LDOS 5.3.1 for the Model III - CMDFILE/CMD Disassembled

CMDFILE/CMD

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LDOS 5.3.1 CMDFILE/CMD Disassembly - The Command File Utility (Model III)

CMDFILE/CMD reads command files (load modules) from disk and SYSTEM files from cassette into one memory image, so that several files or blocks can be joined into one; it can offset the image to load at another address, optionally with a small driver that moves it back and jumps to it, change the transfer address, and write the result to disk as a command file or to tape as a SYSTEM file. It can also take a single member out of a library file such as SYS6/SYS. The command is CMDFILE alone; everything else is asked by prompts (M-40-060). Most answers also take C, which starts CMDFILE again with an empty image, and E, which ends it. The same file runs on the Model I and the Model III: at its start it looks at ROM 0125H and, on the Model I, writes the Model I addresses into six operands and shortens the cassette prompt.

The file is a load module of 2931 bytes: a record of type 1FH with the text Copyright 1991 MISOSYS, Inc., All rights reserved, twelve load blocks for 5400H-5AA9H and 5AB7H-5F18H (2828 bytes) and the transfer address record for 5400H. The image is built from 6000H up to HIGH$, one byte at a time, in the load module format: each file read adds its records, and its transfer record is overwritten by the next file. Disk files are read and written a sector at a time through the buffer 5200H-52FFH below the program, with @VER for the output. Tapes are read and written with the ROM cassette routines; the Model III ROM asks the speed (H 1500 baud, L 500 baud).

What CMDFILE Does

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5400H - Entry: the Model Test and the Model I Operands

LDOS Ready loads CMDFILE/CMD at 5400H-5F18H and jumps to 5400H, the transfer address. The command is CMDFILE alone: everything else is asked by prompts (M-40-060). The same file runs on the Model I and the Model III. The byte at ROM 0125H is the I of Model III Basic in ROM 3.1 (49H); on the Model I ROM the byte is A3H. On the Model I the code stores 03H at 5D00H, which ends the cassette prompt after Ready cassette and enter, and writes the Model I addresses into six operands: ROM 0049H for the Model III speed question 3042H (5984H), HIGH$ 4049H for 4411H (596DH), @FEXT 4473H for 444BH (59A7H), the ROM keyboard driver 03E3H for 3024H in the debounce record (5ABBH), @DODIR 4463H for 4419H (5A3DH) and @CKDRV 44B8H for 4209H (5A38H). On the Model III all six keep the values of the file.

5433H - The Banner and the Log Question

The screen is cleared and the banner displayed (5AD0H: 1CH 1FH, the name and version, the copyright). The first question decides whether each Block loads from line of a disk read also goes to the printer: 5F73H is 00H for N, the answer letter (59H) for Y. As at every Y/N question of CMDFILE, C starts again at 5400H and E ends at @EXIT (5A6EH).

5448H - A New Memory Image

The memory image of the files read is built from 6000H up (5969H stores each byte one place after Register Pair HL). 5F61H holds the address of its last byte; 6003H is the value for an empty image, because a read starts four bytes before that address, over the transfer record of the file read before (5471H). The offset 5F6DH, the highest address loaded 5F69H and the lowest 5F6BH (FFFFH) start again, and so does the switch 5F75H that keeps one load block from being offset.

545EH - The Input Prompt

The stack is set again, since every error of a read comes back here by a JP. Input disk or tape (D,T,E,C,Q) takes six characters at 5F39H; the first, made a capital by AND 5FH, decides: ENTER alone ends the reads (54A1H), Q displays a directory (5A19H), C starts again, E ends, T reads a SYSTEM tape (549CH), D a file from disk (5489H). Any other letter repeats the prompt. Register Pair HL is set to four bytes before the last byte of the image: the read overwrites the transfer record of the file read before, so the files join into one load module.

5489H - Input from Disk and from Tape

D asks for the file specification (Enter input file filespec), which @FSPEC takes into the control block at 5F19H with the default extension CMD (5F16H); @OPEN opens it with the sector buffer 5200H. 5727H reads the records into the image and returns the address of its last byte, which is only then stored at 5F61H: a read that fails ends at 545EH and adds nothing to the image (as the manual says). T reads the next SYSTEM file of the tape through 5873H, with the same rule.

54A1H - The End of the Reads

ENTER alone at the input prompt ends the reads. With nothing read (the end pointer still 6003H) the text No file input, No file to output (5C90H, between rows of asterisks) is displayed and a new image is begun at 5448H.

54B4H - The New Base Address and the Offset

Program loads from base address XXXX to XXXX shows the lowest (5F6BH) and the highest (5F69H) address loaded, written into the text by 594DH. ENTER keeps the addresses (5596H). A new base address in hex gives the offset 5F6DH = base less the lowest address. When the image loads below 4200H the code asks Enter address to restrict offset: the address typed becomes the lowest address, and 565AH then offsets only the load blocks at or above it. ENTER at that question keeps the lowest address, so every block is offset, those below 4200H too, although the manual says CMDFILE never offsets a block below 4200H. The driver record 5ABDH gets its operands: LDIR (B0H) when the offset is positive, LDDR (B8H) when it is negative, the source (5AC3H) and the destination (5AC6H) of the move, the old transfer address (5ACEH), its own load address (5ABFH, the highest address + 1) and the count (5AC9H).

5543H - The Driver Questions and the Driver Record

Do you want to add the offset driver routine: N leaves the file offset without a driver and goes on to the transfer address question (5596H). Y makes the transfer address that of the driver, where it will load (the highest address + 1 + the offset). Then Do you want to disable the interrupts gives 5AC1H a DI (F3H) or a NOP (00H), and Do you want to disable the keyboard debounce adds the six byte record 5AB7H before the driver: a load of 3024H, the ROM keyboard driver, into 4016H, the keyboard device control block, as type 03H, a block that is not offset. The driver record (19 bytes) and a transfer record (5927H) go over the transfer record of the image, and the transfer address question is passed over (55B6H).

5596H - The Transfer Address

Enter new transfer address or <ENTER> to use XXXX shows the transfer address of the image (5F67H, from the last file read). A new address in hex is written into the last two bytes of the image, the address of its transfer record; 5F67H itself keeps the old address.

55B6H - The Output Prompt

Output to disk or tape (D,T,E,C) or <ENTER> to restart: ENTER and C start again at 5400H, E ends, T writes a SYSTEM tape (567CH), D a disk file (55D5H); any other letter repeats the prompt.

55D5H - Output to Disk

Enter filespec to write output takes the file specification into the control block at 5F19H (default extension CMD) and @INIT opens or creates it with the buffer 5200H and records of 256 bytes. The records of the image from 6000H are written one byte at a time by 5654H, which writes each full sector with @VER (write and verify, as the manual says). Type 01H load blocks get their address offset by 565AH; a type 03H record is written as type 01H with its address kept (560CH); the transfer record (type 02H) ends the file: the bytes in the last sector go into the end of file byte (FCB +08H, 5F21H), that sector is written and the file closed. Any other record (the copyright record 1FH, a name record 05H) is copied as it is. ENTER alone at the file specification prompt is not refused: @INIT then works on the control block as the last file left it.

5654H - Write a Byte; the Offset of a Load Address

5654H writes Register A through 5A03H, keeping Register Pair HL. 565AH fetches the load address of a block into Register Pair DE. When the switch 5F75H is set (a type 03H record) the address is kept and the switch cleared. Otherwise an address at or above the lowest address 5F6BH (the restrict address when one was given) gets the offset 5F6DH added; one below it is kept.

567CH - Output to Tape

Enter tape file name takes up to six characters at 5F59H; 597DH asks for the cassette and its speed (ROM 3042H: H 1500 baud, L 500 baud, kept at 4211H). The ROM writes the leader and the sync byte (0287H), then CMDFILE writes the SYSTEM format: 55H, the name in capitals padded with spaces to six, a 3CH block for each load block of the image (the count of data bytes, the load address with its offset, the data, and the checksum: the sum of the address bytes and the data), then 78H and the transfer address. Records of other types are passed over. ROM 022CH, called before each block, is JR 0212H (XOR A, RET) in ROM 3.1, so nothing is shown on the screen while the tape is written. ROM 01F8H turns the cassette off and ends with EI. Y at Module write is complete writes another copy with the same name.

5727H - Reading a Load Module from Disk

The records of the file are read one byte at a time by 59D1H and copied into the image by 5969H, type byte first: a load block (01H, 575CH), the transfer record (02H, 5844H, which ends the read), the end of a library member (04H, 5824H), an ISAM member header (08H, 57C3H) and the end of the ISAM directory (0AH, 57BAH). Any other record (the copyright record 1FH, a name record 05H) is copied as it is, with its length. 57E7H, the operand of CP 00H at 57E6H, holds the ISAM member wanted: 00H while none has been asked for.

575CH - Load Blocks and the Address Load Log

The length and the load address are copied; the address is compared with the lowest address 5F6BH, the last address of the block (the address + the data bytes - 1, a count of 00H giving 256) with the highest 5F69H. Block loads from XXXX to XXXX (5B51H) is displayed for every block, and also printed when the log switch 5F73H is set. Then the data bytes are copied by the loop at 5750H.

57BAH - The ISAM Members of a Library File

A library file (SYS6/SYS, SYS7/SYS) starts with the headers of its members, type 08H records of six bytes: the member number, the entry address, the record of the file where the member starts and the byte in that record. The first header asks File has ISAM overlays, enter # (two hex digits) and the number goes into 57E7H. A header of another member is passed over; the header of the member asked for gives the transfer address (5F67H), @POSN goes to its record and the byte pointer is set to the byte before the member, so the next byte read is its first record. The end of the directory (0AH) means the member is not in the file: Requested file is not a Command or System file. With FFH, as the manual says, no header matches, the 0AH record and the end of member records (04H) are copied like any other, and every member is read into the image. A member whose header gives byte 00H would be taken from the wrong place: the pointer 51FFH set at 5814H makes the next byte read another record (59E3H); no header on the diskette gives 00H.

5824H - The End of a Member and the Transfer Record

The end of a member (04H) ends the read as a transfer record would: the 04H is taken back out of the image and a transfer record 02H 02H with the entry address 5F67H is stored in its place (with FFH the 04H record is copied instead). A transfer record of the file (02H) must have the length 02H; its address goes to 5F67H. Both display Transfer address (entry point) is XXXX, printed too when the log switch is set, and return to the caller with Register Pair HL at the last byte of the image.

5873H - Input from Tape

597DH asks for the cassette and its speed; ROM 0296H finds the leader and the sync byte, and the bytes are read until the 55H of a SYSTEM file. The image gets a name record: type 05H, length 06H and the six characters of the name, which are also copied over FILNAM at 5B6FH for the display. Each 3CH block becomes a load block (01H, the count + 2, the address, the data) and its checksum is compared; a wrong checksum or a mark that is neither 3CH nor 78H turns the cassette off and ends with Tape checksum error detected, reread tape! The 78H mark is followed by the transfer address (ROM 0314H), which gives a transfer record. As the manual says, no Block loads from line is shown for a tape. Found in the code: a block whose address becomes the new lowest address (58D4H) is not compared with the highest address, so the end of the first block of a tape is never counted, and a tape of one block leaves the highest address at 0000H for the base address prompt and the driver.

5927H - The Transfer Record, a Word and the Hex Digits

5927H stores a transfer record (02H, 02H and the address at 5F67H) in the image. 593CH reads a word of the file into Register Pair DE, storing both bytes in the image. 594DH writes the word whose high byte is at Register Pair HL (the low byte at HL - 1) as four hex digits at Register Pair DE: 5950H does one byte, high digit first, and its second digit runs into 5960H, whose RET goes back into 5950H for the second byte; ADD A,90H / DAA / ADC A,40H / DAA makes a digit 0-FH into its character.

5969H - Storing in the Image, the Prompts and the Answers

5969H stores Register A one byte after Register Pair HL and compares the new address with HIGH$ (4411H; 4049H on the Model I): only when they are equal is Out of memory! displayed and the read ended at 545EH, without the part of the file read so far. 597DH is the cassette prompt: on the Model III the ROM's speed question 3042H (H 1500 baud, L 500 baud, ENTER as H; the choice kept at 4211H), on the Model I a wait for any key (ROM 0049H). 598BH takes a file specification of up to 32 characters, @FSPEC and @FEXT CMD; 59ABH an answer of up to 6 characters. BREAK at either ends CMDFILE through @EXIT. 598BH does not test @FSPEC, and returns at once for ENTER alone, leaving the control block 5F19H as it is.

59BCH - The File: Open, Errors and One Byte at a Time

59BCH opens the input file with the sector buffer 5200H; the byte pointer 5F5FH starts at 52FFH, so the first read (59E0H) loads a sector. 59C9H displays the error in Register A (OR C0H: the short message, and @ERROR returns) and goes back to the input prompt. 59D1H reads a byte and turns the end of the file in the middle of a record into Requested file is not a Command or System file. 59E0H takes the next byte from the buffer and reads the next sector with @READ when the pointer passes 52FFH; at the end of the file (error 1CH or 1DH) it closes the file and returns the CARRY FLAG. 5A03H puts a byte into the buffer and writes the full sector with @VER. 5A14H is error 20H, Illegal drive number, for the Q answer.

5A19H - The Directory: Q

Q at the input prompt displays a directory with @DODIR: Qd for drive d (0-7; Q alone is drive 0), Qd/ext for the files of drive d whose extension matches ext (Register B = 02H, the mask after the slash). A drive that is not 0-7, or one @CKDRV finds not ready, gives error 20H (Illegal drive number) and the input prompt; the manual says the entry is ignored. When Q ends the line Register Pair HL passes the 0DH, and the byte after it, left from an earlier answer, is tested for the slash.

5A42H - Hex Numbers, Answers and Capitals

5A42H converts the hex digits at Register Pair DE (Register A the first) up to the 0DH into Register Pair HL, the last four digits counting; any other character returns the CARRY FLAG. 5A5DH turns one character 0-9, A-F into its value with the CARRY FLAG for anything else. 5A6EH asks a Y/N question: C starts CMDFILE again, E ends it, N returns the CARRY FLAG, Y returns NO CARRY with Register A = 59H; any other answer, or ENTER, asks again. 5A97H is 59ABH keeping Register Pair DE. 5A9DH writes a character to the tape as a capital.

5AAAH - The Debounce Record and the Offset Driver

5AAAH-5AB6H are not in the file (the load blocks end at 5AA9H and start again at 5AB7H). 5AB7H-5ABCH is the record that disables the keyboard debounce, copied into the image before the driver (5572H): type 03H, length 04H, the address 4016H and the word 3024H. Written as type 01H with its address kept, it loads 3024H, the ROM's keyboard driver (03E3H on the Model I), into 4016H-4017H, the driver address of the keyboard device control block, in place of 41EDH, SYS0's driver that calls @KITSK (4285H) first. 5ABDH-5ACFH is the driver record, a load block of 17 bytes after its type and length: at the byte after the program it runs DI or NOP, moves the program from where it was loaded to where it belongs with LDIR or LDDR, and jumps to the old transfer address. Its operands are written by 54B4H-5560H.

5AD0H - The Texts

The banner, the prompts and the messages, ended by 03H (the cursor stays after the text, the answer follows) or 0DH (the end of the line). The XXXX places are written by 594DH; FILNAM at 5B6FH gets the name of a tape. 5F16H-5F18H is the default extension CMD.

5F19H - The Cells Beyond the File

The file control block, the answer buffers, the tape name, the pointers and the addresses of the image, the switches; then the memory image itself from 6000H to HIGH$. Below the program, 5200H-52FFH is the sector buffer of the file read or written and the stack grows down from 53FFH.