DOSPLUS 3.5 for the Model I - SYS10/SYS Disassembled

SYS10/SYS

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DOSPLUS 3.5 SYS10/SYS Disassembly - The Library Commands COPY, APPEND and LIST (Model I)

SYS10/SYS is the second of the high overlays, which hold the library commands: it loads at 5200H, over the area 5200H-5BFFH that SYS0/SYS keeps for them, and holds COPY (request code 93H), APPEND (94H) and LIST (95H). CMNDI@ takes these codes from SYS1/SYS's table of the library commands (51C5H, 51B9H and 51D5H) and passes them to the overlay request handler, which loads SYS10/SYS and calls routine 3, 4 or 5 of its table at 5200H with Register Pair HL at the rest of the command line. No file of the diskette requests routine 2 (92H) or calls into SYS10/SYS. The file is a load module of 7 blocks, 1632 bytes, from 5200H to 585FH, with the transfer address 5200H and no gaps; the work area after it runs from 5860H, with a sector buffer at 5900H and the copy buffer from 5A00H to the top of memory.

The Parts of SYS10/SYS

Parameters Stored into the Code

Every switch of the three commands is the operand of an instruction further on: the parameter tables (5570H, 562FH, 56B4H) give EVAL@ (4479H) the operands' addresses, so the value of MOD, for one, goes straight into the LD DE,0000H at 52E4H, which then tests Register E. Each command clears the low bytes of its own switches first. CTL (5553H) is shared: COPY and APPEND set it to FFH, so that every character of a device copy goes out as it is, and LIST clears it and lets its parameter CTL set it. The passwords SPW and DPW are strings: EVAL@ stores the address of the quoted text into the LD BC,0000H at 52FFH and 5308H.

The Three Kinds of COPY

COPY needs both a source and a destination (else error 2FH, I/o field not found) and at least 5B00H of memory (21H). A device on either side makes a device copy (54FEH); a file name as the source a file copy (5326H); a drive as the source a wildmask copy (5287H), to a drive only (a name is 2EH), and not with PROMPT (2EH). The wildmask copy reads directory sectors 2 to the last of the source drive into 5900H and takes each entry in use that is not an extended entry (52C1H): a system file only with SYSTEM, and then without the INVIS and MOD tests; an invisible file only with INVIS; with MOD only a file whose modified flag (bit 6 of +01H) is set; and only names that match the wildmask (WILD@, 575EH). For each, NAME/EXT.PASSWORD:D is built for both sides from the entry, the password being SPW or DPW (5769H), and the file is copied as by a file copy.

Copying a File

A destination given as a drive takes the source's name, extension and password (5333H). QUERY asks Copy ? on the name's line (5725H); the answer is one character by KEYIN@, Y or y for yes, BREAK error 30H. The source is opened, then the destination: with OLD by OPEN@, so that a file not on the destination is passed over; else by INIT@, which creates it when needed. NEW passes over a file that exists, OVER asks Overwrite ? for it, and ECHO shows the name when neither QUERY nor OVER has shown it (53C8H). The destination is then written once at the source's last sector, which gives it all its space before any data moves, and rewound (53F1H). The data goes through the buffer from 5A00H, as many pages as memory holds (one with TINY): READ@ fills the pages, WRITE@ empties them, until READ@ reports the end (1CH or 1DH) (5412H). The destination is closed with the source's end of file byte and ending record; then the source is killed (KILL) or its modified flag cleared, and the destination's directory entry gets the source's flag byte (protection level, invisible, system), logical record length and both password codes, with its own modified flag clear (5463H). The dates are the destination's own.

One Drive: PROMPT and the Overlays

With PROMPT, COPY asks for the disk each step needs: Insert SOURCE disk (ENTER), Insert DESTINATION disk (ENTER) and Insert SYSTEM disk (ENTER) (57EFH). The text flashes on the cursor's line until a key is pressed and is then cleared (56E2H); nothing is asked while a DO file runs. Since OPEN@ and INIT@ are in SYS2/SYS, WRITE@'s allocation in SYS4/SYS and CLOSE@ in SYS3/SYS, COPY has each of them loaded before the prompt that may take the system disk away, by requesting its routine 2, which does nothing (56D0H, 5357H, 53E6H, 5469H). The error exit asks for the system disk before ERROR@ (57E2H).

The Device Copy, LIST and APPEND

The device copy (551AH) opens the source by OPEN@ and the destination by INIT@ and passes the characters through the ROM's 0013H and 001BH, which reach a file through SYS0/SYS and a device through its DCB. A source file ends at its end of file (1CH); a source device ends with ETX (03H, CONTROL-C at the keyboard), and a device that has no character (00H) is asked again. While the source is not the keyboard, each character also scans the keyboard (56D1H): the SPACE BAR pauses and BREAK ends. A destination file is closed. Without CTL, a control code other than the carriage return and every character of 80H or more go out as a period (5553H). LIST (55EFH) takes a source and an optional destination; without one it makes the destination a device block for @DO (LOCDCB% 4488H) and lists to the display. APPEND (5642H) opens its destination by OPEN@ with a logical record length of 1, so the file must exist; it positions it to its end by PEOF@, backs it up by four bytes with CMD (the transfer address record of a load module) or one byte with STRIP, and appends the source. A device as APPEND's destination simply receives the source.

Differences from the Manual

The manual's parameter table of COPY lacks SYSTEM, which its text describes; the bytes have it. Its abbreviation O is given for both OVER and OLD: EVAL@ takes the first name in the table that starts with the letters given, and OVER comes before OLD, so O is OVER and OLD needs OL. LIST's CTL turns more than the control codes 00H-1FH into periods: the bytes do the same to every character of 80H or more and pass the carriage return. The manual says BREAK ends LIST @KI @PR; when the keyboard is the source, SYS10/SYS does not scan the keyboard itself and ends only on 03H. TINY copies through one page at 5A00H, inside the overlay area, as the manual says, but COPY still requires memory up to 5B00H. APPEND opens its destination file without creating it, and with both CMD and STRIP backs up only CMD's four bytes; its test for a file too short to back up looks only at an empty file. A system file taken by SYSTEM in a wildmask copy is not tested against INVIS or MOD. The questions take the answer Y or y; anything else, ENTER alone included, is no, as the manual says.

5200H - The Routine Table

Data: SYS10/SYS's table of routines 2-5, one word each, used by SYS0/SYS's overlay request handler (its 49C9H-49DCH) for the request codes 92H-95H. CMNDI@ takes the codes of the library commands from SYS1/SYS's table: COPY 93H (51C5H), APPEND 94H (51B9H), LIST 95H (51D5H). No file of the diskette requests 92H.

5208H - Routine 2

Nothing to do when SYS0/SYS's record locator brings SYS10/SYS back.

520AH - COPY

Routine 3, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. The eleven switches of COPY are the operands of instructions further on, which EVAL@ stores the values into; COPY clears the low byte of each first, sets CTL (5554H) to FFH so that a device copy passes every character as it is, and clears the two password addresses SPW and DPW. EVAL@ then takes the command line with the block at 5570H: the source field, the destination field, a wildmask and the parameters. Both fields must be given. A device as either field makes a device copy (54FEH), a file name as the source a file copy (5326H), and a drive as the source a wildmask copy of the whole directory (5291H).

5287H - The Wildmask Copy

The source is a drive: every file of its directory that the switches and the wildmask let through is copied to the destination drive under its own name. The destination must be a drive too (a name is error 2EH), and PROMPT is refused (2EH): a wildmask copy cannot be made with one drive. The wildmask is set for WILD@, the source drive must be ready (08H), and directory sectors 2 to the last are read one by one into 5900H.

52C1H - One Directory Entry

Register Pair HL points to an entry of the sector at 5900H. An entry not in use (bit 4 clear) and an extended entry (bit 7) are passed over. A system file (bit 6) is taken only with SYSTEM, and then without the INVIS and MOD tests; an invisible file (bit 3) only with INVIS; with MOD only a file whose bit 6 of +01H is set, which a file gets when it is written to. The name must match the wildmask (WILD@). The file's specification is then built for each side, with SPW or DPW as its password, and the file is copied by 5346H.

5326H - The File Copy

The source is a file. A destination given as a drive alone takes the source's NAME/EXT.PASSWORD with the destination's drive (5333H-5343H). 5346H on is also the copy of each file of a wildmask copy (530EH): QUERY asks Copy ?, the source is opened, the destination is opened (OLD: it must exist, else the file is passed over) or created by INIT@ (NEW: a file that exists is passed over; OVER asks Overwrite ? for it); ECHO shows the name. Before each disk access that may follow a change of diskette, SYS10/SYS has the low overlay it will need loaded (SYS2/SYS, SYS4/SYS, SYS3/SYS: 56D0H) and, with PROMPT, asks for the SOURCE, DESTINATION or SYSTEM disk.

5346H - Copy One File

The copy of one file, for a file copy and for each file of a wildmask copy: the blocks at 586BH (source) and 588CH (destination) hold the two specifications, ended by 03H. A RET NZ or a JUMP to 54F6H passes the file over.

53F1H - The Destination's Size

Before any data is moved, the destination is positioned to the source's last sector and written once, so that it gets all its granules at the start (in one piece when the disk allows), then it is rewound. A source that is empty (end of file byte 00H, ending record 0) is not positioned.

5412H - The Data

The copy loop: as many sectors of the source as the buffer holds (from 5A00H up to the page below the top at 5863H) are read by READ@, each into the next page of the buffer, then written to the destination by WRITE@ from the same pages. The end of the source (error 1CH or 1DH from READ@) ends the loop after the last write.

5463H - Closing the Destination

The destination is closed with the source's end: its end of file byte and ending record are those of the source, since every sector was written whole. The source's entry is read back from the directory and kept at 58ADH; KILL kills the source, otherwise the source's modified flag (bit 6 of +01H) is cleared. Then the destination's entry gets the source's flag byte, logical record length and both password codes, with its own modified flag cleared: the copy keeps the source's protection, invisible and system attributes.

54FEH - The Device Copy

COPY with a device as the source or the destination: the source is opened by OPEN@ (a device gets a control block of type 90H that points to its DCB), the destination by INIT@, and the characters are passed one by one through the ROM's 0013H and 001BH, which work for files and devices alike. LIST (5609H) and APPEND (5681H) use the same loop. The loop ends at the end of a source file (1CH), at an ETX (03H) or BREAK from a source device, and on BREAK from the keyboard unless the keyboard is the source itself. CTL (5554H) decides whether every character goes out as it is or only the printable ones.

551AH - One Character

The loop of the device copy, LIST and APPEND.

5570H - COPY's Evaluation Block

Data: the block that Index Register IX points to for EVAL@ (523BH): EVAL@'s flags, the addresses of the source, destination and wildmask blocks, and the parameter table. Each entry of the table is the name (6 characters), the address its value is stored to (here the operands of instructions of COPY) and a type byte: 20H a switch (the name alone gives FFFFH, =Y or =N and the like), 80H a string (the address of the quoted text is stored). The manual lists the same twelve parameters plus SYSTEM, which its text describes.

55EFH - LIST

Routine 5, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. CTL and PROMPT are cleared (PROMPT is cleared so that the error exit at 57E2H does not ask for the system disk) and EVAL@ takes the command line with the block at 562FH: a source must be given (2FH). The source is opened; a destination makes LIST the device copy of COPY (550CH). Without one, the destination is the display: its control block at 588CH is made type 90H with the address of @DO's DCB from LOCDCB%, without INIT@.

562FH - LIST's Evaluation Block

Data: the block that Index Register IX points to for EVAL@ (55F6H). The wildmask block is the destination block (588BH), so a field with a wildcard goes to the destination.

5642H - APPEND

Routine 4, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. CMD, PROMPT and STRIP are cleared, CTL is set to FFH (every character as it is), and EVAL@ takes the command line with the block at 56B4H: both fields must be given (2FH). The source is opened, and the destination is opened by OPEN@ with a logical record length of 1, so it must exist (an error 18H otherwise). A device destination takes the characters as a device copy. A file is positioned to its end by PEOF@; CMD then backs it up by four bytes, the transfer address record of a load module, and STRIP by one, an end of file mark; then the device copy loop appends the source.

56B4H - APPEND's Evaluation Block

Data: the block that Index Register IX points to for EVAL@ (5650H). As for LIST, the wildmask block is the destination block.

56D0H - Load a Low Overlay

Entered by a GOSUB with a request code in Register A (12H, 22H, 32H: routine 2 of SYS2/SYS, SYS3/SYS, SYS4/SYS, which is XOR A and RET). The overlay request handler drops the return address of the RST 28H, loads the overlay unless it is resident, and its routine 2 returns straight to the caller: the overlay is in memory before a prompt asks for another diskette.

56D1H - The Keyboard

Returns the NZ FLAG at once while a DO file runs (bit 5 of SFLAG1$). Otherwise the keyboard is scanned once: the SPACE BAR waits for the next key, and the Z FLAG is returned when the key is BREAK (01H).

56E2H - The Prompt

With PROMPT given and no DO file running: the text at Register Pair HL, ended by 03H, is shown on the line of the cursor, flashing (on and off every 500 scans of the keyboard), until a key is pressed; the line is then cleared. The registers are kept by SYS0/SYS's wrapper (4525H). 5724H holds 1EH while the text is off.

5712H - Clear the Line

Moves the cursor to the start of its line (carriage return, then up a line) and clears to the end of the line; the flash state at 5724H becomes 1EH, off.

5725H - The Question

Shows the name at Register Pair HL (up to its period or colon) and the question at Register Pair DE (Copy ? or Overwrite ? at column 16 of the same line), and takes an answer of one character by KEYIN@. Returns the Z FLAG when the answer is Y (or y); ENTER alone is no. BREAK ends COPY with error 30H.

5740H - Show a Text

Shows the characters at Register Pair HL through the ROM's 0033H, up to a 03H, a period or a colon, which is not shown. Register Pair HL ends after it.

5750H - Set the Wildmask

When the command had a wildmask (bit 2 of the flags at Index Register IX+00H), WILD@ with Register B = 01H sets its mask from the text at 58ADH.

575EH - Match the Wildmask

Returns the Z FLAG when no wildmask was given, else WILD@'s compare of the 11 bytes of a directory entry's name and extension at Register Pair HL: the Z FLAG when they match.

5769H - Build a Specification

From the 11 bytes of a directory entry's name and extension at Register Pair HL, builds NAME/EXT.PASSWORD:D at Register Pair DE, ended by 03H: trailing spaces are dropped, the extension and its slash only when there is one, the password (Register Pair BC, the address of a quoted string, 0000H for none) up to 8 characters ending at a control code or a quotation mark, and the drive from the flag byte in front of Register Pair DE. Register Pairs BC, DE and HL are kept.

57BAH - Add the Drive

With bit 7 of Register A set, adds a colon and the drive's name (one or two characters from DCTTBL, the drive in bits 0-2) at Register Pair DE; then 03H ends the text. Register Pairs BC and HL are kept; Register A returns 00H with the Z FLAG.

57E2H - The Error Exit

Every error of COPY, APPEND and LIST: with PROMPT, the system disk is asked for, then the error in Register A is posted by ERROR@ with bit 6 set (no frame) and bit 7 clear, so ERROR@ ends with ABORT@.

57EFH - The Texts

Data: the two questions and the three prompts, each ended by 03H. A question starts with a carriage return, sixteen spaces (D0H, the ROM's space compression code) and a move up a line, so that it stands at column 16 of the name's line.

5860H - The Work Area

Not in the file: SYS10/SYS uses the memory after its last byte (585FH) for the copy's pointers, the answer buffer, the three blocks of EVAL@, the sector buffer at 5900H and the copy buffer from 5A00H to the top of memory.