source: rtems/c/src/lib/libbsp/arm/shared/start/start.S @ cfd8d7a

/**
 * @file
 *
 * @brief Boot and system start code.
 */

/*
 * Copyright (c) 2008-2013 embedded brains GmbH.  All rights reserved.
 *
 *  embedded brains GmbH
 *  Obere Lagerstr. 30
 *  82178 Puchheim
 *  Germany
 *  <rtems@embedded-brains.de>
 *
 * The license and distribution terms for this file may be
 * found in the file LICENSE in this distribution or at
 * http://www.rtems.com/license/LICENSE.
 */

#include <rtems/asm.h>
#include <rtems/system.h>       
#include <rtems/score/cpu.h>
        
#include <bspopts.h>
#include <bsp/irq.h>
#include <bsp/linker-symbols.h>

        /* External symbols */
        .extern bsp_reset
        .extern boot_card
        .extern bsp_start_hook_0
        .extern bsp_start_hook_1
        .extern _ARMV4_Exception_undef_default
        .extern _ARMV4_Exception_swi_default
        .extern _ARMV4_Exception_data_abort_default
        .extern _ARMV4_Exception_pref_abort_default
        .extern _ARMV4_Exception_reserved_default
        .extern _ARMV4_Exception_irq_default
        .extern _ARMV4_Exception_fiq_default
        .extern _ARMV7M_Exception_default

        /* Global symbols */
        .globl  _start
        .globl  bsp_start_vector_table_begin
        .globl  bsp_start_vector_table_end
        .globl  bsp_start_vector_table_size
        .globl  bsp_vector_table_size

        .section        ".bsp_start_text", "ax"

#if defined(ARM_MULTILIB_ARCH_V4)

        .arm

/*
 * This is the exception vector table and the pointers to the default
 * exceptions handlers.
 */

bsp_start_vector_table_begin:

        ldr     pc, handler_addr_reset
        ldr     pc, handler_addr_undef
        ldr     pc, handler_addr_swi
        ldr     pc, handler_addr_prefetch
        ldr     pc, handler_addr_abort

        /* Program signature checked by boot loader */
        .word   0xb8a06f58

        ldr     pc, handler_addr_irq
        ldr     pc, handler_addr_fiq

handler_addr_reset:

#ifdef BSP_START_RESET_VECTOR
        .word   BSP_START_RESET_VECTOR
#else
        .word   _start
#endif

handler_addr_undef:

        .word   _ARMV4_Exception_undef_default

handler_addr_swi:

        .word   _ARMV4_Exception_swi_default

handler_addr_prefetch:

        .word   _ARMV4_Exception_data_abort_default

handler_addr_abort:

        .word   _ARMV4_Exception_pref_abort_default

handler_addr_reserved:

        .word   _ARMV4_Exception_reserved_default

handler_addr_irq:

        .word   _ARMV4_Exception_irq_default

handler_addr_fiq:

        .word   _ARMV4_Exception_fiq_default

bsp_start_vector_table_end:

/* Start entry */

_start:

        /*
         * We do not save the context since we do not return to the boot
         * loader.
         */

        /*
         * Set SVC mode, disable interrupts and enable ARM instructions.
         */
        mov     r0, #(ARM_PSR_M_SVC | ARM_PSR_I | ARM_PSR_F)
        msr     cpsr, r0

        /* Initialize stack pointer registers for the various modes */

        /* Enter IRQ mode and set up the IRQ stack pointer */
        mov     r0, #(ARM_PSR_M_IRQ | ARM_PSR_I | ARM_PSR_F)
        msr     cpsr, r0
        ldr     sp, =bsp_stack_irq_end

        /* Enter FIQ mode and set up the FIQ stack pointer */
        mov     r0, #(ARM_PSR_M_FIQ | ARM_PSR_I | ARM_PSR_F)
        msr     cpsr, r0
        ldr     sp, =bsp_stack_fiq_end

        /* Enter ABT mode and set up the ABT stack pointer */
        mov     r0, #(ARM_PSR_M_ABT | ARM_PSR_I | ARM_PSR_F)
        msr     cpsr, r0
        ldr     sp, =bsp_stack_abt_end

        /* Enter UND mode and set up the UND stack pointer */
        mov     r0, #(ARM_PSR_M_UND | ARM_PSR_I | ARM_PSR_F)
        msr     cpsr, r0
        ldr     sp, =bsp_stack_und_end

        /* Enter SVC mode and set up the SVC stack pointer */
        mov     r0, #(ARM_PSR_M_SVC | ARM_PSR_I | ARM_PSR_F)
        msr     cpsr, r0
        ldr     sp, =bsp_stack_svc_end

        /* Stay in SVC mode */

#ifdef ARM_MULTILIB_VFP_D32
        /* Read CPACR */
        mrc p15, 0, r0, c1, c0, 2

        /* Enable CP10 and CP11 */
        orr r0, r0, #(1 << 20)
        orr r0, r0, #(1 << 22)

        /* Clear ASEDIS and D32DIS */
        bic r0, r0, #(3 << 30)

        /* Write CPACR */
        mcr p15, 0, r0, c1, c0, 2
        isb

        /* Enable FPU */
        mov r0, #(1 << 30)
        vmsr FPEXC, r0
#endif

        /*
         * Branch to start hook 0.
         *
         * The previous code and parts of the start hook 0 may run with an
         * address offset.  This implies that only branches relative to the
         * program counter are allowed.  After the start hook 0 it is assumed
         * that the code can run at its intended position.  Thus the link
         * register will be loaded with the absolute address.  In THUMB mode
         * the start hook 0 must be within a 2kByte range due to the branch
         * instruction limitation.
         */

        ldr     lr, =bsp_start_hook_0_done
#ifdef __thumb__
        orr     lr, #1
#endif

        SWITCH_FROM_ARM_TO_THUMB        r0

        b       bsp_start_hook_0

bsp_start_hook_0_done:

        SWITCH_FROM_THUMB_TO_ARM

        /*
         * Initialize the exception vectors.  This includes the exceptions
         * vectors and the pointers to the default exception handlers.
         */

        ldr     r0, =bsp_vector_table_begin
        adr     r1, bsp_start_vector_table_begin
        cmp     r0, r1
        beq     bsp_vector_table_copy_done
        ldmia   r1!, {r2-r9}
        stmia   r0!, {r2-r9}
        ldmia   r1!, {r2-r9}
        stmia   r0!, {r2-r9}

bsp_vector_table_copy_done:

        SWITCH_FROM_ARM_TO_THUMB        r0

        /* Branch to start hook 1 */
        bl      bsp_start_hook_1

        /* Branch to boot card */
        mov     r0, #0
        bl      boot_card

twiddle:

        /* Branch to reset function */
        bl      bsp_reset

        b       twiddle

#elif defined(ARM_MULTILIB_ARCH_V7M)

        .syntax unified

        .extern bsp_stack_main_end

        .thumb

bsp_start_vector_table_begin:

        .word   bsp_stack_main_end
        .word   _start /* Reset */
        .word   _ARMV7M_Exception_default /* NMI */
        .word   _ARMV7M_Exception_default /* Hard Fault */
        .word   _ARMV7M_Exception_default /* MPU Fault */
        .word   _ARMV7M_Exception_default /* Bus Fault */
        .word   _ARMV7M_Exception_default /* Usage Fault */
        .word   _ARMV7M_Exception_default /* Reserved */
        .word   _ARMV7M_Exception_default /* Reserved */
        .word   _ARMV7M_Exception_default /* Reserved */
        .word   _ARMV7M_Exception_default /* Reserved */
        .word   _ARMV7M_Exception_default /* SVC */
        .word   _ARMV7M_Exception_default /* Debug Monitor */
        .word   _ARMV7M_Exception_default /* Reserved */
        .word   _ARMV7M_Exception_default /* PendSV */
        .word   _ARMV7M_Exception_default /* SysTick */
        .rept   BSP_INTERRUPT_VECTOR_MAX + 1
        .word   _ARMV7M_Exception_default /* IRQ */
        .endr

bsp_start_vector_table_end:

        .thumb_func

_start:

        ldr     sp, =bsp_stack_main_end
        ldr     lr, =bsp_start_hook_0_done + 1
        b       bsp_start_hook_0

bsp_start_hook_0_done:

        bl      bsp_start_hook_1
        movs    r0, #0
        bl      boot_card

twiddle:

        bl      bsp_reset
        b       twiddle

#endif /* defined(ARM_MULTILIB_ARCH_V7M) */

        .set    bsp_start_vector_table_size, bsp_start_vector_table_end - bsp_start_vector_table_begin
        .set    bsp_vector_table_size, bsp_start_vector_table_size