DOSPLUS 3.5 for the Model III - SYS16/SYS Disassembled

SYS16/SYS

Other Navigation

DOSPLUS 3.5 SYS16/SYS Disassembly - The Library Commands CONFIG and SYSTEM (Model III)

SYS16/SYS is the last of the high overlays: it loads at 5200H and holds two library commands, routines 3 and 4 of its table at 5200H with the request codes F3H and F4H: CONFIG and SYSTEM. CMNDI@ takes the codes from SYS1/SYS's table of the library commands and passes them to the overlay request handler, which loads SYS16/SYS and calls the routine with Register Pair HL at the rest of the command line. No file of the diskette requests routine 2 (F2H). The file is a load module of 7 blocks, 1703 bytes, from 5200H to 58A6H, with the transfer address 5200H and no gaps; the work area after the file starts at 58A7H. Both commands take their field and parameters by EVAL@, each with its own evaluation block whose three field blocks are all 58A7H.

The Parts of SYS16/SYS

CONFIG

CONFIG (5208H) without a drive lists the eight entries of DCTTBL (44E8H): each line is $ with the drive number in two digits, :name, and the description of its drive control table (527FH): NIL for a drive with the NIL bit; Hard,Fix or Hard,Rem for a rigid drive, Floppy,Sden or Floppy,Dden for a floppy drive; then ,Size=5 or 8, ,Sides=, ,Step= and ,PD=; a rigid drive adds ,CO= (the cylinder offset), ,HO= (the head offset), ,TS= (the sectors per track) and ,WP, a floppy drive ,WP, ,MD, ,HL and ,Skip for the bits set. With a drive (else error 2BH; a NIL drive is error 29H) the parameters change its table (536CH): SIDES (+0CH, not 0), SIZE (5 or 8, bit 7 of +03H), STEP (+04H), PDRIVE (+0AH), WPROT (bit 6), COFFST (+06H-+07H), HOFFST (+05H), TSIZE (+0DH), MDELAY (bit 4), HLOAD (bit 3) and SKIP (bit 2 of +03H); bit 0 of +03H is set, so the diskette is logged again at its next use. Nothing else is checked: any step rate, physical drive or sector count is taken, and only the low byte of a number is used. Nothing is written to a diskette: the change lasts until the system is booted again, or is kept in a configuration file.

SYSTEM

SYSTEM (5500H) alone shows the memory pointers LOW$ (42A7H), HIGH$ (4411H) and TOP$ (42A5H) in hexadecimal. With parameters (5563H): TIME, DATE and LOGO set bits 3, 2 and 1 of the boot flags (+10H of the boot sector, sector 2 of cylinder 0 of drive 0), and STEP, PORT and MODE its +16H, +17H and +18H (the default step rate, and a port and a value to output at boot). When any of these or SAVE is given, the boot sector is read into 4300H and written back. BLINK (its complement) goes to 401CH, CAPS to 4019H, CURSOR (when not 0) to 4023H, and HIGH$ (when 0100H or more) to HIGH$ itself, which must be above 5BFFH (else error 2DH; it is not checked against TOP$); these take effect at once, and SAVE copies the first three to +13H-+15H of the boot sector. HIGH$ is never saved.

With a field SYSTEM writes a configuration file (5654H): a name (else error 2CH) with the default extension CFG, opened by INIT@. The image is built at 5A00H: the 126 bytes of the loader (571BH), the system areas of the table at 577BH, and the memory from HIGH$ + 1 to TOP$, where the drivers and filters are. It is written as a load module whose blocks load 0800H lower than the image (5A00H becomes 5200H), with the transfer address 5200H. Run as a program, the file's loader copies each area back to its place and the high memory above the restored HIGH$, sets the log bit of every drive with a driver, sets up the RS-232 interface by the ROM's 005AH, keeps the cursor position and the resident overlay bytes of the moment, and RETurns to DOSPLUS.

Differences from the Manual

CONFIG's parameter names in the bytes are SIDES, SIZE, STEP, PDRIVE, COFFST, HOFFST, TSIZE, WPROT, MDELAY, HLOAD and SKIP: the manual's PD, CO, HO, TS, WP, MD and HL are abbreviations of them. EVAL@ takes the first entry that starts with what is typed, so S is SIDES, not STEP as the manual says. CONFIG checks only SIDES (not 0) and SIZE (5 or 8). SYSTEM's HIGH is the name HIGH$; CURSOR=0 is ignored, and BLINK, CAPS and CURSOR are kept in the boot sector only with SAVE.

Differences from the Model I

The Model III code is the Model I code with the Model III addresses of SYS0/SYS (DCTTBL 44E8H, the wrapper 4485H, LOCDCT% 44A3H, DISKIO% 4488H, FEXT@ 444BH, LOW$ 42A7H, HIGH$ 4411H, TOP$ 42A5H, the resident overlay bytes 429DH, the boot sector buffer 4300H) and three changes: SYSTEM reads the boot sector without first clearing the double density bit of drive 0 and setting its log bit (11 bytes less, 559DH on); the loader of a configuration file sets up the RS-232 interface by the ROM's 005AH instead of sending ports E8H-EAH (10 bytes less); and the table of the system areas saves 400CH-404BH, 41E5H-4215H, 428DH-42BAH, 42BEH-42CDH, 4400H-4466H, 4467H-44A5H and 44A6H-455AH (seven entries, 4 bytes less). Everything after a change is lower by the bytes left out.

5200H - The Routine Table

Data: SYS16/SYS's table of routines 2-4, one word each, used by SYS0/SYS's overlay request handler (its 49D3H-49E6H) for the request codes F2H-F4H. CMNDI@ takes the codes of the library commands from SYS1/SYS's table: CONFIG F3H (51C1H), SYSTEM F4H (51DAH). No file of the diskette requests F2H.

5206H - Routine 2

Nothing to do when SYS0/SYS's record locator brings SYS16/SYS back.

5208H - CONFIG

Routine 3, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. The parameters (table 549CH) go into the operands of the change routine 536CH: the numbers SIDES, SIZE, STEP, PDRIVE, HOFFST and TSIZE start with the low byte FFH and COFFST as FFFFH (not given), the switches WPROT, MDELAY, HLOAD and SKIP as 53H (not given). EVAL@ takes the field with the block at 5493H. With a field the drive is changed (536CH); without one the eight drives of DCTTBL are listed, each as $nn :name and its description (527FH).

5242H - The List of the Drives

Without a field CONFIG shows the eight entries of DCTTBL, drives 0-7, one line each: $, the drive number in two digits, a space, a colon, the two characters of the drive's name, a space, and the description of its drive control table (527FH).

527FH - The Description of a Drive

Index Register IX is the drive control table of the DCTTBL entry at Index Register IY; the routine runs under 4485H, which keeps the registers. A drive with the NIL bit (bit 3 of DCT+00H) is NIL. Otherwise a rigid drive (bit 5 of DCT+03H) is Hard,Fix or Hard,Rem (bit 1, removable), a floppy drive Floppy,Sden or Floppy,Dden (bit 7 of DCT+0BH); then ,Size=5 or 8 (bit 7 of DCT+03H), ,Sides= (DCT+0CH), ,Step= (DCT+04H), ,PD= (DCT+0AH). A rigid drive goes on with ,CO= (DCT+06H-07H), ,HO= (DCT+05H), ,TS= (DCT+0DH) and ,WP (bit 6); a floppy drive with ,WP (bit 6), ,MD (bit 4), ,HL (bit 3) and ,Skip (bit 2) of DCT+03H. A carriage return ends the line.

536CH - Change a Drive

The field must be a drive (else error 2BH) whose drive control table is not NIL (else error 29H). Bit 0 of DCT+03H is set, so the diskette is logged again at its next use. Each parameter given changes the table: SIDES the surfaces (DCT+0CH; 0 is error 2DH), SIZE 5 or 8 (bit 7 of DCT+03H; any other is 2DH), STEP the step rate code (DCT+04H), PDRIVE the physical drive (DCT+0AH), WPROT bit 6 of DCT+03H, COFFST the cylinder offset (DCT+06H-07H), HOFFST the head offset (DCT+05H), TSIZE the sectors per track (DCT+0DH), MDELAY bit 4, HLOAD bit 3 and SKIP bit 2 of DCT+03H. Only the low byte of a number is used and nothing else is checked.

5431H - CONFIG's Texts

Data: the words of the description of a drive (527FH), each ended by 03H for DSPLY@ (NIL by a carriage return, which ends the line).

5493H - CONFIG's Evaluation Block

Data: the block that Index Register IX points to for EVAL@ (5230H): EVAL@'s flags, the three field blocks, all 58A7H, and the parameter table. Each entry is the name (6 characters), the address its value is stored to (the operands of 536CH) and a type byte (20H a switch, 40H a number). EVAL@ takes the first entry whose name starts with what is typed, so S picks SIDES, the first name that starts with S, and not STEP as the manual says.

5500H - SYSTEM

Routine 4, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. The switches TIME, DATE, LOGO, BLINK and CAPS start as 53H (not given), SAVE, the low bytes of CURSOR and HIGH$ and the write flag 5640H as 00H, the high bytes of STEP, PORT and MODE as FFH (table 57BAH). EVAL@ takes the field and the parameters with the block at 57B1H. Without a field and without parameters the memory pointers LOW$, HIGH$ and TOP$ are shown in hexadecimal (5539H). Otherwise the options are set (5563H), and a field names the configuration file to write (5654H).

5563H - Setting the Options

When DATE, TIME, LOGO, STEP, PORT, MODE or SAVE is given, sector 2 of cylinder 0 of drive 0, the boot sector with the system's options, is read into 4300H and the flag 5640H is set so that it is written back (563FH). DATE, TIME and LOGO set or clear bits 2, 3 and 1 of its +10H, the boot flags; STEP, PORT and MODE go to its +16H, +17H and +18H. BLINK (the complement of its value) goes to 401CH, CAPS to 4019H, CURSOR (not 0) to 4023H, and HIGH$ (0100H or more) to HIGH$ at 4411H, which must stay above 5BFFH (error 2DH). These four take effect at once; SAVE copies the first three into the boot sector's +13H-+15H. HIGH$ is never saved.

5654H - The Configuration File

With a field SYSTEM writes a configuration file: the field must have a name (else error 2CH), which gets the default extension CFG, and INIT@ opens it with the buffer 5900H. The image is built from 5A00H: the 126 bytes of the loader (571BH, which runs at 5200H), then the system areas listed at 577BH, then the memory from HIGH$ + 1 to TOP$ (the drivers and filters above HIGH$). The image is written as a load module whose blocks load at their image address less 0800H (5A00H becomes 5200H), up to 254 bytes each, and a transfer record to 5200H ends it; CLOSE@ closes the file. Run as a program, the file restores the system's state as it was when it was saved.

570FH - Write a Byte

Puts the byte in Register A to the configuration file at 58A8H through the ROM's 001BH; an error is posted.

571BH - The Loader of a Configuration File

Code that SYSTEM copies to 5A00H (5676H) and writes to the file to load at 5200H, so it runs at 5200H, 051BH lower than here; its absolute addresses are those it has there (5260H the table, 527EH the saved data). With the interrupts off it keeps the cursor position (4020H) and the resident overlay bytes (429DH), copies each saved area back to its place, then the memory above HIGH$ (HIGH$ is already restored), sets bit 0 of DCT+03H of every drive with a driver so that each diskette is logged again, has the ROM's 005AH set up the RS-232 interface from the restored control block 41F5H, puts back 429DH and the cursor position, and RETurns with the interrupts on.

577BH - The System Areas

Data: the table of the system areas a configuration file saves (5681H) and its loader restores (5724H, at 5260H there): the address and the length of each, ended by an address whose high byte is 00H.

5799H - SYSTEM's Texts

Data: the three words of the display of the memory pointers (5539H-555AH), each ended by 03H for DSPLY@, and the default extension of a configuration file.

57B1H - SYSTEM's Evaluation Block

Data: the block that Index Register IX points to for EVAL@ (5528H): EVAL@'s flags, the three field blocks, all 58A7H, and the parameter table. Each entry is the name (6 characters), the address its value is stored to (the operands of 5563H-562BH) and a type byte (20H a switch, 40H a number). The manual's HIGH is the name HIGH$, which a name of four characters matches.

581EH - A Number in Decimal

581EH shows the number in Register E, 5820H the number in Register Pair DE, each with up to four leading zeros left out; 5822H leaves out up to Register B of them. The routine runs under 4485H, which keeps the registers. The number is turned into six BCD digits at 58A7H-58A9H (the low two in 58A7H) by 16 doublings with DAA, then into six digits at 58AAH-58AFH; the five from 58ABH are shown, less the leading zeros left out.

5876H - A Number in Hexadecimal

5876H shows Register Pair HL as four hexadecimal digits and an H; 5883H shows Register A as two digits, 588CH the low four bits of Register A as one digit (by ADD 90H, DAA, ADC 40H, DAA).

5897H - The Error Exits

Four entries, each loading its error code into Register A: 5897H 2DH Invalid data provided, 589AH 2BH Illegal devicespec, 589DH 2CH Illegal filespec, 58A0H 29H Device not available. Each LD A,n after the first is the operand of an LD BC,nn entered from the entry above it. 58A2H posts the error in Register A by ERROR@ with bit 6 set (no frame), and ERROR@ ends with ABORT@.

58A7H - The Work Area

Not in the file: SYS16/SYS uses the memory after its last byte (58A6H) for the field block of EVAL@, the digits of a decimal number, the buffer of the configuration file and its image.