I'm surprised because dndbbs does alot of wierd things, like:
Inline assembly to trap and ignore control-break and print-screen,
Port access to 8250 uart for modem i/o,
PSP JFT offset to command tail for increased file handles,
Support for share.exe (which dosbox does not)..
Az.
Just out of the sake of curiosity here is the PSP JFT file handle increase function description:
REM PspTrick.txt describes increasing file handles.
----------2167-------------------------------
INT 21 - DOS 3.3+ - SET HANDLE COUNT
AH = 67h
BX = size of new file handle table for process
The above bios routine is normally used by your program to request more file
handles. Since Dos or windows will not always be able to give you more than
20 handles using interrupt &h21, the basic routine described below will.
Sub Increase.Files
On Local Error Resume Next
Close
InregsX.AX=&H6200
Call InterruptX(&H21,InregsX,OutregsX)
PSP.Segment=OutregsX.BX
Def Seg=PSP.Segment
Command.Line=&H80
Command.Tail=Command.Line+60 ' tail end to copy handles to
For Var=1 To 54 ' 50 file handles
Poke Command.Tail+Var-1,&HFF
Next
For Var=1 To 4 ' DOS handles
File.Handle=Peek(&H18+Var-1)
Poke Command.Tail+Var-1,File.Handle
Next
Poke &H32,54
Poke &H34,Command.Tail
Def Seg
End Sub
Call this routine to give your basic program more file handles than can be
allowed by dos or windows. The first step for requesting more file handles is
to call interrupt &h62 for the segment of the psp. In the psp are located the
current maximum number of handles in the job file table, the address to the
file handles, and the file handles themselves. Since the pointer to the file
handles contains only a offset and not a segment, there must be some memory
area in the psp to store the extended file handles to be assigned. And since
there is no way of knowing what the memory areas are surrounding the psp, the
tail end of where the command line is located is used for the pointer of the
file handles, and the file handles are copied there. An offset 60 bytes from
where the command line is stored is used. This is reasonable if your command
line is less than 60 characters. Next, the default file handles which are
closed are copied to the offset pointed to the command tail plus 50 files,
with &hff indicating the handles. Then, the current file handles are copied
to the command tail. And finally, the psp jtf updated with the new maximum of
file handles, and the pointer to the offset to the command tail containing the
new jft memory area.
After this routine is called by your program when it first starts, the psp is
the resident memory area containing the new jft. Notice however that the
routine must be called each time your program is chained to, and the close
statement must be used before increasing the psp. If you do not use the basic
chain statement, you should not have to reassign the psp parameters. Note also
that since the file handles are more than interrupt &h21 would allow, the
bios will close all file handles with the close statement anyway by counting
the file handles assigned. And finally note that the maximum number of file
handles assigned are added to the number of file handles opened by other
processes in windows, and are used by the global windows handles count.
-end-
