393 lines
16 KiB
Plaintext
393 lines
16 KiB
Plaintext
FORMAT - formats a new disk, clears the FAT and DIRECTORY
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and optionally copies the SYSTEM and COMMAND.COM to this
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new disk.
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Command syntax:
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FORMAT [drive:][/switch1][/switch2]...[/switch16]
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Where "drive:" is a legal drive specification and if
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omitted indicates that the default drive will be used.
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There may be up to 16 legal switches included in the
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command line.
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The OEM must supply five (NEAR) routines to the program
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along with 6 data items. The names of the routines are INIT,
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DISKFORMAT, BADSECTOR, WRTFAT and DONE, and their flow of
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control (by the Microsoft module) is like this:
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+---------+
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| INIT |
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+---------+
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|<------------------------------+
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+------------+ |
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| DISKFORMAT | |
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+------------+ |
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|<-------+ |
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+-----------+ |-This loop is done |- This loop done
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| BADSECTOR | | for each group of | once for each disk
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+-----------+ | bad sectors | to be formatted.
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|----->--+ | If variable HARDFLAG
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| | is set then the loop
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+----------+ | is only performed
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| | | once.
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| WRTFAT | |
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+----------+ |
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| |
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+------+ |
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| DONE | |
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+------+ |
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+---->--------------------------+
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The INIT, DISKFORMAT, and BADSECTOR routines are free
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to use any MS-DOS system calls, except for calls that cause
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disk accesses on the disk being formatted. DONE may use
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ANY calls, since by the time it is called the new disk has
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been formatted.
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The following data must be declared PUBLIC in a module
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provided by the OEM:
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SWITCHLIST - A string of bytes. The first byte is count
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N, followed by N characters which are the switches to
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be accepted by the command line scanner. Alphabetic
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characters must be in upper case (the numeric
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characters 0-9 are allowed). The last three switches,
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normally "O", "V" and "S", have pre-defined meanings.
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The "S" switch is the switch which causes the
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system files IO.SYS, MSDOS.SYS, and COMMAND.COM to be
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transfered to the disk after it is formatted thus
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making a "S"ystem disk. The switch can be some letter
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other than "S", but the last switch in the list is
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assumed to have the meaning "transfer system",
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regardles of what the particular letter is.
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The second to the last switch, "V", causes FORMAT
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to prompt the user for a volume label after the disk
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is formatted. Again, as with "S", the particular
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letter is not important but rather the position in the
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list.
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The third to the last switch, "O", causes FORMAT to
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produce an IBM Personal Computer DOS version 1.X
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compatible disk. Normally FORMAT causes a 0 byte to
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be placed in the first byte of each directory entry
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instead of the 0E5 Hex free entry designator. This
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results in a very marked directory search performance
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increase due to an optimization in the DOS. Disks
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made this way cause trouble on IBM PC DOS 1.X
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versions, however, which did not have this
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optimization. The 0 byte fools IBM 1.X versions into
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thinking these entries are allocated instead of free,
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NOTE that IBM Personnal Computer DOS version 2.00 and
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MS-DOS version 1.25 will have no trouble with these
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disks, since they have the same optimization. The "O"
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switch causes FORMAT to re-do the directory with a 0E5
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Hex byte at the start of each entry so that the disk
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may be used with 1.X versions of IBM PC DOS, as well
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as MS-DOS 1.25/2.00 and IBM PC DOS 2.00. This switch
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should only be given when needed because it takes a
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fair amount of time for FORMAT to perform the
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conversion, and it noticably decreases 1.25 and 2.00
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performance on disks with few directory entries.
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Up to 16 switches are permitted. Normally a "C"
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switch is specified for "Clear". This switch should
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cause the formatting operation to be bypassed (within
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DISKFORMAT or BADSECTOR). This is provided as a
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time-saving convenience to the user, who may wish
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to "start fresh" on a previosly formatted and used
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disk.
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HARDFLAG - BYTE location which specifies whether the
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OEM routine is formatting a fixed disk or a a drive
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with removable media. A zero indicates removable
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media, any other value indicates a fixed disk. The
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status of this byte only effect the messages printed
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by the main format module. This value should be
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set or reset by the OEM supplied INIT routine.
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FATID - BYTE location containing the value to be used
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in the first byte of the FAT. Must be in the range
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F8 hex to FF hex.
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STARTSECTOR - WORD location containing the sector number
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of the first sector of the data area.
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FATSPACE - WORD location containing the address of the
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start of the FAT area. A FAT built in this area
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will be written to disk using the OEM supplied WRTFAT
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subroutine. 6k is sufficient to store any FAT. This
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area must not overlap the FREESPACE area.
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FREESPACE - WORD location which contains the address
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of the start of free memory space. This is where
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the system will be loaded, by the Microsoft module,
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for transferring to the newly formatted disk. Memory
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should be available from this address to the end
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of memory, so it is typically the address of the
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end of the OEM module.
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The following routines must be declared PUBLIC in the
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OEM-supplied module:
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INIT - An initialization routine. This routine is called
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once at the start of the FORMAT run after the switches
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have been processed. This routine should perform
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any functions that only need to be done once per
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FORMAT run. An example of what this routine might
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do is read the boot sector into a buffer so that
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it can be transferred to the new disks by DISKFORMAT.
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If this routine returns with the CARRY flag set it
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indicates an error, and FORMAT will print "Format
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failure" and quit. This feature can be used to detect
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conflicting switches (like specifying both single
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and double density) and cause FORMAT to quit without
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doing anything.
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DISKFORMAT - Formats the disk according to the options
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indicated by the switches and the value of FATID
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must be defined when it returns (although INIT may
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have already done it). This routine is called once
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for EACH disk to be formatted. If neccessary it
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must transfer the Bootstrap loader. If any error
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conditions are detected, set the CARRY flag and return
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to FORMAT. FORMAT will report a 'Format failure'
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and prompt for another disk. (If you only require
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a clear directory and FAT then simply setting the
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appropriate FATID, if not done by INIT, will be all
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that DISKFORMAT must do.)
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BADSECTOR - Reports the sector number of any bad sectors
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that may have been found during the formatting of
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the disk. This routine is called at least once for
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EACH disk to be formatted, and is called repeatedly
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until AX is zero or the carry flag is set. The carry
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flag is used just as in DISKFORMAT to indicate an
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error, and FORMAT handles it in the same way. The
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first sector in the data area must be in STARTSECTOR
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for the returns from this routine to be interpreted
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correctly. If there are bad sectors, BADSECTOR must
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return a sector number in in register BX, the number
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of consecutive bad sectors in register AX, and carry
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clear. FORMAT will then process the bad sectors
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and call BADSECTOR again. When BADSECTOR returns
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with AX = 0 this means there are no more bad sectors;
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FORMAT clears the directory and goes on to DONE,
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so for this last return BX need not contain anything
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meaningful.
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FORMAT processes bad sectors by determining their
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corresponding allocation unit and marking that unit
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with an FF7 hex in the File Allocation Table. CHKDSK
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understands the FF7 mark as a flag for bad sectors
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and accordingly reports the number of bytes marked
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in this way.
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NOTE: Actual formatting of the disk can be done in
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BADSECTOR instead of DISKFORMAT on a "report as you
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go" basis. Formatting goes until a group of bad
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sectors is encountered, BADSECTOR then reports them
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by returning with AX and BX set. FORMAT will then
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call BADSECTOR again and formatting can continue.
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WRTFAT - This routine is called after the disk is
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formatted and bad sectors have been reported. Its
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purpose is to write all copies of the FAT from the
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area of memory referenced by FATSPACE to the drive
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just formatted. It may be possible to use INT 26H
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to perform the write, or a direct BIOS call. Whether
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this is possible depends on whether the FAT ID byte
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is used by the BIOS to determine the media in the
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drive. If it is, these methods will probably fail
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because there is no FAT ID byte on the disk yet (in
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this case WRTFATs primary job is to get the FAT ID
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byte out on the disk and thus solve the chicken and
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egg problem).
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DONE - This routine is called after the formatting is
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complete, the disk directory has been initialized,
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and the system has been transferred. It is called
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once for EACH disk to be formatted. This gives the
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chance for any finishing-up operations, if needed.
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If the OEM desires certain extra files to be put
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on the diskette by default, or according to a switch,
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this could be done in DONE. Again, as in BADSECTOR
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and DISKFORMAT, carry flag set on return means an
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error has occurred: 'Format failure' will be printed
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and FORMAT will prompt for another disk.
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The following data is declared PUBLIC in Microsoft's FORMAT
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module:
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SWITCHMAP - A word with a bit vector indicating what
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switches have been included in the command line. The
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correspondence of the bits to the switches is
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determined by SWITCHLIST. The right-most
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(highest-addressed) switch in SWITCHLIST (which must
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be the system transfer switch, normally "S")
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corresponds to bit 0, the second from the right,
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normally "V" to bit 1, etc. For example, if
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SWITCHLIST is the string "7,'AGI2OVS'", and the user
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specifies "/G/S" on the command line, then bit 6 will
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be 0 (A not specified), bit 5 will be 1 (G specified),
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bits 4,3,2 and 1 will be 0 (neither I,2,O or V
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specified), and bit 0 will be 1 (S specified).
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Bits 0,1 and 2 are the only switches used in
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Microsoft's FORMAT module. These switches are used 1)
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after INIT has been called, to determine if it is
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necessary to load the system; 2) after the last
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BADSECTOR call, to determine if the system is to be
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written, E5 directory conversion is to be done, and/or
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a volume label is to be asked for. INIT may force
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these bits set or reset if desired (for example, some
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drives may never be used as system disk, such as hard
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disks). After INIT, the "S" bit may be turned off
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(but not on, since the system was never read) if
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something happens that means the system should not be
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transferred.
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After INIT, a second copy of SWITCHMAP is made
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internally which is used to restore SWITCHMAP for
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each disk to be formatted. FORMAT itself will turn
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off the system bit if bad sectors are reported in
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the system area; DISKFORMAT and BADSECTOR are also
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allowed to change the map. However, these changes
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affect only the current disk being formatted, since
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SWITCHMAP is restored after each disk. (Changes
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made to SWITCHMAP by INIT do affect ALL disks.)
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DRIVE - A byte containing the drive specified in the
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command line. 0=A, 1=B, etc.
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Once the OEM-supplied module has been prepared, it must linked
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with Microsoft's FORMAT.OBJ module and the FORMES.OBJ module.
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If the OEM-supplied module is called OEMFOR.OBJ, then the
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following linker command will do:
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LINK FORMAT FORMES OEMFOR;
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This command will produce a file called FORMAT.EXE. FORMAT
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has been designed to run under MS-DOS as a simple binary
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.COM file. This conversion is performed by LOCATE (EXE2BIN)
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with the command
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LOCATE FORMAT.EXE FORMAT.COM
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which will produce the file FORMAT.COM.
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;*****************************************
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;
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; A Sample OEM module
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;
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;*****************************************
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CODE SEGMENT BYTE PUBLIC 'CODE'
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; This segment must be
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; named CODE, it must be
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; PUBLIC, and it's
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; classname must be 'CODE'
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ASSUME CS:CODE,DS:CODE,ES:CODE
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; Must declare data and routines PUBLIC
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PUBLIC FATID,STARTSECTOR,SWITCHLIST,FREESPACE
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PUBLIC INIT,DISKFORMAT,BADSECTOR,DONE,WRTFAT
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PUBLIC FATSPACE,HARDFLAG
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; This data defined in Microsoft-supplied module
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EXTRN SWITCHMAP:WORD,DRIVE:BYTE
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INIT:
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; Read the boot sector into memory
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CALL READBOOT
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...
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; Set FATID to double sided if "D" switch specified
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TEST SWITCHMAP,10H
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JNZ SETDBLSIDE
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...
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RET
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DISKFORMAT:
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...
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; Use the bit map in SWITCHMAP to determine
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; what switches are set
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TEST SWITCHMAP,8 ;Is there a "/C"?
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JNZ CLEAR ; Yes -- clear operation
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; requested jump around the
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; format code
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< format the disk >
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CLEAR:
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...
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; Transfer the boot from memory to the new disk
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CALL TRANSBOOT
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...
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RET
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; Error return - set carry
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ERRET:
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STC
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RET
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BADSECTOR:
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...
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RET
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WRTFAT:
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...
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WRTFATLOOP:
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< Set up call to write out a fat to disk>
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...
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MOV BX,[FATSPACE]
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< Write out one fat to disk>
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JC ERRET
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...
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< Decrement fat counter >
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JNZ WRTFATLOOP
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CLC ;Good return
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RET
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DONE:
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...
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RET
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; Default Single sided
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FATID DB 0FEH
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HARDFLAG DB 0
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STARTSECTOR DW 9
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SWITCHLIST DB 5,"DCOVS" ; "OVS" must be the last
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; switches in the list
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FATSPACE DW FATBUF
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FREESPACE DW ENDBOOT
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BOOT DB BOOTSIZE DUP(?) ; Buffer for the
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; boot sector
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FATBUF DB 6 * 1024 DUP(?) ; Fat buffer
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ENDBOOT LABEL BYTE
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CODE ENDS
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END
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