TRS-80 DOS - NEWDOS/80 v2.0 for the Model I - DIRCHECK/CMD Disassembled

DIRCHECK/CMD

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NEWDOS/80 v2.0 DIRCHECK/CMD Disassembly - Directory Check and Listing (Model I)

DIRCHECK/CMD is the NEWDOS/80 utility that tests a diskette's directory and lists it (manual section 6.4). It asks OUTPUT TO PRINTER? and WHICH DRIVE CONTAINS TARGET DISKETTE?, reads the BOOT sector to find the directory (bytes 0 and 1 must be 00H and FEH; byte 2 is the directory's first lump, else lump 17 is assumed), reads the GAT, the HIT and the FDE sectors, and reports every inconsistency it finds before it lists the files. At the end it offers N (exit to DOS at 402DH), Y (another diskette, same printer answer), I (start again), W (rewrite every directory sector with the directory mark) and C (clear the unused directory entries, then do the same as W).

The file loads in two parts: a 32-byte FCB at 5200H-521FH and the program at 5276H-6111H (sixteen load records), with the transfer address 5281H. 5220H-5275H is not in the file and holds work areas. Everything DIRCHECK reads from the diskette goes into memory above the file, at 61BAH-6BB9H; the stack grows down from 61BAH.

All disk access goes through one FCB (5200H) with FCB+0 bit 1 set, so that NEXT (520AH-520BH) names a sector of the whole diskette and SYS0 4436H (READ) and 443CH (WRITE with verify) work on diskette sectors directly. Directory sectors carry the directory mark, so their read must return DOS error 06H; a sector read with no error is unprotected, which DIRCHECK reports once before the list and once after it.

The page shows every byte of the file once, in address order. Calls into SYS0 and the ROM are linked to their pages.

What Is Checked, in Order

Memory Map

Variables

Routines

5200H - The Diskette FCB

The first load record (5200H-521FH) is a 32-byte FCB that DIRCHECK hands to the DOS read routine at 4436H and the write routine at 443CH. It is set up as an open FCB with FCB+0 bit 1 set, so NEXT names a sector of the whole diskette (counted from 0) instead of a sector of a file. DIRCHECK stores the target drive at 5206H, the buffer address at 5203H-5204H and the sector to read or write at 520AH-520BH before each call.

5220H - Work Areas Not in the File

The file has no load record for 5220H-5275H, so these bytes hold whatever was in memory when DIRCHECK was loaded. Every one of them is written before it is read.

5276H - Variables in the File

The last bytes of the second load record's lead-in (5276H-5280H) are variables that DIRCHECK changes while it runs. The program starts at 5281H, just after them.

5281H - Entry Point: The Printer Question

DOS loads DIRCHECK/CMD and jumps to its transfer address 5281H. The reply I at the end (5958H) also comes back here. The program sets its own stack, then asks whether the output goes to the printer until exactly one character is typed and it is N or Y.

5297H - The Drive Question

The reply Y at the end (594BH) comes back here to check another diskette with the same printer answer. The drive number is typed in decimal; anything other than digits, or a value above 255, repeats the question.

52B7H - Start a Check: Clear the Map and Read the BOOT Sector

The W and C functions come back here (592FH) to check the same diskette again after they have rewritten the directory. The granule map is cleared, the FCB is pointed at sector 0, and the BOOT sector is read into 63BAH.

52FFH - Read the GAT, the HIT and the First Two FDE Sectors

Register A holds the lump where the directory starts. The directory's first sector number is computed from it and saved, then the first four directory sectors are read: the GAT into 63BAH, the HIT into 64BAH, and FDE sectors 0 and 1 into the two FDE buffers 61BAH and 62BAH.

5333H - Directory Size and Diskette Size

HIT byte 1FH holds the number of extra FDE sectors (0, 5, 10, 15 or 20). From it DIRCHECK computes the number of directory sectors for the W and C functions, then the number of granules on the diskette from the PDRIVE tracks and sectors per track.

5367H - Is There a Lockout Table?

GAT bytes 60H-BFH hold the lockout (existence) table only when the diskette has 96 lumps or fewer and GAT byte 60H is not FFH; otherwise the allocation bits run on to byte BFH. The GAT check at 53C0H is patched to match: its instruction at 53E5H becomes LD A,17H (so the lockout test at 53E7H runs) or stays JR 53FEH (the lockout test is skipped), and the number of GAT bytes checked, the operand at 53E1H, becomes 60H or C0H.

5383H - Check the Directory and List It

The diskette's name and date are output, then the checks run in order: the GAT (53C0H), every directory entry (543AH), the HIT (5535H), every granule (554EH), the file list (5625H) and the free and locked-out counts (571BH).

53C0H - Check the GAT

Called from 53A4H. The GAT (at 63BAH) has one byte per lump, one bit per granule (bit 0 = the lump's first granule). For every granule that exists on the diskette, the map byte at 65BAH gets bit 6 if the GAT marks it allocated and bit 7 if the lockout table (GAT byte + 60H) marks it locked out. Bits for granules that do not exist (past the lump's granules per lump, or past the end of the diskette) must be set in both tables; a clear one is reported as a bad GAT byte, with the offset of the byte in hexadecimal. The number of GAT bytes checked (the operand at 53E1H) and whether the lockout test runs (the opcode at 53E5H) were set at 5367H-5380H.

5431H - Report a Bad GAT Byte

Called from 5421H and 5429H with Register A = the offset of the bad byte in the GAT.

543AH - Check Every Directory Entry

Called from 53A7H. Every DEC from 00H up is examined until 586AH reports that the entry's FDE sector is past the end of the directory. An FPDE in use must have its name's HIT code in the HIT (the HIT copy's byte is then cleared, so 5535H can report the bytes no entry claims); each of its extent elements must name granules that exist, and those granules are marked in the map (bit 5, and bit 4 when a second file claims one); an FEH element links to an FXDE, which must be in use, be an FXDE and link back. An FXDE met on its own is checked at 54E1H. Every complaint goes out through 582EH as the FPDE's name, its DEC in hexadecimal and a message.

54E1H - An FXDE on Its Own

Reached from 544FH with Index Register IY on an FXDE in use, found while stepping through the DECs. Its bytes +02H to +15H must be 0 (an FXDE holds only its flags, the back link and extent elements); its HIT byte must not be 0; its back link must name an entry in use whose FEH element links to this FXDE.

5535H - Check the HIT

Called from 53AAH. The directory pass at 543AH cleared the HIT copy's byte of every entry it accounted for, so any byte still not 0 belongs to no entry and is reported with its offset in hexadecimal. Byte 1FH (the count of extra FDE sectors) is skipped.

554EH - Check Every Granule

Called from 53ADH. Each granule's map byte now holds bit 7 (locked out), bit 6 (allocated in the GAT), bit 5 (claimed by a file) and bit 4 (claimed by more than one file). A locked-out granule must be allocated and not claimed; any other granule must be allocated exactly when one file claims it. A granule that breaks the rule is reported as lump,granule in hexadecimal with a message, followed by every file whose extents include it.

55DCH - Output an Owner

Called from 55CDH when a file's extent includes the granule being reported. The registers are saved by 5A90H and restored at 5AADH, so the element loop continues where it was.

5625H - List the Files

Called from 53B0H. One line per FPDE in use: the name/extension, S (system file) and I (invisible) at column 14, P= and the access level when the update password is not blank and either the access password is not blank or the level is not 0, EOF = sectors/bytes at column 21 (in decimal), the number of extent elements at column 38 with EXTS, and the sectors the extents cover at column 47.

571BH - Count the Free and Locked-Out Granules

Called from 53B3H. Every granule's map byte is examined: a locked-out granule counts in Register Pair DE of the main register set, a granule that is neither locked out nor allocated counts in Register Pair DE of the alternate set. Both counts are output in decimal.

5758H - Decode an Extent Element

Called from 546EH and 55C4H with Register A = byte 0 of an extent element (the lump where it starts) and Index Register IY +16H/+17H on the element. Byte 1 holds the first granule within the lump in bits 5-7 and the number of granules minus 1 in bits 0-4. Returns Register Pair DE = the diskette granule number where the element starts, Register C = its number of granules and the NZ FLAG; or, for a bad element, Register A = 00H, the Z FLAG and Register Pair HL pointing to the message.

5786H - Compute an FPDE's HIT Code

Called from 5452H with Index Register IY on an FPDE. The 11 characters of the name and extension (bytes +05H to +0FH) are combined: A = 0, then for each character XOR it and rotate left; a result of 00H becomes 01H, because 00H in the HIT means a free entry. The code is stored at 527CH.

579EH - Compare the HIT Byte

Called from 5455H and 54F1H. Returns Register Pair HL pointing to the byte of DIRCHECK's HIT copy for the DEC at 527AH (the HIT byte's offset is the DEC), and the Z FLAG set if it equals the code at 527CH.

57AEH - Output the Name of the Entry at 5279H

57AEH first finds the entry for the DEC at 5279H (Index Register IY is changed); 57B1H outputs the name and extension of the entry at Index Register IY, leaving out spaces and putting a / before the extension when it is not blank.

57E0H - Read an FDE Sector

Called from 587EH and 58B1H with Register A = a DEC (bits 0-4 are its FDE sector) and Register Pair HL = the buffer. The FDE sector must exist: sectors 0-7 plus the extra sectors named by HIT byte 1FH. Returns the Z FLAG after reading the sector into the buffer, or the NZ FLAG (with the CARRY FLAG) if the sector is past the directory. Register Pairs BC and DE are kept.

5801H - Read a Directory Sector

Called with Register Pair HL = the buffer and NEXT set in the FCB. A directory sector is written with the directory mark, so its read must return error 06H. Any other error ends the function; a read without the error means the sector is unprotected, which is reported once per diskette.

5820H - Read a Sector

Called with Register Pair HL = the buffer. The sector named by NEXT (520AH-520BH) of the drive at 5206H is read through the DOS; NEXT goes up by 1 after a read with no error or with error 06H.

5829H - Report a Complaint About an Entry

5829H is entered with Register A = P or X: it completes the message at 5F8AH as FPDE or FXDE HAS BAD CODE IN "HIT" SECTOR. 582EH is entered with Register Pair HL on any message. The line is the name of the entry at 5279H, three spaces, its DEC in hexadecimal, three spaces and the message. 583FH is entered with Register A = a number to show in hexadecimal before the message.

584DH - Report a Granule

Called from 5599H with Register Pair HL = the granule's number on the diskette and Register Pair DE = the message. The granule is shown as bb,r: the lump number in hexadecimal and the granule within the lump.

5867H - Find the Entry for a DEC

5867H loads Register A from 5279H. 586AH and 5893H find the entry for the DEC in Register A (bits 0-4 the FDE sector, bits 5-7 the entry, so A AND E0H is the entry's offset in the sector). 586AH reads a missing sector into the first FDE buffer (61BAH); 5893H looks in both buffers and reads a missing sector into the second (62BAH), so an FPDE in the first buffer stays there while its FXDEs are read. Both return Index Register IY on the entry and the Z FLAG, or the NZ FLAG if the sector is past the directory. Register Pairs DE and HL are kept.

58BDH - The Next DEC

Returns Register A = the DEC after the one at 5279H: the next entry in the same FDE sector, or entry 0 of the next sector after entry 7. 586AH later finds whether that sector exists.

58C5H - The W and C Functions

Reached from 5950H (reply W) and 5955H (reply C) with Register A = the reply letter. Both need SYSTEM option BK = Y and a known directory size. Every directory sector of the last diskette checked is read and written back with the directory mark and a verify read, so that it reads as protected; for C, every FDE entry not in use is also cleared to zeros before the write (the GAT and HIT, the first two sectors, are left as they are). The check then runs again from 52B7H.

5932H - Function Completed: What Next?

Reached from 53BDH at the end of a check. 5935H is also where every ending comes: 5ACBH jumps there after FUNCTION TERMINATED. The output goes back to the display only, and the REPLY menu is repeated until one of N, Y, W, C or I is typed.

595FH - Output a Message and a Blank Line

Called from 5938H with Register Pair HL = a message ended by 03H.

5964H - Unreferenced Code: A Y or N Question

Nothing jumps to, calls or points to 5964H. The routine would display the message at Register Pair HL until exactly one character is typed and it is N (Z FLAG) or Y (NZ FLAG); the program asks its questions at 5281H and 593BH instead.

5974H - Output Messages and Carriage Returns

5974H makes the display the only output device first. 5977H outputs a message ended by 03H and a carriage return; 597AH outputs one carriage return; 597CH outputs Register B carriage returns; 5984H outputs a message ended by 03H. Every character goes through 5A27H.

598EH - Unreferenced Code: Clear the Display

Nothing jumps to, calls or points to 598EH or 5996H. 598EH would output 1CH (cursor home) and then 1FH (clear to the end of the screen); 5996H would output only 1CH.

599BH - Output Characters, Move to a Column, Output Spaces

599BH outputs Register B characters from Register Pair HL. 59A3H outputs spaces until the line reaches column Register B (counted from 0), using the positions left at 5278H; nothing is output if the line is already there or past it. 59AEH outputs Register B spaces.

59B6H - Show a Question and Read the Reply

Called with Register Pair HL = the message. The reply is read into 5220H with the ROM's line input and changed to upper case. Returns Register Pair HL = 5220H, Register A = the first character, Register B = the number of characters typed, and the Z FLAG if the line is empty.

59D1H - Choose the Output Devices

The displacement byte of the JR at 5A6CH (5A6DH) says where output goes: 05H skips the printer call at 5A6EH (display only, the value in the file); 00H falls into it (printer and display). 59D1H sets 05H, 59DBH sets 00H. When the setting changes, a carriage return first ends the line on the old devices. Register Pair AF is kept.

59EFH - Unreferenced Code: At the Top of a Page?

Nothing calls 59EFH except the unreferenced routine at 5A1CH. It would return the Z FLAG when the printer page line count at 5277H is 3CH (60), that is at the top of a page.

59F5H - Count a Line

Called from 5A44H after every carriage return. With the printer in use, the page line count at 5277H goes down by 1; when it reaches 0 it is reloaded with 3CH (60), after six carriage returns if the byte at 5276H is not 0 (it is 00H and never written). In every case the positions left on the line (5278H) are set back to 40H (64).

5A1CH - Unreferenced Code: Feed to the Top of the Page

Nothing jumps to, calls or points to 5A1CH. It would output carriage returns until 59EFH reports the top of a printer page, or until Register C (a limit) runs out.

5A27H - Output a Character

Every character DIRCHECK outputs comes here in Register A. A character other than 0DH goes out through 5A69H and uses up one of the 64 positions of the line (5278H); when none are left, or for 0DH, the line is ended: a space first if nothing was output on it, then 0DH, then 59F5H counts the line. After each line the keyboard is checked: BREAK waits until ENTER or up-arrow is pressed, and up-arrow ends the function with FUNCTION TERMINATED. Register Pairs AF, BC and HL are kept.

5A69H - Send a Character to the Output Devices

Called from 5A27H and 59F5H with Register A = the character. 5A90H saves Register Pairs HL, DE, BC and Index Registers IX and IY; the JUMP to 5AADH restores them. The printer gets every character (5A6EH) when the displacement at 5A6DH is 00H; the display gets every character except a carriage return that is not needed (5A73H).

5A90H - Save the Registers and Continue

Called by a routine that wants its registers back when it ends: 5A90H takes the return address (the address after the CALL 5A90H), saves Register Pairs HL, DE, BC and Index Registers IX and IY, and jumps to that address. The routine ends by jumping to 5AADH, which restores them in the reverse order and returns to the routine's own caller. Used at 55DCH and 5A69H.

5AB5H - Upper Case

Called from 59C3H with Register A = a character; a lower case letter (61H-7AH) is changed to upper case by subtracting 20H.

5ABEH - End the Function

5ABEH is entered with a DOS error code in Register A: SYS0 4409H displays its message. 5AC5H is entered with Register Pair HL on a message to output. Both, and 5A67H, reach 5AC8H, which outputs FUNCTION TERMINATED and goes to the reply menu.

5ACEH - Multiply

5ACEH multiplies Register A by Register L (Register H is cleared); 5AD0H multiplies Register A by Register Pair HL. The 24-bit product is returned in Register A (high byte) and Register Pair HL (middle and low bytes). Register Pairs BC and DE are kept. The work is done by 5AD9H.

5AEEH - Divide

5AEEH divides Register Pair HL by 5; 5AF0H divides Register Pair HL by Register A. Register Pair HL returns the quotient and Register A the remainder, with the Z FLAG set if the remainder is 0. Register C is left holding the divisor and Register B holds 00H.

5B01H - Output a Byte in Hexadecimal

Called with Register A = the byte. The two digits are written at 5269H-526AH and output. Register Pairs BC and HL are kept.

5B29H - Convert a Number to Decimal

5B29H clears Register D so Register E is converted; 5B2BH converts Register Pair DE (0-65535) to five digits at 5269H-526DH and changes the leading zeros (up to four) to spaces. Returns Register Pair HL = the first digit that is not a leading zero, Register B = the number of digits from there, and Register Pair DE = the caller's Register Pair HL.

5B68H - Unreferenced Byte and the Powers of Ten

5B68H is a RET that nothing reaches (5B67H has already returned). 5B69H-5B70H is the table 5B41H uses.

5B71H - Messages

Every message ends with 03H; 0DH inside a message starts a new line. 5984H outputs them character by character through 5A27H.

603AH - Unused Bytes

The rest of the last load record is zeros. Nothing reads them as data; the stack (from 61BAH down) can reach down into them.