Percom DoubleDOS 4.24 for the Model I - COPY/CMD Disassembled

COPY/CMD

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Percom DoubleDOS 4.24 COPY/CMD Disassembly (Model I)

COPY/CMD is DBLDOS's COPY command, which takes the place of TRSDOS's library COPY (the manual's 3.2). It copies one file, a sector at a time through a buffer that fills the memory above 5D00H, and adds two things to TRSDOS's COPY: a copy with one drive, COPY :d filespec1 TO filespec2, which asks for the source and the destination diskette in turn on drive d, and single density files, marked by a dollar sign just before the file name ($NAME/EXT), so that files can be moved between DBLDOS diskettes and single density TRSDOS diskettes. It is the only part of DoubleDOS that reads or writes single density files.

The file is 1024 bytes: a name record, seven load blocks, 5200H-54D7H (728 bytes) and 5CD8H-5CE1H (10 bytes), and the transfer address 5200H. Every loaded byte is on exactly one row below: 568 bytes of code and 170 bytes of tables, texts and variables; the 2048 bytes 54D8H-5CD7H between the blocks are not in the file and hold COPY's copies of SYS2/SYS and SYS3/SYS while it runs. TRSDOS 2.1 has no COPY/CMD (its COPY is a library command of SYS6/SYS), so the code is compared with nothing but DBLDOS 4.20's.

Load Map

How It Works

The command line is taken first (5200H). In a copy with one drive the drive digit is kept at 5468H, inside the prompt text, and put into both specifications (5369H), over a drive the user gave. The buffer is the whole pages from 5D00H to the top of memory (4049H), 162 sectors with 48K.

COPY then makes sure that no overlay will have to be read while the diskettes are changed or set to the other density: an @OPEN and an @CLOSE of a file control block with no file name (5492H) fail, but each loads its overlay at 4E00H, and COPY copies SYS2/SYS to 54D8H and SYS3/SYS to 58D8H with their request codes (524CH). Before each open it puts SYS2/SYS back at 4E00H and its code in 430EH, before each close SYS3/SYS (53D9H), so that the dispatcher of RST 28H finds the overlay in memory. Reading and writing sectors are done by SYS0/SYS itself.

Each pass reads sectors into the buffer until it is full or the source ends (5292H), then writes them to the destination with read back, @VERF (52FDH). The source is opened on the first pass and closed when its end is read, and its end of file offset and sector are kept; the destination is opened or made on the first pass and, after the last, given that end and closed, so that the copy has the size of the source. In a copy with one drive, MOUNT SOURCE DISK ON DRIVE d AND PUSH "ENTER" and MOUNT DESTINATION DISK ... come before each pass, and at the end, when d is 0, MOUNT DBLDOS DISK ON DRIVE 0 AND PUSH "ENTER" (53B2H).

Single Density

Before each pass the density of the file is set by 53F3H: the Doubler gets the command FFH (double) or FEH (single) and the Force Interrupt D0H, with the track register kept around them, and two places of SYS0/SYS are changed. At 4651H the call of 43A5H, which turns a block and sector into the cylinder and the sector of a double density track, 18 sectors, becomes LD (37EEH),DE for single density, so that the block is the track and the sector is the sector, ten a track, as TRSDOS lays out a single density diskette (the CP D at 4650H already set the Z FLAG the RET Z at 4655H needs). The operands at 4A4AH and 4A72H, where SYS0/SYS stops looking for a free granule in the GAT, become 60H instead of C0H. The bytes are at 5424H and 5429H; every error and the end put double density back (53B2H).

Differences Between the Versions

COPY/CMD is the same in 4.23 (all three sets) and 4.24. 4.20 differs by Percom's patch memo DPM-0002 of September 29, 1980 ("The COPY command fails to copy all sectors of files which are longer than the memory buffer used for the copy operation (162 sectors on a 48K machine)"; the memo adds that this made the Microsoft BASIC compiler malfunction under DBLDOS):

Percom's letter of September 8, 1980 has one patch line for COPY/CMD: record 3, offset 75, one byte 64 (40H), the operand at 542EH of OR 40H in the error exit, which makes @ERROR end at the DOS's exit instead of returning (the letter's FILE NOT FOUND loop). Every set in hand, 4.20 included, has 40H there.

Bugs

Every bug found in DoubleDOS is listed, with what a user would do to set it off, on the DoubleDOS reference page.

Differences From the Manual

• The manual (3.2.2) writes the prompts as MOUNT ... AND PUSH ENTER; the text has "ENTER" in quotation marks.
• The manual's first example, COPY $SUPERZAP:1 TO $SUPERZAP:0, is said to make a double density file on drive 0; with the dollar sign before the second name COPY writes it in single density.
• The manual says a copy with two drives aborts when a single density file has no drive in its specification, and that a single density file cannot be on drive 0 with two drives; COPY itself tests neither. The abort comes from the open, which searches the drives in the density set and so cannot read a directory of the other density, and from the error message, which needs SYS4/SYS from the DBLDOS diskette in drive 0 (542EH sets double density first).
• The manual says nothing of the buffer size, of the read back of every sector written, or that the destination is made or overwritten without a question.

Notes

• The file control block at 5492H whose open and close fail is 32 bytes long like any FCB, so it takes in the source FCB at 5497H; @OPEN makes those bytes capitals before it finds no name, which leaves the source specification as 441CH stored it.
• The key typed at a prompt is put at 5200H by the ROM's 0040H, over the first bytes of COPY, which have run (53D0H).
• An error code goes to @ERROR with bit 6 set (542EH); SYS4/SYS shows the message of the code without bit 6.

Places in COPY/CMD

Places Outside COPY/CMD

Outside Routines

5200H - COPY: The Command Line

The transfer address, entered from SYS1/SYS's @RUN (4433H) with Register Pair HL past the name COPY. COPY :d filespec1 TO filespec2 copies with one drive, d (0-3), asking for each diskette in turn (the drive digit goes into the prompt text at 5468H); without :d the two files may be on two drives and nothing is asked. A dollar sign just before a file name marks a single density file (535AH). A bad drive is ILLEGAL DRIVE NUMBER (20H), a bad name or a missing TO is ILLEGAL FILE NAME (13H), both through 542EH.

523FH - COPY: Keep SYS2/SYS and SYS3/SYS in Memory

The buffer is the memory from 5D00H (5CD8H in 4.20, DPM-0002 moved it for the code at 5CD8H) to the top, in pages of 256 bytes. An @OPEN and an @CLOSE of the bad file specification at 5492H (1FH and 0DH) fail, but they load SYS2/SYS and SYS3/SYS into 4E00H; each is copied, 1024 bytes, to 54D8H and 58D8H, with its request code from 430EH. From then on COPY puts the copy back at 4E00H before each open or close (53D9H, 53E1H), so that no overlay is read from a diskette that may have been changed or that is in the other density.

527AH - COPY: The Passes

A read pass fills the buffer from the source (5292H), a write pass writes it to the destination (52FDH), until the source's end has been read (5490H). Then COPY COMPLETED, the DBLDOS diskette is asked for when drive 0 was used alone (53B2H), and DOS READY.

5292H - COPY: Read a Pass

The source diskette is asked for (one drive) and its density set (5392H). The first time the source is opened with the copy of SYS2/SYS (53D9H). Sectors are read into the buffer from 5D00H, the buffer address of the FCB (+03H-+04H) moved on a page each time, until the buffer is full (5491H) or the end of the file (1CH or 1DH), when the end of file offset and sector are kept (548DH-548FH) and the source closed with the copy of SYS3/SYS. 548BH-548CH is the end of the data in the buffer for the write pass.

52FDH - COPY: Write a Pass

The destination diskette is asked for (one drive) and its density set (53A2H). The first time the destination is opened or made with the copy of SYS2/SYS (@INIT). The buffer is written from 5D00H up to the end kept at 548BH, a sector at a time with read back (@VERF). After the last pass the destination FCB gets the source's end of file offset and sector (FCB+05H, +08H, +0AH, +0CH) and is closed with the copy of SYS3/SYS.

535AH - COPY: A File Specification into an FCB

Called with Register Pair HL at the specification and Register Pair DE the FCB. A dollar sign first is stored in the byte before the FCB (5496H for the source, 54B7H for the destination), the mark of a single density file, and passed over. 441CH puts the specification in the FCB, ending it with 03H. In a copy with one drive the drive of the command (5468H) is put into the specification: over the digit after a colon, or with a colon added before the 03H.

5392H - COPY: The Density and the Prompts

5392H for the source and 53A2H for the destination: the density of the file (5496H or 54B7H, 24H single) is set by 53F3H, and in a copy with one drive MOUNT SOURCE DISK ON DRIVE d AND PUSH "ENTER" or MOUNT DESTINATION ... is shown and a key waited for (53BFH). 53B2H sets double density and, when the drive of the command is 0, asks for the DBLDOS diskette.

53D9H - COPY: Put SYS2/SYS or SYS3/SYS Back

53D9H copies COPY's copy of SYS2/SYS (54D8H) to 4E00H and stores its request code (5494H) at 430EH, 53E1H does the same for SYS3/SYS (58D8H, 5495H): the dispatcher of RST 28H then finds the overlay in memory and reads nothing from the diskette.

53F3H - COPY: Set the Density

Register A 00H for double density, any other value for single. The Doubler gets FFH (double) or FEH (single) and the Force Interrupt D0H, with the track register kept around them. SYS0/SYS is patched: the four bytes at 4651H become CALL 43A5H and NOP (double: the block and sector are converted, 18 sectors a track) or LD (37EEH),DE (single: Register E the sector and Register D the track go to the controller as they are), and the operands 4A4AH and 4A72H, the end of the GAT searched for a free granule, C0H or 60H.

542EH - COPY: An Error

Every error of COPY comes here with its code in Register A. Bit 6 is set, double density and the DBLDOS diskette are put back (53B2H), and @ERROR (4409H) shows the message; bit 7 is clear, so SYS4/SYS goes on to the DOS's exit after an error (4030H). Percom's letter of September 8, 1980 patches the operand 542FH (COPY/CMD record 3, offset 75) to 40H, the value in every set in hand.

5438H - COPY: Texts and Variables

The parts of the prompts, each ended by 03H, the drive digit inside the prompt, the end text, the variables of the passes, the bad file specification used to load SYS2/SYS and SYS3/SYS, and the two FCBs, each with its density mark before it.

5CD8H - COPY: The End of a Read Pass (DPM-0002)

Added by Percom's patch memo DPM-0002 (September 29, 1980; 4.23 and 4.24 have it, 4.20 not): the jump at 52DCH comes here. While sectors are left the pass goes on at 52B5H; at a full buffer the end of the data is set past the last sector read. 4.20's JR NZ,52B5H and RET at 52DCH left 548BH at the start of the last sector, so the write pass dropped one sector of each full buffer: DPM-0002's "fails to copy all sectors of files which are longer than the memory buffer".