Subversion Repositories scarts

/* Startup code for SCARTS (16-bit).
 * Copyright (C) 2010, 2011 Embedded Computing Systems Group,
 * Department of Computer Engineering, Vienna University of Technology.
 * Contributed by Martin Walter <mwalter@opencores.org>
 *
 * 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.
 */

        .file   "crt0.S"

.macro CLEAR_REG reg
        ldhi \reg, 0
        ldliu \reg, 0
.endm

.macro CLEAR_MEM_REG addr
        ldli r7, \addr
        CLEAR_REG r13
        sth r13, r7
.endm

.macro STORE_MEM_REG addr
        ldli r7, \addr
        sth     r13, r7
.endm

.macro LOAD_SYM_TO_REG reg symbol
        .global \symbol
        ldhi    \reg, hi(\symbol)
        ldliu   \reg, lo(\symbol)
.endm

        .section .text
        .global _start
        .type start, @function
_start: ; the linker script defines start as the application entry point
        ; clear the bss section ('__bss_start' and '_end' are provided through the linker script)
        LOAD_SYM_TO_REG r5 __bss_start  ; store symbol '__bss_start' in r5
        LOAD_SYM_TO_REG r6 _end         ; store symbol '_end' in r6
        cmp_eq r5, r6                   ; check if address in r5 equals address in r6 (.bss empty)
        jmpi_ct .bss_clear

        ldli r7, 0                      ; load value 0 into r7
.bss_clear_loop:
        sth r7, r5                      ; store value in r7 at address in r5
        addi r5, 2                      ; increase address in r5 by the word size in bytes
        cmp_lt r5, r6                   ; check if address in r5 is less than address in r6
        jmpi_ct .bss_clear_loop

.bss_clear:
        ; clear hardware registers
        CLEAR_REG r0
        CLEAR_REG r1
        CLEAR_REG r2
        CLEAR_REG r3
        CLEAR_REG r4
        CLEAR_REG r5
        CLEAR_REG r6
        CLEAR_REG r7
        CLEAR_REG r8
        CLEAR_REG r9
        CLEAR_REG r10
        CLEAR_REG r11
        CLEAR_REG r12
        CLEAR_REG r13
        CLEAR_REG r14
        CLEAR_REG r15

        ; clear memory-mapped extension module registers
        CLEAR_MEM_REG -24 ; frame pointer W register
        CLEAR_MEM_REG -20 ; frame pointer X register
        CLEAR_MEM_REG -16 ; frame pointer Y register
        CLEAR_MEM_REG -12 ; frame pointer Z register

        ; initialize the FP and SP register to the beginning of the stack
        ; ('__stack' is provided through the linker script)
        LOAD_SYM_TO_REG r13 __stack     ; store symbol '__stack' in r13
        STORE_MEM_REG -16               ; frame pointer register Y (FP)
        STORE_MEM_REG -12               ; frame pointer register Z (SP)

        ; call main
        LOAD_SYM_TO_REG r13 main        ; store symbol 'main' in r13
        jsr r13

        ; call _exit ('_exit' is provided by the libc and loops indefinitely)
        mov r1, r0                      ; move return value of 'main' in r0 to argument register r1
        LOAD_SYM_TO_REG r13 _exit       ; store symbol ' exit' in r13
        jsr r13
        .size   _start, .-_start