C/C++ Users Group Library 1996 July/C-C++ Users Group Library July 1996.iso/vol_200/284_01/porting.doc

Text File | 1989-03-11 | 5.6 KB | 118 lines

Porting Portable 8080 system to other systems


Introduction

    Although this program was carefully created considering the
    portability, the porting of the program requires more than
    recompiling the program.
    In this documentation, topics important to the porting are
    explained.

1. The nature of compilers

    The characteristics of a C compiler changes as the system changes.
    Particularly, the difference of data type and expression between
    two systems is very significant.
    You need to make changes in the program with taking special care
        because the program is very sensitive with the data expression on
    memory. The include file, "compile.h" is prepared for this purpose.
    You need to appropriately set macros defined in this file.

    In multi-byte integers, when a least significant byte locates first
    in memory, it is called Little Indian, when a most significant byte
    locates first, it is called Big Indian.
    Intel micro processors and DEC VAX-11 use a Little Indian scheme
    whereas Motolora processors and IBM370 architecture use Big Indian
    scheme.
    There are macros, LITTLEINDEAN and BIGINDEAN in compile.h.
    You need to preset these for your machine.

    In compile.h, there are four other definitions that define
    basic data type: BYTE(1 byte), WORD(2 bytes), BOOL(1 bit) and EXTRA
    (3 bytes)(all are unsigned integer).
    Although the size of BYTE and WORD must be 1 byte and 2 bytes
    respectively, the size of BOOL and EXTRA can be longer, so please
    select fast access one.

    Besides the points discussed above, it is assumed that memory is
    addressed by byte unit (1 byte represents 8 bits), a number is
    expressed in two's complement .. etc.
    Although this assumption doesn't cause any problems, the situation
    could be changed in the future.

2. Low-level Input/Output (BIOS)

    In portable 8080, a module corresponding to BIOS for CP/M is written
    in C.
    You need to create this part suitable for your host operating system
    because it plays an important role as interface between CP/M
    and the host operating system.

    The file, "bios.c" performs four things: simulation of direct
    I/O, access to a virtual disk, access to a physical disk, character
    I/O. In the current version, the program is created based on the
    assumption
    of the combination of MS-DOS and NEC PC-9801. Turbo C special features
    are used to call ROM-BIOS in NEC.

    Direct I/O access simulates 8080 instructions IN and OUT and
    has nothing to do with CP/M. When you create functions that simulate
    devices attached to an I/O port, you can execute special programs.
    This module includes an IoMap table, in which you can set a validity of
    each port for all 256 ports. Currently, all ports are set as invalid.
    When you set a macro INOUT in config.h to 1, this feature is available.

    Access to virtual disk simulates a floppy disk drive under virtual
    CP/M. In the virtual CP/M, a floppy disk under CP/M becomes a file.
    The virtual CP/M also allows you to access up to 8 disk drives
    assigning each disk drive to a file in the host operating system.
    The contents of each file is the same as an 8 inch single sided
    single density when it is dumped from the first sector of the disk.
    That part is written using only UNIX standard functions. Therefore,
    would be no trouble to port to the other operating system.

    Access to a physical disk allows you to assign one of  eight virtual
    disk drives to a physical eight inch disk drive.
    This feature is intended to transfer files between other real CP/Ms.
    This part of the program is hardware dependent because it uses
    a sector-address scheme.
    In the current version, it is set in such a way that it calls ROM-BIOS
    in NEC PC-9801. When using other hardware, the program needs to be
    rewritten.

    The character I/O part performs CP/M console, printer output, and
    auxiliary input and output. They make use of system calls
    in the host operating system. In the current MS-DOS version, they are
    mapped to four file handles: 0, 1, 3 and 4.
    As for the console input, you have to handle a raw character input
    , that is, no echo and no buffering, and control C character under
    MSDOS, moreover, newline character under UNIX.

3. Command Line Interface and Boot File

    To start portable 8080, you need to give program options in the command
    line. Although the current version distinguishes lower-case letters from
    upper-case letters in the option characters, some systems don't.
    In that case, you need to make a change to the program so that
    all lower-case letters are converted to upper-case letters (The same
    is true for console output. CP/M application programs are designed in
    such a way that it can run with input of upper-case letters.)

    Some options that require a file name have a default file name.
    You need to use a default file name suitable for the host operating
    system. All default filenames are defined in "mon.h".

    Among default files, there is a boot file. This is the file that
    includes a program read into 8080 when the portable 8080 starts.
    In the current version, the boot program is recorded in the Intel
    hexa format. If there is a better format for the host operating
    system, you might make a change. The boot file is read every time
    CP/M does a warm boot. When you have a slow file access system or
    small CPU, you need to make a change such as changing a format of the
    boot file, which will be processed faster or modifying the program
    so that it will record a boot image in the first place and it will
    not have to read the boot file from the second time.