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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 bootex.asm -f bin -o bootex.bin ;;
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pascal@24476
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10 ;; ;;
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pascal@24476
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11 ;; ;;
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pascal@24476
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12 ;; Features: ;;
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pascal@24476
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13 ;; ~~~~~~~~~ ;;
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pascal@24476
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14 ;; - exFAT supported using BIOS int 13h function 42h. ;;
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pascal@24476
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15 ;; ;;
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pascal@24476
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16 ;; - Loads a 16-bit executable file in the MS-DOS .COM or .EXE format ;;
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pascal@24476
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17 ;; from the root directory of a disk and transfers control to it ;;
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pascal@24476
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18 ;; (the "ProgramName" variable holds the name of the file to be loaded) ;;
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pascal@24476
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19 ;; Its maximum size can be up to 636KB without Extended BIOS Data area. ;;
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pascal@24476
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20 ;; ;;
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pascal@24476
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21 ;; - Prints an error if the file isn't found or couldn't be read ;;
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pascal@24476
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22 ;; ("File not found" or "Read error") ;;
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pascal@24476
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23 ;; and waits for a key to be pressed, then executes the Int 19h ;;
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pascal@24476
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24 ;; instruction and lets the BIOS continue bootstrap. ;;
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pascal@24476
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25 ;; ;;
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pascal@24476
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26 ;; ;;
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pascal@24476
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27 ;; Known Bugs: ;;
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pascal@24476
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28 ;; ~~~~~~~~~~~ ;;
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pascal@24476
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29 ;; - All bugs are fixed as far as I know. The boot sector has been tested ;;
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pascal@24476
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30 ;; on a 128MB qemu image. ;;
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pascal@24476
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31 ;; ;;
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pascal@24476
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32 ;; ;;
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pascal@24476
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33 ;; Memory Layout: ;;
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pascal@24476
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34 ;; ~~~~~~~~~~~~~~ ;;
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pascal@24476
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35 ;; The diagram below shows the typical memory layout. The actual location ;;
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pascal@24476
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36 ;; of the boot sector and its stack may be lower than A0000H if the BIOS ;;
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pascal@24476
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37 ;; reserves memory for its Extended BIOS Data Area just below A0000H and ;;
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pascal@24476
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38 ;; reports less than 640 KB of RAM via its Int 12H function. ;;
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pascal@24476
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39 ;; ;;
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pascal@24476
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40 ;; physical address ;;
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pascal@24476
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41 ;; +------------------------+ 00000H ;;
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pascal@24476
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42 ;; | Interrupt Vector Table | ;;
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pascal@24476
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43 ;; +------------------------+ 00400H ;;
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pascal@24476
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44 ;; | BIOS Data Area | ;;
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pascal@24476
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45 ;; +------------------------+ 00500H ;;
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pascal@24476
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46 ;; | PrtScr Status / Unused | ;;
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pascal@24476
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47 ;; +------------------------+ 00600H ;;
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pascal@24476
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48 ;; | Loaded Image | ;;
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pascal@24476
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49 ;; +------------------------+ nnnnnH ;;
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pascal@24476
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50 ;; | Available Memory | ;;
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pascal@24476
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51 ;; +------------------------+ A0000H - 2KB ;;
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pascal@24476
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52 ;; | Boot Sector | ;;
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pascal@24476
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53 ;; +------------------------+ A0000H - 1.5KB ;;
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pascal@24476
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54 ;; | 1.5KB Boot Stack | ;;
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pascal@24476
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55 ;; +------------------------+ A0000H ;;
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pascal@24476
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56 ;; | Video RAM | ;;
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pascal@24476
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57 ;; ;;
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pascal@24476
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58 ;; ;;
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pascal@24476
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59 ;; Boot Image Startup (register values): ;;
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pascal@24476
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60 ;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
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pascal@24476
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61 ;; dl = BIOS boot drive number (e.g. 80H) ;;
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pascal@24476
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62 ;; cs:ip = program entry point ;;
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pascal@24476
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63 ;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
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pascal@24476
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64 ;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
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pascal@24476
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65 ;; EXE program defaults: ds = es = EXE data - 10h (fake MS-DOS psp), ;;
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pascal@24476
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66 ;; ax = 0ffffh (both FCB in the PSP don't have a valid drive identifier), ;;
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pascal@24476
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67 ;; cs:ip and ss:sp depends on EXE header ;;
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pascal@24476
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68 ;; Magic numbers: ;;
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pascal@24476
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69 ;; si = 16381 (prime number 2**14-3) ;;
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pascal@24476
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70 ;; di = 32749 (prime number 2**15-19) ;;
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pascal@24476
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71 ;; bp = 65521 (prime number 2**16-15) ;;
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pascal@24476
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72 ;; The magic numbers let the program know whether it has been loaded by ;;
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pascal@24476
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73 ;; this boot sector or by MS-DOS, which may be handy for universal, bare- ;;
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pascal@24476
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74 ;; metal and MS-DOS programs. ;;
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pascal@24476
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75 ;; ;;
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pascal@24476
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76 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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77
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pascal@24476
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78 %define bx(label) bx+label-boot
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pascal@24476
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79
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pascal@24476
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80 [BITS 16]
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pascal@24476
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81 [CPU 386]
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pascal@24476
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82
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pascal@24476
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83 ImageLoadSeg equ 60h
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pascal@24476
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84 StackSize equ 1536
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pascal@24476
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85
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pascal@24476
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86 [SECTION .text]
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pascal@24476
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87 [ORG 0]
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pascal@24476
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88
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pascal@24476
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89 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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90 ;; Boot sector starts here ;;
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pascal@24476
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91 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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92
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pascal@24476
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93 boot:
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pascal@24476
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94 jmp short start ; Windows checks for this jump
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pascal@24476
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95 nop
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pascal@24476
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96 bsOemName DB "EXFAT " ; 0x03
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pascal@24476
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97 times 53 db 0 ; 0x0B
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pascal@24476
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98
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pascal@24476
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99 ;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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100 ;; BPB starts here ;;
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pascal@24476
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101 ;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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102
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pascal@24479
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103 bpbSectorStart DQ 0 ; 0x40 partition first sector
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pascal@24479
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104 bpbSectorCount DQ 0 ; 0x48 partition sectors count
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pascal@24479
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105 bpbFatSectorStart DD 0 ; 0x50 FAT first sector
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pascal@24479
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106 bpbFatSectorCount DD 0 ; 0x54 FAT sectors count
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pascal@24479
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107 bpbClusterSectorStart DD 0 ; 0x58 first cluster sector
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pascal@24479
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108 bpbClusterCount DD 0 ; 0x5C total clusters count
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pascal@24479
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109 bpbRootDirCluster DD 0 ; 0x60 first cluster of the root dir
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pascal@24479
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110 bpbVolumeSerial DD 0 ; 0x64 volume serial number
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pascal@24479
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111 bpbFSVersionMinor DB 0 ; 0x68
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pascal@24479
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112 bpbFSVersionMajor DB 0 ; 0x69
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pascal@24479
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113 bpbVolumeStateFlags DW 0 ; 0x6A
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pascal@24479
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114 bpbSectorSizeBits DB 0 ; 0x6C sector size as (1 << n)
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pascal@24479
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115 bpbSectorPerClusterBits DB 0 ; 0x6D sector per cluster as (1 << n)
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pascal@24479
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116 bpbNumberOfFATs DB 0 ; 0x6E always 1
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pascal@24479
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117 bpbDriveNumber DB 0 ; 0x6F alaways 0x80
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pascal@24479
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118 bpbAllocatedPercent DB 0 ; 0x70 percentage of allocated space
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pascal@24476
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119
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pascal@24476
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120 ;;;;;;;;;;;;;;;;;;;
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pascal@24476
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121 ;; BPB ends here ;;
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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 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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125 ;; Boot sector code starts here ;;
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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 start:
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pascal@24476
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129 cld
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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 ;; How much RAM is there? ;;
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pascal@24476
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133 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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134
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pascal@24476
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135 int 12h ; get conventional memory size (in KBs)
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pascal@24476
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136 mov cx, 106h
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pascal@24476
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137 dec ax
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pascal@24476
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138 dec ax ; reserve 2K bytes for the code and the stack
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pascal@24476
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139 shl ax, cl ; and convert it to 16-byte paragraphs
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pascal@24476
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140
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pascal@24476
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141 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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142 ;; Reserve memory for the boot sector and its stack ;;
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pascal@24476
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143 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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144
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pascal@24476
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145 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
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pascal@24476
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146 mov ss, ax
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pascal@24476
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147 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
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pascal@24476
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148
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pascal@24476
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149 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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150 ;; Copy ourselves to top of memory ;;
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pascal@24476
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151 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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152
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pascal@24476
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153 mov si, 7C00h
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pascal@24476
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154 xor di, di
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pascal@24476
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155 mov ds, di
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pascal@24476
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156 rep movsw ; move 512 bytes (+ 12)
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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 ;; Jump to the copy ;;
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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 push es
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pascal@24479
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163 push byte main
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pascal@24476
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164 retf
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pascal@24476
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165
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pascal@24476
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166 main:
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pascal@24476
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167 push cs
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pascal@24476
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168 pop ds
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pascal@24476
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169
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pascal@24476
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170 xor ebx, ebx
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pascal@24476
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171 mov [bx], dx ; store BIOS boot drive number
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pascal@24476
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172
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pascal@24476
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173 mov esi, [bx(bpbRootDirCluster)] ; esi=cluster # of root dir
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pascal@24476
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174
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pascal@24479
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175 push byte ImageLoadSeg
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pascal@24476
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176 pop es
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pascal@24476
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177
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pascal@24476
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178 RootDirReadContinue:
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pascal@24476
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179 call ReadCluster ; read one sector of root dir
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pascal@24476
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180 pushf ; save carry="not last sector" flag
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pascal@24476
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181
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pascal@24476
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182 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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183 ;; Look for the COM/EXE file to load and run ;;
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pascal@24476
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184 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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185
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pascal@24476
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186 xor di, di ; es:di -> root entries array
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pascal@24476
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187
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pascal@24476
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188 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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189 ;; Looks for the file/dir ProgramName ;;
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pascal@24476
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190 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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191 ;; Input: ES:DI -> root directory array ;;
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pascal@24476
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192 ;; Output: ESI = cluster number ;;
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pascal@24476
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193 ;; dword [bx+FileSize] file size ;;
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pascal@24476
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194 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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195
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pascal@24476
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196 CurNameSize equ 3
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pascal@24476
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197 StartCluster equ 14h
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pascal@24476
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198 FileSize equ 18h
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pascal@24476
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199
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pascal@24476
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200 FindNameCycle:
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pascal@24476
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201 pusha
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pascal@24476
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202
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pascal@24476
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203 xor ax, ax
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pascal@24476
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204 or al, [es:di]
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pascal@24476
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205 je FindNameFailed
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pascal@24476
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206
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pascal@24476
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207 cmp al, 0c0h ; EXFAT_ENTRY_FILE_INFO ?
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pascal@24476
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208 jne NotFileInfo
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pascal@24476
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209
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pascal@24476
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210 mov bl, 30
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pascal@24476
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211 CopyInfo:
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pascal@24476
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212 mov ax, [es:di+bx]
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pascal@24476
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213 mov [bx], ax
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pascal@24476
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214 dec bx
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pascal@24476
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215 dec bx
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pascal@24476
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216 jnz CopyInfo
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pascal@24476
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217
|
pascal@24476
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218 NotFileInfo:
|
pascal@24476
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219 mov al, 0c1h ; EXFAT_ENTRY_FILE_NAME ?
|
pascal@24476
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220 mov cx, NameLength+1
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pascal@24476
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221 mov si, ProgramName ; ds:si -> program name
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pascal@24476
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222 CheckName:
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pascal@24476
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223 scasw ; compare UTF-16
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pascal@24476
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224 lodsb ; with ASCII
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pascal@24476
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225 loope CheckName
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pascal@24476
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226 je FindNameFound ; cx = 0
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pascal@24476
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227 popa ; restore ax, cx, si, di
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pascal@24476
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228
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pascal@24479
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229 add di, byte 32
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pascal@24476
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230 cmp di, bp
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pascal@24476
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231 jne FindNameCycle ; next root entry
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pascal@24476
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232 popf ; restore carry="not last sector" flag
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pascal@24476
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233 jc RootDirReadContinue ; continue to the next root dir cluster
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pascal@24476
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234 FindNameFailed: ; end of root directory (dir end reached)
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pascal@24476
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235 call Error
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pascal@24476
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236 db "File not found."
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pascal@24476
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237 FindNameFound:
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pascal@24476
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238 mov esi, [bx+StartCluster]
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pascal@24476
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239
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pascal@24476
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240 ;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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241 ;; Load the entire file ;;
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pascal@24476
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242 ;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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243
|
pascal@24476
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244 push es
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pascal@24476
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245 xor bp, bp
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pascal@24476
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246 FileReadContinue:
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pascal@24476
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247 shr bp, 4 ; bytes to paragraphs
|
pascal@24476
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248 mov di, es
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pascal@24476
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249 add di, bp ; adjust segment for next sector
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pascal@24476
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250 mov es, di ; es:0 updated
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pascal@24476
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251 call ReadCluster ; read one cluster of root dir
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pascal@24476
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252 sub [bx+FileSize], ebp
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pascal@24476
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253 ja FileReadContinue
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pascal@24476
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254 pop bp
|
pascal@24476
|
255
|
pascal@24476
|
256 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
|
257 ;; Type detection, .COM or .EXE? ;;
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pascal@24476
|
258 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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pascal@24476
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259
|
pascal@24476
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260 mov ds, bp ; bp=ds=seg the file is loaded to
|
pascal@24476
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261
|
pascal@24476
|
262 add bp, [bx+08h] ; bp = image base
|
pascal@24476
|
263 mov ax, [bx+06h] ; ax = reloc items
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pascal@24476
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264 mov di, [bx+18h] ; di = reloc table pointer
|
pascal@24476
|
265
|
pascal@24476
|
266 cmp word [bx], 5A4Dh ; "MZ" signature?
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pascal@24476
|
267 je RelocateEXE ; yes, it's an EXE program
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pascal@24476
|
268
|
pascal@24476
|
269 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
270 ;; Setup and run a .COM program ;;
|
pascal@24476
|
271 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
|
pascal@24525
|
272 ;; AX=0ffffh BX=0 CX=0 DX=drive ;;
|
pascal@24476
|
273 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
274
|
pascal@24525
|
275 mov ax, 0ffffh ; both FCB in the PSP don't have a valid drive identifier
|
pascal@24525
|
276 mov di, 100h ; ip
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pascal@24476
|
277 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
|
pascal@24476
|
278 mov ss, bp
|
pascal@24476
|
279 xor sp, sp
|
pascal@24476
|
280 push bp ; cs, ds and es
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pascal@24476
|
281 jmp short Run
|
pascal@24476
|
282
|
pascal@24476
|
283 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
284 ;; Relocate, setup and run a .EXE program ;;
|
pascal@24476
|
285 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
|
pascal@24476
|
286 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
|
pascal@24525
|
287 ;; AX=0ffffh BX=0 CX=0 DX=drive ;;
|
pascal@24476
|
288 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
289
|
pascal@24476
|
290 ReloCycle:
|
pascal@24476
|
291 add [di+2], bp ; item seg (abs)
|
pascal@24476
|
292 les si, [di] ; si = item ofs, es = item seg
|
pascal@24476
|
293 add [es:si], bp ; fixup
|
pascal@24476
|
294 scasw ; di += 2
|
pascal@24476
|
295 scasw ; point to next entry
|
pascal@24476
|
296
|
pascal@24476
|
297 RelocateEXE:
|
pascal@24476
|
298 dec ax ; 32768 max (128KB table)
|
pascal@24476
|
299 jns ReloCycle ; leave with ax=0ffffh: both FCB in the
|
pascal@24476
|
300 ; PSP don't have a valid drive identifier
|
pascal@24476
|
301 les si, [bx+0Eh]
|
pascal@24476
|
302 add si, bp
|
pascal@24476
|
303 mov ss, si ; ss for EXE
|
pascal@24476
|
304 mov sp, es ; sp for EXE
|
pascal@24476
|
305
|
pascal@24476
|
306 lea si, [bp-10h] ; ds and es both point to the segment
|
pascal@24476
|
307 push si ; containing the PSP structure
|
pascal@24476
|
308
|
pascal@24476
|
309 add bp, [bx+16h] ; cs for EXE
|
pascal@24525
|
310 mov di, [bx+14h] ; ip for EXE
|
pascal@24476
|
311 Run:
|
pascal@24476
|
312 pop ds
|
pascal@24476
|
313 push bp
|
pascal@24525
|
314 push di
|
pascal@24476
|
315 push ds
|
pascal@24476
|
316 pop es
|
pascal@24476
|
317
|
pascal@24476
|
318 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
319 ;; Set the magic numbers so the program knows that it ;;
|
pascal@24476
|
320 ;; has been loaded by this bootsector and not by MS-DOS ;;
|
pascal@24476
|
321 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
322 mov si, 16381 ; prime number 2**14-3
|
pascal@24476
|
323 mov di, 32749 ; prime number 2**15-19
|
pascal@24476
|
324 mov bp, 65521 ; prime number 2**16-15
|
pascal@24476
|
325
|
pascal@24476
|
326 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
327 ;; All done, transfer control to the program now ;;
|
pascal@24476
|
328 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
329 retf
|
pascal@24476
|
330
|
pascal@24476
|
331 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
332 ;; Reads a exFAT cluster ;;
|
pascal@24476
|
333 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
334 ;; Input: EDX:EAX = LBA ;;
|
pascal@24476
|
335 ;; EBX = 0 ;;
|
pascal@24476
|
336 ;; CX = sector cnt ;;
|
pascal@24476
|
337 ;; ESI = cluster no ;;
|
pascal@24476
|
338 ;; ES:0 -> buffer adrs ;;
|
pascal@24476
|
339 ;; Output: EBX = 0 ;;
|
pascal@24476
|
340 ;; CX = next cnt ;;
|
pascal@24476
|
341 ;; EBP = bytes/sector;;
|
pascal@24476
|
342 ;; ES:0 -> next adrs ;;
|
pascal@24476
|
343 ;; C=0 for last sector ;;
|
pascal@24476
|
344 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
345
|
pascal@24476
|
346 ReadCluster:
|
pascal@24476
|
347 inc cx ; jcxnz
|
pascal@24479
|
348 add eax, byte 1
|
pascal@24476
|
349 loop ReadSectorC
|
pascal@24476
|
350
|
pascal@24476
|
351 mov cl, [bx(bpbSectorSizeBits)]
|
pascal@24476
|
352 dec cx
|
pascal@24476
|
353 dec cx
|
pascal@24476
|
354 mul ebx ; edx:eax = 0
|
pascal@24476
|
355 inc ax
|
pascal@24476
|
356 shl eax, cl ; eax=# of exFAT entries per sector
|
pascal@24476
|
357 lea edi, [esi-2] ; edi=cluster #-2
|
pascal@24476
|
358 xchg eax, esi
|
pascal@24476
|
359 div esi ; eax=FAT sector #, edx=entry # in sector
|
pascal@24476
|
360
|
pascal@24525
|
361 imul si, dx, byte 4 ; si=entry # offset in sector
|
pascal@24476
|
362
|
pascal@24476
|
363 cdq
|
pascal@24476
|
364 add eax, [bx(bpbFatSectorStart)] ; sector # relative to FAT32
|
pascal@24476
|
365 call ReadSectorC ; read 1 FAT32 sector
|
pascal@24476
|
366
|
pascal@24476
|
367 mov esi, [es:si] ; esi=next cluster #
|
pascal@24476
|
368
|
pascal@24476
|
369 xor eax, eax
|
pascal@24476
|
370 inc ax
|
pascal@24476
|
371 mov cl, [bx(bpbSectorPerClusterBits)]
|
pascal@24476
|
372 shl eax, cl ; 10000h max (32MB cluster)
|
pascal@24476
|
373 xchg eax, ecx
|
pascal@24476
|
374 xchg eax, edi ; get cluster #-2
|
pascal@24476
|
375 mul ecx
|
pascal@24476
|
376
|
pascal@24476
|
377 add eax, [bx(bpbClusterSectorStart)]
|
pascal@24476
|
378 ReadSectorC:
|
pascal@24476
|
379 adc edx, ebx
|
pascal@24476
|
380
|
pascal@24476
|
381 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
382 ;; Reads a sector using BIOS Int 13h ;;
|
pascal@24476
|
383 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
384 ;; Input: EDX:EAX = LBA ;;
|
pascal@24476
|
385 ;; BX = 0 ;;
|
pascal@24476
|
386 ;; CX = sector count ;;
|
pascal@24476
|
387 ;; ES:0 -> buffer address ;;
|
pascal@24476
|
388 ;; Output: BX = 0 ;;
|
pascal@24476
|
389 ;; CX = next count ;;
|
pascal@24476
|
390 ;; EBP = bytes/sector ;;
|
pascal@24476
|
391 ;; ES:0 -> next address ;;
|
pascal@24476
|
392 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
393
|
pascal@24476
|
394 ReadSector:
|
pascal@24476
|
395
|
pascal@24476
|
396 xor ebp, ebp
|
pascal@24476
|
397 inc bp
|
pascal@24476
|
398
|
pascal@24476
|
399 pushad
|
pascal@24476
|
400
|
pascal@24476
|
401 add eax, [bx(bpbSectorStart)]
|
pascal@24476
|
402 adc edx, [bx(bpbSectorStart)+4]
|
pascal@24476
|
403
|
pascal@24476
|
404 push edx
|
pascal@24476
|
405 push eax
|
pascal@24476
|
406 push es
|
pascal@24476
|
407 push bx
|
pascal@24476
|
408 push bp ; sector count word = 1
|
pascal@24476
|
409 mov cx, 16
|
pascal@24476
|
410 push cx ; packet size byte = 16, reserved byte = 0
|
pascal@24476
|
411 ReadSectorRetry:
|
pascal@24476
|
412 mov si, sp
|
pascal@24476
|
413 mov ah, 42h ; ah = 42h = extended read function no.
|
pascal@24476
|
414 mov dl, [bx]
|
pascal@24476
|
415 int 13h ; extended read sectors (DL, DS:SI)
|
pascal@24476
|
416
|
pascal@24476
|
417 jnc ReadSuccess
|
pascal@24476
|
418
|
pascal@24476
|
419 xor ax, ax
|
pascal@24476
|
420 int 13h ; reset drive (DL)
|
pascal@24476
|
421 loop ReadSectorRetry
|
pascal@24476
|
422
|
pascal@24476
|
423 call Error
|
pascal@24476
|
424 db "Read error."
|
pascal@24476
|
425
|
pascal@24476
|
426 ReadSuccess:
|
pascal@24476
|
427 mov cl, [bx(bpbSectorSizeBits)]
|
pascal@24476
|
428 shl word [si+16+8], cl ; (e)bp si+16: EDI ESI EBP ESP EBX EDX ECX EAX
|
pascal@24476
|
429 popa ; sp += 16
|
pascal@24476
|
430 popad ; real registers
|
pascal@24476
|
431
|
pascal@24476
|
432 stc
|
pascal@24476
|
433 loop ReadSectorNext
|
pascal@24476
|
434
|
pascal@24479
|
435 cmp esi, byte -10 ; carry=0 if last cluster, and carry=1 otherwise
|
pascal@24476
|
436 ReadSectorNext:
|
pascal@24491
|
437 mov dl, [bx] ; restore BIOS boot drive number
|
pascal@24476
|
438 ret
|
pascal@24476
|
439
|
pascal@24476
|
440 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
441 ;; Error Messaging Code ;;
|
pascal@24476
|
442 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
443
|
pascal@24476
|
444 Error:
|
pascal@24476
|
445 pop si
|
pascal@24478
|
446
|
pascal@24478
|
447 PutStr:
|
pascal@24476
|
448 mov ah, 0Eh
|
pascal@24476
|
449 mov bl, 7
|
pascal@24476
|
450 lodsb
|
pascal@24476
|
451 int 10h
|
pascal@24476
|
452 cmp al, "."
|
pascal@24476
|
453 jne PutStr
|
pascal@24476
|
454
|
pascal@24476
|
455 cbw
|
pascal@24476
|
456 int 16h ; wait for a key...
|
pascal@24476
|
457 int 19h ; bootstrap
|
pascal@24476
|
458
|
pascal@24476
|
459 Stop:
|
pascal@24476
|
460 hlt
|
pascal@24476
|
461 jmp short Stop
|
pascal@24476
|
462
|
pascal@24476
|
463 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
464 ;; Fill free space with zeroes ;;
|
pascal@24476
|
465 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
466
|
pascal@24476
|
467 times (512-13-($-$$)) db 0
|
pascal@24476
|
468
|
pascal@24476
|
469 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
470 ;; Name of the file to load and run ;;
|
pascal@24476
|
471 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
472
|
pascal@24476
|
473 ProgramName db "startup.bin" ; name and extension
|
pascal@24476
|
474 NameLength equ $-ProgramName
|
pascal@24476
|
475
|
pascal@24476
|
476 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
477 ;; End of the sector ID ;;
|
pascal@24476
|
478 ;;;;;;;;;;;;;;;;;;;;;;;;;;
|
pascal@24476
|
479
|
pascal@24476
|
480 dw 0AA55h ; BIOS checks for this ID
|