DDT - DEEP DISK TESTER by Richard Karsmakers

When  I  recently  visited the CCV  (that,  my  friends,  it  the
Computer  Club Veldhoven,  one of the cosiest computer  clubs  in
Southern Netherlands) someone (his name slipped my  mind,  sorry)
gave me the idea to write a program that can test every  data-bit
of a disk - also when the disk was already written on. He came up
with the above name as well (through lack of sheer creativity,  I
would never have been able to think of something quite like it  -
especially  when  writing'n'programming on a 40  degrees  Celcius
attic).

The program just asks you to insert the disk to be  tested,  then
checks the bootsector (to get number of sides, tracks and sectors
per  track) and starts testing every single bit it  can  normally
read. The Deep Disk Tester cannot test protected disks (e.g. with
checksum  errors  or something of the kind  deliberately  brought
upon  it) - these erroneous tracks will simply be ignored in  the
test.

How does it work?

The actual test routine is actually made up like this:

1 - Read a sector
2 - Xor all bytes with 255 (every bit is inverted)
3 - Write the sector back
4 - Read it again and compare it with the sector as it should be
5 - If everything is OK, then the whole things should be Xor-ed
    again and written back

This way, every single bit of the disk is tested.

Originally published in ST NEWS Volume 2 Issue 5.

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*       Agf Basic Listing       *
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' DDT - Deep Disk Tester Rev.1.0
'
' Program design, development and programming by Richard Karsmakers
' Idea by Mr. I-forgot-his-name (in Veldhoven), but not mine anyway...
' Sunday, July 19th 1987
'
Alert 1,"Please insert disk|to be tested|in Drive A",1,"OK",Dummy%
'
' Read bootsector of disk to analyse the number of sides, tracks, sectors
'
Boot$=Space$(512)                                       !For bootsector
Check$=Space$(512)                                     !For check-sector
Dim B%(512)                                            !Wrong byte arrays
A%=Xbios(8,L:Varptr(Boot$),L:0,W:0,W:1,W:0,W:0,W:1)     !Read bootsector
If A%<>0                                                !Error occured?
  Alert 1,"An error occured!|Test aborted!",1,"Oh",Dummy%
  Edit
Endif
'
Sec%=Asc(Mid$(Boot$,20,1))+256*(Asc(Mid$(Boot$,21,1)))  !Sectors on disk
Spt%=Asc(Mid$(Boot$,25,1))+256*(Asc(Mid$(Boot$,26,1)))  !Sectors per track
Sid%=Asc(Mid$(Boot$,27,1))+256*(Asc(Mid$(Boot$,28,1)))  !Sides
Tps%=(Sec%/Spt%)/Sid%                                   !Tracks per side
'
Cls
Print "The disk has the following characteristics:"
Print "Total number of sectors  : ";Sec%
Print "Sectors per track        : ";Spt%
Print "Number of sides          : ";Sid%
Print "Nunber of tracks per side: ";Tps%
'
' The actual reading/checking takes place here
'
For S%=0 To Sid%-1                                      !Sides
  For T%=0 To Tps%-1                                    !Tracks per side
    For C%=1 To Spt%                                    !Sectors per track
      Print "Testing side: ";S%;", track: ";T%;", sector: ";C%
      @Check
    Next C%
  Next T%
Next S%
'
' The check routine
'
Procedure Check
  ' Read in sector
  A%=Xbios(8,L:Varptr(Check$),L:0,W:0,W:C%,W:T%,W:S%,W:1)
  If A%<>0
    Print "Read error on side: ";S%;", track: ";T%;", sector: ";C%
    Goto Label1
  Endif
  ' Buffer contents
  Buffer$=Check$
  ' Invert bits
  For X%=1 To Len(Check$)
    Mid$(Check$,X%,1)=Chr$(Asc(Mid$(Check$,X%,1)) Xor 255)
  Next X%
  ' Write sector back
  A%=Xbios(9,L:Varptr(Check$),L:0,W:0,W:C%,W:T%,W:S%,W:1)
  If A%<>0
    Print "Write error on side: ";S%;", track: ";T%;", sector: ";C%
    Goto Label1
  Endif
  ' Read it again
  A%=Xbios(8,L:Varptr(Check$),L:0,W:0,W:C%,W:T%,W:S%,W:1)
  If A%<>0
    Print "Read error on side: ";S%;", track: ";T%;", sector: ";C%
    Goto Label1
  Endif
  ' Invert bits
  For X%=1 To Len(Check$)
    Mid$(Check$,X%,1)=Chr$(Asc(Mid$(Check$,X%,1)) Xor 255)
  Next X%
  ' Check if buffer$ is still equal to the sector
  P%=0
  Arrayfill B%(),0
  For X%=1 To Len(Check$)
    If Mid$(Check$,X%,1)<>Mid$(Buffer$,X%,1)
      B%(P%)=X%
      Inc P%
    Endif
  Next X%
  ' Faulty bits?
  If P%>0
    Print "Byte faulty on side: ";S%;", track: ";T%;", sector: ";C%
    For X%=0 To P%
      Print "Faulty byte #";P%+1;": ";B%(P%)
    Next X%
    Goto Label1
  Endif
  ' Write sector back
  A%=Xbios(9,L:Varptr(Buffer$),L:0,W:0,W:C%,W:T%,W:S%,W:1)
  If A%<>0
    Print "Write error on side: ";S%;", track: ";T%;", sector: ";C%
  Endif
  Label1:
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