive identifier
|
pascal@24476
|
403 les si, [bx+0Eh]
|
pascal@24476
|
404 add si, bp
|
pascal@24476
|
405 mov ss, si ; ss for EXE
|
pascal@24476
|
406 mov sp, es ; sp for EXE
|
pascal@24476
|
407
|
pascal@24476
|
408 lea si, [bp-10h] ; ds and es both point to the segment
|
pascal@24476
|
409 push si ; containing the PSP structure
|
pascal@24476
|
410
|
pascal@24476
|
411 add bp, [bx+16h] ; cs for EXE
|
pascal@24942
|
412 mov di, [bx+14h] ; ip for EXE
|
pascal@24476
|
413 Run:
|
pascal@24476
|
414 pop ds
|
pascal@24476
|
415 push bp
|
pascal@24942
|
416 push di
|
pascal@24476
|
417 push ds
|
pascal@24476
|
418 pop es
|
pascal@24942
|
419 mov [80h], ax ; clear cmdline
|
pascal@24942
|
420 dec ax ; both FCB in the PSP don't have a valid drive identifier
|
pascal@24476
|
421
|
pascal@24476
|
422 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
423 ;; Set the magic numbers so the program knows that it ;;
|
pascal@24476
|
424 ;; has been loaded by this bootsector and not by MS-DOS ;;
|
pascal@24476
|
425 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
426 mov si, 16381 ; prime number 2**14-3
|
pascal@24476
|
427 mov di, 32749 ; prime number 2**15-19
|
pascal@24476
|
428 mov bp, 65521 ; prime number 2**16-15
|
pascal@24476
|
429
|
pascal@24476
|
430 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
431 ;; All done, transfer control to the program now ;;
|
pascal@24476
|
432 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
433 retf
|
pascal@24476
|
434
|
pascal@24476
|
435 ReadCXSectors:
|
pascal@24476
|
436 mov bp, cx
|
pascal@24476
|
437 add bp, ax ; adjust LBA for cluster data
|
pascal@24476
|
438
|
pascal@24476
|
439 mov di, cx ; no file size limit
|
pascal@24476
|
440
|
pascal@24476
|
441 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
442 ;; Reads sectors using BIOS Int 13h ;;
|
pascal@24476
|
443 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
444 ;; Input: DX:AX = LBA relative to FAT ;;
|
pascal@24476
|
445 ;; BX = 0 ;;
|
pascal@24476
|
446 ;; CX = sector count ;;
|
pascal@24476
|
447 ;; DI = file sectors ;;
|
pascal@24476
|
448 ;; ES:BX -> buffer address ;;
|
pascal@24476
|
449 ;; Output: ES:BX -> next address ;;
|
pascal@24476
|
450 ;; BX = 0 ;;
|
pascal@24476
|
451 ;; CX or DI = 0 ;;
|
pascal@24476
|
452 ;; DL = drive number ;;
|
pascal@24476
|
453 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
454
|
pascal@24476
|
455 ReadSector:
|
pascal@24476
|
456 add ax, [bx(bpbHiddenSectors)]
|
pascal@24476
|
457 adc dx, [bx(bpbHiddenSectors)+2]
|
pascal@24476
|
458 add ax, [bx(bpbReservedSectors)]
|
pascal@24476
|
459
|
pascal@24476
|
460 push si
|
pascal@24476
|
461 ReadSectorNext:
|
pascal@24476
|
462 adc dx, bx
|
pascal@24476
|
463 push di
|
pascal@24476
|
464 push cx
|
pascal@24476
|
465
|
pascal@24476
|
466 push bx
|
pascal@24476
|
467 push bx
|
pascal@24476
|
468 push dx ; 32-bit LBA: up to 2TB
|
pascal@24476
|
469 push ax
|
pascal@24476
|
470 push es
|
pascal@24476
|
471 push bx
|
pascal@24476
|
472 inc bx ; sector count word = 1
|
pascal@24476
|
473 push bx
|
pascal@24476
|
474 dec bx
|
pascal@24476
|
475 mov di, 16 ; packet size byte = 16, reserved byte = 0
|
pascal@24476
|
476 push di
|
pascal@24476
|
477
|
pascal@24476
|
478 xchg ax, cx ; save low LBA
|
pascal@24476
|
479 xchg ax, dx ; get high LBA
|
pascal@24476
|
480 cwd ; clear dx (LBA offset <2TB)
|
pascal@24476
|
481 div word [bx(bpbSectorsPerTrack)] ; up to 8GB disks
|
pascal@24476
|
482
|
pascal@24476
|
483 xchg ax, cx ; restore low LBA, save high LBA / SPT
|
pascal@24476
|
484 div word [bx(bpbSectorsPerTrack)]
|
pascal@24476
|
485 ; ax = LBA / SPT
|
pascal@24476
|
486 ; dx = LBA % SPT = sector - 1
|
pascal@24476
|
487 inc dx
|
pascal@24476
|
488
|
pascal@24476
|
489 xchg cx, dx ; restore high LBA / SPT, save sector no.
|
pascal@24476
|
490 div word [bx(bpbHeadsPerCylinder)]
|
pascal@24476
|
491 ; ax = (LBA / SPT) / HPC = cylinder
|
pascal@24476
|
492 ; dx = (LBA / SPT) % HPC = head
|
pascal@24476
|
493 mov ch, al
|
pascal@24476
|
494 ; ch = LSB 0...7 of cylinder no.
|
pascal@24476
|
495 mov al, 64
|
pascal@24476
|
496 mul ah
|
pascal@24476
|
497 or cl, al
|
pascal@24476
|
498 ; cl = MSB 8...9 of cylinder no. + sector no.
|
pascal@24476
|
499 mov dh, dl
|
pascal@24476
|
500 ; dh = head no.
|
pascal@24476
|
501
|
pascal@24476
|
502 ReadSectorRetry:
|
pascal@24476
|
503 mov dl, [bx]
|
pascal@24476
|
504 ; dl = drive no.
|
pascal@24476
|
505 mov ah, 42h ; ah = 42h = extended read function no.
|
pascal@24476
|
506 mov si, sp
|
pascal@24476
|
507 int 13h ; extended read sectors (DL, DS:SI)
|
pascal@24476
|
508 jnc ReadSectorNextSegment
|
pascal@24476
|
509
|
pascal@24476
|
510 mov ax, 201h ; al = sector count = 1
|
pascal@24476
|
511 ; ah = 2 = read function no.
|
pascal@24476
|
512 int 13h ; read sectors (AL, CX, DX, ES:BX)
|
pascal@24476
|
513
|
pascal@24476
|
514 jnc ReadSectorNextSegment
|
pascal@24476
|
515 cbw ; ah = 0 = reset function
|
pascal@24476
|
516 int 13h ; reset drive (DL)
|
pascal@24476
|
517
|
pascal@24476
|
518 dec di
|
pascal@24476
|
519 jnz ReadSectorRetry ; extra attempt
|
pascal@24476
|
520
|
pascal@24476
|
521 call Error
|
pascal@24476
|
522 db "Read error."
|
pascal@24476
|
523
|
pascal@24476
|
524 ReadSectorNextSegment:
|
pascal@24476
|
525
|
pascal@24476
|
526 pop ax ; al = 16
|
pascal@24476
|
527 mul byte [bx(bpbBytesPerSector)+1] ; = (bpbBytesPerSector/256)*16
|
pascal@24476
|
528 pop cx ; sector count = 1
|
pascal@24476
|
529 pop bx
|
pascal@24476
|
530 add [si+6], ax ; adjust segment for next sector
|
pascal@24476
|
531 pop es ; es:0 updated
|
pascal@24476
|
532 pop ax
|
pascal@24476
|
533 pop dx
|
pascal@24476
|
534 pop di
|
pascal@24476
|
535 pop di
|
pascal@24476
|
536
|
pascal@24476
|
537 add ax, cx ; adjust LBA for next sector
|
pascal@24476
|
538
|
pascal@24476
|
539 pop cx ; cluster sectors to read
|
pascal@24476
|
540 pop di ; file sectors to read
|
pascal@24476
|
541 dec di ; keep C
|
pascal@24476
|
542 loopne ReadSectorNext ; until cluster sector count or file sector count is reached
|
pascal@24476
|
543 pop si
|
pascal@24942
|
544 mov ax, bx ; clear ax
|
pascal@24476
|
545 mov dx, [bx] ; pass the BIOS boot drive to Run or Error
|
pascal@24476
|
546
|
pascal@24476
|
547 ret
|
pascal@24476
|
548
|
pascal@24942
|
549 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24942
|
550 ;; Fill free space with zeroes ;;
|
pascal@24942
|
551 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24942
|
552
|
pascal@24942
|
553 times (512-13-20-($-$$)) db 0
|
pascal@24942
|
554
|
pascal@24476
|
555 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
556 ;; Error Messaging Code ;;
|
pascal@24476
|
557 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
558
|
pascal@24476
|
559 Error:
|
pascal@24476
|
560 pop si
|
pascal@24478
|
561
|
pascal@24478
|
562 PutStr:
|
pascal@24476
|
563 mov ah, 0Eh
|
pascal@24476
|
564 mov bl, 7
|
pascal@24476
|
565 lodsb
|
pascal@24476
|
566 int 10h
|
pascal@24476
|
567 cmp al, "."
|
pascal@24476
|
568 jne PutStr
|
pascal@24476
|
569
|
pascal@24476
|
570 cbw
|
pascal@24476
|
571 int 16h ; wait for a key...
|
pascal@24476
|
572 int 19h ; bootstrap
|
pascal@24476
|
573
|
pascal@24476
|
574 Stop:
|
pascal@24476
|
575 hlt
|
pascal@24476
|
576 jmp short Stop
|
pascal@24476
|
577
|
pascal@24476
|
578 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
579 ;; Name of the file to load and run ;;
|
pascal@24476
|
580 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
581
|
pascal@24476
|
582 ProgramName db "STARTUP BIN" ; name and extension each must be
|
pascal@24476
|
583 ; padded with spaces (11 bytes total)
|
pascal@24476
|
584
|
pascal@24476
|
585 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
586 ;; End of the sector ID ;;
|
pascal@24476
|
587 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
588
|
pascal@24476
|
589 ClusterList dw 0AA55h ; BIOS checks for this ID
|
pascal@24479
|
590
|