TRS-80 DOS - NEWDOS/80 v2.0 for the Model I - 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 I)

SYS7/SYS holds ten library commands. It loads into the overlay area at 4D00H-51E7H (1,256 bytes in five load records, transfer address 4D00H). SYS1 calls it with LD A,E9H / RST 28H (function 7) and the sub-function from its command table in Register C; the SYS0 dispatcher (4BC2H) loads SYS7 when 4317H does not already hold its slot number (09H). SYSTEM, PDRIVE and PURGE are only started here: SYS7 reads the drive and checks the diskette password, then passes the rest of the command line to SYS17, SYS16 or SYS3.

The page shows every byte of the file once, in address order. Each row says what every register and address it uses holds at that moment.

Sub-Functions of Code E9H

Parameters and Passwords

DUMP

4D00H - Function Dispatcher

SYS7 is entered from the SYS0 RST 28H dispatcher at 4BC2H, which has loaded SYS7 into 4D00H-51FFH and CALLs 4D00H with Register A = the RST 28H code, Register C = the sub-function and Register Pair HL = the rest of the command line, all as SYS1 left them. Only function 7 (code E9H) exists. Register C comes from byte 1 of SYS1's command table entry (4F58H): 1 SYSTEM, 2 HIMEM, 3 PDRIVE, 4 AUTO, 5 ATTRIB, 6 PROT, 7 DUMP, 8 the second half of DUMP (reached only through the 49D3H chain set up at 5137H), 9 PURGE, 0AH TIME, 0BH DATE. Any other code or sub-function returns error 2AH.

4D32H - Error 2AH, and the TIME and DATE Commands

4D32H is reached from 4D06H for a code that is not E9H (NZ FLAG) and falls through from 4D31H, 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 SYS0 44ACH; with a parameter they set it at 4DA7H.

4D4CH - Unreferenced Error Exit

Nothing in SYS7, and no other module, reaches 4D4CH: no branch, table entry or pushed address names it.

4D50H - Error Exits and the End of the Command

4D50H returns error 20H (from 4EA2H, a drive number of 256 or more). 4D54H 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; 4D58H accepts only the end of the line. 4D5EH is the common error exit through SYS0 4409H, which displays the error and ends the command.

4D61H - SYSTEM, PDRIVE and PURGE Commands

These three read only [password]:d or d and check the diskette password at 4E89H; then they pass the rest of the command line to another overlay with Register B = the drive: SYSTEM to SYS17 function 1 (code 33H), PDRIVE to SYS16 function 1 (code 32H), PURGE to SYS3 function 7 sub-function 6 (code E5H, Register C = 06H).

4D76H - HIMEM Command

Without a parameter HIMEM displays the address held in 4049H (HIMEM) as four hexadecimal digits. With one it stores the value, which may be decimal or hexadecimal with a trailing H (4F9EH); it must be 7000H or higher, and it is lowered to the top of memory found at reset (43A9H) if it is above it.

4DA7H - TIME and DATE: Set the Clock or Date

Three fields of two decimal digits, separated by the character stored at 4DCBH (: or /), are stored downward from Register Pair DE: hours, minutes and seconds at 4043H-4041H, or month, day and year at 4046H-4044H. 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.

4DD4H - 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.

4DF3H - ATTRIB Command

SYS1 has opened the file (FCB at Register Pair DE) and, because the command table entry has bit 3 of byte 3 set, left the command line pointer on the stack under the dispatcher's return address. 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 504DH, separated by commas or spaces; then the directory sector is written back. Keywords: INV and VIS (invisible bit), PROT=level (508CH), ACC=password, UPD=password, ASE=Y/N, ASC=Y/N, UDF=Y/N and LRL=n.

4E10H - 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.

4E23H - 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.

4E4DH - 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 508CH) in bits 0-2 of byte 0. 4E5BH then continues with the next keyword, or at the end of the line writes the directory sector.

4E71H - 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.

4E89H - 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 47ECH, error 08H if no diskette turns) and its GAT is read into 4200H. 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 436CH) 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.

4EC5H - 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 (4F09H). The keywords are in the table at 50C0H.

4ED1H - 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 4F09H finds them and gives error 34H.

4EEFH - PROT RUF, UNLOCK and LOCK

These only set a bit in the operand at 4F13H; the files are changed after the last keyword (4F12H). Bit 2 RUF, bit 0 UNLOCK, bit 1 LOCK. When both LOCK and UNLOCK are given, UNLOCK wins (4F1BH).

4F02H - PROT PW=

PW=password stores the new password's code in GAT bytes CEH-CFH. A later LOCK uses the new code, because 4F17H reads it from the GAT copy after every keyword has been handled.

4F09H - 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.

4F6BH - 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.

4F71H - Find a Keyword

4F71H 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. 4F7DH 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.

4F93H - Read an Optional Number

4F93H: at the end of the line RETURN with Register Pair DE unchanged (the default the caller put there); after a separator read a number. 4F99H: a separator and a number must follow. 4F9EH 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.

4FF5H - Read a Password and Encode It

4FFEH 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. 501CH then encodes the 8 characters into a 16-bit code in Register Pair DE with the same steps as SYS2 5155H (a blank name gives 4296H, PASSWORD 42E0H). The buffer is blank again afterwards.

504DH - ATTRIB Keyword Table

Data. Searched by 4F71H (loaded into Register Pair BC at 4E0AH): each entry is the keyword in ASCII, a 00H that ends it, and the two-byte address of its handler (low byte first). A 00H in place of a keyword ends the table. The text only has to start with the keyword.

508CH - Access Level Table

Data. Searched by 4F7DH for PROT= (loaded into Register Pair BC at 4E63H, with Register D = 01H): each entry is the level name in ASCII, a 00H that ends it, and the access level for bits 0-2 of FPDE byte 0. A 00H in place of a name ends the table.

50C0H - PROT Keyword Table

Data. Searched by 4F71H (loaded into Register Pair BC at 4ECBH): each entry is the keyword in ASCII, a 00H that ends it, and the two-byte address of its handler (low byte first). A 00H in place of a keyword ends the table.

50EDH - DUMP Command

DUMP filespec,start,end[,entry[,load]] writes memory from start to end to the file (opened by SYS1 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 4D61H, inside SYS7 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 49D3H chain then brings DUMP back as sub-function 8.

5142H - DUMP, Sub-Function 8: Write the Data

Entered through 49D3H with Register Pair DE = the FCB and the values pushed at 5116H-511DH still on the stack. 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 (SYS0 4ADBH writes them 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 (51B4H 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 4428H.

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

51ACH writes Register B (the record type) and Register C (the length byte). 51B4H writes the address in Register Pair DE as two bytes, translated when it lies between start and end: address - start + load. 51D3H 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.

51DCH - Unused Bytes

The end of the file. Nothing in SYS7 reads or writes these bytes; the password and text buffer starts after them at 51E8H.