Subversion Repositories openrisc_2011-10-31

/*
 * crt0_redboot.S -- Minimal startup file for MN10300 targets running Redboot.
 *
 * Copyright (c) 2001 Red Hat, Inc.
 * Derived from crt0_cygmon.S - Copyright (c) 1995, 1996, 1997, 2000 Red Hat, Inc.
 *
 * The authors hereby grant permission to use, copy, modify, distribute,
 * and license this software and its documentation for any purpose, provided
 * that existing copyright notices are retained in all copies and that this
 * notice is included verbatim in any distributions. No written agreement,
 * license, or royalty fee is required for any of the authorized uses.
 * Modifications to this software may be copyrighted by their authors
 * and need not follow the licensing terms described here, provided that
 * the new terms are clearly indicated on the first page of each file where
 * they apply.
 */

/*
 * This file contains the minimal startup code necessary.
 * This will not do any hardware initialization.  It is assumed that we are talking to Redboot
 * and therefore the hardware will be initialized properly.
 */

/*
 * Set up some room for a stack. We just grab a chunk of memory.
 */
#define STACK_SIZE  0x4000
#define GLOBAL_SIZE 0x2000

#define STARTUP_STACK_SIZE      0x0100

        .comm   __memsize, 12
        .comm   __lstack, STARTUP_STACK_SIZE
        .comm   __stackbase,4

        .section .text
        .global _start
_start:
        /*
         * Setup a small stack so we can run some C code,
         * and get the usable memory size.
         */
        mov     __lstack,a0
        add     STARTUP_STACK_SIZE-4,a0
        mov     a0,sp

        /*
         * zero out the bss section.
         */
        .global __memsize
        .global _get_mem_info
zerobss:
        mov     __bss_start, a0                         # These variables are defined in the linker script
        mov     _end, a1

        cmp     a0, a1                                  # If no bss, then do nothing
        beq     7f

        clr     d0
3:
        movbu   d0,(a0)                                 # Clear a byte and bump pointer
        inc     a0
        cmp     a0, a1
        bne     3b

7:
        /*
         * Setup the stack pointer -- 
         *    get_mem_info returns the top of memory, so just use that In
         *    addition, we must subtract 24 bytes for the 3 8 byte
         *    arguments to main, in case main wants to write them back to
         *    the stack.  The caller is supposed to allocate stack space
         *    for parameters in registers in the old MIPS ABIs.  We must
         *    do this even though we aren't passing arguments, because
         *    main might be declared to have them.
         *    Some ports need a larger alignment for the stack, so we
         *    subtract 32, which satisifes the stack for the arguments and
         *    keeps the stack pointer better aligned.
         */
        mov     __memsize, d0
        call    _get_mem_info,[],0

        sub     32, a0
        mov     a0, sp

        mov     __stackbase, a1
        mov     a0, (a1)                                # keep this for future ref

        call    ___main,[],0                            # Call __main to run ctors/dtors
        clr     d0
        clr     d1
        mov     d0, (4,sp)
        or      0x0800,psw                              # Enable interrupts
        call    _main,[],0                              # Call main program
        call    _exit,[],0
        
/* EOF crt0_redboot.S */