DOSPLUS 3.5 for the Model III - MAP/CMD Disassembled

MAP/CMD

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DOSPLUS 3.5 MAP/CMD Disassembly - The Disk and File Mapper (Model III)

MAP/CMD lists, file by file, the cylinders and sectors a diskette gives to each file, run from the DOS command level as MAP [FROM] :dr [TO] filespec/@devicespec [USING] wildmask (SYSTEM,INVIS,HEX); its heading reads MAP - DOSPLUS Disk/file mapper - 3.50. It is a load module of 3 blocks, 721 bytes, at 5200H-54D0H with the transfer address 5200H, after the two comment records (the name MAP and the copyright notice). MAP/CMD is on the Model III master only.

The first line of the listing is the diskette's name and date from the GAT. Each file shown then takes one line per extent: the name and extension in a field of 16 columns, the first cylinder and sector, a minus sign and the last cylinder and sector, three decimal digits each (or two hexadecimal digits with HEX); the further extents of the file follow on lines of their own, under the first.

The Parts of MAP/CMD

How MAP Works

EVAL@ takes the fields and the parameters (5208H). With nothing at all on the command line MAP shows an asterisk and evaluates the reply, up to 63 characters, as a new command line; BREAK is the error Terminated (5212H). The source field must be a drive (Illegal devicespec otherwise), and without one MAP maps drive 0 (522BH). The three parameters are switches whose values EVAL@ stores straight into the operands of three LD DE instructions, which the code tests with INC E and DEC E (52A8H, 52B6H, 53ABH).

The output is opened first (53EFH): without a destination it is the display; a destination with a name is opened by INIT@ as a file, using the field's own text as the file control block and 5700H as the buffer; a device gets its DCB from LOCDCB%, and MAP makes the first bytes of the destination block a control block of type 90H, a FORCE to that DCB, so that every character goes out through the same block by the ROM's 001BH (542EH). At the end a file is closed by CLOSE@ (541CH).

The drive is checked by DCHECK (Drive not available), the GAT is read by SREAD and its name and date make the first line (5242H). Each entry sector of the directory, from sector 2 to the last, is read into 5600H (528BH); an entry is shown when it is active, is not an extended entry, passes SYSTEM for a system file or INVIS for an invisible file (a system file needs only SYSTEM), and matches the wildmask, which WILD@ set from the wildmask field at the start (5426H). For each extent the starting granule and the granule after the last are turned into a cylinder and a sector with the drive control table's granules per cylinder and sectors per granule (538AH); a last sector that falls before the start of a cylinder becomes the last sector of the cylinder before. A link byte FEH reads the extended entry's sector into 4300H by 449AH and the extents go on there (5357H). Between lines the SPACE BAR pauses and BREAK ends the listing, except while a DO file runs (5437H).

Differences from the Manual

The manual's examples agree with the bytes on the form of a line, and the abbreviations S, I and H are the first letters EVAL@ takes. It does not say that MAP with no drive maps drive 0, that MAP alone prompts with an asterisk, that a system file is shown with SYSTEM even when it is invisible, or that the SPACE BAR and BREAK work only when no DO file runs.

With HEX, the two digits of each cylinder and sector are sent by the ROM's 0033H, the display, and not to the output (53ECH): MAP :2 @PR (HEX) prints the names, commas and minus signs while the hexadecimal numbers appear on the screen, and a file gets the listing without them. The decimal digits go to the output as they should (53C7H).

5200H - MAP

MAP/CMD's transfer address, entered from the DOS command level with Register Pair HL at the command line after the word MAP: MAP [FROM] :dr [TO] filespec/@devicespec [USING] wildmask (SYSTEM,INVIS,HEX). MAP reads the GAT of the drive for the diskette's name and date, then every entry sector of the directory, and for each active file that passes the SYSTEM and INVIS switches and the wildmask shows its name and each extent as the first and the last cylinder and sector, through the extended entries. The output goes to the display, a device or a file. It returns to the DOS by RET.

5212H - No Field: the Asterisk Prompt

When the command line holds no field and no parameter, MAP shows an asterisk and takes up to 63 characters as a new command line, which EVAL@ evaluates again; BREAK is the error 30H, Terminated.

522BH - The Drive

The source field must be a drive (:dr), with the flag bits 7 and 3 and no name; without a source field MAP maps drive 0. Any other source field is the error 2BH, Illegal devicespec.

5242H - The Output, the Wildmask and the Diskette

Opens the output (53EFH), sets the wildmask when one was given (WILD@ with Register B = 01H), checks the drive with DCHECK, reads the GAT into 5600H and shows the diskette's name (GAT+D0H) and date (GAT+D8H) as the first line.

528BH - The Directory Entries

Reads the entry sectors of the directory, sector 2 up to the last (DCT+0EH less 1), into 5600H. An entry is shown when it is active (bit 4), not an extended entry (bit 7), a system file (bit 6) only with SYSTEM, an invisible file (bit 3) only with INVIS, and its name and extension match the wildmask.

52BEH - The Name

Compares the name and extension of the entry with the wildmask, then sends the name and, when there is one, a slash and the extension, without their padding spaces; Register E counts the 16 columns down for the spaces before the first extent.

52F6H - The Extents

Each extent of the entry (+16H on, two bytes: the cylinder, then the starting granule in bits 7-5 and the granules less 1 in bits 4-0) is shown on a line of its own as the first cylinder and sector, a minus sign and the last cylinder and sector; the first line after the name, the others after 16 spaces. 5357H follows a link (FEH) to an extended entry and ends at FFH. Between lines the SPACE BAR pauses and BREAK ends MAP.

5357H - A Link or the End of the Entry

FEH links to the extended entry whose logical file number follows: its sector is read into 4300H by 449AH and the extents go on there. FFH ends the entry; when the name has had no extent, a carriage return ends its line.

5370H - The Next Entry

The next of the eight entries of the sector, then the next sector up to the last of the directory (DCT+0EH less 1); at the end the output is closed and MAP returns to the DOS.

538AH - A Granule to a Cylinder and a Sector

Register D = a cylinder and Register E = a granule counted from that cylinder (it may pass the granules of one cylinder): returns Register D = the cylinder of the granule and Register E = its first sector, by SYS0/SYS's 8 bit divide (4494H) and multiply (4491H).

539CH - Show a Cylinder and a Sector

Sends Register D, a comma and Register E as numbers: three decimal digits each, or with HEX two hexadecimal digits each (53D6H).

53AAH - A Number

Sends Register A as three decimal digits (000-255) to the output, or with HEX as two hexadecimal digits (53D6H). Register Pair DE is saved.

53D6H - A Number in Hexadecimal

Two hexadecimal digits of Register A, made by the DAA method; each digit goes to the ROM's 0033H, so with HEX the digits of the cylinders and sectors always go to the display, while the commas, spaces and names go to the output of MAP.

53EFH - Open the Output

No destination field: device 1, the display. A destination with a name, or with a drive, is opened by INIT@ as a file with the field's text as its file control block (54F4H) and the buffer 5700H. A device: its DCB from LOCDCB%, and 54F4H made a control block of type 90H (a FORCE) pointing to it, so every character goes through 54F4H.

541CH - Close the Output

CLOSE@ of the output when it is a file; a device (type 90H at 54F4H) needs nothing.

5426H - WILD@ When a Wildmask Was Given

Calls WILD@ (447CH) only when bit 2 of the evaluation block's flags is set; without a wildmask it returns the Z FLAG, so every name matches.

542EH - Send a Character

Sends Register A through the ROM's 001BH to the control block at 54F4H: the file control block of an output file or MAP's FORCE block of a device. Register Pair DE is saved.

5437H - The SPACE BAR and BREAK

While a DO file runs (bit 5 of SFLAG1$ at 4297H) nothing is tested. Otherwise the keyboard is scanned once: the SPACE BAR waits for the next key, and BREAK (01H), pressed or taken as that next key, returns the Z FLAG.

5448H - The Errors

5448H the error 2BH, Illegal devicespec; 544BH, inside the LD BC at 544AH, 08H, Drive not available; 544EH, inside the LD BC at 544DH, 30H, Terminated; 5450H any error code in Register A. Each is posted with bit 6 set (no frame) and bit 7 clear, so ERROR@ ends through ABORT@.

5455H - The Heading, the Evaluation Block and the Parameters

Data: the heading, the evaluation block of EVAL@ (5208H) and the parameter block (9 byte entries: a six character name, the address for the value, the type byte 20H for a logical value). The address of each value is the operand of a LD DE instruction, so the switches are read straight from the code. 54D1H on is not loaded.