arch/z80/src/z80
^^^^^^^^^^^^^^^^

The arch/z80 directories contain files to support a variety of 8-bit architectures
from ZiLOG (and spin-architectures such as the Rabbit2000).  The arch/z80/src/z80
sub-directory contains logic unique to the classic Z80 chip.

Files in this directory include:

z80_head.asm
    This is the main entry point into the Z80 program.  This includes the
    handler for the RESET, power-up interrupt vector and address zero and all
    RST interrupts.

z80_rom.asm
    Some architectures may have ROM located at address zero.  In this case, a
    special version of the "head" logic must be used.  This special "head"
    file is probably board-specific and, hence, belongs in the board-specific
    configs/<board-name>/src directory.  This file may, however, be used as
    a model for such a board-specific file.

    z80_rom.S is enabled by specifying CONFIG_LINKER_ROM_AT_0000 in the
    configuration file.

    A board specific version in the configs/<board-name>/src directory can be
    used by:

    1. Define CONFIG_ARCH_HAVEHEAD
    2. Add the board-specific head file, say <filename>.asm, to
       configs/<board-name>/src
    3. Add a file called Make.defs in the configs/<board-name>/src directory
       containing the line:  HEAD_ASRC = <file-name>.asm

Make.defs
    This is the standard makefile fragment that must be provided in all
    chip directories.  This fragment identifies the chip-specific file to
    be used in building libarch.

chip.h
    This is the standard header file that must be provided in all chip
    directories.

z80_initialstate.c, z80_copystate.c,  z80_restoreusercontext.asm, and
z80_saveusercontext.asm, switch
    These files implement the Z80 context switching logic

z80_schedulesigaction.c and  z80_sigdeliver.c
    These files implement Z80 signal handling.
