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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@24535
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14 ;; - FAT32 supported using BIOS int 13h function 42h (IOW, it will only ;;
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pascal@24535
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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@25460
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20 ;; Its maximum size can be up to 637KB without Extended BIOS Data area. ;;
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pascal@24476
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21 ;; ;;
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pascal@24476
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22 ;; - Prints an error if the file isn't found or couldn't be read ;;
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pascal@24476
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23 ;; ("File not found" or "Read error") ;;
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pascal@24476
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24 ;; and waits for a key to be pressed, then executes the Int 19h ;;
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pascal@24476
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25 ;; instruction and lets the BIOS continue bootstrap. ;;
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pascal@24476
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26 ;; ;;
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pascal@24476
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27 ;; ;;
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pascal@24476
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28 ;; Known Bugs: ;;
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pascal@24476
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29 ;; ~~~~~~~~~~~ ;;
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pascal@24476
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30 ;; - 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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31 ;; on my HDD and an 8GB USB stick. ;;
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pascal@24476
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32 ;; ;;
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pascal@24476
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33 ;; ;;
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pascal@24476
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34 ;; Memory Layout: ;;
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pascal@24476
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35 ;; ~~~~~~~~~~~~~~ ;;
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pascal@24476
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36 ;; The diagram below shows the typical memory layout. The actual location ;;
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pascal@24476
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37 ;; 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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38 ;; reserves memory for its Extended BIOS Data Area just below A0000H and ;;
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pascal@24476
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39 ;; reports less than 640 KB of RAM via its Int 12H function. ;;
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pascal@24476
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40 ;; ;;
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pascal@24476
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41 ;; physical address ;;
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pascal@24476
|
42 ;; +------------------------+ 00000H ;;
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pascal@24476
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43 ;; | Interrupt Vector Table | ;;
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pascal@24476
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44 ;; +------------------------+ 00400H ;;
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pascal@24476
|
45 ;; | BIOS Data Area | ;;
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pascal@24476
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46 ;; +------------------------+ 00500H ;;
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pascal@24476
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47 ;; | PrtScr Status / Unused | ;;
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pascal@24476
|
48 ;; +------------------------+ 00600H ;;
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pascal@24476
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49 ;; | Loaded Image | ;;
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pascal@24476
|
50 ;; +------------------------+ nnnnnH ;;
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pascal@24476
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51 ;; | Available Memory | ;;
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pascal@25460
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52 ;; +------------------------+ A0000H - 1KB ;;
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pascal@24476
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53 ;; | Boot Sector | ;;
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pascal@25460
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54 ;; +------------------------+ A0000H - 0.5KB ;;
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pascal@25460
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55 ;; | 0.5KB Boot Stack | ;;
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pascal@24476
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56 ;; +------------------------+ A0000H ;;
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pascal@24476
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57 ;; | Video RAM | ;;
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pascal@24476
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58 ;; ;;
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pascal@24476
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59 ;; ;;
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pascal@24476
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60 ;; Boot Image Startup (register values): ;;
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pascal@24476
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61 ;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
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pascal@24945
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62 ;; ax = 0ffffh (both FCB in the PSP don't have a valid drive identifier), ;;
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pascal@25454
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63 ;; bx = 0, dl = BIOS boot drive number (e.g. 0, 80H) ;;
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pascal@24476
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64 ;; cs:ip = program entry point ;;
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pascal@24476
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65 ;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
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pascal@24476
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66 ;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
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pascal@24476
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67 ;; EXE program defaults: ds = es = EXE data - 10h (fake MS-DOS psp), ;;
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pascal@24476
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68 ;; cs:ip and ss:sp depends on EXE header ;;
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pascal@24476
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69 ;; Magic numbers: ;;
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pascal@24476
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70 ;; si = 16381 (prime number 2**14-3) ;;
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pascal@24476
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71 ;; di = 32749 (prime number 2**15-19) ;;
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pascal@24476
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72 ;; bp = 65521 (prime number 2**16-15) ;;
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pascal@24476
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73 ;; The magic numbers let the program know whether it has been loaded by ;;
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pascal@24476
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74 ;; this boot sector or by MS-DOS, which may be handy for universal, bare- ;;
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pascal@24476
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75 ;; metal and MS-DOS programs. ;;
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pascal@24945
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76 ;; The command line contains no arguments. ;;
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pascal@24476
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77 ;; ;;
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pascal@24476
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78 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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79
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pascal@24491
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80 %define bx(label) bx+label-boot
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pascal@25449
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81 %define si(label) si+label-boot
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pascal@25449
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82 ClusterMask equ 1 ; +9 bytes
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pascal@25460
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83 NullEntryCheck equ 1 ; +5 bytes
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pascal@25449
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84 ReadRetry equ 1 ; +7 bytes
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pascal@25458
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85 LBA48bits equ 1 ; +15 bytes
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pascal@25449
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86 CHSsupport equ 1 ; +27 bytes
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pascal@25458
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87 CHSupTo8GB equ 1 ; +11 bytes
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pascal@25458
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88 CHSupTo32MB equ 1 ; +7 bytes
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pascal@25458
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89 SectorOf512Bytes equ 1 ; -5 bytes
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pascal@25458
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90 Always2FATs equ 0 ; -4 bytes
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pascal@24491
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91
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pascal@24476
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92 [BITS 16]
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pascal@24476
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93
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pascal@24478
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94 ImageLoadSeg equ 60h ; <=07Fh because of "push byte ImageLoadSeg" instructions
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pascal@25460
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95 StackSize equ 512
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pascal@24476
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96
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pascal@24476
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97 [SECTION .text]
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pascal@24476
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98 [ORG 0]
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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 ;; Boot sector 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@24491
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104 boot:
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pascal@25458
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105 DriveNumber equ boot+0
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pascal@25458
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106 HiLBA equ boot+2
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pascal@24476
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107 jmp short start ; MS-DOS/Windows checks for this jump
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pascal@24476
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108 nop
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pascal@24476
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109 bsOemName DB "BootProg" ; 0x03
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pascal@24476
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110
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pascal@24476
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111 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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112 ;; BPB1 starts here ;;
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pascal@24476
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113 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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114
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pascal@24479
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115 bpbBytesPerSector DW 0 ; 0x0B
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pascal@24479
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116 bpbSectorsPerCluster DB 0 ; 0x0D
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pascal@24479
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117 bpbReservedSectors DW 0 ; 0x0E
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pascal@24479
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118 bpbNumberOfFATs DB 0 ; 0x10
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pascal@24479
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119 bpbRootEntries DW 0 ; 0x11
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pascal@24479
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120 bpbTotalSectors DW 0 ; 0x13
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pascal@24479
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121 bpbMedia DB 0 ; 0x15
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pascal@24479
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122 bpbSectorsPerFAT DW 0 ; 0x16
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pascal@24479
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123 bpbSectorsPerTrack DW 0 ; 0x18
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pascal@24479
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124 bpbHeadsPerCylinder DW 0 ; 0x1A
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pascal@24479
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125 bpbHiddenSectors DD 0 ; 0x1C
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pascal@24479
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126 bpbTotalSectorsBig DD 0 ; 0x20
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pascal@24476
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127
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pascal@24476
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128 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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129 ;; BPB1 ends here ;;
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pascal@24476
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130 ;;;;;;;;;;;;;;;;;;;;
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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 ;; BPB2 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@24479
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136 bsSectorsPerFAT32 DD 0 ; 0x24
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pascal@24479
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137 bsExtendedFlags DW 0 ; 0x28
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pascal@24479
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138 bsFSVersion DW 0 ; 0x2A
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pascal@24479
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139 bsRootDirectoryClusterNo DD 0 ; 0x2C
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pascal@24479
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140 bsFSInfoSectorNo DW 0 ; 0x30
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pascal@24479
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141 bsBackupBootSectorNo DW 0 ; 0x32
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pascal@24479
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142 bsreserved times 12 DB 0 ; 0x34
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pascal@24479
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143 bsDriveNumber DB 0 ; 0x40
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pascal@24479
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144 bsreserved1 DB 0 ; 0x41
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pascal@24479
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145 bsExtendedBootSignature DB 0 ; 0x42
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pascal@24479
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146 bsVolumeSerialNumber DD 0 ; 0x43
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pascal@25458
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147 bsVolumeLabel times 11 DB " " ; 0x47 "NO NAME "
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pascal@25458
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148 bsFileSystemName times 8 DB " " ; 0x52 "FAT32 "
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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 ;; BPB2 ends here ;;
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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 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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155 ;; Boot sector code starts here ;;
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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 start:
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pascal@24476
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159 cld
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pascal@24476
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160
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pascal@24476
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161 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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162 ;; How much RAM is there? ;;
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pascal@24476
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163 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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164
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pascal@24476
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165 int 12h ; get conventional memory size (in KBs)
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pascal@25460
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166 dec ax ; reserve 1K bytes for the code and the stack
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pascal@24525
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167 mov cx, 106h
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pascal@24525
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168 shl ax, cl ; and convert it to 16-byte paragraphs
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pascal@24476
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169
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pascal@24476
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170 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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171 ;; Reserve memory for the boot sector and its stack ;;
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pascal@24476
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172 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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173
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pascal@24525
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174 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
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pascal@24525
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175 mov ss, ax
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pascal@24525
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176 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
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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 ;; Copy ourselves to top of memory ;;
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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 mov si, 7C00h
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pascal@24476
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183 xor di, di
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pascal@24476
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184 mov ds, di
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pascal@25449
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185 push es
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pascal@25449
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186 mov [si(DriveNumber)], dx ; store BIOS boot drive number
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pascal@24478
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187 rep movsw
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pascal@24476
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188
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pascal@24476
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189 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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190 ;; Jump to the copy ;;
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pascal@24476
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191 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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192
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pascal@25450
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193 push byte main
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pascal@24476
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194 retf
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pascal@24476
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195
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pascal@24476
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196 main:
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pascal@24476
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197 push cs
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pascal@24476
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198 pop ds
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pascal@24476
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199
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pascal@25449
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200 xor ebx, ebx
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pascal@24476
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201
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pascal@25449
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202 %if ClusterMask != 0
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pascal@24491
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203 and byte [bx(bsRootDirectoryClusterNo+3)], 0Fh ; mask cluster value
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pascal@25449
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204 %endif
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pascal@24491
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205 mov esi, [bx(bsRootDirectoryClusterNo)] ; esi=cluster # of root dir
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pascal@24476
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206
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pascal@24478
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207 push byte ImageLoadSeg
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pascal@24478
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208 pop es
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pascal@25449
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209
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pascal@25449
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210 RootDirReadContinue:
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pascal@25458
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211 call ReadClusterSector ; read one sector of the root dir
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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@24476
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214 ;; Look for the COM/EXE file to load and run ;;
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pascal@24476
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215 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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216
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pascal@24476
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217 xor di, di ; es:di -> root entries array
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pascal@24476
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218
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pascal@24476
|
219 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24478
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220 ;; Looks for a file/dir by its name ;;
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pascal@24476
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221 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24478
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222 ;; Input: DS:SI -> file name (11 chars) ;;
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pascal@24478
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223 ;; ES:DI -> root directory array ;;
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pascal@24525
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224 ;; BP = paragraphs in sector ;;
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pascal@24476
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225 ;; Output: ESI = cluster number ;;
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pascal@24476
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226 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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227
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pascal@24476
|
228 FindNameCycle:
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pascal@25449
|
229 %if NullEntryCheck != 0
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pascal@24525
|
230 cmp byte [es:di], bh
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pascal@24478
|
231 je ErrFind ; end of root directory (NULL entry found)
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pascal@25449
|
232 %endif
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pascal@24478
|
233 pusha
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pascal@25454
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234 mov cl, NameLength
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pascal@24525
|
235 mov si, ProgramName ; ds:si -> program name
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pascal@24476
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236 repe cmpsb
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pascal@24525
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237 je FindNameFound
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pascal@24478
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238 popa
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pascal@24525
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239 add di, byte 32
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pascal@24476
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240 dec bp
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pascal@24476
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241 dec bp
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pascal@24476
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242 jnz FindNameCycle ; next root entry
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pascal@25458
|
243 loop RootDirReadContinue ; next sector in cluster
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pascal@25458
|
244 cmp esi, 0FFFFFF6h ; carry=0 if last cluster, and carry=1 otherwise
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pascal@25458
|
245 jnc RootDirReadContinue ; continue to the next root dir cluster
|
pascal@24478
|
246 ErrFind:
|
pascal@24478
|
247 call Error ; end of root directory (dir end reached)
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pascal@24476
|
248 db "File not found."
|
pascal@24476
|
249 FindNameFound:
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pascal@24525
|
250 push word [es:di+14h-11]
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pascal@24525
|
251 push word [es:di+1Ah-11]
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pascal@24478
|
252 pop esi ; esi = cluster no. cx = 0
|
pascal@24476
|
253
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pascal@24525
|
254 dec dword [es:di+1Ch-11] ; load ((n - 1)/256)*16 +1 paragraphs
|
pascal@24525
|
255 imul di, [es:di+1Ch+1-11], byte 16 ; file size in paragraphs (full pages)
|
pascal@24476
|
256
|
pascal@24476
|
257 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
258 ;; Load the entire file ;;
|
pascal@24476
|
259 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
260
|
pascal@24476
|
261 push es
|
pascal@24476
|
262 FileReadContinue:
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pascal@24476
|
263 push di
|
pascal@25458
|
264 call ReadClusterSector ; read one sector of the boot file
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pascal@25458
|
265 dec cx
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pascal@24476
|
266 mov di, es
|
pascal@24478
|
267 add di, bp
|
pascal@24478
|
268 mov es, di ; es:bx updated
|
pascal@24476
|
269 pop di
|
pascal@24478
|
270
|
pascal@24476
|
271 sub di, bp
|
pascal@24476
|
272 jae FileReadContinue
|
pascal@24943
|
273 xor ax, ax
|
pascal@24476
|
274 pop bp
|
pascal@24476
|
275
|
pascal@24476
|
276 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
277 ;; Type detection, .COM or .EXE? ;;
|
pascal@24476
|
278 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
279
|
pascal@24476
|
280 mov ds, bp ; bp=ds=seg the file is loaded to
|
pascal@24535
|
281
|
pascal@24476
|
282 add bp, [bx+08h] ; bp = image base
|
pascal@24476
|
283 mov di, [bx+18h] ; di = reloc table pointer
|
pascal@24476
|
284
|
pascal@24476
|
285 cmp word [bx], 5A4Dh ; "MZ" signature?
|
pascal@24476
|
286 je RelocateEXE ; yes, it's an EXE program
|
pascal@24476
|
287
|
pascal@24476
|
288 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
289 ;; Setup and run a .COM program ;;
|
pascal@24535
|
290 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
|
pascal@25454
|
291 ;; AX=0ffffh BX=0 DX=drive and ;;
|
pascal@25454
|
292 ;; cmdline=void ;;
|
pascal@24476
|
293 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
294
|
pascal@24535
|
295 mov di, 100h ; ip
|
pascal@24476
|
296 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
|
pascal@24476
|
297 mov ss, bp
|
pascal@24476
|
298 xor sp, sp
|
pascal@24476
|
299 push bp ; cs, ds and es
|
pascal@24476
|
300 jmp short Run
|
pascal@24476
|
301
|
pascal@24476
|
302 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
303 ;; Relocate, setup and run a .EXE program ;;
|
pascal@24476
|
304 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
|
pascal@24476
|
305 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
|
pascal@25454
|
306 ;; AX=0ffffh BX=0 DX=drive cmdline=void ;;
|
pascal@24476
|
307 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
308
|
pascal@24476
|
309 ReloCycle:
|
pascal@24476
|
310 add [di+2], bp ; item seg (abs)
|
pascal@24476
|
311 les si, [di] ; si = item ofs, es = item seg
|
pascal@24476
|
312 add [es:si], bp ; fixup
|
pascal@24525
|
313 scasw ; di += 2
|
pascal@24525
|
314 scasw ; point to next entry
|
pascal@24476
|
315
|
pascal@24476
|
316 RelocateEXE:
|
pascal@24942
|
317 dec word [bx+06h] ; reloc items, 32768 max (128KB table)
|
pascal@24942
|
318 jns ReloCycle
|
pascal@24942
|
319
|
pascal@24945
|
320 les si, [bx+0Eh]
|
pascal@24945
|
321 add si, bp
|
pascal@24945
|
322 mov ss, si ; ss for EXE
|
pascal@24945
|
323 mov sp, es ; sp for EXE
|
pascal@24476
|
324
|
pascal@24476
|
325 lea si, [bp-10h] ; ds and es both point to the segment
|
pascal@24476
|
326 push si ; containing the PSP structure
|
pascal@24476
|
327
|
pascal@24476
|
328 add bp, [bx+16h] ; cs for EXE
|
pascal@24535
|
329 mov di, [bx+14h] ; ip for EXE
|
pascal@24476
|
330 Run:
|
pascal@24476
|
331 pop ds
|
pascal@24476
|
332 push bp
|
pascal@24535
|
333 push di
|
pascal@24476
|
334 push ds
|
pascal@24476
|
335 pop es
|
pascal@24942
|
336 mov [80h], ax ; clear cmdline
|
pascal@24942
|
337 dec ax ; both FCB in the PSP don't have a valid drive identifier
|
pascal@24476
|
338
|
pascal@24476
|
339 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
340 ;; Set the magic numbers so the program knows that it ;;
|
pascal@24476
|
341 ;; has been loaded by this bootsector and not by MS-DOS ;;
|
pascal@24476
|
342 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
343 mov si, 16381 ; prime number 2**14-3
|
pascal@24476
|
344 mov di, 32749 ; prime number 2**15-19
|
pascal@24476
|
345 mov bp, 65521 ; prime number 2**16-15
|
pascal@24476
|
346
|
pascal@24476
|
347 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
348 ;; All done, transfer control to the program now ;;
|
pascal@24476
|
349 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
350 retf
|
pascal@24476
|
351
|
pascal@25458
|
352 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@25458
|
353 ;; Error Messaging Code ;;
|
pascal@25458
|
354 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@25458
|
355
|
pascal@25458
|
356 Error:
|
pascal@25458
|
357 pop si
|
pascal@25458
|
358 puts:
|
pascal@25458
|
359 mov ah, 0Eh
|
pascal@25458
|
360 mov bl, 7
|
pascal@25458
|
361 lodsb
|
pascal@25458
|
362 int 10h
|
pascal@25458
|
363 cmp al, '.'
|
pascal@25458
|
364 jne puts
|
pascal@25458
|
365 cbw
|
pascal@25458
|
366 int 16h ; wait for a key...
|
pascal@25458
|
367 int 19h ; bootstrap
|
pascal@25458
|
368
|
pascal@25458
|
369 Stop:
|
pascal@25458
|
370 hlt
|
pascal@25458
|
371 jmp short Stop
|
pascal@25458
|
372
|
pascal@25458
|
373 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@25458
|
374 ;; Reads a FAT32 sector ;;
|
pascal@25458
|
375 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@25458
|
376 ;; Inout: ES:BX -> buffer ;;
|
pascal@25458
|
377 ;; EAX = prev sector ;;
|
pascal@25458
|
378 ;; CX = rem sectors in cluster ;;
|
pascal@25458
|
379 ;; ESI = next cluster ;;
|
pascal@25458
|
380 ;; Output: EAX = current sector ;;
|
pascal@25458
|
381 ;; CX = rem sectors in cluster ;;
|
pascal@25458
|
382 ;; ESI = next cluster ;;
|
pascal@25458
|
383 ;; BP -> para / sector ;;
|
pascal@25458
|
384 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@25458
|
385
|
pascal@25458
|
386 ReadClusterSector:
|
pascal@25458
|
387 %if SectorOf512Bytes != 0
|
pascal@25458
|
388 mov bp, 32 ; bp = paragraphs per sector
|
pascal@25458
|
389 %else
|
pascal@24525
|
390 mov bp, [bx(bpbBytesPerSector)]
|
pascal@24525
|
391 shr bp, 4 ; bp = paragraphs per sector
|
pascal@25458
|
392 %endif
|
pascal@25449
|
393 mov dx, 1 ; adjust LBA for next sector
|
pascal@24525
|
394 inc cx
|
pascal@24525
|
395 loop ReadSectorLBA
|
pascal@24525
|
396
|
pascal@25449
|
397 mul ebx ; edx:eax = 0
|
pascal@25458
|
398 %if SectorOf512Bytes != 0
|
pascal@25458
|
399 mov al, 128 ; ax=# of FAT32 entries per sector
|
pascal@25458
|
400 %else
|
pascal@24945
|
401 imul ax, bp, byte 4 ; ax=# of FAT32 entries per sector
|
pascal@25458
|
402 %endif
|
pascal@24525
|
403 lea edi, [esi-2] ; esi=cluster #
|
pascal@24476
|
404 xchg eax, esi
|
pascal@24478
|
405 div esi ; eax=FAT sector #, edx=entry # in sector
|
pascal@24476
|
406
|
pascal@24525
|
407 imul si, dx, byte 4 ; si=entry # in sector, clear C
|
pascal@25449
|
408 %if LBA48bits != 0
|
pascal@25458
|
409 xor dx, dx
|
pascal@25449
|
410 %endif
|
pascal@25458
|
411 call ReadSectorLBAfromFAT ; read 1 FAT32 sector
|
pascal@24476
|
412
|
pascal@25449
|
413 %if ClusterMask != 0
|
pascal@24478
|
414 and byte [es:si+3], 0Fh ; mask cluster value
|
pascal@25449
|
415 %endif
|
pascal@24478
|
416 mov esi, [es:si] ; esi=next cluster #
|
pascal@24476
|
417
|
pascal@25458
|
418 %if Always2FATs != 0
|
pascal@25458
|
419 imul eax, dword [bx(bsSectorsPerFAT32)], 2
|
pascal@25458
|
420 %else
|
pascal@24525
|
421 movzx eax, byte [bx(bpbNumberOfFATs)]
|
pascal@24525
|
422 mul dword [bx(bsSectorsPerFAT32)]
|
pascal@25458
|
423 %endif
|
pascal@24525
|
424
|
pascal@24525
|
425 xchg eax, edi
|
pascal@25454
|
426 movzx ecx, byte [bx(bpbSectorsPerCluster)] ; 8..128
|
pascal@24945
|
427 mul ecx ; edx:eax=sector number in data area
|
pascal@24525
|
428 add eax, edi
|
pascal@25458
|
429 %if LBA48bits != 0
|
pascal@25458
|
430 adc dx, bx
|
pascal@25458
|
431 %endif
|
pascal@24476
|
432
|
pascal@25458
|
433 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@25458
|
434 ;; Reads a sector form the start of FAT ;;
|
pascal@25458
|
435 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@25458
|
436
|
pascal@25458
|
437 ReadSectorLBAfromFAT:
|
pascal@25458
|
438 add eax, [bx(bpbHiddenSectors)]
|
pascal@25449
|
439 %if LBA48bits != 0
|
pascal@25449
|
440 adc dx, bx
|
pascal@25449
|
441 mov word [bx(HiLBA)], dx
|
pascal@25449
|
442 %endif
|
pascal@25454
|
443 mov dx, [bx(bpbReservedSectors)]
|
pascal@24476
|
444
|
pascal@24478
|
445 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
446 ;; Reads a sector using BIOS Int 13h fn 42h ;;
|
pascal@24478
|
447 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
448 ;; Input: EAX = LBA ;;
|
pascal@24478
|
449 ;; CX = sector count ;;
|
pascal@24478
|
450 ;; ES:BX -> buffer address ;;
|
pascal@24478
|
451 ;; Output: CF = 0 if no more sectors ;;
|
pascal@24478
|
452 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
453
|
pascal@24476
|
454 ReadSectorLBA:
|
pascal@25449
|
455 add eax, edx
|
pascal@25449
|
456 %if LBA48bits != 0
|
pascal@24535
|
457 adc word [bx(HiLBA)], bx
|
pascal@25449
|
458 %endif
|
pascal@25449
|
459 mov dx, [bx(DriveNumber)] ; restore BIOS boot drive number
|
pascal@24476
|
460 pusha
|
pascal@24476
|
461
|
pascal@24478
|
462 push bx
|
pascal@25449
|
463 %if LBA48bits != 0
|
pascal@24491
|
464 push word [bx(HiLBA)] ; 48-bit LBA
|
pascal@25449
|
465 %else
|
pascal@25449
|
466 push bx
|
pascal@25449
|
467 %endif
|
pascal@24478
|
468 push eax
|
pascal@24476
|
469 push es
|
pascal@24476
|
470 push bx
|
pascal@24478
|
471 push byte 1 ; sector count word = 1
|
pascal@24525
|
472 push byte 16 ; packet size byte = 16, reserved byte = 0
|
pascal@24525
|
473
|
pascal@25449
|
474 %if CHSsupport != 0
|
pascal@25458
|
475 %if CHSupTo8GB != 0
|
pascal@25449
|
476 push eax
|
pascal@25449
|
477 pop cx ; save low LBA
|
pascal@25449
|
478 pop ax ; get high LBA
|
pascal@25449
|
479 cwd ; clear dx (assume LBA offset <1TB)
|
pascal@25449
|
480 idiv word [bx(bpbSectorsPerTrack)] ; up to 8GB disks, avoid divide error
|
pascal@25449
|
481
|
pascal@25449
|
482 xchg ax, cx ; restore low LBA, save high LBA / SPT
|
pascal@25458
|
483 %else
|
pascal@25449
|
484 ; Busybox mkdosfs creates fat32 for floppies.
|
pascal@25449
|
485 ; Floppies may support CHS only.
|
pascal@25458
|
486 %if CHSupTo32MB != 0
|
pascal@25458
|
487 xor dx, dx ; clear dx (LBA offset <32MB)
|
pascal@25458
|
488 %else
|
pascal@25449
|
489 cwd ; clear dx (LBA offset <16MB)
|
pascal@25458
|
490 %endif
|
pascal@25450
|
491 xor cx, cx ; high LBA / SPT = 0
|
pascal@25458
|
492 %endif
|
pascal@25449
|
493 idiv word [bx(bpbSectorsPerTrack)]
|
pascal@25449
|
494 ; ax = LBA / SPT
|
pascal@25449
|
495 ; dx = LBA % SPT = sector - 1
|
pascal@25449
|
496 inc dx
|
pascal@25449
|
497
|
pascal@25449
|
498 xchg cx, dx ; restore high LBA / SPT, save sector no.
|
pascal@25450
|
499 idiv word [bx(bpbHeadsPerCylinder)]
|
pascal@25449
|
500 ; ax = (LBA / SPT) / HPC = cylinder
|
pascal@25449
|
501 ; dx = (LBA / SPT) % HPC = head
|
pascal@25449
|
502
|
pascal@25458
|
503 xchg ch, al ; clear al
|
pascal@25449
|
504 ; ch = LSB 0...7 of cylinder no.
|
pascal@25458
|
505 %if CHSupTo8GB != 0 || CHSupTo32MB != 0
|
pascal@25458
|
506 shr ax, 2
|
pascal@25458
|
507 or cl, al
|
pascal@25449
|
508 ; cl = MSB 8...9 of cylinder no. + sector no.
|
pascal@25458
|
509 %endif
|
pascal@25449
|
510 mov dh, dl
|
pascal@25449
|
511 ; dh = head no.
|
pascal@25449
|
512 mov dl, [bx(DriveNumber)] ; restore BIOS boot drive number
|
pascal@25449
|
513 %endif
|
pascal@25449
|
514
|
pascal@25454
|
515 ReadSectorRetry:
|
pascal@24525
|
516 mov si, sp
|
pascal@24478
|
517 mov ah, 42h ; ah = 42h = extended read function no.
|
pascal@24478
|
518 int 13h ; extended read sectors (DL, DS:SI)
|
pascal@24478
|
519 jnc ReadSuccess ; CF = 0 if no error
|
pascal@24476
|
520
|
pascal@25449
|
521 %if CHSsupport != 0
|
pascal@25449
|
522 mov ax, 201h ; al = sector count = 1
|
pascal@25449
|
523 ; ah = 2 = read function no.
|
pascal@25449
|
524 int 13h ; read sectors (AL, CX, DX, ES:BX)
|
pascal@25449
|
525
|
pascal@25449
|
526 jnc ReadSuccess ; CF = 0 if no error
|
pascal@25449
|
527 %endif
|
pascal@25449
|
528 %if ReadRetry != 0
|
pascal@25458
|
529 %if CHSsupport != 0
|
pascal@25449
|
530 cbw ; ah = 0 = reset function
|
pascal@25458
|
531 %else
|
pascal@24945
|
532 xor ax, ax ; ah = 0 = reset function
|
pascal@25458
|
533 %endif
|
pascal@24476
|
534 int 13h ; reset drive (DL)
|
pascal@24476
|
535
|
pascal@25457
|
536 dec bp ; up to 32 retries
|
pascal@25454
|
537 jnz ReadSectorRetry
|
pascal@25449
|
538 %endif
|
pascal@24525
|
539
|
pascal@24476
|
540 call Error
|
pascal@24476
|
541 db "Read error."
|
pascal@24476
|
542
|
pascal@24478
|
543 ReadSuccess:
|
pascal@24476
|
544
|
pascal@24476
|
545 popa ; sp += 16
|
pascal@24478
|
546 popa
|
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@25458
|
553 times (512-13-($-$$)) db 0
|
pascal@24476
|
554
|
pascal@24476
|
555 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
556 ;; Name of the file to load and run ;;
|
pascal@24476
|
557 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
558
|
pascal@25463
|
559 NameLength equ 11
|
pascal@25463
|
560 ProgramName times NameLength db 0 ; name and extension
|
pascal@24476
|
561
|
pascal@24476
|
562 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
563 ;; End of the sector ID ;;
|
pascal@24476
|
564 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
565
|
pascal@24476
|
566 dw 0AA55h ; BIOS checks for this ID
|