cmdline.txt

汇编源代码大全

By: Dave M. Walker
Subj: Command Line Parms
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Let's see... we'll start with a listing of the parameters for @PARAM
from TRSDOS 6.x:

  Parses an optional parameter string.  Its primary function is to parse
  command parameters contained in a command line starting with a
  parentheses.  The acceptable parameter format is:
    PARM=X'nnnn' ... hexadecimal entry
    PARM=nnnnn   ... decimal entry
    PARM="string"... alphanumeric entry
    PARM=flag    ... ON, OFF, Y, N, YES, or NO
      Note: Entering a parameter with no equal sign or value is the same
      as using PARM=ON.  Entering PARM= with no value is the same as
      using PARM=OFF.

  Entry Conditions:
    A  = 17 [SVC number, akin to function in AH]
    DE = Pointer to beginning of your parameter table
    HL = Pointer to command line to parse [unnecessary for the PC]

  Exit Conditions:
    Success always.
      If Z is set, either valid parameters or no parameters were found.
      If NZ is set, a bad parameter was found.

  General:
    NZ is not returned if parameter types other than those specified are
    entered.  The application must check the validity of the response
    byte.

  The valid parameters are contained in a user table which must be in
  one of the following formats.  (Parameter names must consist of
  alphanumeric characters, the first of which is a letter.)

  For use with TRSDOS Version 6 [Model IV], use this format:

    The parameter table starts with a single byte X'80'.  Each parameter
    is stored in a variable length field as described below.

    1) Type Byte (Type and length byte)
       Bit 7 - If set, accept numeric value
       Bit 6 - If set, accept flag parameter
       Bit 5 - If set, accept "string" value
       Bit 4 - If set, accept first character of name as abbreviation
       Bits 3-0 - Length of parameter name

    2) Actual parameter name

    3) Response byte (Type and length found)
       Bit 7 - Numeric value found
       Bit 6 - Flag parameter found
       Bit 5 - String parameter found
       Bits 4-0 - Length of parameter entered.  If length is 0 and the
           2-byte vector points to a quotation mark (X'22'), then the
           parameter was a null string.  Otherwise, a length of 0
           indicates that the parameter was longer than 31 characters.

    4) 2-byte address vector to receive the parsed parameter values.

    The 2-byte memory area pointed to by the address field of your table
    receives the value of PARM if PARM is non-string.  If a string is
    entered, the 2-byte memory area receives the address of the first
    byte of "string".  The entries ON, YES, and Y return a value of
    X'FFFF'; OFF NO, and N return X'0000'.  If a paraemter name is
    specified on the command line and is followed by an equal sign and
    no value, then X'0000' or NO is returned.  If a parameter name is
    used on the command line without the equal sign, then a value of
    X'FFFF' or ON is assumed.  For any allowed parameter that is
    unchanged and the response byte is 0.

    The parameter table is terminated with a single byte X'00'.

The other parameter format that was alluded to was used in LDOS for the
TRS-80 I/III.  Briefly, this format was:

  - A 6-character parameter name, left-justified, padded with blanks.
  - An address to store the parsed values
    [repeat for all parms]
  - A null to terminate the table

So the table would look like this using PC-eze:

VidType dw    -1                  ;Parameters & default values
PortNum dw    1
        db    'VIDEO '            ;Parameter name
        dw    OFFSET VidType      ;Address to store response
        db    'PORT  '            ;Another...
        dw    OFFSET PortNumber
        db    0                   ;Terminating null

No distinction was made between paramater types.  The programmer was
left to figure that one out.

The first method described is a little more complicated, but easier on
the applications programmer.  (That's the point to all this, right?)

This idea probably won't catch on... (I can see the error message now:
"This program requires TOADPARM because Microsoft can't design a decent
Operating System.") ... but it would be an EXCELLENT idea for Rex Conn
to implement in the next version of 4DOS.

I suppose the two things that really bug me the most about MS-DOS are:

1.  Lack of a task scheduler for the NMI (IRQ 8).  LDOS had system
    routines that kept track of the system timer and issued vectors upon
    request.  No need to save registers or fool with resetting the
    hardware timer... just call the system with the address of your
    routine and it's done.  It even had 2 priority levels, fast and
    slow.

2.  Lack of chained device support.  LDOS would allow you to chain your
    driver, filter, hotkey, or whatever via system calls.  No need to
    mess around with grabbing interrupts and such.

Ah well, maybe IBM has developed a better interface with OS/2.  Somehow
I don't really think so, though.  *sigh*