arch/arm/core/exc_exit.S

/*
 * Copyright (c) 2013-2014 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @file
 * @brief ARM Cortex-M and Cortex-R exception/interrupt exit API
 *
 *
 * Provides functions for performing kernel handling when exiting exceptions or
 * interrupts that are installed directly in the vector table (i.e. that are not
 * wrapped around by _isr_wrapper()).
 */

#include <toolchain.h>
#include <linker/sections.h>
#include <offsets_short.h>
#include <arch/cpu.h>

_ASM_FILE_PROLOGUE

GTEXT(z_arm_exc_exit)
GTEXT(z_arm_int_exit)
GDATA(_kernel)
#if defined(CONFIG_CPU_CORTEX_R)
GTEXT(z_arm_pendsv)
#endif

/**
 *
 * @brief Kernel housekeeping when exiting interrupt handler installed
 *            directly in vector table
 *
 * Kernel allows installing interrupt handlers (ISRs) directly into the vector
 * table to get the lowest interrupt latency possible. This allows the ISR to
 * be invoked directly without going through a software interrupt table.
 * However, upon exiting the ISR, some kernel work must still be performed,
 * namely possible context switching. While ISRs connected in the software
 * interrupt table do this automatically via a wrapper, ISRs connected directly
 * in the vector table must invoke z_arm_int_exit() as the *very last* action
 * before returning.
 *
 * e.g.
 *
 * void myISR(void)
 *     {
 *     printk("in %s\n", __FUNCTION__);
 *     doStuff();
 *     z_arm_int_exit();
 *     }
 *
 * @return N/A
 */

SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, z_arm_int_exit)

/* z_arm_int_exit falls through to z_arm_exc_exit (they are aliases of each
 * other)
 */

/**
 *
 * @brief Kernel housekeeping when exiting exception handler installed
 *            directly in vector table
 *
 * See z_arm_int_exit().
 *
 * @return N/A
 */

SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, z_arm_exc_exit)
#if defined(CONFIG_CPU_CORTEX_R)
    /* r0 contains the caller mode */
    push {r0, lr}
#endif

#ifdef CONFIG_PREEMPT_ENABLED
    ldr r0, =_kernel

    ldr r1, [r0, #_kernel_offset_to_current]

    ldr r0, [r0, #_kernel_offset_to_ready_q_cache]
    cmp r0, r1
    beq _EXIT_EXC

#if defined(CONFIG_CPU_CORTEX_M)
    /* context switch required, pend the PendSV exception */
    ldr r1, =_SCS_ICSR
    ldr r2, =_SCS_ICSR_PENDSV
    str r2, [r1]
#elif defined(CONFIG_CPU_CORTEX_R)
    bl z_arm_pendsv
#endif

_ExcExitWithGdbStub:

_EXIT_EXC:
#endif /* CONFIG_PREEMPT_ENABLED */

#ifdef CONFIG_STACK_SENTINEL
#if defined(CONFIG_CPU_CORTEX_M)
    push {r0, lr}
    bl z_check_stack_sentinel
#if defined(CONFIG_ARMV6_M_ARMV8_M_BASELINE)
    pop {r0, r1}
    mov lr, r1
#else
    pop {r0, lr}
#endif /* CONFIG_ARMV6_M_ARMV8_M_BASELINE */
#else
    bl z_check_stack_sentinel
#endif /* CONFIG_CPU_CORTEX_M */
#endif /* CONFIG_STACK_SENTINEL */

#if defined(CONFIG_CPU_CORTEX_M)
    bx lr
#elif defined(CONFIG_CPU_CORTEX_R)
    /* Restore the caller mode to r0 */
    pop {r0, lr}

    /*
     * Restore r0-r3, r12 and lr stored into the process stack by the mode
     * entry function. These registers are saved by _isr_wrapper for IRQ mode
     * and z_arm_svc for SVC mode.
     *
     * r0-r3 are either the values from the thread before it was switched out
     * or they are the args to _new_thread for a new thread.
     */
    push {r4, r5}

    cmp r0, #RET_FROM_SVC
    cps #MODE_SYS
    ldmia sp!, {r0-r5}
    beq _svc_exit

    cps #MODE_IRQ
    b _exc_exit

_svc_exit:
    cps #MODE_SVC

_exc_exit:
    mov r12, r4
    mov lr, r5
    pop {r4, r5}
    movs pc, lr
#endif