DOSPLUS 3.5 for the Model I - SYS12/SYS Disassembled

SYS12/SYS

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DOSPLUS 3.5 SYS12/SYS Disassembly - The Library Commands AUTO, BREAK, CLOCK, DATE, DEBUG, ERROR, I, LIB, PAUSE, SCREEN, TIME and VERIFY (Model I)

SYS12/SYS is the fourth of the high overlays: it loads at 5200H and holds twelve small library commands, routines 3 to 14 of its table at 5200H with the request codes B3H to BEH: AUTO, BREAK, CLOCK, DATE, DEBUG, ERROR, I, LIB, PAUSE, SCREEN, TIME and VERIFY. CMNDI@ takes the codes from SYS1/SYS's table of the library commands and passes them to the overlay request handler, which loads SYS12/SYS and calls the routine with Register Pair HL at the rest of the command line. No file of the diskette requests routine 2 (B2H). The file is a load module of 5 blocks, 1098 bytes, from 5200H to 5652H, with the transfer address 5200H; the nine bytes after the routine at 5560H are not loaded (its work area), and the work area after the file starts at 5653H.

The Parts of SYS12/SYS

AUTO

AUTO (521CH) takes an optional drive first (FSPEC@ and LOCDEV@; error 20H for a wrong one) and writes the rest of the line, its 0DH included, into +E0H of that diskette's GAT, padding the 32 bytes with spaces; a longer command is cut to 31 characters and 0DH. The drive must be ready (08H) and writable (0FH). AUTO alone stores only the 0DH, which clears the command. Its last act is to store 0DH at SYS1/SYS's command pointer (4310H), so that a semicolon in the new AUTO command is not taken as the start of a further command of this line.

DATE and TIME

Given a text, DATE and TIME read up to three decimal numbers separated by any character that is not a digit (537CH): DATE puts the first into the month, the second into the day and the third into the year of DATE$ (4044H) and of the date the start-up saved (4315H), TIME into the hours, minutes and seconds of TIME$ (4041H). Each value is taken modulo 100 (so a year 1983 becomes 83), a value left out keeps the old one, and none is checked. DATE alone (5292H) shows Www - Mmm d, 19yy - n: the weekday from the days since 1 January 1900 divided by 7 (5307H), the names from tables of three letters, the year as 1900 plus DATE$'s year, and the day of the year. The count takes every year divisible by 4 as a leap year, so the weekday is right from March 1900 to 1999; the manual accepts only 1900 to 1999. TIME alone shows the time by GTTIME@.

The Switches

CLOCK, DEBUG, VERIFY and BREAK (54A5H) take ON (also YES, or nothing) or OFF (also NO) through PARAM@ (5527H), whose table has eight byte entries: OFF and NO store into an operand that is tested, ON and YES into a byte nothing reads. DEBUG sets bit 2 of SFLAG1$, VERIFY bit 3, and BREAK OFF sets bit 0, which disables the BREAK key. CLOCK puts SYS0/SYS's clock display task (462FH) into interrupt slot 2 by SET@ or takes it out by RESET@.

ERROR, I, LIB, PAUSE and SCREEN

ERROR n (53B0H) shows the message of error n (above 255 is error 2DH) and ERROR alone that of the last error posted, through ERROR@ with bits 7 and 6 set, which returns. I (53CAH) sets bit 0 of DCT+03H, the flag that has a diskette logged at its next access, for the drive given or for drives 1 to 7; with MOUNT it reads each ready floppy drive's GAT at once and sets the drive's number of sides (DCT+0CH) from bit 5 of the GAT's +CDH. LIB (542FH) has SYS1/SYS's routine 9 return its table of the library commands and lists the names five to a line. PAUSE (546BH) waits for ENTER, reading the keyboard even while a DO file runs; BREAK ends it with error 30H. SCREEN (5481H) sends the 16 lines of the screen at 3C00H. LIB writes to @DO and SCREEN to @PR, unless a device or a file is given (54F3H).

Differences from the Manual

I without a drive flags drives 1 to 7 only; drive 0 is not logged again (the manual says all disks). The values of DATE and TIME are not checked. SYS1/SYS's routine 9, which its page found unused by any file, is requested here, by LIB.

5200H - The Routine Table

Data: SYS12/SYS's table of routines 2-14, one word each, used by SYS0/SYS's overlay request handler (its 49C9H-49DCH) for the request codes B2H-BEH. CMNDI@ takes the codes of the library commands from SYS1/SYS's table (51BCH-51DFH): AUTO B3H, BREAK B4H, CLOCK B5H, DATE B6H, DEBUG B7H, ERROR B8H, I B9H, LIB BAH, PAUSE BBH, SCREEN BCH, TIME BDH, VERIFY BEH. No file of the diskette requests B2H.

521AH - Routine 2

Nothing to do when SYS0/SYS's record locator brings SYS12/SYS back.

521CH - AUTO

Routine 3, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. A line that starts with a drive (:d) sets the AUTO command of that drive's diskette, else of drive 0; the rest of the line, up to 32 characters with its 0DH, goes into the GAT at +E0H, padded with spaces (a line of 32 characters or more is cut and ended with 0DH), and the GAT is written back. AUTO alone clears the command. The drive must be ready (08H) and not write protected (0FH). The 0DH stored at SYS1/SYS's command pointer keeps CMNDI@ from running a ; in the AUTO text as a further command.

527EH - DATE

Routine 6. With a text, up to three numbers MM/DD/YY (any character that is not a digit separates them) are stored, each modulo 100, into DATE$ (4044H year, 4045H day, 4046H month) and into the date the start-up saved at 4315H; a number that is not given keeps its old value, and the values are not checked. Without a text the date is shown as Www - Mmm d, 19yy - n: the weekday, the month's name, the day, the year as 1900 plus DATE$'s year, and the day of the year.

5307H - Days since 1900

Returns Register Pair HL = the days from 1 January of year 0 to the date in DATE$, from 0: 365 for each year before DATE$'s year plus one for each of them that is divisible by 4 (year 0 included), then 5324H adds the months and the day (with 29 February in a year divisible by 4). Day 0 is counted as a Sunday, so the weekday is right for the years 1901 to 1999. 5324H alone, with Register Pair HL = 0000H, gives the day of the year less 1. Register Pair DE is kept.

5359H - A Hyphen

Puts a space, a hyphen and a space at Register Pair DE and moves Register Pair DE past them.

5365H - TIME

Routine 13. With a text, up to three numbers HH:MM:SS are stored, each modulo 100, into TIME$ (4041H seconds, 4042H minutes, 4043H hours); a number not given keeps its old value. Without a text the time is shown by GTTIME@ and DSPLY@.

537CH - Three Numbers

Sets the three bytes at Register Pair DE (DATE$, the saved date or TIME$) from the text at Register Pair HL: the first number goes to +02H (the month or the hours), the second to +01H, the third to +00H, each modulo 100 by DIVD@. A value that is not given (the end of the line comes first) keeps the old one, which is copied to 5653H-5655H before the numbers are read.

53B0H - ERROR

Routine 8: ERROR n shows the message of error n (0-255, else 2DH), ERROR alone that of the last error posted (4304H). ERROR@ is called with bits 7 and 6 set: no frame, and it returns here instead of ending through ABORT@.

53CAH - I

Routine 9: the drive given (EVAL@'s block at 55FCH, a drive only, else 20H), or drives 1 to 7, are marked to be logged again at their next access (bit 0 of DCT+03H). With MOUNT, each ready floppy drive's GAT is read at once and the number of sides is set from bit 5 of its +CDH (DCT+0CH).

542FH - LIB

Routine 10: the names of the library commands from SYS1/SYS's table (5106H, which SYS1/SYS's routine 9 returns, request 09H), five to a line in columns of 12, after two spaces, to @DO or to the device or file given (54F3H).

546BH - PAUSE

Routine 11: waits for ENTER, with bit 5 of SFLAG1$ (a DO file runs) cleared so that the keyboard is read even during a DO file; ENTER puts SFLAG1$ back, BREAK ends with error 30H (and the bit stays clear).

5481H - SCREEN

Routine 12: the 16 lines of 64 characters of the video memory at 3C00H, each followed by a carriage return, to @PR or to the device or file given (54F3H). On the Model I a code below 20H is sent as that code plus 40H, the character the display shows for it.

54A5H - CLOCK, DEBUG, VERIFY and BREAK

Routines 5, 7, 14 and 4: each takes ON or OFF from the command line (5527H: the Z FLAG for ON, or for nothing). CLOCK puts the clock display task (462FH) into interrupt slot 2 by SET@ or takes it out by RESET@; DEBUG sets or clears bit 2 of SFLAG1$, VERIFY bit 3; BREAK clears bit 0 (the BREAK key works) for ON and sets it for OFF.

54DAH - The Error Exits

Seven entries, each loading its error code into Register A: 54DAH 20H Improper drive number, 54DDH 2DH Invalid data provided, 54E0H 30H Terminated, 54E3H 2BH Illegal devicespec, 54E6H 2EH Invalid parameter, 54E9H 08H Drive not available, 54ECH 0FH Write protected disk. Each LD A,n after the first is the operand of an LD BC,nn entered from the entry above it. 54EEH posts the error in Register A by ERROR@ with bit 6 set (no frame), and ERROR@ ends with ABORT@.

54F3H - The Output

For LIB and SCREEN: Register A is the device used when no field is given (01H @DO, 02H @PR). EVAL@ takes a field with the block at 5605H: a device gives its DCB, a file is opened by INIT@ with its buffer at 5693H, and a drive is error 2BH. Register Pair DE returns the control block for the ROM's 001BH.

5527H - ON or OFF

PARAM@ takes the parameters from the command line at Register Pair HL with the table at 55D1H (eight bytes an entry: the name, then the address of its value): OFF and NO store their value into 5537H, the operand of LD DE,0000H at 5536H; ON and YES store theirs into 5691H, which nothing reads. Returns the Z FLAG for ON, for nothing given or for OFF=N, the NZ FLAG for OFF; an unknown parameter is error 2EH. Register Pairs BC and DE are kept.

553EH - A Decimal Number

Reads the digits at Register Pair HL into Register Pair DE. The number ends at a character that is not a digit, which is passed over, with the NC FLAG; or at the end of the line (a control code or a semicolon, 55B2H), which is not, with the C FLAG.

5560H - Decimal Digits

Puts the number in Register Pair DE (0-65535) at Register Pair HL as decimal digits without leading zeros (at least one digit) and returns Register Pair DE after them. The number is turned into six BCD digits at 55A9H-55ABH (sixteen doublings by ADC and DAA), and the digits into ASCII at 55ACH-55B1H by RLD.

55A9H - The Digits

Not in the file (the load module skips 55A9H-55B1H): the work area of 5560H.

55B2H - The End of the Line

Tests the character at Register Pair HL: a control code or a semicolon is the end of the line (the C FLAG, Register Pair HL unchanged); any other character is returned in Register A with the NC FLAG and Register Pair HL past it.

55BDH - A Request

Entered by a GOSUB with a request code in Register A (09H: SYS1/SYS's routine 9). The overlay request handler drops the return address of the RST 28H, so the routine returns straight to the caller.

55BEH - A Space

Sends a space to the control block at Register Pair DE; Register Pair AF is kept.

55C6H - Close the Output

When the control block at Register Pair DE is a file (type 80H), it is closed by CLOSE@.

55D1H - The Parameter Tables

Data: the table of ON and OFF for PARAM@ (eight bytes an entry: the name, then the address of the value), the table of I for EVAL@ (nine bytes: the name, the address, the type byte), and the two evaluation blocks of I (55FCH) and of LIB and SCREEN (5605H).

560EH - The Names of the Days and Months

Data: three letters each, for DATE (529DH, 52B7H), and the days of the months (5330H).

5653H - The Work Area

Not in the file: SYS12/SYS uses the memory after its last byte (5652H) for the field of EVAL@ or FSPEC@, the text of DATE and TIME, and the buffer of an output file.