DOSPLUS 3.5 for the Model III - SYS7/SYS Disassembled

SYS7/SYS

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DOSPLUS 3.5 SYS7/SYS Disassembly - EVAL@, WILD@ and LOCDEV@ (Model III)

SYS7/SYS is the low overlay of the command line routines that the library commands and the utilities share: EVAL@ (4479H, request code 63H), the command evaluator, WILD@ (447CH, 64H), the wildmask, and LOCDEV@ (447FH, 65H), the lookup of a device or drive name. Its routine 6, which takes one field of a command line, is requested by SYS11/SYS (66H). The file is a load module of 4 blocks, 997 bytes, from 4E00H to 51E4H, with the transfer address 4E00H. The wildmask is kept outside the overlay, at 42B0HH-42BAHH, so that it lasts while other overlays load.

The Parts of SYS7/SYS

EVAL@

EVAL@ takes Register Pair HL = the command line and Index Register IX = the 9 byte evaluation block: a flag byte (bit 0 source, bit 1 destination, bit 2 wildmask, bit 3 parameters filled) and the addresses of the source, destination and wildmask blocks and of the parameter block. Each block is 33 bytes: a flag byte and up to 32 bytes of text ended by 03H. Fields are separated by spaces or commas. Each one is first taken into 4300HH by routine 6; when it is the word FROM, TO or USING, the field after it goes straight into that block (4E94H); otherwise a field with a wildcard (?, * or !) goes to the wildmask block, and any other to the source block, then the destination block, then the wildmask block, and is copied there (4EB6H). A field given twice is an error. A comma or a left parenthesis starts the parameters, which end the evaluation: anything after their closing parenthesis is not looked at.

Routine 6 (4F3CH) copies NAME/EXT.PASSWORD:DRIVE, @XX or :D, letters made upper case, and sets the block's flag byte: bit 6 a name, bit 5 a wildcard, bit 7 a device or a drive, with the number LOCDEV@ returns in bits 0-3. A name is up to 8 characters, an extension 3, a password 8, a device or drive name 2; longer parts are cut. A drive after a name with a wildcard is not taken into that field: it becomes the next field, which is how COPY !/TXT:1 :0 gives !/TXT as the wildmask and :1 as the source, as the manual says.

The parameter block has 9 byte entries: a six character name, the address for the value, and a type byte (bit 7 a string, bit 6 a number, bit 5 a logical value), ended by 00H. A name may be shortened to its first letters (4FEEH). A name alone stores FFFFH; NAME=Y, YES or ON stores FFFFH and N, NO or OFF 0000H (5164H); a value in quotation marks stores the address of its first character (5142H); a number ending in H is hexadecimal (51A9H), any other is decimal (518EH). A value whose type bit is clear is an error.

Every error of EVAL@ returns Register A = 2EH, Invalid parameter, with the NZ FLAG, whatever routine found it: an empty part, an unknown device, a second source, an unknown parameter name or a value of the wrong type.

WILD@ and LOCDEV@

WILD@ with Register B not 00H takes a file specification at Register Pair HL and makes the wildmask at 42B0HH from it: the name and the extension, upper case and padded with spaces; a * fills the rest of its part with ?, a ! the rest of the name and the whole extension (4F14H). A part that is not given stays spaces. With Register B = 00H, WILD@ compares the 11 bytes at Register Pair HL, a name and an extension as a directory entry holds them, with the wildmask, each ? matching any character (4F0AH).

LOCDEV@ takes Register Pair DE pointing to a prefix and a two character name. After a colon the name is a drive, looked up in DCTTBL (44E8HH), and Register A returns 08H plus the drive number; after anything else it is a device, looked up in the DCB table (44A6HH), and Register A returns the device number, 0 (KI) to 5 (U2). A one character name matches a table name whose second character is a space. A name not found returns error 29H, Device not available (506DH).

Differences from the Manual

EVAL@ returns one error code, 2EH, for every error. WILD@ compares a name and an extension in directory form, 11 bytes, not a file specification ended by 03H or 0DH, and setting a wildmask always returns the Z FLAG: no wildmask is refused. LOCDEV@ does not check the @ before a device name and compares the names as they are, without making them upper case.

Differences from the Model I

The code is the Model I SYS7/SYS at the same addresses; only the addresses in SYS0/SYS differ: the wildmask is at 42B0H-42BAH (Model I 435EH-4368H), the system buffer at 4300H (4200H), the register saving wrapper is called through 4485H (4525H), DCTTBL is at 44E8H (43ABH) and the DCB table at 44A6H (4369H).

42B0H - WILD@'s Wildmask

Not in the file: WILD@ keeps the wildmask it was given in SYS0/SYS's RAM at 42B0H-42BAH, between BREAK$ (42ADH-42AFH) and the saved date (42BBH-42BDH), so the mask lasts from the call that sets it to the calls that compare with it, while other overlays load.

4E00H - The Routine Table

Data: SYS7/SYS's table of routines 2-7, one word each, used by SYS0/SYS's overlay request handler (its 49D3H-49E6H) for the request codes 62H-67H. EVAL@ (4479H) requests 63H, WILD@ (447CH) 64H, LOCDEV@ (447FH) 65H, and SYS11/SYS requests 66H (its 5409H); no file of the diskette requests 62H or 67H.

4E0CH - Routine 2

Nothing to do when SYS0/SYS's record locator brings SYS7/SYS back.

4E0EH - EVAL@ - The Command Evaluator

Routine 3, requested by EVAL@ (4479H). Register Pair HL points to the command line (ended by 03H, 0DH, any other control character or a semicolon), Index Register IX to the 9 byte evaluation block: +00H the flags (bit 0 source, bit 1 destination, bit 2 wildmask, bit 3 parameters), +01H, +03H and +05H the addresses of the source, destination and wildmask blocks (33 bytes each: a flag byte and the field's text), +07H the address of the parameter block. Each field is taken into 4300H first; after the word FROM, TO or USING the next field goes straight into that block, otherwise a field with a wildcard goes to the wildmask block and any other to the first of the source and destination blocks still free. A comma or a left parenthesis starts the parameters (50D7H), which end the evaluation. Returns the Z FLAG and Register A = 00H, or the NZ FLAG and Register A = 2EH (Invalid parameter) for every error, with Register Pair HL where the scan stopped.

4E12H - The Next Field

Skips spaces; a comma or a left parenthesis starts the parameters, the end of the line ends EVAL@, anything else is a field.

4E4DH - The Source Block

Reached after FROM, or for a field without a keyword while the source is free (4EACH): sets bit 0 of the flags and returns Register Pair DE = the source block to the address on the stack. A second source is an error.

4E68H - The Destination Block

Reached after TO, or for a field without a keyword while the source is filled and the destination free (4EB2H). A second destination is an error.

4E83H - The Wildmask Block

Reached after USING, for a field with a wildcard character, or for a third field without a keyword. A second wildmask is an error.

4E94H - The Field After a Keyword

Reached by the RETurn of 4E5DH, 4E78H or 4E93H after FROM, TO or USING, with Register Pair DE = the chosen block: the field after the keyword goes straight into it.

4E9CH - A Field Without a Keyword

The field in 4300H goes to the wildmask block when it has a wildcard (bit 5 of its flag byte), else to the source block when that is free, else to the destination block when that is free, else to the wildmask block; 4EB6H then copies it there.

4EB6H - Copy the Field

Reached by the RETurn of 4E5DH, 4E78H or 4E93H for a field without a keyword: copies its flag byte and 32 bytes of text from 4300H to the block at Register Pair DE.

4EC3H - The Error Return

4EC3H also drops the return address pushed at 4E38H. EVAL@ returns error 2EH (Invalid parameter) for every error, whatever the routine that found it.

4EC8H - Compare With a Pattern

Register Pair DE = a text, Register Pair BC = a pattern, Register A = the number of bytes. Each byte of the pattern must equal the text's byte, except that a ? matches any byte. Returns the Z FLAG when all match, else the NZ FLAG; the registers other than Register Pair AF are saved (4485H).

4EDBH - WILD@

Routine 4, requested by WILD@ (447CH). Register B = 00H: compare the 11 bytes at Register Pair HL, a name and an extension as a directory entry holds them (padded with spaces), with the wildmask at 42B0H; the Z FLAG when they match. Register B not 00H: Register Pair HL points to a file specification NAME/EXT, whose two parts become the wildmask, upper case and padded with spaces (a * fills the rest of its part with ?, a ! the rest of the name and the whole extension); a part not given stays spaces. Setting the mask always returns the Z FLAG. The registers other than Register Pair AF are saved (4485H).

4F14H - Copy a Part of the Wildmask

Copies up to Register B characters from Register Pair HL to Register Pair DE, letters upper case, ending at the first character a file name may not have (5043H). A * fills the rest of the part with ?, a ! fills it and Register C bytes more.

4F2DH - Fill With Question Marks

Stores Register B plus Register C question marks from Register Pair DE on; every register is saved (4485H and Register Pair AF on the stack).

4F3CH - Take a Field

Routine 6 (request 66H, made by SYS11/SYS), also called by EVAL@ (4E3CH, 4E94H). Register Pair HL points into the command line, Register Pair DE to a 33 byte block. Skips spaces and commas, then copies one field into the block from +01H, ended by 03H: a file specification NAME/EXT.PASSWORD:DRIVE (any part after the name may be missing) or a device @XX or a drive :D, and sets the flag byte at +00H: bit 6 a name, bit 5 a wildcard in the name or extension, bit 7 a device or drive with the number LOCDEV@ gives in bits 0-3 (bit 3 for a drive). After a name with a wildcard a colon is not taken: the drive is left as the next field. Returns the Z FLAG with Register Pair DE = the block, or the NZ FLAG when the field or one of its parts is empty or the device is not found.

4F7CH - A Device or a Drive

Register A = the @ or the colon, after a name or (from 4FA1H) at the start of the field. The two character name is copied after it and looked up by LOCDEV@.

4FABH - Copy One Part of a Field

Copies up to Register B characters (letters made upper case, digits and #$%&+<>?*!) from Register Pair HL to Register Pair DE and puts 03H after them; characters beyond Register B are passed over. The part ends at the end of the line, a left parenthesis or a comma, which stay at Register Pair HL, or at any other character, which is passed. Returns Register A = the character that ended the part, and the NZ FLAG when the part is empty, else the Z FLAG with the C FLAG set when it had a ?, * or !.

4FEEH - Find a Parameter Name

Register Pair DE = the name (at 4300H, ended by 03H), Register Pair BC = the parameter block, 9 byte entries (a six character name padded with spaces, the address for the value, the type byte) ended by 00H. A name may be shortened: the first entry whose name starts with the given characters is taken. Returns the Z FLAG with Register Pair DE = the entry's type byte (+08H), or the NZ FLAG and Register A = FFH when no entry matches.

502BH - Skip Spaces and Commas

502CH returns Register A = the first character at Register Pair HL that is not a space or a comma, with Register Pair HL at it; the C FLAG when it ends the line.

503AH - The End of the Line

Sets the C FLAG when Register A is below 20H (03H, 0DH or another control character) or is 3BH, a semicolon; else the NC FLAG.

5043H - A File Name Character

Sets the C FLAG when Register A is a digit, a letter (returned upper case: 504AH ANDs it with 5FH) or one of #$%&+<>?*! (5053H); else the NC FLAG. 504AH is the entry that only makes a letter upper case (other characters below 41H are tested against the list too).

506DH - LOCDEV@

Routine 5, requested by LOCDEV@ (447FH), and called by 4F8CH. Register Pair DE points to a two character device name after a prefix: after a colon it is a drive, looked up by the names in DCTTBL (44E8H), else a device, looked up in the DCB table (44A6H); the prefix itself (@) is not checked, and the names are compared as they are, without making them upper case. A one character name matches a table name whose second character is a space. Returns the Z FLAG with Register A = the device number (0-5) or 08H plus the drive number (0-7), or the NZ FLAG with Register A = 29H (Device not available). The registers other than Register Pair AF are saved (4485H).

50D7H - The Parameters

Routine 7 (request 67H, which no file of the diskette makes), reached by the JUMP at 4E2BH with Register Pair HL at the comma or left parenthesis and Register Pair DE = the parameter block: 9 byte entries (a six character name, the address for the value, the type byte: bit 7 a string, bit 6 a number, bit 5 a logical value), ended by 00H. A parameter is NAME or NAME=value; the values are Y, YES or ON (FFFFH), N, NO or OFF (0000H), a number (hexadecimal when it ends in H, else decimal), or a string in double or single quotation marks, whose address is stored. A name alone stores FFFFH and needs bit 5. Parameters are separated by commas and end at the end of the line or a right parenthesis. Returns the Z FLAG, or the NZ FLAG with Register A = 2EH (Invalid parameter) for an unknown name, a value of a type the entry does not allow, or anything else after a parameter.

510BH - Store the Value

Register Pair BC = the value or a string's address, Register Pair DE = the entry's type byte, after the word with the address for the value. Then a comma starts the next parameter; the end of the line or a right parenthesis ends EVAL@.

5128H - A Value

After the equal sign: a logical value, a string in quotation marks or a number, each allowed only when its bit of the type byte is set.

5164H - A Logical Value

Reads a word starting with Y, N, ON or OF at Register Pair HL: Register Pair BC = FFFFH for Y and ON, 0000H for N and OF, then the rest of the word is skipped and the Z FLAG returned. Anything else returns the NZ FLAG.

518EH - A Decimal Number

Reads the digits at Register Pair HL into Register Pair BC (the number times 10 plus each digit, without an overflow test), stopping at the first other character.

51A9H - A Hexadecimal Number

Reads the hexadecimal digits at Register Pair HL into Register Pair BC; returns the Z FLAG only when an H follows them (Register Pair HL past the H), else the NZ FLAG.

51D7H - The Keywords

Data: the three words that name the next field, each followed by the 03H that ends a field, so that only a field that is the whole word matches (4E43H, 4E5EH, 4E79H).