TRS-80 DOS - VTOS v4.0.2 for the Model I - SYS6/SYS Disassembled

SYS6/SYS - Library Command Overlay

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VTOS 4.0 SYS6/SYS - Library Command Overlay (Model I)

SYS6/SYS holds the library commands of VTOS 4.0: ALLOC, APPEND, ATTRIB, AUTO, BUILD, CHAIN, CLOCK, COPY, DATE, DEBUG, DEVICE, DIR, DUMP, FILTER, FREE, KILL, LIB, LINK, LIST, LOAD, MEMORY, PRINT, PROT, PURGE, RENAME, RESET, ROUTE, RUN, SET, SPOOL, SYSTEM, TIME, TRACE, VERIFY and XFER, plus SYSGEN (run by SYSTEM (SYSGEN)) and O!, which displays the copyright notice. SYS1 finds the command in its command table (4EADH) and calls SYS6 with RST 28H, A = 88H and Register B = the command's ISAM number (SYS1 4EA2H).

SYS6/SYS is a partitioned data set (PDS): a directory of 37 ISAM entries, each giving an ISAM number, an entry (transfer) address and a triad pointer to the member that holds the code, followed by the 29 members. Only the member for the command is loaded. Every member loads at 5200H, except SET/FILTER, which loads at 5A00H, and each command is entered at its own address, so one member can serve several commands:

• DATE (15H, 5200H) and TIME (16H, 522DH)
• DEBUG (14H, 5200H), CLOCK (17H, 5241H), TRACE (1AH, 5257H) and VERIFY (1BH, 5267H)
• APPEND (31H, 5200H) and COPY (32H, 5270H)
• LIST (41H, 5200H) and PRINT (42H, 5206H)
• SET (65H, 5A01H) and FILTER (66H, 5A00H)
• LOAD (81H, 5200H) and RUN (82H, 520DH)
• SPOOL (A2H) is entered at 5208H.

The sections below follow the order of the members in the file. Each gives the member's offset in the file, what it loads, and its code. Bytes that belong to a member's work areas but are not loaded from the file (FCBs, buffers, gaps between load blocks) are shown as DEFS rows without bytes.

About this disassembly

How the SYS6 File Is Processed into ISAM Entries and PDS Members

05 06 53 59 53 36 20 20
1F 91 0D 2A 20 2A 20 2A 20 4E 20 4F 20 54 20 49 20 43 20 45 20 2A 20 2A 20 2A 0D ...
08 06 11 00 52 01 00 C9
08 06 15 00 52 02 00 1D
08 06 16 2D 52 02 00 1D
08 06 13 00 52 02 00 B2 ...

The directory follows the header record (05H, 0000H-0007H) and the copyright record (1FH, 91H bytes of data, 0008H-009AH). Each entry is eight bytes: type 08H, length 06H, the ISAM number, the entry address and the triad. The 37 entries run from 009BH to 01C2H.

AUTO stores a command line that VTOS runs every time the system starts. The member loads at 5200H-524CH (77 bytes) and is entered at 5200H with HL pointing to the rest of the command line after AUTO. It copies 32 bytes from there into the GAT sector of drive 0 at offset E0H (42E0H while the sector is in the buffer at 4200H) and writes the sector back. AUTO with nothing after it stores just the carriage return, which leaves no command. Error codes returned: 14H (GAT read error) and 15H (GAT write error).

5200H - AUTO Command

Read the GAT of drive 0, put the command line into it at offset E0H and write it back.

521CH - Error Exit

Reached with the error code in Register A.

5221H - Read the GAT

Reads sector 0 of the directory track of the drive in Register C into 4200H. Returns Z if it was read, or NZ with Register A = 14H (GAT read error). DE and HL are preserved.

5234H - Write the GAT

Writes the buffer at 4200H back to sector 0 of the directory track of the drive in Register C, then reads it back to verify it. Returns Z if all went well, or NZ with Register A = 15H (GAT write error). DE and HL are preserved.

One member serves both commands. It loads at 5200H-524BH and 524FH-528CH (138 bytes); the three bytes at 524CH-524EH are not in the file and hold the three numbers typed. DATE (ISAM 15H) enters at 5200H and TIME (ISAM 16H) at 522DH, both with HL pointing to what follows the command name. Each expects three fields of exactly two digits, separated by / for DATE (DATE MM/DD/YY) and : for TIME (TIME HH:MM:SS). The values are not range-checked. Anything else gives BAD FORMAT.

5200H - DATE Command (ISAM 15H)

Stores month, day and year in 4046H, 4045H and 4044H (the order in which the SYS0 routine at 4470H shows them as MM/DD/YY), and the packed form of the date in 4306H-4307H.

522DH - TIME Command (ISAM 16H)

Stores hours, minutes and seconds in 4043H, 4042H and 4041H, the clock that the interrupt routine advances.

5243H - BAD FORMAT Exit

Shared by DATE and TIME.

525AH - Read Three Two-Digit Fields

HL points to the text, Register C holds the separator. Stores the three values from 524EH downward. Returns Z if all three fields were two digits each and the first two were followed by the separator; otherwise returns NZ. What follows the third field is not checked.

526FH - Read a Two-Digit Number

Returns Z with the value (0-99) in Register A, or NZ if either of the next two characters is not a digit.

5286H - Read One Digit

Fetches the character at (HL) and moves HL past it. Returns Carry set with the digit value (0-9) in Register A if it was 0-9, or No Carry otherwise.

ALLOC (ALLOC filespec (SIZE=n)) opens the file, creating it if it does not exist, allocates disk space for it and marks it so that the space is kept when the file is closed. SIZE (or S) is the size in K: the program writes one sector of E5H at record n x 4 - 1, which makes the DOS allocate everything up to it, then puts back the file's old end of file. Without SIZE only the mark is set. The member loads at 5200H-52A2H and 52C3H-52D3H (180 bytes). 52A3H-52C2H (the FCB) is not in the file, and the 256-byte sector buffer at 52D4H lies past the end of the member.

5200H - ALLOC Command

HL points to the text after ALLOC.

5253H - Set the Keep-Space Flag

Sets bit 7 of byte 1 of the file's directory entry. The SYS3 close routine does not release unused space of a file with this bit set (4E97H in SYS3).

5269H - Error Exit

Register A holds the error code: from the open, the write, or the directory read or write.

526EH - Message Exits

Display a message and return to VTOS READY through 4030H.

52C3H - Parameter Table

Used by the SYS0 parameter scan at 4476H: 6-character names padded with spaces, each followed by the address that receives the value, ended by 00H.

KILL (KILL filespec) deletes a file. The member loads at 5200H-5238H (57 bytes); the 32-byte FCB at 5239H lies just past its end.

5200H - KILL Command

HL points to the text after KILL.

5218H - Error Exit

Register A holds the error code from the open or the kill.

521DH - No Filespec

LIB lists the names of the library commands, four to a line. It reads them from the command table of SYS1 at 4EADH, which is still in memory because SYS1 has just dispatched the command. The table has 8-byte entries (six characters of name and a two-byte handler) and ends with 00H, so BOOT is listed as well. The member loads at 5200H-522FH (48 bytes).

5200H - LIB Command

The spaces are sent as the Model I space compression codes: a character from C0H to FFH displays (code - C0H) spaces.

One member holds four commands, each switched on or off: DEBUG (ISAM 14H, entry 5200H), CLOCK (ISAM 17H, entry 5241H), TRACE (ISAM 1AH, entry 5257H) and VERIFY (ISAM 1BH, entry 5267H). Each command is on unless (OFF), (NO) or (N) is given; ON, YES and Y are accepted and have no further effect. DEBUG also takes (EXT) or (E), which loads the extended debugger in SYS9. The member loads at 5200H-52F2H (243 bytes).

5200H - DEBUG Command (ISAM 14H)

DEBUG ON sets bit 7 of the system flags at 430FH and arms the BREAK key: 4315H-4317H become JP 400FH, the DEBUG entry. DEBUG OFF clears bit 7 and puts a RET at 4315H.

523EH - Load the Extended Debugger

Called from 5215H when EXT was given.

5241H - CLOCK Command (ISAM 17H)

CLOCK ON adds a timer task in slot 6 whose task block at 4DABH points to the SYS0 routine at 4DAEH, which shows the time at the top right of the screen. CLOCK OFF removes it.

5257H - TRACE Command (ISAM 1AH)

TRACE ON adds a timer task in slot 11. Its task block is the two bytes at 4DDBH (DDH 4DH), which point to the SYS0 routine at 4DDDH: it fetches the interrupted program's address from the stack and shows it in hexadecimal at 3C2EH, at the top of the screen. TRACE OFF removes the task.

5267H - VERIFY Command (ISAM 1BH)

Changes the SYS0 jump vector for writing a record, JP 48C0H at 4439H. VERIFY ON makes it jump to 48DBH, the routine behind 443CH that writes and then verifies; VERIFY OFF puts back 48C0H.

5276H - Read the Parameters

Two entries: 5276H with the DEBUG table at 52B2H and 527BH with the ON/OFF table at 52C2H. The scan stores FFFFH (or the value given) at the address of each keyword it finds: OFF, NO and N go to 5290H, the operand of the LD BC at 528FH; ON, YES and Y go to the spare bytes at 5297H. Returns Z if OFF, NO or N was given, NZ otherwise.

5299H - PARAMETER ERROR

Reached from 528CH. The return address of the scan routine is left on the stack; 4030H resets the stack.

52B2H - Parameter Tables

6-character names padded with spaces, each followed by the address that receives the value. The DEBUG table starts at 52B2H and runs on into the ON/OFF table at 52C2H; both end at 52F2H.

ISAM 1DH displays the copyright notice COPYRIGHT (C) 1980 BY RANDOLPH V. COOK, ALL RIGHTS RESERVED. The text is stored with 90H added to every character, so it cannot be read in a dump of the file. The member loads at 5200H-524BH (76 bytes).

5200H - Display the Copyright Notice

The first byte of the text block is the key; each following byte has the key subtracted and is displayed, until a 00H byte.

MEMORY shows or lowers the top of the memory available to programs, the address kept at 4049H-404AH. MEMORY alone displays it as HIGH = X'nnnn'. MEMORY (HIGH=n) or (H=n) sets it to n, which must be above 5200H and not above the current value; otherwise RANGE ERROR is displayed. The member loads at 5200H-5286H (135 bytes).

5200H - MEMORY Command

HL points to the text after MEMORY.

5239H - Message Exits

Display a message and return to VTOS READY through 4030H.

5267H - Parameter Table and Display Line

There is no SYSGEN command in the SYS1 table: this member is run by the SYSTEM member (ISAM A1H, 5622H there) when SYSTEM (SYSGEN) or SYSTEM (SYSGEN=NO) is given, with HL holding the value of the SYSGEN parameter. A non-zero value saves the current configuration in the file CONFIG/SYS.CCC:0; 0000H (NO or OFF) deletes the file. The file is written as a load module: every saved area of memory becomes a load record, so loading the file puts the areas back. The member loads at 5200H-53A2H and 53B2H-5464H (598 bytes). 53A3H-53B1H (the end of the FCB) is not in the file, and the file buffer at 5500H lies past the member.

5200H - SYSGEN Entry

HL = the SYSGEN value from SYSTEM.

520DH - Save the Configuration

Creates CONFIG/SYS.CCC:0 and writes: a 05H header record with the name CONFIG, a load record that shows *** CONFIGURING *** near the bottom of the screen, a load record that puts a RET at 4012H (the interrupt hook) while the rest loads, the system areas listed at 542FH, the memory above the top of memory, the real bytes of 4012H-4014H, a record that clears the banner again, and a transfer record.

52CEH - Save an Area of Memory

DE = the address of the area, BC = its length. Writes it as load records (type 01H) of at most 254 bytes each, with the same load address, to the file whose FCB is at 5392H.

5307H - Write a Load Record

B = number of bytes, DE = the load address, HL = where the data is now. Writes one load record (type 01H) to the file.

5329H - Delete the Configuration

Reached when the SYSGEN value is 0000H.

535DH - Message and Error Exits

5392H - FCB

The filespec is stored in the FCB itself; opening the file replaces it with the FCB data.

53B2H - Write a Byte to the File

Writes Register A to the file whose FCB is at DE. Errors end the command.

542FH - Table of Saved System Areas

Each entry is a length and an address; the table ends with a length of 0000H.

DIR (DIR name/ext:d (A,I,S,P)) lists the files on one drive, or on every drive that is ready when no drive is given. The name and extension are a pattern: characters that are left out match anything, so DIR /CMD lists every file with the extension CMD. The entries are found through the hash index table (sector 1 of the directory track). Normally three names are shown on a line, each followed by S (system file), I (invisible), P (password protected) and + (updated) where they apply. System and invisible files are only listed with S and I. A adds the protection level, the number of records (EOF=), the space allocated in K (SIZ= or, for files marked by ALLOC, SIZ:) and the date, one file to a line. P also sends the listing to the printer. SHIFT and @ pause the listing, BREAK stops it. The member loads at 5200H-5701H (1,282 bytes) and uses 5800H-58FFH for the hash index table and 5900H-59FFH for extended directory entries.

5200H - DIR Command

HL points to the text after DIR.

5203H - Fetch the Ending Record Number

Entry: Register A = offset of the ending record number in the directory entry at 42xxH (entry+14H). Returns DE = the number of 256-byte sectors that hold data: the ending record number, minus 1 if the last sector is only partly used (the EOF byte at 5211H is not 00H). HL is left pointing to 5211H.

5213H - Read the Pattern and Drive

Copies up to eight name characters to 56F6H and up to three extension characters to 56FEH (both start as spaces, which match anything), then a drive number after :.

5268H - List One Drive

Register C = the drive. Displays the heading, then scans the hash index table.

52D2H - Next Entry of the Hash Index Table

The position in the table is the directory entry code: bits 0-4 give the directory sector (from sector 2 on) and bits 5-7 the entry within it. The table is walked in the order 00H, 20H, 40H ... E0H, 01H, 21H ..., so the entries are visited sector by sector.

52F6H - Drive Not Ready

5308H - Examine a Directory Entry

HL points into the hash index table at 5800H. An entry in use has a non-zero hash byte. Reads the directory sector that holds the entry, unless it is already in the buffer at 4200H, and decides whether the file is to be listed.

535DH - Show the Name and Flags

Each file takes a field of 20 characters (Register C counts what is left of it).

5410H - Output a Flag Character

Counts the character in the field (Register C) and outputs it.

5414H - Show the Details (A)

HL points to the directory entry. Fills in and displays prot / EOF=nnnnn / SIZ=nnnnn.n K DD-MMM-YY.

550AH - Count the Granules of a File

HL points to the directory entry. Adds up the granules of every extent (bits 0-4 of the second byte of each two-byte extent, plus 1) until an FFH byte. An FEH byte links to an extended entry, whose code is in the byte after it; that entry is read and its extents are added as well. Returns DE = the granules and BC = the number of extents.

556CH - Output Routines

556CH displays the text at HL; 5577H outputs the character in Register A. Both also send it to the printer when P was given.

5584H - Error Exits

55A2H - Write a Number in Decimal

HL = the number, DE = where the five characters go. Leading zeros are written as spaces.

55DDH - Divide a 24-Bit Number

HL points to a 24-bit number (high byte first), Register C = the divisor. Returns DE = the quotient (16 bits). A divisor of 0 stands for 256: then DE is simply the two high bytes.

5603H - Pause and BREAK Check

Returns NZ if BREAK is pressed. SHIFT and @ together pause until another key is pressed (BREAK still stops). Does nothing while a chain (DO) file is running (bit 5 of 430FH).

562FH - Parameter Table

5650H - Text

FREE shows, for every drive that is ready, one line: DRIVE n - diskname mm/dd/yy FILES=fff/ttt, SPACE=fffff/ttttt K. FILES gives the free directory entries and the directory's capacity, SPACE the free and total space in K. FREE (P) also prints the lines. The member loads at 5200H-53D1H (466 bytes).

5200H - FREE Command

HL points to the text after FREE.

5222H - One Drive

Register C = the drive.