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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@24525
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20 ;; Its maximum size can be up to 636KB 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
|
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
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42 ;; +------------------------+ 00000H ;;
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pascal@24476
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43 ;; | Interrupt Vector Table | ;;
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pascal@24476
|
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
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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@24525
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52 ;; +------------------------+ A0000H - 2KB ;;
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pascal@24476
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53 ;; | Boot Sector | ;;
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pascal@24525
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54 ;; +------------------------+ A0000H - 1.5KB ;;
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pascal@24525
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55 ;; | 1.5KB 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@24945
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63 ;; bx = cx = 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@25449
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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@25449
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85 LBA48bits equ 1 ; +13 bytes
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pascal@25449
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86 CHSsupport equ 1 ; +27 bytes
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pascal@25449
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87 CHShardDisk equ 0 ; +11 bytes
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pascal@24491
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88
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pascal@24476
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89 [BITS 16]
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pascal@24476
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90
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pascal@24478
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91 ImageLoadSeg equ 60h ; <=07Fh because of "push byte ImageLoadSeg" instructions
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pascal@24525
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92 StackSize equ 1536
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pascal@24476
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93
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pascal@24476
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94 [SECTION .text]
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pascal@24476
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95 [ORG 0]
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pascal@24476
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96
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pascal@24476
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97 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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98 ;; Boot sector starts here ;;
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pascal@24476
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99 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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100
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pascal@24491
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101 boot:
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pascal@24476
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102 jmp short start ; MS-DOS/Windows checks for this jump
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pascal@24476
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103 nop
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pascal@24476
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104 bsOemName DB "BootProg" ; 0x03
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pascal@24476
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105
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pascal@24476
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106 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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107 ;; BPB1 starts here ;;
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pascal@24476
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108 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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109
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pascal@24479
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110 bpbBytesPerSector DW 0 ; 0x0B
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pascal@24479
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111 bpbSectorsPerCluster DB 0 ; 0x0D
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pascal@24479
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112 bpbReservedSectors DW 0 ; 0x0E
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pascal@24479
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113 bpbNumberOfFATs DB 0 ; 0x10
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pascal@24479
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114 bpbRootEntries DW 0 ; 0x11
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pascal@24479
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115 bpbTotalSectors DW 0 ; 0x13
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pascal@24479
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116 bpbMedia DB 0 ; 0x15
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pascal@24479
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117 bpbSectorsPerFAT DW 0 ; 0x16
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pascal@24479
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118 bpbSectorsPerTrack DW 0 ; 0x18
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pascal@24479
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119 bpbHeadsPerCylinder DW 0 ; 0x1A
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pascal@24479
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120 bpbHiddenSectors DD 0 ; 0x1C
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pascal@24479
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121 bpbTotalSectorsBig DD 0 ; 0x20
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pascal@24476
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122
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pascal@24476
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123 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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124 ;; BPB1 ends here ;;
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pascal@24476
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125 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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126
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pascal@24476
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127 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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128 ;; BPB2 starts here ;;
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pascal@24476
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129 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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130
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pascal@24479
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131 bsSectorsPerFAT32 DD 0 ; 0x24
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pascal@24479
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132 bsExtendedFlags DW 0 ; 0x28
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pascal@24479
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133 bsFSVersion DW 0 ; 0x2A
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pascal@24479
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134 bsRootDirectoryClusterNo DD 0 ; 0x2C
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pascal@24479
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135 bsFSInfoSectorNo DW 0 ; 0x30
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pascal@24479
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136 bsBackupBootSectorNo DW 0 ; 0x32
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pascal@24479
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137 bsreserved times 12 DB 0 ; 0x34
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pascal@24479
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138 bsDriveNumber DB 0 ; 0x40
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pascal@25449
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139 %if LBA48bits != 0
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pascal@25449
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140 HiLBA equ boot+0
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pascal@25449
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141 DriveNumber equ bsDriveNumber+0
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pascal@25449
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142 %else
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pascal@25449
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143 DriveNumber equ boot+0
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pascal@25449
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144 %endif
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pascal@24479
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145 bsreserved1 DB 0 ; 0x41
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pascal@24479
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146 bsExtendedBootSignature DB 0 ; 0x42
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pascal@24479
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147 bsVolumeSerialNumber DD 0 ; 0x43
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pascal@24476
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148 bsVolumeLabel DB "NO NAME " ; 0x47
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pascal@24476
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149 bsFileSystemName DB "FAT32 " ; 0x52
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pascal@24476
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150
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pascal@24476
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151 ;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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152 ;; BPB2 ends here ;;
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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 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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156 ;; Boot sector code starts here ;;
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pascal@24476
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157 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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158
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pascal@24476
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159 start:
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pascal@24476
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160 cld
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pascal@24476
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161
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pascal@24476
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162 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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163 ;; How much RAM is there? ;;
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pascal@24476
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164 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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165
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pascal@24476
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166 int 12h ; get conventional memory size (in KBs)
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pascal@24525
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167 dec ax
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pascal@24525
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168 dec ax ; reserve 2K bytes for the code and the stack
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pascal@24525
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169 mov cx, 106h
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pascal@24525
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170 shl ax, cl ; and convert it to 16-byte paragraphs
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pascal@24476
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171
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pascal@24476
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172 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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173 ;; Reserve memory for the boot sector and its stack ;;
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pascal@24476
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174 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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175
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pascal@24525
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176 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
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pascal@24525
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177 mov ss, ax
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pascal@24525
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178 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
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pascal@24476
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179
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pascal@24476
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180 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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181 ;; Copy ourselves to top of memory ;;
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pascal@24476
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182 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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183
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pascal@24476
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184 mov si, 7C00h
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pascal@24476
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185 xor di, di
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pascal@24476
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186 mov ds, di
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pascal@25449
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187 push es
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pascal@25449
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188 mov [si(DriveNumber)], dx ; store BIOS boot drive number
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pascal@24478
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189 rep movsw
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pascal@24476
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190
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pascal@24476
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191 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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192 ;; Jump to the copy ;;
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pascal@24476
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193 ;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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194
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pascal@25450
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195 push byte main
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pascal@24476
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196 retf
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pascal@24476
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197
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pascal@24476
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198 main:
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pascal@24476
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199 push cs
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pascal@24476
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200 pop ds
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pascal@24476
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201
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pascal@25449
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202 xor ebx, ebx
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pascal@24476
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203
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pascal@25449
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204 %if ClusterMask != 0
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pascal@24491
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205 and byte [bx(bsRootDirectoryClusterNo+3)], 0Fh ; mask cluster value
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pascal@25449
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206 %endif
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pascal@24491
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207 mov esi, [bx(bsRootDirectoryClusterNo)] ; esi=cluster # of root dir
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pascal@24476
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208
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pascal@24478
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209 push byte ImageLoadSeg
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pascal@24478
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210 pop es
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pascal@25449
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211
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pascal@25449
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212 RootDirReadContinue:
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pascal@24478
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213 call ReadCluster ; read one cluster of root dir
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pascal@24478
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214 pushf ; save carry="not last cluster" flag
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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 ;; Look for the COM/EXE file to load and run ;;
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pascal@24476
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218 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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219
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pascal@24476
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220 xor di, di ; es:di -> root entries array
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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@24478
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223 ;; Looks for a file/dir by its name ;;
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pascal@24476
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224 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24478
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225 ;; Input: DS:SI -> file name (11 chars) ;;
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pascal@24478
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226 ;; ES:DI -> root directory array ;;
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pascal@24525
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227 ;; BP = paragraphs in sector ;;
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pascal@24476
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228 ;; Output: ESI = cluster number ;;
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pascal@24476
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229 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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230
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pascal@24476
|
231 FindNameCycle:
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pascal@25449
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232 %if NullEntryCheck != 0
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pascal@24525
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233 cmp byte [es:di], bh
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pascal@24478
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234 je ErrFind ; end of root directory (NULL entry found)
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pascal@25449
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235 %endif
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pascal@24478
|
236 pusha
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pascal@24525
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237 mov cl, 11
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pascal@24525
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238 mov si, ProgramName ; ds:si -> program name
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pascal@24476
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239 repe cmpsb
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pascal@24525
|
240 je FindNameFound
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pascal@24478
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241 popa
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pascal@24525
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242 add di, byte 32
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pascal@24476
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243 dec bp
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pascal@24476
|
244 dec bp
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pascal@24476
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245 jnz FindNameCycle ; next root entry
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pascal@24478
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246 popf ; restore carry="not last cluster" flag
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pascal@24476
|
247 jc RootDirReadContinue ; continue to the next root dir cluster
|
pascal@24478
|
248 ErrFind:
|
pascal@24478
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249 call Error ; end of root directory (dir end reached)
|
pascal@24476
|
250 db "File not found."
|
pascal@24476
|
251 FindNameFound:
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pascal@24525
|
252 push word [es:di+14h-11]
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pascal@24525
|
253 push word [es:di+1Ah-11]
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pascal@24478
|
254 pop esi ; esi = cluster no. cx = 0
|
pascal@24476
|
255
|
pascal@24525
|
256 dec dword [es:di+1Ch-11] ; load ((n - 1)/256)*16 +1 paragraphs
|
pascal@24525
|
257 imul di, [es:di+1Ch+1-11], byte 16 ; file size in paragraphs (full pages)
|
pascal@24476
|
258
|
pascal@24476
|
259 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
260 ;; Load the entire file ;;
|
pascal@24476
|
261 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
262
|
pascal@24476
|
263 push es
|
pascal@24476
|
264 FileReadContinue:
|
pascal@24476
|
265 push di
|
pascal@24478
|
266 call ReadCluster ; read one cluster of root dir
|
pascal@24476
|
267 mov di, es
|
pascal@24478
|
268 add di, bp
|
pascal@24478
|
269 mov es, di ; es:bx updated
|
pascal@24476
|
270 pop di
|
pascal@24478
|
271
|
pascal@24476
|
272 sub di, bp
|
pascal@24476
|
273 jae FileReadContinue
|
pascal@24943
|
274 xor ax, ax
|
pascal@24476
|
275 pop bp
|
pascal@24476
|
276
|
pascal@24476
|
277 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
278 ;; Type detection, .COM or .EXE? ;;
|
pascal@24476
|
279 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
280
|
pascal@24476
|
281 mov ds, bp ; bp=ds=seg the file is loaded to
|
pascal@24535
|
282
|
pascal@24476
|
283 add bp, [bx+08h] ; bp = image base
|
pascal@24476
|
284 mov di, [bx+18h] ; di = reloc table pointer
|
pascal@24476
|
285
|
pascal@24476
|
286 cmp word [bx], 5A4Dh ; "MZ" signature?
|
pascal@24476
|
287 je RelocateEXE ; yes, it's an EXE program
|
pascal@24476
|
288
|
pascal@24476
|
289 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
290 ;; Setup and run a .COM program ;;
|
pascal@24535
|
291 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
|
pascal@24535
|
292 ;; AX=0ffffh BX=0 CX=0 DX=drive ;;
|
pascal@24942
|
293 ;; and cmdline=void ;;
|
pascal@24476
|
294 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
295
|
pascal@24535
|
296 mov di, 100h ; ip
|
pascal@24476
|
297 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
|
pascal@24476
|
298 mov ss, bp
|
pascal@24476
|
299 xor sp, sp
|
pascal@24476
|
300 push bp ; cs, ds and es
|
pascal@24476
|
301 jmp short Run
|
pascal@24476
|
302
|
pascal@24476
|
303 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
304 ;; Relocate, setup and run a .EXE program ;;
|
pascal@24476
|
305 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
|
pascal@24476
|
306 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
|
pascal@24942
|
307 ;; AX=0ffffh BX=0 CX=0 DX=drive cmdline=void ;;
|
pascal@24476
|
308 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
309
|
pascal@24476
|
310 ReloCycle:
|
pascal@24476
|
311 add [di+2], bp ; item seg (abs)
|
pascal@24476
|
312 les si, [di] ; si = item ofs, es = item seg
|
pascal@24476
|
313 add [es:si], bp ; fixup
|
pascal@24525
|
314 scasw ; di += 2
|
pascal@24525
|
315 scasw ; point to next entry
|
pascal@24476
|
316
|
pascal@24476
|
317 RelocateEXE:
|
pascal@24942
|
318 dec word [bx+06h] ; reloc items, 32768 max (128KB table)
|
pascal@24942
|
319 jns ReloCycle
|
pascal@24942
|
320
|
pascal@24945
|
321 les si, [bx+0Eh]
|
pascal@24945
|
322 add si, bp
|
pascal@24945
|
323 mov ss, si ; ss for EXE
|
pascal@24945
|
324 mov sp, es ; sp for EXE
|
pascal@24476
|
325
|
pascal@24476
|
326 lea si, [bp-10h] ; ds and es both point to the segment
|
pascal@24476
|
327 push si ; containing the PSP structure
|
pascal@24476
|
328
|
pascal@24476
|
329 add bp, [bx+16h] ; cs for EXE
|
pascal@24535
|
330 mov di, [bx+14h] ; ip for EXE
|
pascal@24476
|
331 Run:
|
pascal@24476
|
332 pop ds
|
pascal@24476
|
333 push bp
|
pascal@24535
|
334 push di
|
pascal@24476
|
335 push ds
|
pascal@24476
|
336 pop es
|
pascal@24942
|
337 mov [80h], ax ; clear cmdline
|
pascal@24942
|
338 dec ax ; both FCB in the PSP don't have a valid drive identifier
|
pascal@24476
|
339
|
pascal@24476
|
340 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
341 ;; Set the magic numbers so the program knows that it ;;
|
pascal@24476
|
342 ;; has been loaded by this bootsector and not by MS-DOS ;;
|
pascal@24476
|
343 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
344 mov si, 16381 ; prime number 2**14-3
|
pascal@24476
|
345 mov di, 32749 ; prime number 2**15-19
|
pascal@24476
|
346 mov bp, 65521 ; prime number 2**16-15
|
pascal@24476
|
347
|
pascal@24476
|
348 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
349 ;; All done, transfer control to the program now ;;
|
pascal@24476
|
350 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
351 retf
|
pascal@24476
|
352
|
pascal@24525
|
353 ReadCluster:
|
pascal@24525
|
354 mov bp, [bx(bpbBytesPerSector)]
|
pascal@24525
|
355 shr bp, 4 ; bp = paragraphs per sector
|
pascal@25449
|
356 mov dx, 1 ; adjust LBA for next sector
|
pascal@24525
|
357 inc cx
|
pascal@24525
|
358 loop ReadSectorLBA
|
pascal@24525
|
359
|
pascal@24478
|
360 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
361 ;; Reads a FAT32 cluster ;;
|
pascal@24478
|
362 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
363 ;; Inout: ES:BX -> buffer ;;
|
pascal@24478
|
364 ;; ESI = cluster no ;;
|
pascal@24478
|
365 ;; Output: ESI = next cluster ;;
|
pascal@24525
|
366 ;; BP -> para / sector ;;
|
pascal@24478
|
367 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
368
|
pascal@25449
|
369 mul ebx ; edx:eax = 0
|
pascal@24945
|
370 imul ax, bp, byte 4 ; ax=# of FAT32 entries per sector
|
pascal@24525
|
371 lea edi, [esi-2] ; esi=cluster #
|
pascal@24476
|
372 xchg eax, esi
|
pascal@24478
|
373 div esi ; eax=FAT sector #, edx=entry # in sector
|
pascal@24476
|
374
|
pascal@24525
|
375 imul si, dx, byte 4 ; si=entry # in sector, clear C
|
pascal@25449
|
376 %if LBA48bits != 0
|
pascal@25449
|
377 xor dx, dx ; clear C
|
pascal@25449
|
378 %endif
|
pascal@24478
|
379 call ReadSectorLBAabsolute ; read 1 FAT32 sector
|
pascal@24476
|
380
|
pascal@25449
|
381 %if ClusterMask != 0
|
pascal@24478
|
382 and byte [es:si+3], 0Fh ; mask cluster value
|
pascal@25449
|
383 %endif
|
pascal@24478
|
384 mov esi, [es:si] ; esi=next cluster #
|
pascal@24476
|
385
|
pascal@24525
|
386 movzx eax, byte [bx(bpbNumberOfFATs)]
|
pascal@24525
|
387 mul dword [bx(bsSectorsPerFAT32)]
|
pascal@24525
|
388
|
pascal@24525
|
389 xchg eax, edi
|
pascal@24491
|
390 movzx ecx, byte [bx(bpbSectorsPerCluster)]
|
pascal@24945
|
391 mul ecx ; edx:eax=sector number in data area
|
pascal@24525
|
392 add eax, edi
|
pascal@24476
|
393
|
pascal@24478
|
394 ReadSectorLBAabsolute:
|
pascal@25449
|
395 %if LBA48bits != 0
|
pascal@25449
|
396 adc dx, bx
|
pascal@25449
|
397 mov word [bx(HiLBA)], dx
|
pascal@25449
|
398 %endif
|
pascal@25449
|
399 add eax, [bx(bpbHiddenSectors)]
|
pascal@25449
|
400 %if LBA48bits != 0
|
pascal@25449
|
401 adc word [bx(HiLBA)], bx
|
pascal@25449
|
402 %endif
|
pascal@24525
|
403 mov dx, word [bx(bpbReservedSectors)]
|
pascal@24476
|
404
|
pascal@24478
|
405 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
406 ;; Reads a sector using BIOS Int 13h fn 42h ;;
|
pascal@24478
|
407 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24478
|
408 ;; Input: EAX = LBA ;;
|
pascal@24478
|
409 ;; CX = sector count ;;
|
pascal@24478
|
410 ;; ES:BX -> buffer address ;;
|
pascal@24478
|
411 ;; Output: CF = 0 if no more sectors ;;
|
pascal@24478
|
412 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
413
|
pascal@24476
|
414 ReadSectorLBA:
|
pascal@25449
|
415 add eax, edx
|
pascal@25449
|
416 %if LBA48bits != 0
|
pascal@24535
|
417 adc word [bx(HiLBA)], bx
|
pascal@25449
|
418 %endif
|
pascal@25449
|
419 mov dx, [bx(DriveNumber)] ; restore BIOS boot drive number
|
pascal@24476
|
420 pusha
|
pascal@24476
|
421
|
pascal@24478
|
422 push bx
|
pascal@25449
|
423 %if LBA48bits != 0
|
pascal@24491
|
424 push word [bx(HiLBA)] ; 48-bit LBA
|
pascal@25449
|
425 %else
|
pascal@25449
|
426 push bx
|
pascal@25449
|
427 %endif
|
pascal@24478
|
428 push eax
|
pascal@24476
|
429 push es
|
pascal@24476
|
430 push bx
|
pascal@24478
|
431 push byte 1 ; sector count word = 1
|
pascal@24525
|
432 push byte 16 ; packet size byte = 16, reserved byte = 0
|
pascal@24525
|
433
|
pascal@25449
|
434 %if CHSsupport != 0
|
pascal@25449
|
435 %if CHShardDisk != 0
|
pascal@25449
|
436 push eax
|
pascal@25449
|
437 pop cx ; save low LBA
|
pascal@25449
|
438 pop ax ; get high LBA
|
pascal@25449
|
439 cwd ; clear dx (assume LBA offset <1TB)
|
pascal@25449
|
440 idiv word [bx(bpbSectorsPerTrack)] ; up to 8GB disks, avoid divide error
|
pascal@25449
|
441
|
pascal@25449
|
442 xchg ax, cx ; restore low LBA, save high LBA / SPT
|
pascal@25449
|
443 %else
|
pascal@25449
|
444 ; Busybox mkdosfs creates fat32 for floppies.
|
pascal@25449
|
445 ; Floppies may support CHS only.
|
pascal@25449
|
446 cwd ; clear dx (LBA offset <16MB)
|
pascal@25450
|
447 xor cx, cx ; high LBA / SPT = 0
|
pascal@25450
|
448 %endif
|
pascal@25449
|
449 idiv word [bx(bpbSectorsPerTrack)]
|
pascal@25449
|
450 ; ax = LBA / SPT
|
pascal@25449
|
451 ; dx = LBA % SPT = sector - 1
|
pascal@25449
|
452 inc dx
|
pascal@25449
|
453
|
pascal@25449
|
454 xchg cx, dx ; restore high LBA / SPT, save sector no.
|
pascal@25450
|
455 idiv word [bx(bpbHeadsPerCylinder)]
|
pascal@25449
|
456 ; ax = (LBA / SPT) / HPC = cylinder
|
pascal@25449
|
457 ; dx = (LBA / SPT) % HPC = head
|
pascal@25449
|
458
|
pascal@25449
|
459 mov ch, al
|
pascal@25449
|
460 ; ch = LSB 0...7 of cylinder no.
|
pascal@25449
|
461 %if CHShardDisk != 0
|
pascal@25449
|
462 shl ah, 6
|
pascal@25449
|
463 or cl, ah
|
pascal@25449
|
464 ; cl = MSB 8...9 of cylinder no. + sector no.
|
pascal@25449
|
465 %endif
|
pascal@25449
|
466 mov dh, dl
|
pascal@25449
|
467 ; dh = head no.
|
pascal@25449
|
468 mov dl, [bx(DriveNumber)] ; restore BIOS boot drive number
|
pascal@25449
|
469 %endif
|
pascal@25449
|
470
|
pascal@24525
|
471 ReadSectorLBARetry:
|
pascal@24525
|
472 mov si, sp
|
pascal@24478
|
473 mov ah, 42h ; ah = 42h = extended read function no.
|
pascal@24478
|
474 int 13h ; extended read sectors (DL, DS:SI)
|
pascal@24478
|
475 jnc ReadSuccess ; CF = 0 if no error
|
pascal@24476
|
476
|
pascal@25449
|
477 %if CHSsupport != 0
|
pascal@25449
|
478 mov ax, 201h ; al = sector count = 1
|
pascal@25449
|
479 ; ah = 2 = read function no.
|
pascal@25449
|
480 int 13h ; read sectors (AL, CX, DX, ES:BX)
|
pascal@25449
|
481
|
pascal@25449
|
482 jnc ReadSuccess ; CF = 0 if no error
|
pascal@25449
|
483 %endif
|
pascal@25449
|
484 %if ReadRetry != 0
|
pascal@25449
|
485 %if CHSsupport != 0
|
pascal@25449
|
486 cbw ; ah = 0 = reset function
|
pascal@25449
|
487 %else
|
pascal@24945
|
488 xor ax, ax ; ah = 0 = reset function
|
pascal@25449
|
489 %endif
|
pascal@24476
|
490 int 13h ; reset drive (DL)
|
pascal@24476
|
491
|
pascal@24525
|
492 dec bp
|
pascal@24525
|
493 jnz ReadSectorLBARetry
|
pascal@25449
|
494 %endif
|
pascal@24525
|
495
|
pascal@24476
|
496 call Error
|
pascal@24476
|
497 db "Read error."
|
pascal@24476
|
498
|
pascal@24478
|
499 ReadSuccess:
|
pascal@24476
|
500
|
pascal@24476
|
501 popa ; sp += 16
|
pascal@24478
|
502
|
pascal@24478
|
503 popa
|
pascal@24478
|
504
|
pascal@24476
|
505 stc
|
pascal@24478
|
506 loop ReadSectorNext
|
pascal@24476
|
507
|
pascal@24478
|
508 cmp esi, 0FFFFFF8h ; carry=0 if last cluster, and carry=1 otherwise
|
pascal@24476
|
509
|
pascal@24478
|
510 ReadSectorNext:
|
pascal@24476
|
511 ret
|
pascal@24476
|
512
|
pascal@24942
|
513 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24942
|
514 ;; Fill free space with zeroes ;;
|
pascal@24942
|
515 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24942
|
516
|
pascal@24942
|
517 times (512-13-20-($-$$)) db 0
|
pascal@24942
|
518
|
pascal@24476
|
519 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
520 ;; Error Messaging Code ;;
|
pascal@24476
|
521 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
522
|
pascal@24476
|
523 Error:
|
pascal@24476
|
524 pop si
|
pascal@24478
|
525 puts:
|
pascal@24476
|
526 mov ah, 0Eh
|
pascal@24476
|
527 mov bl, 7
|
pascal@24476
|
528 lodsb
|
pascal@24476
|
529 int 10h
|
pascal@24478
|
530 cmp al, '.'
|
pascal@24478
|
531 jne puts
|
pascal@24476
|
532 cbw
|
pascal@24535
|
533 int 16h ; wait for a key...
|
pascal@24535
|
534 int 19h ; bootstrap
|
pascal@24525
|
535
|
pascal@24525
|
536 Stop:
|
pascal@24525
|
537 hlt
|
pascal@24525
|
538 jmp short Stop
|
pascal@24476
|
539
|
pascal@24476
|
540 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
541 ;; Name of the file to load and run ;;
|
pascal@24476
|
542 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
543
|
pascal@24476
|
544 ProgramName db "STARTUP BIN" ; name and extension each must be
|
pascal@25449
|
545 times (510-($-$$)) db ' ' ; padded with spaces (11 bytes total)
|
pascal@24476
|
546
|
pascal@24476
|
547 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
548 ;; End of the sector ID ;;
|
pascal@24476
|
549 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
550
|
pascal@24476
|
551 dw 0AA55h ; BIOS checks for this ID
|