DOSPLUS 3.5 for the Model III - DIRCHECK/CMD Disassembled

DIRCHECK/CMD

Other Navigation

DOSPLUS 3.5 DIRCHECK/CMD Disassembly - The Directory Checker (Model III)

DIRCHECK/CMD checks the directory of a diskette and can repair some of its faults, run from the DOS command level as DIRCHECK [FROM] :dr [TO] filespec/devicespec (GAT,HIT,FILES,CYL0); its heading reads DIRCHECK - DOSPLUS directory checker - 3.50. It is a load module of 8 blocks, 1914 bytes, at 5200H-5979H with the transfer address 5200H, after the two comment records (the name DIRCHECK and the copyright notice). DIRCHECK/CMD is on the Model III master only.

DIRCHECK reads every sector of the directory cylinder into 5D00H on, so it needs HMEM$ at 7F00H or above. From the file entries it builds its own granule allocation table at 5B00H and its own hash index table at 5C00H, then compares them with the diskette's. Each fault is one line on the output (the display, a device or a file), and the last line is DIRCHECK complete, nnn total errors, the count of the lines sent before it.

The Parts of DIRCHECK/CMD

How DIRCHECK Works

The drive must be given as :dr (drive 0 when none is given); with nothing on the command line an asterisk asks for it. The cylinder count is GAT+CCH plus 35, at most 96 on a floppy drive and 200 on a rigid drive (527BH). DIRCHECK's GAT starts with each cylinder holding only the granules the cylinder does not have, its HIT with 00H (5295H).

Each active entry that is not an extended entry gets the hash code of its name at its logical file number in the HIT (52BFH). Each extent is taken granule by granule: a cylinder past the count is Granule assigned past cyl count, a granule that another extent took already is Granule multiply assigned; the granule is set in DIRCHECK's GAT and counted (52FDH). The fifth pair (+1EH) must be FFH or FEH: an extent there is Terminating SD not found, a link FEH anywhere else or to an entry that is not an extended entry linking back is Invalid linking SD, and both are made FFH FFH. A linked extended entry gets the file's hash code and is made active if it was not (Extended directory entry deleted); its extents are counted with the file's (534CH). When the extents hold fewer granules than the sector count needs, EOF greater than allocated space, and the sector count is cut to the granules found (5384H). An active extended entry that no file links to is Extended directory entry unassigned at nnH and its flag byte is cleared (53A5H).

Then BOOT/SYS must be the first entry of sector 2 and DIR/SYS the first of sector 3, by their hash codes A2H and C4H, each with sectors (53D8H). On a floppy drive a granule in use that the lock out table locks out is Locked gran assigned to file at nnH; the locked out granules are then counted as in use, and each cylinder whose byte differs from the diskette's GAT is Extraneous or unassigned gran at nnH (53FDH). Each HIT byte that differs is Extraneous HIT code (DIRCHECK has no entry there) or Invalid HIT code (544CH). Messages about a file come after a line with its name and extension (564EH); the numbers are hexadecimal. The SPACE BAR pauses after each line and each entry, BREAK ends with Terminated, and while a DO file runs the keyboard is not looked at (55D0H).

Only with GAT, HIT or FILES is anything written. GAT writes DIRCHECK's GAT as sector 0 with the diskette's +CEH-+FFH (password code, name and date), 35H at +CBH, the count at +CCH and, on a floppy, the sides from the drive's configuration at +CDH (5461H). HIT writes DIRCHECK's HIT as sector 1, FILES writes the entry sectors with the repairs made in them (54A3H).

Differences from the Manual

The manual gives no limits; the bytes refuse to run below an HMEM$ of 7F00H and use at most 96 cylinders on a floppy and 200 on a rigid drive. DIRCHECK makes the repairs to its buffers in every case; they reach the diskette only with FILES. CYL0 marks every granule of cylinder 0 as in use in DIRCHECK's GAT (also with GAT, which then writes FFH for cylinder 0), not only the bootstrap's; the error is gone only when the diskette's byte is FFH too. The GAT written by GAT keeps the locked out granules as in use and rebuilds the lock out table from the mask and the diskette's; its bytes +C0H-+CAH are not copied but come from DIRCHECK's table (FFH for fewer than 192 cylinders). More granules in the extents than the sector count needs are not reported. The total counts every line sent before it, the name lines not included.

When the cylinder count is too large, the message Cylinder count of nnn invalid shows the byte at 597BH, which is not yet set at that point (55FDH): the number shown is not the diskette's count.

5200H - DIRCHECK

DIRCHECK/CMD's transfer address, entered from the DOS command level with Register Pair HL at the command line after the word DIRCHECK: DIRCHECK [FROM] :dr [TO] filespec/devicespec (GAT,HIT,FILES,CYL0). DIRCHECK reads the whole directory cylinder of the drive, builds its own granule allocation table and hash index table from the file entries, reports every difference and every faulty entry, and with GAT, HIT or FILES writes its own tables or the repaired entries back. It needs HMEM$ at 7F00H or above for its buffers.

5214H - The Fields and the Asterisk Prompt

EVAL@ takes the drive, the output and the parameters into the blocks of 5701H. When the command line holds no field and no parameter, DIRCHECK shows an asterisk and takes up to 63 characters into 5B00H, which EVAL@ evaluates again; BREAK is the error 30H, Terminated.

5237H - The Drive and the Output

The source field must be a drive (:dr), with the flag bits 7 and 3 and no name; without a source field DIRCHECK checks drive 0. Any other source field is the error 2BH, Illegal devicespec. The drive is kept at 597AH and the output is opened (5548H).

5256H - Read the Directory

DCHECK of the drive, then every sector of the directory cylinder, 0 up to DCT+0EH less 1, is read by SREAD into 5D00H on: the GAT at 5D00H, the HIT at 5E00H and the entries from 5F00H.

527BH - The Cylinder Count

The GAT's cylinder count (GAT+CCH plus 35) may be at most 96 on a floppy drive and 200 on a rigid drive; above that the message Cylinder count of nnn invalid is shown and the greatest count is used. The count is kept at 597BH. The message shows the byte at 597BH, which is stored only after it.

5295H - Empty Tables

The mask of the granules a cylinder does not have: FFH with the bits 0 up to DCT+10H less 1 reset, kept at 597CH. DIRCHECK's own GAT at 5B00H is made of the mask for each cylinder of the count and FFH for the rest; its own HIT at 5C00H is cleared to 00H.

52BFH - The Entries

Every entry of the sectors 2 on (5F00H up), 32 bytes each, is looked at. An inactive entry (bit 4 clear) is passed over; an extended entry (FXDE, bit 7) is checked at 53A5H. For a file's first entry the logical file number (DEC) is kept at 597DH, the hash code of its name is made and put into the HIT at 5C00H plus the DEC, and the granules its sector count needs (+14H divided by DCT+0FH, rounded up) are kept at 597FH.

52FDH - The Extents

Each entry has four extents at +16H and a fifth pair at +1EH, which must hold FFH (the end) or FEH and the logical file number of an extended entry. Each extent (a cylinder, then the starting granule in bits 7-5 and the granules less 1 in bits 4-0) is taken granule by granule, from its last one down: a cylinder past the count is Granule assigned past cyl count, a granule already set in DIRCHECK's GAT is Granule multiply assigned; the granule is then set and counted in Register Pair DE.

534CH - A Link or the End

FFH ends the entry. FEH is right only in the fifth pair, and the extended entry it names must be an FXDE whose back link (+01H) is this entry; it is then made active if it is not (Extended directory entry deleted), gets the file's hash code in the HIT, and its own extents are taken with the same count. Any other FEH is Invalid linking SD, and the pair is made FFH FFH.

5384H - The Granules Needed

When the extents hold fewer granules than the sector count needs, the message EOF greater than allocated space is shown and the sector count at +14H is set to the granules found times DCT+0FH. More granules than needed are not reported.

53A5H - An Extended Entry

An active extended entry must be linked from the entry its back link names: that entry must be active and hold FEH and this entry's number in its fifth pair. Otherwise the message Extended directory entry unassigned at nnH is shown and the extended entry's flag byte is set to 00H.

53C4H - The Next Entry

After each entry the keyboard is looked at (SPACE BAR pauses, BREAK is Terminated), then the next entry, 20H on, up to the end of the last directory sector.

53D8H - BOOT/SYS and DIR/SYS

The first entry of sector 2 (logical file number 00H) must have the hash code A2H, that of BOOT/SYS, and the first of sector 3 (01H) C4H, that of DIR/SYS; each must have a sector count that is not 0000H.

53FDH - Compare the GATs

For each cylinder of the count: with CYL0, cylinder 0 of DIRCHECK's own GAT is set to FFH. On a floppy drive a granule in use that the diskette's lock out table (GAT+60H) locks out is Locked gran assigned to file at nnH, and the lock out table is copied into DIRCHECK's tables with the mask (the locked out granules count as in use). Then every byte that differs from the diskette's GAT is Extraneous or unassigned gran at nnH, the cylinder.

544CH - Compare the HITs

Each of the 256 bytes of DIRCHECK's own HIT is compared with the diskette's HIT: a code where DIRCHECK has 00H is Extraneous HIT code at nnH, any other difference Invalid HIT code at nnH, the logical file number.

5461H - GAT: Write DIRCHECK's GAT

With GAT, DIRCHECK's own GAT is written as sector 0 of the directory cylinder (SWRITE): the diskette's bytes +CEH-+FFH (the password code, the name and the date) are copied into it, +CBH is set to 35H, +CCH to the cylinder count less 35, and +CDH to 01H on a rigid drive or, on a floppy, the sides less 1 in bit 5 from DCT+0CH: so the surface count comes from the drive's configuration.

54A3H - HIT and FILES

With HIT, DIRCHECK's own HIT is written as sector 1; with FILES, the entry sectors 2 up to DCT+0EH less 1 are written back from the buffers, with the repairs made in them.

54DCH - The Total

The count of messages at 5979H goes into the line DIRCHECK complete, nnn total errors, which is sent like the messages (and counted after it is sent); the output is closed and DIRCHECK returns to the DOS.

54F2H - An Entry's Logical File Number

54F2H: the logical file number (DEC) of the entry at Register Pair HL in Register B: the entry's place in its sector (bits 7-5 of Register L) OR its sector less 2 (Register H less 5FH). 54FCH: the reverse, Register Pair HL to the entry of logical file number Register B.

5505H - The Hash Code of a Name

The 11 characters at Register Pair HL, each XORed in and the result rotated left; 00H becomes 01H, as the DOS's hash codes are never 00H.

5518H - Set, Reset and Test a Bit

Bit Register E (0-7) of Register A is set (5518H), reset (5528H) or tested (5538H) by an instruction whose second byte is made from Register E and stored into it before it runs.

5548H - The Output

No destination: device 1 (@DO). A destination with a name or a drive (flag bits 6 or 3): INIT@ with the field's text at 59A3H as the file control block and the buffer 5A00H. Any other destination: its device number (flag bits 0-2) is given to LOCDCB%, and 59A3H becomes a FORCE control block (type 90H, the DCB address at 59A4H). Every character goes out by the ROM's 001BH with Register Pair DE = 59A3H; 5575H closes a file at the end.

5588H - A Message Line

Sends the text at Register Pair HL up to and with its 0DH, looks at the keyboard (BREAK is Terminated) and counts one error at 5979H.

559EH - Numbers in the Texts

559EH: Register A as two hexadecimal digits at Register Pair HL. 55B2H: Register A as three decimal digits at Register Pair HL. Register Pair HL ends after the digits.

55D0H - The Keyboard

While a DO file runs (SFLAG1$ bit 5) the keyboard is not looked at. Otherwise the SPACE BAR waits for the next key; BREAK, then or at once, returns the Z FLAG.

55E1H - Keep the Registers

Called at the start of a message routine: the rest of the routine, from the return address, is called as a subroutine (the address stored into the CALL at 55EEH) with every register saved, so the routine returns to its own caller with all the registers and flags as they were.

55FAH - The Messages

Each message routine keeps the registers (55E1H). 55FAH the cylinder count; 560CH-5634H a message after the file's name and extension (564EH, the entry of logical file number 597DH), 563CH one with the logical file number in hexadecimal, 568AH-56A5H BOOT/SYS and DIR/SYS, 56AEH and 56C1H one with the cylinder (the low byte of Index Register IX), 56D1H and 56E1H one with the place in the HIT (Register L). 56C1H does not keep the registers.

56F1H - The Errors

56F1H the error 21H, No memory space available; 56F4H, inside the LD BC at 56F3H, 2BH, Illegal devicespec; 56F7H, inside the LD BC at 56F6H, 08H, Drive not available; 56FAH, inside the LD BC at 56F9H, 30H, Terminated; 56FCH any error code in Register A. Each is posted with bit 6 set (no frame) and bit 7 clear, so ERROR@ ends through ABORT@.

5701H - The Evaluation Block, the Texts and the Variables

Data: the evaluation block and its parameter table (GAT, HIT, FILES, CYL0, each a logical value stored into the operand of a LD DE), the heading, the total line and the messages, each ended by 0DH, with the places their numbers are written into, and the count of the messages. 597AH on is not loaded: the variables, the field blocks, the output's buffer and the tables.