TRS-80 DOS - NEWDOS/80 v2.0 for the Model III - SYS7/SYS Disassembled

SYS7/SYS

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NEWDOS/80 v2.0 SYS7/SYS Disassembly - SYSTEM, HIMEM, PDRIVE, AUTO, ATTRIB, PROT, DUMP, PURGE, TIME and DATE (Model III)

SYS7/SYS is the overlay that carries out ten library commands. Its five load records fill 4D00H-51E7H of the overlay area (1,256 bytes) and its transfer address is 4D00H. SYS1/SYS runs it with RST 28H code E9H (directory slot 09H, function 7) and the command's sub-function in Register C, taken from byte 1 of the command's entry in SYS1/SYS's command table: 1 SYSTEM, 2 HIMEM, 3 PDRIVE, 4 AUTO, 5 ATTRIB, 6 PROT, 7 DUMP, 9 PURGE, 0AH TIME, 0BH DATE. Sub-function 8 is the second half of DUMP, which SYS7/SYS calls itself through SYS0/SYS 4978H. The dispatcher at 4D00H sends each sub-function to its command; any other code or sub-function gives error 2AH.

The page shows every byte of the file once, in address order. Bytes that are not in the file are shown as a DEFS row without a byte column.

Commands

Keyword Tables

DUMP File Format

4D00H - Function Dispatcher

SYS7/SYS (directory slot 09H) is loaded by the SYS0/SYS RST 28H dispatcher into 4D00H-51E7H of the overlay area and entered at 4D00H by the CALL at 4BC2H, so the word on top of the stack is the dispatcher's return address 4BC5H. Register A holds the RST 28H code, Register C the sub-function and Register Pair HL the rest of the command line, as SYS1/SYS left them. Only function 7 (code E9H) exists. Register C comes from byte 1 of SYS7/SYS's entries in SYS1/SYS's command table (4F6FH-50CDH): 1 SYSTEM, 2 HIMEM, 3 PDRIVE, 4 AUTO, 5 ATTRIB, 6 PROT, 7 DUMP, 9 PURGE, 0AH TIME, 0BH DATE; 8 is the second half of DUMP, reached only through the 4978H chain set up at 513EH. Any other code or sub-function returns error 2AH.

4D34H - Error 2AH, and the TIME and DATE Commands

4D34H is reached from 4D06H for a code that is not E9H (NZ FLAG) and falls through from 4D33H, where the Z FLAG says whether the sub-function was 0BH (DATE). TIME and DATE without a parameter display the clock as HH:MM:SS or the date as MM/DD/YY through the ROM routines at 3036H and 3033H; with a parameter they set it at 4DAEH.

4D53H - Unreferenced Error Exit

No branch, table entry or pushed address in SYS7/SYS names 4D53H, so these two rows are never executed by SYS7/SYS's own code.

4D57H - Error Exits and the End of the Command

4D57H returns error 20H (from 4EA9H, a drive number of 256 or more). 4D5BH accepts the end of the line (Z FLAG) or a separator (NZ FLAG, Register Pair HL past it) and gives error 34H for anything else; 4D5FH accepts only the end of the line. 4D65H is the common error exit through SYS0/SYS 4409H, which displays the error and ends the command.

4D68H - SYSTEM, PDRIVE and PURGE Commands

These three read only [password]:d or d and check the diskette password at 4E90H; then they pass the rest of the command line to another overlay with Register B = the drive (427EH): SYSTEM to SYS17/SYS function 1 (code 33H), PDRIVE to SYS16/SYS function 1 (code 32H), PURGE to SYS3/SYS function 7 sub-function 6 (code E5H, Register C = 06H).

4D7DH - HIMEM Command

Without a parameter HIMEM displays the address held in 4411H (HIMEM) as four hexadecimal digits. With one it stores the value, which may be decimal or hexadecimal with a trailing H (4FA5H); it must be 7000H or higher, and it is lowered to the top of memory found at reset (42C9H) if it is above it.

4DAEH - TIME and DATE: Set the Clock or Date

Three fields of two decimal digits, separated by the character stored at 4DD2H (: or /), are stored downward from Register Pair DE: hours, minutes and seconds at 4219H-4217H, or month, day and year at 421CH-421AH. The values are not range-checked. Interrupts are off while the fields are stored, so the clock does not tick in between. A field that is not two digits, or a wrong separator, gives error 2FH; anything but the end of the line after the third field gives error 34H, after the values are already stored.

4DDBH - AUTO Command

Stores the rest of the command line, up to and including its carriage return, in bytes E0H-FFH of the GAT of drive 0: the command the reset code runs automatically. At most 31 characters fit with the carriage return; longer text gives error 2FH and nothing is written. AUTO with nothing after it stores only the carriage return, which removes the AUTO command.

4DFAH - ATTRIB Command

SYS1/SYS has opened the file (FCB at Register Pair DE) and, because its command table entry has bit 3 of byte 3 set, left the command line pointer on the stack under the dispatcher's return address 4BC5H. ATTRIB drops 4BC5H, so it returns straight to the command's return address, SYS0/SYS 4408H. The file must have been opened with full access (access level 0: its update password, or any password when option AA is off), otherwise error 19H. Its FPDE is read and changed by the keywords in the table at 5054H, separated by commas or spaces; then the directory sector is written back. Keywords: INV and VIS (invisible bit), PROT=level (5093H), ACC=password, UPD=password, ASE=Y/N, ASC=Y/N, UDF=Y/N and LRL=n.

4E17H - ATTRIB LRL=

LRL=n sets the record length (FPDE byte 4) to n, 1-256; 256 is stored as 00H. Other values give error 2FH.

4E2AH - ATTRIB UDF=, ASE= and ASC=

Each changes one bit of FPDE byte 1: UDF (bit 5, the file has been updated) is set by Y and cleared by N; ASE (bit 7, the file may not be extended) and ASC (bit 6, CLOSE keeps the space beyond EOF) are cleared by Y and set by N, because the bits stand for the opposite of the keyword. Anything but Y or N gives error 2FH.

4E54H - ATTRIB INV, VIS and PROT=

INV sets and VIS clears bit 3 of FPDE byte 0 (invisible). PROT=level stores the access level (LOCK 7, EXEC 6, READ 5, WRITE 4, RENAME or NAME 2, KILL 1, FULL 0; table 5093H) in bits 0-2 of byte 0. 4E62H then continues with the next keyword, or at the end of the line writes the directory sector.

4E78H - ATTRIB ACC= and UPD=

ACC=password stores the password's code at FPDE bytes 18-19 (the access password), UPD=password at bytes 16-17 (the update password). A blank password (nothing after the =) gives the code 4296H.

4E90H - Read a Drive and Check the Diskette Password

Used by PROT, SYSTEM, PDRIVE and PURGE. The text is password:d, :d or d. The drive is selected (SYS0/SYS 4791H, error 08H if no diskette turns) and its GAT is read into 4300H. The password code read (4296H, the blank code, when no password was typed) is then compared with the diskette password code in GAT bytes CEH-CFH; when they differ the result is error 37H, but only while option AA (bit 7 of 428CH) is on. So with option AA on, a diskette that has a password needs it even when none is typed. Returns with Register Pair HL after the drive number.

4ECCH - PROT Command

PROT [password]:d,keyword,... changes the diskette's GAT: PW=password (a new diskette password), NAME=name and DATE=date (8 characters each); and it applies LOCK, UNLOCK and RUF to all the diskette's files after the last keyword (4F10H). The keywords are in the table at 50C7H.

4ED8H - PROT DATE= and NAME=

Copies up to 8 characters, up to a comma, a space or the end of the line, to GAT bytes D8H-DFH (DATE=) or D0H-D7H (NAME=), padded with spaces. Characters after the eighth are left in the line, where 4F10H finds them and gives error 34H.

4EF6H - PROT RUF, UNLOCK and LOCK

These only set a bit in the operand at 4F1AH; the files are changed after the last keyword (4F19H). Bit 2 RUF, bit 0 UNLOCK, bit 1 LOCK. When both LOCK and UNLOCK are given, UNLOCK wins (4F22H).

4F09H - PROT PW=

PW=password stores the new password's code in GAT bytes CEH-CFH. A later LOCK uses the new code, because 4F1EH reads it from the GAT copy after every keyword has been handled.

4F10H - PROT: Next Keyword, Then Change the Files

After the last keyword the GAT is written back. Then, if LOCK, UNLOCK or RUF was given, every FDE sector of the directory (8 plus the extra sectors counted in HIT byte 1FH) is read and each FPDE in use is changed: RUF clears the updated bit (byte 1 bit 5) of every file; LOCK sets both password codes of every file that is neither a system file nor invisible to the diskette password, UNLOCK sets them to the blank code 4296H. Each sector is written back.

4F72H - A Separator Must Follow

Steps Register Pair HL over a comma or spaces; any other character, or the end of the line, gives error 34H.

4F78H - Find a Keyword

4F78H searches a table of keyword entries (the name, 00H, and a two-byte handler address) and jumps to the handler of the keyword at Register Pair HL, with Register Pair HL past the keyword. 4F84H does the search for any table with Register D bytes after each name and returns Register Pair BC pointing at them. No match gives error 34H. The text only has to start with the keyword, so anything typed after it is read by the handler.

4F9AH - Read an Optional Number

4F9AH: at the end of the line RETURN with Register Pair DE unchanged (the default the caller put there); after a separator read a number. 4FA0H: a separator and a number must follow. 4FA5H reads a number: decimal, or hexadecimal with a trailing H (a letter A-H after the decimal digits makes the reading start again as hexadecimal). Returns Register Pair DE = the value; no digit, a missing H or a value over FFFFH gives error 2FH.

4FFCH - Read a Password and Encode It

5005H copies a name of up to 8 characters (a letter, then letters and digits) to 51E8H-51EFH, padded with spaces, and leaves Register Pair HL after it. If the text does not start with a letter nothing is taken and the name is blank. 5023H then encodes the 8 characters into a 16-bit code in Register Pair DE with the same steps as SYS2/SYS's password encoder (5152H): a blank name gives 4296H, PASSWORD gives 42E0H. The buffer is blank again afterwards.

5054H - ATTRIB Keyword Table

Each entry is the keyword, a 00H and the two-byte address of its handler; a 00H in place of a keyword ends the table. 4F78H looks the keywords up in this order with Register Pair BC = 5054H (4E11H), and the text only has to start with a keyword.

5093H - Access Level Table

Used by ATTRIB PROT= (4E6AH): each entry is the level name, a 00H and the level byte stored in bits 0-2 of FPDE byte 0; a 00H in place of a name ends the table. RENAME and NAME both give level 2, and no name gives level 3. RENAME comes before NAME, so the longer name is tried first.

50C7H - PROT Keyword Table

Each entry is the keyword, a 00H and the two-byte address of its handler; a 00H in place of a keyword ends the table. 4F78H looks the keywords up in this order with Register Pair BC = 50C7H (4ED2H). UNLOCK comes before LOCK in the table.

50F4H - DUMP Command

DUMP filespec,start,end[,entry[,load]] writes memory from start to end to the file (opened by SYS1/SYS in the DOS FCB at 4480H) in load module format. Numbers are decimal or hexadecimal with H. The entry address defaults to 402DH (DOS READY); the load address, where the data will be loaded later, defaults to start. With entry = FFFFH the file is written without records instead (two address bytes, then the data) and no load address is read. The file's sector buffer is set to 4D68H, inside SYS7/SYS itself (over the code for SYSTEM to ATTRIB, which DUMP does not need). Before the dump one sector is written at relative sector (count + 4) / 252 of the file, so that all the space the file needs is allocated at once; the 4978H chain then brings DUMP back as sub-function 8.

5149H - DUMP, Sub-Function 8: Write the Data

Entered through 4978H with Register Pair DE = the FCB and the values pushed at 511DH-5124H still on the stack under the dispatcher's return address 4BC5H. The file is rewound and the bytes are sent one at a time through the ROM output routine at 001BH with Register Pair DE = the FCB; the ROM finds that the FCB's first byte is not the output device type and jumps through 4033H to SYS0/SYS 4A80H, which writes the byte to the file. Load module records are type 01H, a length byte (the data length plus 2; 00H means 256), the two-byte load address (51BBH translates it) and up to 254 data bytes; the last record is the transfer record 02H 02H and the entry address. Finally the file is rewound again and closed through SYS0/SYS 4428H.

51B3H - DUMP: Write a Record Header and an Address

51B3H writes Register B (the record type) and Register C (the length byte). 51BBH writes the address in Register Pair DE as two bytes, translated when it lies between start and end: address - start + load. 51DAH writes the byte in Register A through ROM 001BH with the FCB in the alternate Register Pair DE, and ends DUMP with the error on a write error.