LDOS 5.3.1 for the Model III - LCOMM/CMD Disassembled

LCOMM/CMD

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LDOS 5.3.1 LCOMM/CMD Disassembly - The Terminal Program (Model III)

LCOMM/CMD is the terminal program of LDOS 5 for the Model I and Model III (COMM on version 6, M-40-060). It talks to a device that a serial driver has been set to, usually the CL device, never to the RS-232 hardware itself: LCOMM devspec (XLATES=X'fftt', XLATER=X'fftt', NULL=ON/OFF, XON=d, XOFF=d). KI/DVR must be active, because the functions are given with CLEAR and the keys of the top row, which KI/DVR returns as the key plus 80H: CLEAR 1 to CLEAR 7 choose the KI, DO, PR, CL, FS (file send) and FR (file receive) devices and DTD (dump to disk), and a second key, CLEAR : (ON), CLEAR - (OFF), CLEAR 9 (ID), CLEAR 0 (RES), CLEAR SHIFT % (REWND) or CLEAR SHIFT ampersand (PEOF), acts on it; CLEAR with SHIFT and a key switches DUPLX, ECHO, ECOLF, ACCLF, DCC, 8-B and HNDSH, clears the screen (CLS), runs a DOS command (CMD) or ends LCOMM (EXIT); CLEAR 8 shows the menu.

The file is a load module of 2646 bytes: a record of type 1FH with the text Copyright 1991 MISOSYS, Inc., All rights reserved, thirteen load blocks for 6000H-674AH, 67EBH-6802H, 6804H-681DH and 6C00H-6E6DH (2539 bytes) and the transfer address record for 6C00H. The start-up at 6C00H opens the device, sets up six buffers and two background tasks, and is then itself given to the buffers: every buffer is a chain of pages of 256 bytes, from 6C00H to HIGH$, taken and given back as it grows and shrinks (the dynamic buffering of the manual). Task 8 reads the line into the receive buffer and sends from the send buffer on every clock tick (30 a second); task 9 empties the printer buffer. The main loop at 6000H moves the characters between the buffers, the video and the files. Most switches are the operands of the instructions that test them.

What LCOMM Does

About This Page

6000H - The Main Loop: the Buffer Warning and the Keyboard Buffer

After the start-up (6C00H) LCOMM runs this loop until EXIT. Each pass takes one character to send, from the keyboard buffer 67EBH or else from the file being sent, then one character from the receive buffer 67F3H, and ends with the device steps of 63C7H (one character to the line, one key, one character to the printer, one character written to the receive file). Many switches of LCOMM are the operands of the instructions that test them: LD A,nn / OR A and LD B,nn / INC B / DEC B load the switch and set the Z FLAG when it is 00H. The first one, the operand 6001H, is set to 07H by 64AAH when fewer than eight free pages (2K) are left: the warning is displayed and the XOFF character is put in the one character slot 6412H of the send routine.

6036H - A Character to Send

The character in Register C is first translated by the XS parameter (603CH replaces 6038H). With DUPLX on (half duplex) it is shown and written like a received character by 60FAH. When the line is on (63E0H) it goes into the send buffer 67F7H; with ECOLF on a carriage return also gets a line feed.

6060H - A Received Character

When the line is on, the next character of the receive buffer 67F3H, filled by the task 63DFH, is taken. With DCC on a control character is shown as two hex digits between braces before it is used. Bit 7 is cleared unless 8-B is on. With HNDSH on the XON and XOFF characters (6099H, 609DH, the parameters, by default 11H and 13H) start and stop the sending (6406H), and DC2 (12H) and DC4 (14H) switch the FR device on and off; these four are not shown.

60B8H - Echo, Line Ends and the Output

With ECHO on the received character goes back into the send buffer, and a carriage return gets a line feed too when ECOLF is on. The first line feed after a carriage return is dropped unless ACCLF is on: the operand 60E8H is set at each carriage return to the ACCLF switch and at each line feed to 0AH. DEL (7FH) is dropped; every other character goes to the video, the printer and the receive buffer through 60FAH.

60FAH - The Output of a Character: Video, Receive Buffer, Printer

The character in Register C goes to the video when DO is on (a form feed 0CH clears the screen), into the receive file buffer 67FFH when FR is on, and into the printer buffer 67EFH when PR is on. The routine then runs on into 6128H, one step of DTD.

6128H - Dump To Disk

With DTD on, one character of the receive file buffer is written to the FR file each time this runs (from 60FAH and at the end of every pass, 63D4H). A character is taken from the buffer even when no FR file is open, and is then lost. A write error is shown and switches DTD and FR off.

614AH - The Command Keys

A key with bit 7 set (KI/DVR gives CLEAR with a key as the key plus 80H) comes here from 643EH. Each command loads Register Pair HL with the address of its switch (an operand of the main loop), Register Pair BC with the control block of the device's buffer (0000H when it has none), Register Pair DE with the device's file control block (0000H for the devices that are not files) and Index Register IX with the sector buffer of a file, then 621CH takes the second key. CLEAR SHIFT ! to CLEAR SHIFT ) are DUPLX, ECHO, ECOLF, ACCLF, DCC, CLS and 8-B, CLEAR SHIFT asterisk is HNDSH, CLEAR SHIFT 0 (A0H) a DOS command, CLEAR SHIFT = (BDH) EXIT; CLEAR 1 to CLEAR 7 are KI, DO, PR, CL, FS, FR and DTD, CLEAR 8 the menu. REWND (CLEAR SHIFT %), PEOF (CLEAR SHIFT ampersand), ID (CLEAR 9) and RES (CLEAR 0) count only as the second key.

61F3H - EXIT

The two tasks are removed, the line driver gets the control request 58H, FR is switched off and an open FR file is closed. LCOMM ends at @EXIT, or at @ERROR when the close fails. The FS file is not closed and the printer buffer is not emptied.

621CH - ON and OFF

After a device or switch key the second key decides (6242H): CLEAR - stores 00H, CLEAR : stores FFH at Register Pair HL. ON is taken for a file device only while its file is open. For the CL device ON also lets the sending go on (6406H), as the manual says ON overrides an XOFF. HNDSH takes ON or OFF the same way; any key that is not a command makes it the pause character: the sending stops after that character until an XON comes (6427H).

6242H - The Second Key

6242H waits for the key after a device or switch key. CLEAR - (ADH) returns 00H, OFF. CLEAR : (BAH) returns FFH, ON, when Register Pair DE is 0000H (the byte at ROM 0000H, F3H, has bit 7 set) or points to an open file; ON for a file device without an open file is refused like an unknown key. Every other second key drops the return address of the caller (624FH), so that the store of the switch is skipped: CLEAR 9 is ID, CLEAR 0 RES, CLEAR SHIFT % REWND and CLEAR SHIFT ampersand PEOF; any other key displays Unacceptable command sequence!.

6276H - CLS

CLEAR SHIFT ( clears the screen and puts the cursor at the top left; nothing is sent to the line.

6280H - The Menu

CLEAR 8 displays the menu 6573H, five lines in the order of the keys: the shifted functions with an asterisk above each that is on, the labels, the keys, the device labels and an asterisk below each device that is on. The two asterisk lines are cleared and the table 6694H (15 entries of a switch address and a place in the text) puts an asterisk where the switch is not 00H; the CL device gets two, for the send switch 6406H and the line switch 63E0H. With HNDSH on, the pause character is shown in hex at the end of the first line (00H when none). The names of the open FS and FR files follow, then the free memory in K (6306H).

6306H - The Free Memory

The count of free pages at 6803H, divided by four, is the free memory in K: two decimal places, the first a space below 10K, are written at 66F0H-66F1H and the line Memory: nnK is displayed.

632DH - RES

CLEAR 0 after a device key. With no buffer (Register Pair BC = 0000H: DO and the switches) it is refused. For KI, PR, CL and DTD the buffer at Register Pair BC is emptied (6335H), its pages given back. For FS the switch is cleared and the file closed; for FR the FR and DTD switches are cleared and the file closed. A file's buffer is not emptied: characters received for the FR file and not yet written are lost to it and stay in 67FFH for the next file.

6335H - Empty a Buffer

Register Pair BC points to the control block of a buffer: +00H-+01H the place where the next byte is put (low byte, page), +02H-+03H the place where the next byte is taken. The take place is set to the put place, and every page from the old take page up to the put page is given back to the free list by 64ECH, which also returns the next page of the buffer's chain.

634BH - RES of a File Device

FS: the FS switch 601EH is cleared. FR: DTD (6129H) and FR (610FH) are cleared. Then the file is closed with @CLOSE; an error is shown by 63A1H.

6362H - REWND and PEOF

CLEAR SHIFT % and CLEAR SHIFT ampersand after FS or FR: @REW or @PEOF on the file; for a device that is not a file the text Unacceptable command sequence! is shown. Their errors (for @PEOF also the end of file error it returns) are not shown.

6371H - ID

CLEAR 9 after FS or FR: File name: is asked, the answer (31 characters) is taken into the file's own sector buffer (Index Register IX, 6A00H or 6B00H) and given to @FSPEC; the FS file is opened with @OPEN, the FR file with @INIT (an existing file is opened, a new one created), both with that sector buffer and records of 256 bytes. A file already open gives File already open. The result of @FSPEC is not tested: a bad name reaches @OPEN or @INIT, whose error is shown.

63A7H - Take a Line; File Already Open; the Switch Helpers

63A7H takes a line at Register Pair HL with ROM 0040H and turns the cursor on again; 63B2H displays File already open. 63B8H, 63BDH and 63C2H switch FS, FR and DTD off.

63C7H - The Device Steps of the Main Loop

Each pass of the main loop sends one character to the line (6405H) and writes one to the printer (6477H) with the interrupts off, as the tasks do on every clock tick, takes one key (6434H) and writes one byte of the receive buffer to the FR file (6128H).

63D7H - The Line Task

6CB3H adds the block 63D7H as task 8, which the clock interrupt runs on every tick (30 a second): its routine 63D9H takes a character from the line into the receive buffer 67F3H (63DFH) and sends one from the send buffer (6405H). A received character is translated by the XR parameter (63F0H replaces 63ECH); a null is kept only when the operand 63F5H is not 00H. 6CF0H fills that operand from 6E64H, a byte that the parameter table does not reach: NULL stores its value at 6E65H-6E66H, so NULL=OFF does not drop the nulls.

6405H - Send One Character to the Line

Nothing is sent while the send switch 6406H is 00H (after an XOFF or the pause character) or while the driver answers the status request 00H with the NZ FLAG (not ready). The one character slot 6412H (the XOFF of the warning) goes first, else the next character of the send buffer 67F7H. When the character sent is the pause character of HNDSH (642BH), the send switch is cleared.

6434H - One Key from the Keyboard

ROM 002BH takes a key. A key with bit 7 set and the NO CARRY FLAG is a command (614AH). With KI on, every other key goes into the keyboard buffer 67EBH; BREAK (01H) without the CARRY FLAG sends a modem break instead: the control request 01H, the send buffer emptied, FS switched off, a wait of about 0.12 second (ROM 0060H with Register Pair BC = 2000H), and a null into the keyboard buffer; the driver ends the break when it sends that null. A key with the CARRY FLAG from the keyboard driver is taken as a character.

6475H - The Printer Task

6CBBH adds the block 6475H as task 9, run on every clock tick; the main loop also calls its routine (63D0H). When the printer is ready (the ROM's @CTL with the request 00H to the printer's control block 4025H returns the Z FLAG), one character of the printer buffer 67EFH is printed.

648FH - Put a Byte into a Buffer

Each of the six buffers is a chain of pages of 256 bytes, taken from the free list in the page table 6900H as it grows and given back as it is emptied; its control block holds the put place (+00H low byte, +01H page) and the take place (+02H, +03H). When the put place reaches the end of a page, a new page is linked to it (64D4H) and the count of free pages 6803H goes down; with seven or fewer left (below 2K), the warning switch 6001H is set. When no page is left, the put place stays on the last byte, so the next byte overwrites it.

64B4H - Take a Byte from a Buffer

The take place (+02H, +03H) equal to the put place means an empty buffer (the Z FLAG). Otherwise the byte is returned with the NZ FLAG; when the take place passes the end of a page, the page is given back to the free list and the take place moves to the next page of the chain.

64D4H - Take a Page from the Free List

The page table 6900H holds at 69nnH the page that follows page nn in its chain (00H for the last). 6900H is the first page of the free list, 6901H its last. 64D4H unlinks the first free page and links it after page Register H; the last free page is never given out, so the call fails (the Z FLAG) when only one is left. 64ECH gives page Register H back at the end of the free list and returns the page that followed it.

6503H - CMD: a DOS Command

CLEAR SHIFT 0 asks Enter command: and takes up to 64 characters at 67ABH. With bit 4 of 4758H set (the only file that sets it), SYS1/SYS carries the command out through @CMNDR (429CH) and returns without loading a program, which would overwrite LCOMM; the tasks go on buffering the line meanwhile. Command completed is displayed afterwards.

6528H - The Texts of the Commands and the Menu

The texts end with 0DH (a new line after them) or 03H (the cursor stays after them). 1DH puts the cursor at the start of its line. The menu text 6573H-6693H has five lines; the asterisks are written into the first and the last line by 6280H, at the places that the table 6694H gives.

6694H - The Menu Table

15 entries of two words: the address of a switch and the place of its asterisk in the menu text (6280H). The last entry must be HNDSH: 62ADH reads its switch after the loop.

66D0H - The Texts of the Menu's Last Line and the Messages

FS-Spec:, FR-Spec: and Memory: follow one another on the line after the menu; the two warnings end with a new line.

674BH - The Control Blocks and the Buffers

674BH-67EAH are not in the file: the control block of the line device, the file control blocks of the FS and FR files (their first bytes cleared by the start-up) and the line buffer. 67EBH-6802H are the six buffer control blocks, set up by the start-up; 6803H, not in the file, counts the free pages. Above the routines at 6804H-681DH, 681EH-68FFH are not used; the page table is at 6900H, the sector buffers of the two files at 6A00H and 6B00H, and the buffer pages from 6C00H, over the start-up, up to HIGH$.

6804H - The File Room Test and the Buffer Calls

The FS file is read only while at least 18 pages are free (6022H). 6812H and 6818H call the put and take routines with the interrupts off, since the tasks use the same buffers and the page table.

6C00H - The Start-up: the Device and the Parameters

LDOS Ready loads LCOMM/CMD at 6000H-6E6DH and jumps to 6C00H, the transfer address, with Register Pair HL at the rest of the command line. The command is LCOMM devspec (parameters) (M-40-060): XLATES or XS=X'fftt' and XLATER or XR=X'fftt' translate one character sent and received, NULL or N keeps or drops received nulls, XON and XOFF set the handshake characters. KI/DVR must be active (bit 4 of DFLAG$). The device specification must start with an asterisk and is opened as a device; its errors end LCOMM through @ERROR.

6C3EH - The Free List and the Six Buffers

The pages from 6C00H, where the start-up itself lies, up to the last whole page below HIGH$ are chained into the free list of the page table 6900H. Each of the six buffers gets its first page (6C9BH) and an empty control block; the free pages left, less the last one, are counted into 6803H.

6CB3H - The Tasks, the Line Driver and the Parameters

The line task (63D7H) goes into task slot 8 and the printer task (6475H) into slot 9; both run on every clock tick. The line driver gets the control request 57H with Index Register IY at the receive routine 63DFH. The screen scrolls by ten lines, the cursor is turned on, the parameter values are stored in the operands of the code that uses them, and the main loop starts.

6D05H - The Start-up Errors

Four texts, displayed by @LOGOT before @ABORT. The entries 6D09H, 6D0DH and 6D11H lie inside LD IX instructions: each DD byte makes the LD HL before it a part of an LD IX, which loads Index Register IX and changes nothing that counts.

6D1AH - The Texts of the Start-up

The banner, the menu hint, the lines that scroll the screen and the four error texts. They lie in the page 6D00H, which becomes buffer room once the main loop runs.

6E23H - The Parameter Table and the Values

The table of @PARAM: eight entries of a name of six characters and the address where the value goes (a word: FFFFH for ON or a name alone, 0000H for OFF, else the number), ended by 00H. XLATES and XS store at 6E66H-6E67H, XLATER and XR at 6E68H-6E69H, NULL and N at 6E65H-6E66H, XON at 6E6AH-6E6BH, XOFF at 6E6CH-6E6DH. NULL's word overlaps the low byte of XS: NULL alone, NULL=ON or N stores FFH at 6E66H, so that LCOMM then sends FFH for a null; NULL=OFF stores 00H there. The start-up reads the null switch from 6E64H instead, so no NULL parameter keeps the nulls out.