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/*
 * Copyright (c) 2007 Petr Stepan, Pavel Jancik
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup arm32
 * @{
 */
/** @file
 *  @brief Userspace.
 */

#include <userspace.h>

/** Struct to hold general purpose register values */
typedef struct {
    uint32_t r0;
    uint32_t r1;
    uint32_t r2;
    uint32_t r3;
    uint32_t r4;
    uint32_t r5;
    uint32_t r6;
    uint32_t r7;
    uint32_t r8;
    uint32_t r9;
    uint32_t r10;
    uint32_t r11;
    uint32_t r12;
    uint32_t sp;
    uint32_t lr;
    uint32_t pc;
} ustate_t;

/** Changes processor mode and jumps to the address specified in the first parameter.
 *
 *  @param kernel_uarg   Userspace settings (entry point, stack, ...).
 */
void userspace(uspace_arg_t *kernel_uarg)
{

    volatile ustate_t ustate;

    // set first parameter
    ustate.r0 = (uintptr_t) kernel_uarg->uspace_uarg;

    // clear other registers
    ustate.r1 = ustate.r2  = ustate.r3  = ustate.r4  =
        ustate.r5 = ustate.r6  = ustate.r7  = ustate.r8  =
        ustate.r9 = ustate.r10 = ustate.r11 = ustate.r12 =
        ustate.lr = 0;

    //set user stack
    ustate.sp = ((uint32_t)kernel_uarg->uspace_stack) +
            PAGE_SIZE - sizeof(void*);

    //set where uspace execution starts
    ustate.pc = (uintptr_t) kernel_uarg->uspace_entry;

    //status register in user mode
    ipl_t cpsr = current_status_reg_read();
    cpsr &= ~STATUS_REG_MODE_MASK | USER_MODE;

    ipl_t tmpsr = (cpsr & ~STATUS_REG_MODE_MASK) | SUPERVISOR_MODE;

    asm __volatile__ (
        // save pointer into ustate struct
        "mov r0, %0         \n"
        // save cspr
        "mov r1, %1         \n"
        // change mode into any exception mode
        "msr cpsr_c, %2         \n"
        // set saved cpsr
        "msr spsr_c, r1 \n"

        "mov sp, r0 \n"
        // replace almost all registers
        "ldmfd sp!, {r0-r12, sp, lr}^\n"
        //jump to the usermode
        "ldmfd sp!, {pc}^"
    : // no output
    : "r"(&ustate), "r"(cpsr), "r"(tmpsr) //
    : "r0","r1"
    );

    // unreachable
    while(1) ;
}


/** @}
 */