DOSPLUS 3.5 for the Model III - SYS11/SYS Disassembled

SYS11/SYS

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DOSPLUS 3.5 SYS11/SYS Disassembly - The Library Commands ASSIGN, FILTER, FORCE, JOIN and RESET (Model III)

SYS11/SYS is the third of the high overlays, which hold the library commands: it loads at 5200H, over the area 5200H-5BFFH that SYS0/SYS keeps for them, and holds FORCE (request code A3H), RESET (A4H), ASSIGN (A5H), JOIN (A6H) and FILTER (A7H). CMNDI@ takes these codes from SYS1/SYS's table of the library commands (51CBH, 51D7H, 51B7H, 51CFH and 51CAH) and passes them to the overlay request handler, which loads SYS11/SYS and calls routines 3 to 7 of its table at 5200H with Register Pair HL at the rest of the command line. No file of the diskette requests routine 2 (A2H). The file is a load module of 6 blocks, 1402 bytes, from 5200H to 5779H, with the transfer address 5200H; the work area after it holds the blocks of the command line fields and, at 5800H, the filter file's buffer. SYS11/SYS itself requests SYS7/SYS's routine 6 (66H, one command line field) for ASSIGN and SYS3/SYS's routine 6 (26H, the specification of an open file) for the device list.

The Parts of SYS11/SYS

Devices, DCBs and the DCB Table

Each of the six character devices (0 @KI, 1 @DO, 2 @PR, 3 @RS, 4 @U1, 5 @U2) has an entry of 11 bytes in SYS0/SYS's DCB table (44A6H): +00H its DCB's address, +02H its filter table, +04H the control block it is JOINed to, +06H and +08H the driver and type byte saved by FORCE or JOIN, +09H its name. A DCB starts with its type byte (bit 0 input, 1 output, 2 control, 3 NIL, 4 FORCE, 5 JOIN, 6 filter) and the address of its driver at +01H. @RS, @U1 and @U2, like drives 4-7 in DCTTBL, share SYS0/SYS's NIL block, whose driver address is FFFFH: before one of them is changed it gets 20 bytes of its own below HMEM$, made a NIL block (5679H). An entry is found from EVAL@'s flag byte of a field, bits 0-2 the number and bit 3 a drive (569FH).

FORCE and JOIN

The two commands share their code: FORCE enters with LD A,90H and JOIN inside the LD BC,A03EH that follows it, where the bytes read as LD A,A0H; the value is stored as the operand of an OR that later sets the device's type byte (520EH). Without fields they list the devices (5228H): $nn and @XX, the directions the device can do (< input, > output), then FORCE and the device or file it goes to, NIL, or the address of its driver, and for a JOINed device JOIN and the device or file it is linked to. With fields (52F2H), the source must be a device (2BH); it is reset first, and a destination that is the same device leaves it so. A file as the destination gets 288 bytes below HMEM$ for its buffer and control block and is opened by INIT@; a device gives its DCB through LOCDCB%. The source's driver and type are saved in its entry, its type byte loses its direction bits (so the ROM leaves its I/O to SYS0/SYS) and gains bit 7 with the FORCE or JOIN bit, and its DCB+01H points to the target (FORCE) or to the entry's +04H, which holds the target (JOIN).

RESET

RESET (5375H) undoes FORCE, JOIN and NIL for one device or for devices 0 to 5 (5618H): a file the device went to is closed and its block given back when it is the lowest one below HMEM$, the saved driver and type byte are put back. A filter stays.

ASSIGN

ASSIGN (539FH) takes its two fields one by one through SYS7/SYS's routine 6, so the rest of the line is left for a driver's parameters. The first must be a device or a drive (2BH); a device is reset first. With a file as the second field, the driver program is RUN (540CH) with Index Register IX at the first field's DCB or drive control table (one of its own), Index Register IY at its entry and Register Pair HL at its parameters; OVLYH$ is set to FFH because the program may load over SYS11/SYS. Otherwise both fields must be devices or both drives (2BH), the second must have a driver (29H), and its DCB (8 bytes) or drive control table (20 bytes) is copied over the first one's; a drive then has its NIL bit cleared and is logged at its next access.

FILTER

FILTER (5426H) needs a device (2FH, 2BH). With a file, the device's filter bit (bit 6 of the type byte) is cleared, its old table is given back when it is the lowest block below HMEM$, and the file is read (5549H): pairs old=new, each code two hexadecimal digits or a character in double or single quotation marks, separated by commas or ends of lines, with comments from a period to the end of a line. The table is built down from HMEM$, a count byte and up to 255 pairs, and its address goes to +02H of the entry. The filter is then switched on unless NO or OFF was given or the device has no table; MAP lists the table five pairs to a line (54EBH), printable codes quoted and the others in hexadecimal.

Differences from the Manual

RESET without a field resets the six devices only; the manual says all devices and disk drives, but the bytes never touch DCTTBL, and RESET with a drive is error 2BH. The manual's description of the second form of ASSIGN names the two fields the other way round from its own example (ASSIGN :5 :4) and from the bytes: the first field receives the second one's driver. FILTER also takes ON and OFF; ON and YES are stored into the file buffer and do nothing, since the filter is switched on anyway. A destination of FORCE or JOIN that is a drive is not refused: its number is taken as a device number. The directions of the two devices are not compared, as the manual warns.

Differences from the Model I

The code is the Model I SYS11/SYS with the Model III addresses of SYS0/SYS (HMEM$ 4411H, SFLAG1$ 4297H, OVLYH$ 429EH, the DCB table 44A6H, DCTTBL 44E8H, the command file control block 42DEH, LOCDCB% 44A0H, the 8 bit multiply 4491H, the wrapper 4485H) except for the reading of the filter file (5549H-55AEH), which is six bytes longer, so everything after it is six bytes higher. The Model III reads each byte without passing over spaces (559CH); spaces, control codes and comments are passed over only before a code (5549H), and spaces after a hexadecimal code or a closing single quotation mark (5592H). So a quoted space or period is a code, but a space after a closing double quotation mark is error 2DH.

5200H - The Routine Table

Data: SYS11/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 A2H-A7H. CMNDI@ takes the codes of the library commands from SYS1/SYS's table: FORCE A3H (51CBH), RESET A4H (51D7H), ASSIGN A5H (51B7H), JOIN A6H (51CFH), FILTER A7H (51CAH). No file of the diskette requests A2H. The words for FORCE and JOIN point three bytes apart, into the same instruction (5210H).

520CH - Routine 2

Nothing to do when SYS0/SYS's record locator brings SYS11/SYS back.

520EH - FORCE and JOIN

Routines 3 (FORCE, 520EH) and 6 (JOIN, 5211H), entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. FORCE loads Register A with 90H and JOIN, entering inside the LD BC,A03EH, with A0H: the bits given to the device's type byte (bit 7 with bit 4 FORCE or bit 5 JOIN) go to 5359H, the operand of OR 00H at 5358H. EVAL@ then takes the command line with the block at 5730H. With no field at all, the six devices are listed with their settings (5228H); otherwise the device is routed (52F2H).

5228H - The Device List

FORCE or JOIN alone lists the six character devices, one line each: $nn, the device's number in two decimal digits, @ and its name, the directions it can do (< input, - , > output), then FORCE and the device or file it is routed to, NIL, or the address of its driver; a JOINed device adds JOIN and the device or file it is linked to.

524CH - One Device's Line

Index Register IY points to the device's entry in the DCB table, whose first word is the address of its DCB. The direction bits come from the DCB's type byte, or from the type saved at entry+08H while the device is NIL, FORCEd or JOINed. The registers are kept by SYS0/SYS's wrapper (4485H).

52F2H - Routing a Device

FORCE or JOIN with fields: both are needed (2FH), and the source must be a device (2BH). The source device is first reset (5618H); a destination that is the same device ends the command there (FORCE @PR @PR resets @PR). A destination with a name is a file: 288 bytes are taken below HMEM$ for its buffer and file control block and it is opened by INIT@; else it is a device and LOCDCB% gives its DCB. The source gets a DCB of its own if it shares the NIL block (5679H), its driver and type are saved in its entry (+06H, +08H), its type gets bit 7 and the FORCE or JOIN bit, and DCB+01H points to the target (FORCE) or to the entry's +04H, which holds the target (JOIN).

5375H - RESET

Routine 4, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. EVAL@ takes the command line with the block at 5739H, whose three blocks are all 577AH. A source must be a device (2BH: a drive cannot be RESET), which is reset by 5618H; without one, devices 0-5 are reset in turn. The drives are not touched.

539FH - ASSIGN

Routine 5, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. The two fields are taken one by one by SYS7/SYS's routine 6 (request 66H), not by EVAL@, so the rest of the line stays for a driver's parameters. The first must be a device or a drive (2BH); a device is reset first. A second field with a name is a driver program: it is RUN with Index Register IX at the first field's DCB and Register Pair HL at the rest of the line (540CH). Otherwise the second field must be of the same kind as the first (2BH) and have a driver (29H), and its DCB (8 bytes) or drive control table (20 bytes) is copied over the first one's; a drive gets its NIL bit cleared and is logged again.

5409H - One Field

Requests SYS7/SYS's routine 6 (66H), which takes one field of the command line at Register Pair HL into the block at Register Pair DE. The overlay request handler drops the return address of the RST 28H, so the routine returns straight to the caller of 5409H.

540CH - A Driver Program

ASSIGN with a file name as its second field: the first field gets a DCB of its own if it shares the NIL block, the name goes to the file control block at 42DEH that CMNDI@ uses, OVLYH$ is set to FFH (the program may load over SYS11/SYS), and RUN@ loads and runs the driver with Index Register IX at the DCB or drive control table, Index Register IY at its entry and Register Pair HL at the rest of the command line, for its parameters.

5426H - FILTER

Routine 7, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. The parameters NO/OFF (54D2H) and MAP (54E6H) and the count of the table (55AFH) are cleared, and EVAL@ takes the command line with the block at 5743H: a device must be given (2FH, 2BH). With a file as the second field, the device's filter is switched off (bit 6 of its type byte), its old table is given back when it is the lowest block in high memory, and the file's pairs are read into a new table below HMEM$, whose address goes to +02H of the device's entry. Then the filter is switched on unless NO or OFF was given and the device has a table; MAP lists the table.

54EBH - MAP

Lists the device's table, five pairs to a line, each as old=new: a printable character in single quotation marks, any other code (below 20H, or 80H and above) as two hexadecimal digits and H. The pairs are listed from the first read, at the top of the table, down. The SPACE BAR pauses at the end of a line and BREAK ends the list (55FCH).

5530H - Show a Code

A code of 20H-7FH is shown as the character in single quotation marks; any other in hexadecimal, two digits and H (55B5H).

5549H - Reading the Filter File

5549H reads one code into Register C: two hexadecimal digits, or a character between double or single quotation marks; it returns the Z FLAG with Register A = the next character, or the NZ FLAG at the end of the file (1CH). Spaces, control codes and comments (from a period to the end of its line) are passed over before a code, and spaces after a hexadecimal code or a closing single quotation mark (5592H); the byte after a closing double quotation mark is taken as it is. 559CH gets the next byte of the file without passing over anything, so a quoted space or period is a code. Any error other than the end of the file is posted.

55AFH - The Count of Pairs

Data: the number of pairs read from the filter file, cleared by 542AH, counted up by 54B2H and copied below the table by 54B9H as its first byte.

55B0H - Hexadecimal Output

55B0H shows Register Pair HL as four hexadecimal digits and H; 55B5H shows Register A as two digits and H; 55BDH shows Register A as two digits; 55C6H shows the low four bits of Register A as one digit.

55D1H - Two Decimal Digits

Shows Register A (0-99) as two decimal digits, the device number of the list. Register Pair DE is kept.

55E8H - A Hexadecimal Digit

Turns the character in Register A (0-9, A-F or a-f) into its value 00H-0FH with the NC FLAG; the C FLAG for any other character.

55FCH - The Keyboard

Returns the NZ FLAG at once while a DO file runs (bit 5 of SFLAG1$). Otherwise the keyboard is scanned once: the SPACE BAR waits for the next key, and the Z FLAG is returned when the key is BREAK (01H).

560DH - Spaces

Shows Register A spaces (Register A 1 or more).

5618H - Reset a Device

The device or drive named by Register E (bits 0-2 the number, bit 3 a drive) is put back as it was before FORCE, JOIN or NIL: with nothing of these set (bits 3-5 of the type byte) nothing is done. A FORCE or JOIN to a file closes the file and gives its 288 byte block back when it is the lowest block below HMEM$; a FORCEd or JOINed device gets its saved driver back; the saved type from the entry's +08H is restored in every case. A filter (bit 6) is left as it is, since the saved type was taken from the type byte. The registers are kept by SYS0/SYS's wrapper (4485H).

565BH - Find a DCB

Looks up the DCB address in Register Pair HL among the six entries of the DCB table: the Z FLAG with Index Register IY at the entry, the NZ FLAG when it is not there. Register Pairs BC and DE are kept.

5679H - A DCB of Its Own

Points Index Register IX to the DCB or drive control table of the device or drive in Register E and Index Register IY to its entry. When the driver address at its +01H is FFFFH (the NIL block 43CBH, which @RS, @U1, @U2 and drives 4-7 share), 20 bytes are taken below HMEM$, made a NIL block (08H, then 00H) and put into the entry, so that it can be changed without changing the others.

569FH - Find the Entry

Register E holds a device or drive as EVAL@'s flag byte gives it: bits 0-2 the number, bit 3 a drive. Index Register IY returns at its entry (in the DCB table, 11 bytes an entry, or DCTTBL, 4 bytes an entry) and Index Register IX at the DCB or drive control table the entry names. Register Pairs DE and HL are kept.

56C8H - A Device's Name

Shows @, the two characters of the name at +09H of the DCB table entry at Index Register IY, and a space (56D9H).

56DEH - A File's Specification

Has SYS3/SYS's routine 6 (request 26H) put the specification back into the copy of a file control block at Register Pair DE, then shows it by DSPLY@. Nothing is shown when the routine returns the NZ FLAG.

56ECH - Memory below HMEM$

56ECH takes Register Pair BC bytes below the top of memory: HMEM$ goes down by Register Pair BC and Register Pair HL returns the first byte of the block. 56F7H gives Register Pair BC bytes at Register Pair HL back when they start just above HMEM$, the lowest block; any other block stays taken.

570BH - The Error Exits

Five entries, each loading its error code into Register A: 570BH 2BH Illegal devicespec, 570EH 2CH Illegal filespec, 5711H 2FH I/o field not found, 5714H 2DH Invalid data provided, 5717H 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, so only one load counts. 5719H posts the error in Register A by ERROR@ with bit 6 set (no frame), and ERROR@ ends with ABORT@.

571EH - The Texts

Data: the three words of the device list, each ended by 03H for DSPLY@.

5730H - The Evaluation Blocks

Data: the blocks that Index Register IX points to for EVAL@: the flags EVAL@ sets (bit 0 a source, bit 1 a destination, bit 2 a wildmask, bit 3 parameters), the addresses of the source, destination and wildmask blocks, and of the parameter table. FORCE and JOIN use 5730H, RESET 5739H (one block for every field) and FILTER 5743H; the empty table at 5742H serves FORCE, JOIN and RESET. A parameter entry is the name (6 characters), the address its value is stored to and a type byte (20H a logical value, so the name alone sets it).

577AH - The Work Area

Not in the file: SYS11/SYS uses the memory after its last byte (5779H) for the two blocks of EVAL@ (or of SYS7/SYS's routine 6 for ASSIGN) and the filter file's buffer.