LDOS 5.3.1 for the Model III - QFB/CMD Disassembled

QFB/CMD

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LDOS 5.3.1 QFB/CMD Disassembly - The Quick Format and Backup (Model III)

QFB/CMD, the LDOS Quick Format and Backup, makes a mirror image copy of a floppy disk in one pass: QFB :s :d (QUERY, ALL, V1, V2) (M-40-060, where DISKCOPY is the version 6 utility of the same kind). For each cylinder it formats the destination with the Write Track command, reads the source cylinder into memory, writes it and, with V1 (the default), reads it back and compares the sum of its bytes with the source's. With V2 the whole destination is read back once more at the end. Only the cylinders that hold data are read and written unless ALL is given; QUERY asks the three questions. The source must be a floppy (or a drive with its own driver, a MemDISK), the destination a floppy of the same size; its drive code table takes the source's density, sides and cylinders.

The file is a load module of 4121 bytes without a copyright record: seventeen load blocks for 5200H-5697H, 570CH-5CF0H and 5CF3H-6246H (4049 bytes) and the transfer address record for 5200H. One file serves the Model I and the Model III: the start-up tests the ROM and stores the Model I addresses of four system cells into the operands. Six format tables describe the tracks of 5 and 8 inch disks in single and double density, two of them with a closer interleave for the FAST speed. While QFB copies, the RST 38H vector at 4012H holds a RET, so the clock stops; the drive code tables are put back as they were at the end.

What QFB Does

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5200H - The Start: the Banner, the Parameters and the Drives

LDOS Ready loads QFB/CMD at 5200H-6246H and jumps to 5200H, the transfer address, with Register Pair HL at the rest of the command line. The command is QFB :s :d (parameters) (M-40-060, version 5): the source and destination drives, and QUERY (Q), ALL (A), V1 and V2. 6201H fits the file to the Model I or the Model III and saves the drive code tables; the parameters in parentheses go to @PARAM, and the drive digits before them are collected at 5684H (the source) and 5685H (the destination). A drive that is not given is asked for.

5234H - Asking for the Drives

A drive missing from the command line is asked for: Source drive ? takes one character, Destination drive ? up to ten. The source must differ from every destination; a bad entry clears the digit and asks again. BREAK at a question ends QFB through 5C37H. The questions of QUERY follow.

5282H - The Questions of QUERY

With QUERY (or Q) the three questions are asked for each of ALL, V1 and V2 whose low byte is still 01H, the mark of a parameter not given on the command line; the answer (00H for N, FFH for Y) goes into its high byte. @PARAM stores FFFFH or 0000H for a parameter that is given, so that it is not asked. Then the ALL byte 567DH is complemented: from here on FFH means copy only the cylinders in use.

52BDH - Loading the Disks and the Source

After the prompt, ENTER starts the copy and BREAK ends QFB. The source drive must be a floppy (no hard disk, bit 3 of byte +03H of its drive code table) and must pass the index pulse test of 5A04H. Its boot sector gives the directory cylinder, and the allocation table there, read with the deleted data mark that a directory sector must have, gives the cylinders and the sides. A disk whose table has bit 4 of byte CDH set is refused. The answer ENTER of 54C1H and a source error (55EBH) come back to 52CFH.

533AH - The Destination Drives

Each destination digit is copied to 5687H and checked by 535FH: the drive must not be write protected or a hard disk, and must be of the same size as the source; its drive code table then takes the source's density, size, sides, cylinders and sectors. The tables of the drives go to 5689H (the source) and 568BH (the destination). The code is written for a list of destinations ended by 00H, but 5578H takes only one.

53C4H - The Copy, Cylinder by Cylinder

For each cylinder from 0 to the highest (byte +06H): every destination is formatted (5A33H; cylinder 0 only after the index pulse test of 5A04H), then the source cylinder is read into memory from 6700H (60CFH), then it is written to each destination (5B6FH) and, with V1, verified at once (5B90H); a verify error writes the cylinder once more. A destination with an error is dropped with the message Bad disk in drive (55F6H). The cylinders that are not in use are not read or written unless ALL was given. 4012H gets C9H, a RET for the RST 38H interrupt: the clock interrupt is off while QFB copies. SHIFT @ pauses, BREAK stops (61C1H).

5462H - The Second Pass and the End

With V2 each destination is read back from its highest cylinder down to cylinder 0, and the sums of the copied cylinders are compared (5B90H). An error of this pass stops the pass for that disk but gives no message and does not drop it. Then the destinations that are left are counted into 5692H, the disks made since QFB started, and the count is shown with Duplication complete. ENTER copies again to new disks with the same drives and parameters, R starts again with the questions, BREAK ends QFB.

54DAH - The Next Destination

569BH is the index of the current drive in the table at 5689H: 0 the source, 1 the destination. 54DAH steps to the next index whose digit in the copy at 5687H is not 00H (a dropped destination has 00H), puts the drive number into the driver call (5CBEH) and points Index Register IY at the drive's table, with the NZ FLAG. At index 2 it puts 0 back and returns with the Z FLAG.

5507H - The Memory Test and the Format Table

The cylinder buffer runs from 6700H, one page of 256 bytes for each sector of the cylinder, and HIGH$ must not be below its end plus two pages. The sectors are taken from byte +07H of the source's drive code table with the mask 0FH, which drops bit 4: a track of 18 sectors (11H) counts as two, one of 30 (1DH) as 14. The format table is chosen by bit 5 (8 inch) and bit 6 (double density) of byte +03H, and for double density by bit 3 of SFLAG$ (FAST), which gives the tables with the closer interleave.

5564H - A Decimal Number Not Used

5564H takes the decimal digits at Register Pair HL into Register E (the value times ten plus the digit, until a character that is not a digit). No instruction of QFB calls it.

5577H - Collecting the Drive Digits

5577H starts at Register Pair HL, 5578H at the character after it. Colons, spaces and other characters below the digit 0 are passed over; the digits 0-7 are stored at Register Pair DE until 5686H. The left parenthesis or ENTER ends the search with the Z FLAG; a character from 8 up gives the NZ FLAG, the error; when 5686H is reached the rest is not looked at.

559BH - The Questions and the Answers

559BH asks a question with Y or N for an answer: FFH for Y, 00H for N, any other answer asks again. 55B2H displays the question at Register Pair HL and takes a line of up to Register B characters at 56ECH by the ROM's line input; it returns with the CARRY FLAG for BREAK, or with the first character as a capital in Register A.

55C2H - The Errors of a Step

5696H counts the errors of the step just made (5CCAH). After the source read (55C2H) one more read of the cylinder is made; if that fails too, Source disk error is shown and ENTER starts the copy again from the source's boot sector (BREAK ends QFB). After a format, write or verify of a destination (55EEH), the destination is dropped: its digit in the copy at 5687H becomes 00H and Bad disk in drive is shown with the digit.

5618H - The Errors That End QFB

Four texts, displayed by @LOGOT before 5C37H puts the system back and ends QFB. The entries 561CH, 5620H and 5624H lie inside LD IX instructions: each DD byte makes the LD HL after it a part of an LD IX, which loads Index Register IX and changes nothing that counts.

562DH - The Parameter Table and the Values

The table of @PARAM in the form of LDOS 5: six characters of the name, padded with spaces, and the address of the value, ended by 00H. @PARAM stores FFFFH (or 0000H for =N) at the address of each parameter given. 565EH puts the defaults back for the restart R; 5669H clears the drives and the tables of drives. The values in the file are those of a first start: each parameter's low byte 01H means not given, the high byte is its default.

570CH - The Texts

The banner, the questions and the messages of QFB. A text ends with 0DH (a new line after it) or 03H (the cursor stays after it); 1CH puts the cursor at the top left of the screen and 1FH clears the screen from the cursor down. The count of the disks is written into the text at 596FH and the letter s at 5979H.

5A04H - The Index Pulse Test

A drive is ready when its index pulse (bit 1 of the controller's status) goes off, on and off again within 1000H status reads after a restore. A drive with its own driver (bit 4 of byte +04H, a MemDISK) is taken as ready at once. 5A21H counts Register Pair BC down; at 0000H it drops its return address and gives the NZ FLAG and Register A = 20H to the caller of 5A04H.

5A33H - Formatting a Cylinder

The format table (5A38H, chosen by 5507H) starts with the sectors of a track, the step of the sector numbers from one cylinder to the next, the sector numbers in the order on the track and the bytes that wrap their pointer back. The program after them builds the image of one track at 6700H: a count byte and a value give the value that many times (00H 256 times); F1H and F2H repeat what is between them once for each sector; F3H keeps the place of the sector's three identification bytes in the list at 6600H; F4H ends the track with 256 bytes FFH and leaves the order of the sectors for the read and the write; F5H with a count and two bytes gives the two bytes that many times (6DH B6H, the double density fill). Then each side is written with the Write Track command.

5B57H - Is the Cylinder Copied?

5B57H returns the Z FLAG when the cylinder at 569AH is not copied: when the source's allocation table (6500H) gives it the same bits in use (65xxH) as locked out (6560H + the cylinder). With ALL every cylinder but cylinder 0 is copied without the test. 5B6FH writes, 5B81H reads and 5B90H verifies a cylinder through 5BA6H, which goes through the sectors in the order the format table gives.

5C18H - The End of QFB

5C18H and 5C1BH display an error with @LOGOT, then Program aborted! and, when disks were made, their count. 5C37H puts the RST 38H vector back (and EI), turns the cursor on, puts the eight drive code tables back as they were at the start (each keeps the cylinder its head is on), asks for the system disk and ends through @EXIT. The note that the clock is no longer right is shown every time.

5C7AH - The Calls of the Disk Driver

Each entry loads Register B with a function of the driver and goes through 5CBCH: interrupts off, Register C the drive number (5CBEH), CALL 5CC8H, JP (IY), which jumps to the driver through byte +00H of the drive code table; Register Pair HL, Register Pair DE and Register Pair BC come back as they were. The functions of the Model III's floppy driver: 00H nothing, 01H select, 04H restore, 05H step in, 06H seek, 07H wait until not busy, 09H read, 0AH verify, 0CH and 0DH write, 0EH write with the deleted data mark, 0FH Write Track. 5CCAH counts an error, 5CD2H and 5CDFH show a cylinder as two digits.

5CF3H - The Format Table: 5 Inch Single Density

10 sectors a track, the sector numbers two apart on the track (5538H): the count of the sectors, the step from cylinder to cylinder, the sector numbers as they follow one another on the track, the wrap bytes, the program of the track and, after F4H, the order in which the sectors are read and written.

5D34H - The Format Table: 5 Inch Double Density

18 sectors a track, the sector numbers three apart (5556H): the count of the sectors, the step from cylinder to cylinder, the sector numbers as they follow one another on the track, the wrap bytes, the program of the track and, after F4H, the order in which the sectors are read and written.

5D90H - The Format Table: 8 Inch Single Density

16 sectors a track (553FH): the count of the sectors, the step from cylinder to cylinder, the sector numbers as they follow one another on the track, the wrap bytes, the program of the track and, after F4H, the order in which the sectors are read and written.