firmware/os/cpu/cortexm4/atomic.c

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <atomic.h>

uint32_t atomicAddByte(volatile uint8_t *byte, uint32_t addend)
{
    uint32_t prevVal, storeFailed, tmp;

    do {
        asm volatile(
            "ldrexb %0,     [%4] \n"
            "add    %2, %0, %3   \n"
            "strexb %1, %2, [%4] \n"
            :"=r"(prevVal), "=r"(storeFailed), "=r"(tmp), "=r"(addend), "=r"(byte)
            :"3"(addend), "4"(byte)
            :"memory"
        );
    } while (storeFailed);

    return prevVal;
}

uint32_t atomicAdd32bits(volatile uint32_t *word, uint32_t addend)
{
    uint32_t prevVal, storeFailed, tmp;

    do {
        asm volatile(
            "ldrex  %0,     [%4] \n"
            "add    %2, %0, %3   \n"
            "strex  %1, %2, [%4] \n"
            :"=r"(prevVal), "=r"(storeFailed), "=r"(tmp), "=r"(addend), "=r"(word)
            :"3"(addend), "4"(word)
            :"memory"
        );
    } while (storeFailed);

    return prevVal;
}

uint32_t atomicXchgByte(volatile uint8_t *byte, uint32_t newVal)
{
    uint32_t prevVal, storeFailed;

    do {
        asm volatile(
            "ldrexb %0,     [%3] \n"
            "strexb %1, %2, [%3] \n"
            :"=r"(prevVal), "=r"(storeFailed), "=r"(newVal), "=r"(byte)
            :"2"(newVal), "3"(byte)
            :"memory"
        );
    } while (storeFailed);

    return prevVal;
}

uint32_t atomicXchg32bits(volatile uint32_t *word, uint32_t newVal)
{
    uint32_t prevVal, storeFailed;

    do {
        asm volatile(
            "ldrex %0,     [%3] \n"
            "strex %1, %2, [%3] \n"
            :"=r"(prevVal), "=r"(storeFailed), "=r"(newVal), "=r"(word)
            :"2"(newVal), "3"(word)
            :"memory"
        );
    } while (storeFailed);

    return prevVal;
}

bool atomicCmpXchgByte(volatile uint8_t *byte, uint32_t prevVal, uint32_t newVal)
{
    uint32_t currVal, storeFailed;

    do {
        asm volatile(
            "ldrexb %0,     [%1] \n"
            :"=r"(currVal), "=r"(byte)
            :"1"(byte)
            :"memory"
        );

        if (currVal != prevVal)
            return false;

        asm volatile(
            "strexb %0, %1, [%2] \n"
            :"=r"(storeFailed), "=r"(newVal), "=r"(byte)
            :"1"(newVal), "2"(byte)
            :"memory"
        );
    } while (storeFailed);

    return true;
}

bool atomicCmpXchg32bits(volatile uint32_t *word, uint32_t prevVal, uint32_t newVal)
{
    uint32_t currVal, storeFailed;

    do {
        asm volatile(
            "ldrex %0,     [%1] \n"
            :"=r"(currVal), "=r"(word)
            :"1"(word)
            :"memory"
        );

        if (currVal != prevVal)
            return false;

        asm volatile(
            "strex %0, %1, [%2] \n"
            :"=r"(storeFailed), "=r"(newVal), "=r"(word)
            :"1"(newVal), "2"(word)
            :"memory"
        );
    } while (storeFailed);

    return true;
}