Black Box 4/BlackBox.cdr/progc/c_all592.arj/TI353.ASC

Text File | 1992-02-25 | 8KB | 331 lines

  PRODUCT  :  Turbo C                                NUMBER  :  353
  VERSION  :  2.0
       OS  :  DOS
     DATE  :  February 25, 1992                        PAGE  :  1/4

    TITLE  :  Creating a New Data Segment




  Sometimes people have  the  need  to  allow  more  than  one data
  segment in their program and they can not change to a HUGE memory
  model. This technical information handout explains what is needed
  to  add  an  extra data segment to your Turbo C program. You will
  need an Assembler to reassemble the start-up code.

  The first change you will need to make is to the Turbo C start-up
  code. This code defines the segments and their classes as well as
  their group. To define a new segment in your  program,  you  will
  need to add the definition of the new segment and its class. This
  definition must be placed before all of the  other  segments that
  the  start-up  code  defines.  See  the following listing  as  an
  example of the existing  start-up  code. The bold text is the new
  segment definition that we are adding.

          NAME    c0
          PAGE    60,132
  ;[]------------------------------------------------------------[]
  ;|      C0.ASM -- Start Up Code                                 |
  ;|                                                              |
  ;|      Turbo-C Run Time Library        version 2.0             |
  ;|                                                              |
  ;|      Copyright (c) 1988 by Borland International Inc.        |
  ;|      All Rights Reserved.                                    |
  ;[]------------------------------------------------------------[]

          INCLUDE RULES.ASI

  _Strict87_      equ     false           ; emulation skips peculiar details

  ;       Segment and Group declarations

  _MYSEG  SEGMENT BYTE PUBLIC 'NEWSEG'       ; Definition of new
  _MYSEG  ENDS                               ; Data Segment
  _TEXT   SEGMENT BYTE PUBLIC 'CODE'
  _TEXT   ENDS
  _DATA   SEGMENT PARA PUBLIC 'DATA'
  _DATA   ENDS
                          Figure 1: c0.asm

  Now that you  have  changed  the  start-up code, you will need to
  reassemble  it  for  the  memory  model that you need. The  files
  RULES.ASI  and  EMUVARS.ASI  will  need  to  be  in your  current













  PRODUCT  :  Turbo C                                NUMBER  :  353
  VERSION  :  2.0
       OS  :  DOS
     DATE  :  February 25, 1992                        PAGE  :  2/4

    TITLE  :  Creating a New Data Segment




  directory.  The  batch  file,  BUILD-C0.BAT,  should  be  used to
  reassemble  the  start-up  code.  It  takes  as  a  command  line
  parameter the  model name (TINY, SMALL, MEDIUM, COMPACT, LARGE, &
  HUGE). Place the modified assembled start-up code in your project
  directory.

  Now that we have changed the start-up code, we  need  to  compile
  the  .C file that will be using the data segment. We will use the
  following .C module as an example.

  char c_buffer1[30000];
  char c_buffer2[30000];
                         Figure 2: module1.c

  There are several compiler directives that we will  need  to pass
  to TCC to compile this module for the other segment. Following is
  the command line used:

  TCC -m? -c -v -zBnewseg -zD_myseg -zGnewgroup -zR_myseg
      -zSnewgroup -zTnewseg module1.c

  The -m? option is used to specify the memory model for the module
  to  be compiled in. The ? character should  be  replaced  by  the
  letter  for  the  model that you wish to use. The -c option tells
  the  compiler  not  to invoke the  linker.  Using  -v  tells  the
  compiler  to  include  full debug information. The  rest  of  the
  directives specify the names of the segment, class, and group for
  both the DATA area and the BSS area. These different  options are
  discussed in the Turbo C Reference Guide in Appendix C  under the
  section  Segment-Naming Control. Essentially, _myseg is the  name
  of the segment. This  name  should match what was placed into the
  start-up code. Newseg is  the  name of the class for the segments
  and should correspond to the name in '' in the start-up code. The
  newgroup is  the  name  of  the  group  that the segments will be
  placed in.

  The other module that we are using in our example follows  in the
  next  figure.  This  module  will  need to specify  the  external
  variables with the far key word. Please keep in mind that  if you
  are in one  of  the  near  data  memory  models  (TINY,SMALL, and
  MEDIUM) that the functions by default only take an  offset  as  a
  parameter. The segment used to  reference this offset is the data
  segment (DS) by default. If you want to use the external  data in













  PRODUCT  :  Turbo C                                NUMBER  :  353
  VERSION  :  2.0
       OS  :  DOS
     DATE  :  February 25, 1992                        PAGE  :  3/4

    TITLE  :  Creating a New Data Segment




  a Turbo C RTL function, you will need to copy the  information to
  a local variable using the  function  movedata().  Otherwise, the
  COMPACT, LARGE, and HUGE memory models will work fine as  long as
  you specify that the external variables are far.

  #include <dos.h>
  #include <stdio.h>

  extern char far c_buffer1[30000];
  extern char far c_buffer2[30000];
  char c_buffer3[30000];
  char c_buffer4[30000];

  void show_segment(void far *ptr);

  main()
  {
    printf("local proc\n");
    printf("extern data ");
    show_segment(c_buffer1);
    printf("local data ");
    show_segment(c_buffer3);

    return 0;
  }

  void show_segment(void far *ptr)
  {
          printf("segment:%04X\n",FP_SEG(ptr));
  }
                         Figure 3: module2.c

  This  module  can  be compiled with a simple command line (again,
  remembering to replace  the  ?  with  the  letter  of  the memory
  model):

  TCC -m? -c -v module2.c

  Now that  each  of  the  modules  are  compiled, we can link them
  together.  We  are  calling  TLINK  directly because we  want  to
  specify the location of the start-up code. If we  pass  the  .OBJ
  files to TCC, it may use the wrong start-up code. The  TLINK line
  is as follows (replacing the ? with letter of the memory model):













  PRODUCT  :  Turbo C                                NUMBER  :  353
  VERSION  :  2.0
       OS  :  DOS
     DATE  :  February 25, 1992                        PAGE  :  4/4

    TITLE  :  Creating a New Data Segment




  TLINK /v /c c0? module1 module2, example, example, \tc\lib\c?

  The  resulting executable program (EXAMPLE.EXE) will display  the
  segments of the default segment global variables and the external
  segment global variables.



















































  PRODUCT  :  Turbo C                                NUMBER  :  353
  VERSION  :  2.0
       OS  :  DOS
     DATE  :  February 25, 1992                        PAGE  :  1/4

    TITLE  :  Creating a New Data Segment










                            Figures


       Figure 1: c0.asm  . . . . . . . . . . . . . . . . . . 1
       Figure 2: module1.c . . . . . . . . . . . . . . . . . 2
       Figure 3: module2.c . . . . . . . . . . . . . . . . . 3