TEC-OS

TEC-OS21

21. From prompt to program ​

The CCP reads your command through the BDOS, parses its name and either runs a built-in or loads a file. A program command ends that path with page zero prepared and a jump to 0100h. This chapter follows the code from the command prompt to that jump. Appendix J gives the exact command grammar.

The minimal CCP and the shell ​

The ROM's CCP is small, and this chapter follows it. Its KEYTAB holds DIR, TYPE, ERA, REN, SAVE, USER, CON and UNLOAD, and it still runs a .COM or a .SVC, changes drive and reads one line of STARTUP.CMD (src/tables.asm:53-76, docs/shell.md:3-5). The rest is in SHELL.SVC, a resident service that the starter card's startup file installs. Its own table holds COPY, DEL and SERVICES, and DEL rewrites its word as ERA and hands the piece to the ROM (drivers/shell.asm:545-552).

The shell takes the prompt through a hook in the ROM. ROM service 16, TNSHELL, records a table of four entries in the shell's pages: LINE, PAGE, HREC and HSTORE (src/abi.inc:226, drivers/shell.asm:61-64, docs/shell.md:273-320). At each prompt MAINLOOP tests the hook. With a shell holding it, SHLINE calls LINE, which prints the prompt, reads or takes the next piece and writes it zero-ended into the command buffer with its origin, FFh for a line of STARTUP.CMD. The ROM then runs that piece as a typed line. With no shell the ROM prints its own prompt and takes a function 47 line, then its one startup line, then a line read with function 10 (src/cpm/ccp.asm:97-158, src/cpm/ccp.asm:248-294). TYPE sends every byte, and DIR its row breaks, through PAGE, which gives the shell's [more] pause. With no shell the ROM prints the byte (src/cpm/ccpfile.asm:266-288, docs/shell.md:304-307). Chapter 22 follows the shell's lines of pieces, Chapter 23 its history and Chapter 26 the startup file.

Code and working storage ​

The CCP uses CP/M calls for its ordinary work: function 10 reads a line, function 15 opens a file and function 9 prints a string through 0005h. Its own code stays in ROM while program files load into the transient program area (TPA). The four source files are assembled in this order (src/rom.asm:31-35):

FileWork
src/cpm/ccp.asmBoot entry, prompt, command dispatch and program loading
src/cpm/ccpfile.asmDIR, TYPE and their output through the shell's pager
src/cpm/ccpmut.asmERA, REN, a name check and the shared BDOS call helper
src/cpm/ccpcmd.asmOther built-ins, file-name parsing, page-zero preparation and startup

The messages and KEYTAB are in the ROM data block. Each keyword in KEYTAB has a zero terminator followed by its handler address. A final zero ends the table, which holds eight records (src/tables.asm:53-76). CCPBAS is DBBBh and the CCP ends at E3C2h. Its 2,056 bytes are followed by the BDOS.

The working state is in RAM. CMDFCB and RENFCB hold parsed file references. The command buffer follows them and CCPCLR marks the start of the state cleared by warm boot (src/ram.asm:148-180). The state runs from CCPRAM at BCF2h to BE76h, with CCPCLR at BDBCh. CPMINIT clears from CCPCLR through the BDOS state, leaving the command buffer below it intact (src/boot.asm:398-407). Chapter 22 explains the retained line. Appendix C lists the memory locations.

File operations share a short call helper. A CALL DOSSEQ has an inline byte containing twice the BDOS function number plus a file control block (FCB) selection bit. Bit 0 selects CMDFCB when clear and RENFCB when set. DOSSEQ advances the stacked return address past that byte, decodes it into C and DE and jumps to the BDOS. The BDOS returns after the inline byte (src/cpm/ccpmut.asm:172-183). The CCP uses this form for 18 calls. DIR's searches use functions 17 and 18, TYPE's reads use 20 and ERA's deletion uses 19 (src/cpm/ccpfile.asm:74-75, src/cpm/ccpfile.asm:187-189, src/cpm/ccpfile.asm:371-373, src/cpm/ccpmut.asm:57-61).

The CCP also reads the console geometry and mode, the loader's result and the program ceiling at 0007h. Its direct state includes SHOWN, the shell's table or 0, HFLAG for the shell's history input, WRFLAG for the disk reset, STFLAG for a line's origin, CHPOS for a function 47 line and a dropped line, and PRGCODE for the previous result (src/cpm/ccp.asm:46-158, src/cpm/ccp.asm:203-223).

Entry from boot ​

The prompt must return to the selected drive and user area after a program ends. Both are packed into 0004h: the user in bits 4 to 7 and the drive in bits 0 to 3. Cold boot sets the byte to zero for A and user 0. Warm boot preserves it and enters CCPENT with the byte in C (src/boot.asm:114-115, src/boot.asm:150-152, src/boot.asm:293-308).

CCPENT establishes the CCP stack and checks the saved drive. A drive past D or without a mounted volume becomes A. Otherwise the selection would raise Select and its warm boot would repeat the failed selection. The chosen drive is held in BOOTDRV while the disk state is reset (src/cpm/ccp.asm:46-75).

Function 13 resets the disks with WRFLAG set, preserving the allocation vectors for unchanged drives. Warm boot has cleared the BDOS user variable so function 32 restores the saved user. STBOOT then handles the first record of A:STARTUP.CMD once after cold boot. Finally function 14 selects the saved drive when it is not A and STARTED prints a new line before the prompt (src/cpm/ccp.asm:74-96, src/cpm/bdosfile.asm:46-77). Chapter 20 explains the allocation-vector reset and Chapter 26 explains startup.

A drive left with no volume is the unavailable-drive case. CD never leaves a drive empty, since it puts one volume in place of another, but a program can empty a drive through the ROM's UNMNT service. When 0004h then names that drive at warm boot, the CCP takes A instead, as no selection of the empty drive could succeed (src/cpm/ccp.asm:74-96, docs/compatibility.md).

The prompt and its input ​

MAINLOOP resets the stack and calls SAVEDU before each prompt. SAVEDU reads the user with function 32 and the drive with function 25, then packs them into 0004h. With a shell holding the hook, SHLINE calls its LINE entry, which prints the prompt itself. Otherwise the ROM prints a nonzero user number in decimal before the drive letter and >, giving A:SYSTEM> or 3A:SYSTEM> (src/cpm/ccp.asm:110-144, src/cpm/ccp.asm:306-324). A program's ordinary exit preserves that selection. Removing the current volume gives the fallback to A described above. Cold reset starts from A and user 0.

With the shell, the line comes from LINE: a remaining piece, the rest of the startup file, a script line or a typed line, written zero-ended at CMDTXT with its origin in A. SHLINE sets HFLAG around the call so that the shell's own function 10 call offers history, and bounds the line with a zero at the buffer's last byte (src/cpm/ccp.asm:110-124, src/cpm/ccp.asm:251-282). Chapter 22 explains the shell's order and Chapter 23 storage and recall.

With no shell, input has three sources in priority order. A function 47 line flagged in CHPOS is echoed and taken whole. Otherwise STLINE supplies the one startup line, or function 10 reads the keyboard with HFLAG clear (src/cpm/ccp.asm:126-182).

STFLAG is FFh for a startup line and zero for typed input, and with the shell it is the origin LINE returned. Typed input uses CMDBUF, the maximum-length byte, followed by CMDLEN and 128 bytes at CMDTXT. Warm boot sets the maximum to 127 (src/cpm/ccp.asm:141-158, src/ram.asm:152-157, src/boot.asm:406-407).

MLSKIP passes over spaces and returns to the prompt for an empty line. MLTAKE converts lower-case letters to capitals up to the line's zero and clears PRGCODE (src/cpm/ccp.asm:184-223). The ROM sees no ! or &: the shell has already split the line, and with no shell they are ordinary characters. Chapter 13 explains the practical result rules.

The parsed command ​

A drive selection is handled before keyword dispatch. MLTAKE recognises a letter A to P followed by a colon and only spaces after it. It selects that drive with function 14 and updates 0004h through SAVEDU. A missing volume raises Select before that update so the error's warm boot restores the previous drive (src/cpm/ccp.asm:224-249).

Other pieces enter NOTDRIVE. It starts a new output line and calls CMDSKIP to store the word's start in CMDSTRT. CMDPARSE parses a file reference into CMDFCB. ARGSTRT is then set to its delimiter for the handler's arguments. Invalid syntax reaches BADCMD before dispatch (src/cpm/ccp.asm:339-348, src/cpm/ccp.asm:483-528).

PARSEFCB clears all 36 bytes of the destination FCB: zero drive, eleven spaces for name and type and zeros for the remainder. Reusing an FCB after TYPE therefore starts a later load at record zero. FCBBASE records the FCB's address while the parser advances DE. On return HL points to the reference's delimiter (src/cpm/ccpcmd.asm:443-531).

An initial letter and colon set the drive byte to 1 through 16 for A to P. The parser fills up to eight name bytes and three type bytes after a dot. FCBEND recognises zero, space, equals and dot. PARSTAR fills the remaining field positions with question marks and skips text to the delimiter. VALIDCHR checks the thirteen reserved characters in BADCHARS. PARLONG skips an overlong field and returns carry (src/cpm/ccpcmd.asm:485-569, src/cpm/ccpcmd.asm:602-662, src/text.asm:58-59). Appendix J gives the complete exclusion list, padding rules and accepted command forms.

UNAMBIG checks the stored FCB through FCBBASE. It rejects a blank name or any question mark in the eleven name/type positions. TYPE, REN, SAVE and program dispatch use that check (src/cpm/ccpcmd.asm:581-622). The shell's COPY has its own parser and check, PARSEFCB and UNAMBIG in drivers/shellcmd.asm:221-336.

The keyword loop compares the original command text at CMDSTRT with KEYTAB, not the parsed FCB. Its order is DIR, TYPE, ERA, REN, SAVE, USER, CON and UNLOAD. COPY, DEL and SERVICES are not in it: the shell takes them before the ROM sees the piece, and DEL reaches the ROM as ERA (src/tables.asm:60-76, drivers/shell.asm:545-552). ISCMD requires a space or zero immediately after the keyword. A:DIR and DIR.COM therefore name a program file rather than built-in DIR. Both fail when the selected search finds no DIR.COM (src/cpm/ccp.asm:351-376, src/cpm/ccpcmd.asm:689-708, src/tables.asm:53-76).

A match jumps to the handler address in the table. With no match the CCP requires an unambiguous file name. Type SVC calls SVCGO to load and install a service. Other types are replaced by COM so TAS.TXT searches for TAS.COM (src/cpm/ccp.asm:374-428). A startup service whose INIT reports TNENODV has the quiet-success exception. Other installation failures reach BADCMD (src/cpm/ccp.asm:396-412). A service whose execution record asks to be entered is entered after it installs, or found and entered without a file read (src/loader.asm:734-783). Chapter 25 describes installation.

BADCMD prints the word at CMDSTRT up to space or zero, then ? and a new line. Built-ins can move CMDSTRT to an argument. CON moves it again for a separated width so its error may name that width. ERRGO sets FF00h before printing the error message. Successful handlers retain the zero set at piece entry. They finish at MAINLOOP or at STARTED, which adds a new line first (src/cpm/ccp.asm:464-471, src/cpm/ccp.asm:536-570, src/cpm/ccpcmd.asm:105-111).

The built-in handlers ​

The handlers use the same FCB and DMA interfaces as a disk program. This table locates their implementations, the ROM's and the shell's. Appendix J gives syntax and Appendix D gives recovery from messages.

CommandRoutineSource
DIRCMDDIRsrc/cpm/ccpfile.asm:17-255
TYPECMDTYPEsrc/cpm/ccpfile.asm:354-420
ERACMDERAsrc/cpm/ccpmut.asm:10-67
RENCMDRENsrc/cpm/ccpmut.asm:81-153
SAVECMDSAVEsrc/cpm/ccpcmd.asm:266-390
USERCMDUSERsrc/cpm/ccpcmd.asm:223-260
CONCMDCONsrc/cpm/ccpcmd.asm:55-220
UNLOADCMDUNLsrc/cpm/ccpcmd.asm:13-18, src/loader.asm:97-126
COPY, the shell'sCMDCOPYdrivers/shellcmd.asm:54-154
DEL, the shell'sCMDDELdrivers/shell.asm:543-552
SERVICES, the shell'sCMDSVCdrivers/shellcmd.asm:15-50

Directory listing and text output ​

DIR turns a blank name into eleven question marks and sets DMA to LOADBUF. Functions 17 and 18 return matching directory entries. DIR skips a system file by testing bit 7 of the second type byte. Its parsed FCB has extent zero so the search returns each file once (src/cpm/ccpfile.asm:17-104).

DIRNCOL is the console width VWID divided by 13, with a minimum of one. A zero width uses 80 for serial output. DIR prints each name and type, padding to twelve characters except at a row's end, with a separating space before the next entry (src/cpm/ccpfile.asm:57-73, src/cpm/ccpfile.asm:106-180). The layout differs from Digital Research's DIR. The footer calls function 46 for the listed drive and divides its three-byte free-record count by eight to print KiB. The default drive stays unchanged. No listed file gives NO FILE (src/cpm/ccpfile.asm:198-255, src/cpm/bdosfn.asm:55-126).

Both DIR and TYPE print through LSTPUT. With a shell holding the hook it sends each byte to the shell's PAGE entry, whose carry stops the listing. With no shell it prints the byte and returns carry clear, so a bare listing never pauses (src/cpm/ccpfile.asm:261-288). The pager is the shell's. PGRST takes its dimensions from TNINFO or uses 24 rows and 80 columns for serial, and reserves a row for [more]. PGPUT resets its column at carriage return, steps back at backspace and advances to the next multiple of eight at a tab. It counts a new line at LF or before a printable character beyond the last column (drivers/shellio.asm:345-449). At a pause function 6 reads a key without echo, and UNMORE erases the prompt with CR, six spaces and CR. The key mask makes # equivalent to ^C and ; equivalent to Esc. ^C and # drop the rest of the line. Esc, Q, q and ; stop only the listing. Other keys continue (drivers/shellio.asm:450-502). Chapter 22 explains the distinction.

TYPE opens its file and reads 128-byte records into LOADBUF. It prints through the pager until 1Ah, the first Ctrl-Z, or the file's end. It then closes the file. No name or a missing file produces NO FILE (src/cpm/ccpfile.asm:354-420).

Erase, rename and save ​

ERA tests all eleven stored name/type bytes for question marks before printing ALL (Y/N)?. Function 1 reads the first echoed answer byte. Return alone cancels deletion. Otherwise ERA drains the answer to Return and deletes only for an initial Y or y. Other patterns delete without that question. Function 19 performs the deletion and no match gives NO FILE (src/cpm/ccpmut.asm:10-67).

REN parses NEW into RENFCB and OLD into CMDFCB. The names share a drive from either reference and different explicit drives are rejected. Function 17 checks the new name first. A match gives FILE EXISTS before mutation. Otherwise REN copies twelve bytes from RENFCB to CMDFCB+16, placing the new name at offset 17 for function 23. An absent old name gives NO FILE (src/cpm/ccpmut.asm:81-149).

SAVE converts a decimal page count with a carry check at every arithmetic step. It rejects values above 255 and counts reaching the high byte of the word at 0006h. On the starter card with the shell installed that byte is A7h: 166 pages cover 0100h through A6FFh. Both 167 and 320 are rejected in this capture (src/cpm/ccpcmd.asm:266-307):

text
TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>SAVE 320 B:X.COM
320?

A:SYSTEM>SAVE 167 B:X.COM
167?

A:SYSTEM>

SAVE erases an existing file, makes it again and writes two 128-byte records per page from 0100h. A failed make, write or close gives NO SPACE. After a failed write it attempts close before reporting the error. A successful close records the partial file. The error path discards the close result so the message does not certify that update. Digital Research's CP/M 2.2 SAVE leaves the file open on that path (src/cpm/ccpcmd.asm:309-390).

SAVE reads the TPA. The other file-operation handlers use resident workspace and page-zero buffers so they leave program memory available to save. Loading a COM program or a service overwrites that memory, including a GLCD service loaded by CON (src/cpm/ccpcmd.asm:315-360, src/loader.asm:862-906, src/cpm/ccp.asm:625-663). The shell's COPY uses the DMA at 0080h and also leaves the TPA alone (drivers/shellcmd.asm:93-94).

Selection and consoles ​

USER validates a single digit 0 to 9 or a two-digit value 10 to 15 and calls function 32. CON uses its device-name table to set the IOBYTE console field through CONFLD. PICO aliases CRT and GLCD aliases UC1. Selecting UC1 calls GLCLD to load GLCD.SVC from A if required. A failed load puts the field back to the active mode (src/cpm/ccpcmd.asm:55-220, src/cpm/ccpcmd.asm:223-246, src/loader.asm:862-887).

CON's report prints CON: and the mode read from CONMOD after the BIOS has acted on the field. A missing display or keyboard can force TTY while a failed GLCD load restores the previous mode. Output uses the selected console and BAT discards it. Chapter 17 explains the BIOS transition (src/cpm/ccpcmd.asm:187-214, src/console.asm:339-347).

A width after CRT or PICO is parsed as two decimal digits. CON finds the PICO version-3 record with TNFIND and calls its PICOWID entry for 80, 40 or 32 columns. A joined name and width, a width after another device, an unsupported width or a missing PICO interface is an error. In startup the missing-interface path passes quietly. A separated width becomes the error word while a joined form names the whole token (src/cpm/ccpcmd.asm:105-180). This PICO capture shows both:

text
TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>CON PICO 40
CON: CRT:
A:SYSTEM>CON CRT80
CRT80?

A:SYSTEM>CON PICO 50
50?

A:SYSTEM>CON TTY 80
80?

A:SYSTEM>CON CRT: 32
CON: CRT:
A:SYSTEM>

PICOWID also rejects a change while the display is claimed. An accepted width change clears the screen at the next console call. Its state in PIBLK survives warm boot. Reset initialises the PICO console to 40 columns when the display probe succeeds and the Matrix switch is enabled. Otherwise serial remains selected. Bare CON CRT and CON PICO retain the chosen width and any active claim (src/console.asm:32-45, src/video.asm:18-24, src/pico.asm:44-68, src/pico.asm:70-94, src/cpm/ccpcmd.asm:105-191, src/console.asm:111-133).

Copies and resident services ​

COPY is the shell's. It parses the source into the default FCB at 005Ch and the destination into its own CFCB, substituting the current drive for zero. A destination with a blank name takes the source's eleven name/type bytes. After checking both for ambiguity, COPY compares all twelve bytes for a self-copy and rejects extra operands before opening either file (drivers/shellcmd.asm:54-92, drivers/shellcmd.asm:156-212).

The copy uses DMA at 0080h and leaves the TPA untouched. It opens the source, erases and makes the destination and transfers records through functions 20 and 21. CCOUNT counts records and PUTHEX prints the count in hexadecimal. A write error closes the partial destination before WRITE ERROR. Retention of the written records depends on that close succeeding. The error path ignores its result (drivers/shellcmd.asm:93-154).

SERVICES, the shell's too, walks the owner list from the lowest owner's page, which the ROM passes to LINE in B, upwards, printing each name and decimal page count. The page count is the next owner's page, or the stub's for the last, less the owner's own (drivers/shellcmd.asm:15-50). UNLOAD, the ROM's, calls SVCUNL for the lowest owner, the newest service. It fails there if removal is disallowed or REMOVE returns carry. It does not skip to another service (src/cpm/ccpcmd.asm:13-18, src/loader.asm:97-126). Chapter 25 explains the registry and removal checks.

Program lookup and capacity ​

A COM command uses LOADA on the named drive or the current drive. LOADA first calls LOADCOM in the current user area. Only a missing file permits a retry in user 0 and user 0 is skipped when already current. Function 32 changes the user before that retry and restores it afterwards. No system attribute is required (src/cpm/ccp.asm:584-609).

LOADCOM distinguishes absence from an unloadable file with flags. Carry and zero mean missing. Carry with NZ means a file was found but could not load. LOADA returns the latter failure immediately. The CCP retries drive A only after absence on the first drive, when no drive was explicit and the current drive is not A. It writes 1 into the FCB drive byte and calls LOADA again. A's current user therefore precedes A's user 0 (src/cpm/ccp.asm:428-440).

This starter-card capture contrasts a plain command with an explicit B drive. The plain TAS reaches A, and prints its usage line, while B:TAS stays on B:

text
TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>B:
B:WORK>TAS
usage: TAS NAME [OUT.TYP]

B:WORK>B:TAS
B:TAS?

B:WORK>

A service command calls LOADCOM directly through SVCGO. It searches only its named or current drive and the current user area. It has neither the user-0 retry nor the drive-A fallback (src/cpm/ccp.asm:385-395, src/loader.asm:901-906).

LOADCOM opens CMDFCB and starts at 0100h. READSRC sets DMA with function 26 before each function-20 read. Each successful record advances the destination by 128 bytes. The loop stops at EOF or at the page given by 0007h, the high byte of the entry word at 0006h (src/cpm/ccp.asm:625-648, src/cpm/ccp.asm:713-719).

Reaching that page does not establish that the file is oversized. LOADLIM reads once more into workspace LOADBUF. EOF means an exact fit. A further record or another error returns carry with NZ. Below the ceiling, LOADEND also requires EOF for success. LOADOK stores the record-rounded end in LOADTOP for the service loader then calls close. It clears carry without checking close's result (src/cpm/ccp.asm:659-700). Thus a larger file stops lookup rather than falling through to another drive. In the default BDOS error mode a card read failure prints Bad Sector and warm-boots before this routine returns (src/cpm/bdoscon.asm:47-64).

With nothing installed the starter card's resident entry is at B6E9h. Its load ceiling is B600h, allowing 46,336 bytes from 0100h, 233 fewer than the TPA's byte-address limit. The startup file installs the shell, whose first page is A700h, so the starter card's prompt loads at most 42,496 bytes. An installed service lowers the entry word to its first page and lowers the load ceiling with it (src/cpm/ccp.asm:637-639, src/loader.asm:494-507).

The capacity fixture places FITS, BIG and ARGS on B. FITS and BIG contain RET followed by zeros. ARGS has the complete listing below and is assembled on the PC by TAS, as Chapter 27's HELLO is. FITS has 42,496 bytes and BIG has 42,497:

sh
node -e 'const b = n => { const x = Buffer.alloc(n); x[0] = 0xC9; return x; };
require("fs").writeFileSync("build/fits.com", b(42496));
require("fs").writeFileSync("build/big.com", b(42497));'
node --input-type=module -e '
import { writeFileSync } from "node:fs";
import { assembleProgram } from "./tools/lib/assemble.mjs";
const [src, out] = process.argv.slice(1);
writeFileSync(out, (await assembleProgram(src)).bytes);
' build/args.asm build/args.com
cp dist/starter.img build/ccp.img
node tools/tecvol.mjs put build/ccp.img B build/args.com
node tools/tecvol.mjs put build/ccp.img B build/fits.com
node tools/tecvol.mjs put build/ccp.img B build/big.com

TAS writes the 76-byte ARGS.COM. FITS returned to the prompt and BIG was rejected:

text
TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>B:
B:WORK>FITS

B:WORK>BIG
BIG?

B:WORK>

The same fixture also demonstrates user fallback. Under user 3, ARGS is found in B's user 0 and TAS in A's user 0. DIR still lists only the empty current area:

text
TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>B:
B:WORK>USER 3
3B:WORK>ARGS
0
0
[]
3B:WORK>TAS
usage: TAS NAME [OUT.TYP]

3B:WORK>B:TAS
B:TAS?

3B:WORK>DIR
NO FILE

3B:WORK>

Page zero before entry ​

A successful load reaches PREPPAGE. It parses the first two argument references into the FCBs at 005Ch and 006Ch, ignoring parse errors for those program arguments. It then copies the command tail to 0081h, writes its length at 0080h and appends zero. Function 26 restores DMA to 0080h. The tail includes the initial space. The shell ends a piece before the spaces in front of its separator, so they are not in the tail. Its letters have already been converted to capitals (src/cpm/ccpcmd.asm:402-440, drivers/shell.asm:321-373).

The two FCBs start sixteen bytes apart. Parsing the second overwrites the last twenty bytes of the first. The tail begins at 0080h within the second FCB's last sixteen bytes so those bytes are shared with tail storage. Each FCB's drive and eleven name/type bytes remain intact (src/cpm/ccpcmd.asm:402-440). The complete FCB and DMA contracts are explained in Chapter 10.

ARGS prints those drive and name fields, then the tail between brackets. This complete listing is the build/args.asm used in the capacity-card recipe above:

asm
; ARGS: prints the two FCBs and the command tail that the CCP leaves in
; page zero: each FCB's drive byte as a digit and its eleven name bytes,
; then the tail between brackets.
BDOS    EQU     $0005

        ORG     $0100
        LD      HL,$005C        ; the first FCB
        CALL    SHOWFCB
        LD      HL,$006C        ; the second
        CALL    SHOWFCB
        LD      A,'['
        CALL    PUT
        LD      HL,$0080        ; the tail's length, then its characters
        LD      B,(HL)
TAIL:   LD      A,B
        OR      A
        JR      Z,TEND
        INC     HL
        LD      A,(HL)
        CALL    PUT
        DEC     B
        JR      TAIL
TEND:   LD      A,']'
        JP      PUT

SHOWFCB:LD      A,(HL)          ; the drive: 0 for the current one
        ADD     A,'0'
        CALL    PUT
        LD      A,' '
        CALL    PUT
        LD      B,11            ; the name and type, as stored
NAME:   INC     HL
        LD      A,(HL)
        CALL    PUT
        DJNZ    NAME
        LD      A,13
        CALL    PUT
        LD      A,10

; Print A by function 2, keeping B and HL.
PUT:    PUSH    HL
        PUSH    BC
        LD      E,A
        LD      C,2
        CALL    BDOS
        POP     BC
        POP     HL
        RET

PUT saves BC and HL across function 2, preserving the caller's count and pointer. SHOWFCB prints eleven name/type bytes and TAIL uses the length byte at 0080h. In this capture the parsed names use padded FCB fields while the tail preserves the spaces within the piece:

text
TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>B:
B:WORK>args one.txt a:*.c
0 ONE     TXT
1 ????????C
[ ONE.TXT A:*.C]
B:WORK>ARGS X Y ! ARGS
0 X
0 Y
[ X Y]
B:WORK>ARGS
0
0
[]
B:WORK>

The first FCB has drive zero for the current drive and the second has 1 for A. The star in *.C expands to eight question marks. ARGS X Y loses the space before !, which the shell leaves off the piece. With no arguments both names are blank and the tail length is zero (src/cpm/ccpcmd.asm:457-531, src/cpm/ccpcmd.asm:632-645).

The jump and return ​

After PREPPAGE, the CCP writes the load drive from CMDFCB to 0050h. Zero means a plain name loaded on the current drive. An explicit drive keeps its FCB number so B:ARGS gives 2. A plain command found by fallback on A gives 1 because lookup set the FCB byte to A (src/cpm/ccp.asm:431-461).

CMDRUN resets SP to CSTKTOP, pushes 0000h and jumps to 0100h. The source reserves a 32-byte CCP stack, leaving thirty bytes below that return word. A guard separates the stack from command scratch (src/cpm/ccp.asm:464-471, src/layout.asm:114-115, src/ram.asm:190-202). CP/M 2.2's eight levels provide sixteen bytes. Chapter 15 distinguishes configured stack sizes from measured use and bounds.

The jump goes through HL, because a service's entry on install uses the same path to enter the service at its own address. CMDRUN loads 0100h first, so a program starts with HL = 0100h and DE = 0000h, and with A = FFh when its line came from STARTUP.CMD and 0 otherwise. CP/M 2.2 promises a program no register at entry (src/cpm/ccp.asm:447-473, docs/compatibility.md:185-190).

A top-level RET reaches the warm-boot jump at 0000h. A direct jump there or function 0 reaches warm boot too (src/cpm/ccp.asm:469-471, src/cpm/bdos.asm:216-221). Warm boot flushes the block cache before re-entering the CCP. A failed flush prints Write lost and sets the drop flag, so the shell cancels the line's pending pieces (src/boot.asm:141-152, src/cache.asm:634-640). The CCP enters at STARTED and prints a new line before its prompt. A program whose output already ended with a new line therefore has a blank line before that prompt.

TEC-OS and Thorium documentation