esp-idf/components/esp_hw_support/include/spinlock.h

/*
 * SPDX-FileCopyrightText: 2015-2022 Espressif Systems (Shanghai) CO LTD
 *
 * SPDX-License-Identifier: Apache-2.0
 */
#pragma once

#include <stdint.h>
#include <stdbool.h>
#include "sdkconfig.h"
#include "hal/cpu_hal.h"
#include "compare_set.h"

#if __XTENSA__
#include "xtensa/xtruntime.h"
#endif

#ifdef __cplusplus
extern "C" {
#endif

#ifdef CONFIG_SPIRAM_WORKAROUND_NEED_VOLATILE_SPINLOCK
#define NEED_VOLATILE_MUX volatile
#else
#define NEED_VOLATILE_MUX
#endif

#define SPINLOCK_FREE          0xB33FFFFF
#define SPINLOCK_WAIT_FOREVER  (-1)
#define SPINLOCK_NO_WAIT        0
#define SPINLOCK_INITIALIZER   {.owner = SPINLOCK_FREE,.count = 0}
#define CORE_ID_REGVAL_XOR_SWAP (0xCDCD ^ 0xABAB)

typedef struct {
    NEED_VOLATILE_MUX uint32_t owner;
    NEED_VOLATILE_MUX uint32_t count;
}spinlock_t;

/**
 * @brief Initialize a lock to its default state - unlocked
 * @param lock - spinlock object to initialize
 */
static inline void __attribute__((always_inline)) spinlock_initialize(spinlock_t *lock)
{
    assert(lock);
#if !CONFIG_FREERTOS_UNICORE
    lock->owner = SPINLOCK_FREE;
    lock->count = 0;
#endif
}

/**
 * @brief Top level spinlock acquire function, spins until get the lock
 *
 * This function will:
 * - Save current interrupt state, then disable interrupts
 * - Spin until lock is acquired or until timeout occurs
 * - Restore interrupt state
 *
 * @note Spinlocks alone do no constitute true critical sections (as this
 *       function reenables interrupts once the spinlock is acquired). For critical
 *       sections, use the interface provided by the operating system.
 * @param lock - target spinlock object
 * @param timeout - cycles to wait, passing SPINLOCK_WAIT_FOREVER blocs indefinitely
 */
static inline bool __attribute__((always_inline)) spinlock_acquire(spinlock_t *lock, int32_t timeout)
{
#if !CONFIG_FREERTOS_UNICORE && !BOOTLOADER_BUILD
    uint32_t result;
    uint32_t irq_status;
    uint32_t ccount_start;
    uint32_t core_id, other_core_id;

    assert(lock);
    irq_status = XTOS_SET_INTLEVEL(XCHAL_EXCM_LEVEL);

    if(timeout != SPINLOCK_WAIT_FOREVER){
        RSR(CCOUNT, ccount_start);
    }

    /*spin until we own a core */
    RSR(PRID, core_id);

    /* Note: coreID is the full 32 bit core ID (CORE_ID_REGVAL_PRO/CORE_ID_REGVAL_APP) */

    other_core_id = CORE_ID_REGVAL_XOR_SWAP ^ core_id;
    do {

        /* lock->owner should be one of SPINLOCK_FREE, CORE_ID_REGVAL_PRO,
         * CORE_ID_REGVAL_APP:
         *  - If SPINLOCK_FREE, we want to atomically set to 'core_id'.
         *  - If "our" core_id, we can drop through immediately.
         *  - If "other_core_id", we spin here.
         */
        result = core_id;

#if defined(CONFIG_ESP32_SPIRAM_SUPPORT)
        if (esp_ptr_external_ram(lock)) {
            compare_and_set_extram(&lock->owner, SPINLOCK_FREE, &result);
        } else {
#endif
        compare_and_set_native(&lock->owner, SPINLOCK_FREE, &result);
#if defined(CONFIG_ESP32_SPIRAM_SUPPORT)
        }
#endif
        if(result != other_core_id) {
            break;
        }

        if (timeout != SPINLOCK_WAIT_FOREVER) {
            uint32_t ccount_now;
            ccount_now = cpu_hal_get_cycle_count();
            if (ccount_now - ccount_start > (unsigned)timeout) {
                XTOS_RESTORE_INTLEVEL(irq_status);
                return false;
            }
        }
    }while(1);

    /* any other value implies memory corruption or uninitialized mux */
    assert(result == core_id || result == SPINLOCK_FREE);
    assert((result == SPINLOCK_FREE) == (lock->count == 0)); /* we're first to lock iff count is zero */
    assert(lock->count < 0xFF); /* Bad count value implies memory corruption */

    lock->count++;
    XTOS_RESTORE_INTLEVEL(irq_status);
    return true;

#else  // !CONFIG_FREERTOS_UNICORE
    return true;
#endif
}

/**
 * @brief Top level spinlock unlock function, unlocks a previously locked spinlock
 *
 * This function will:
 * - Save current interrupt state, then disable interrupts
 * - Release the spinlock
 * - Restore interrupt state
 *
 * @note Spinlocks alone do no constitute true critical sections (as this
 *       function reenables interrupts once the spinlock is acquired). For critical
 *       sections, use the interface provided by the operating system.
 * @param lock - target, locked before, spinlock object
 */
static inline void __attribute__((always_inline)) spinlock_release(spinlock_t *lock)
{
#if !CONFIG_FREERTOS_UNICORE && !BOOTLOADER_BUILD
    uint32_t irq_status;
    uint32_t core_id;

    assert(lock);
    irq_status = XTOS_SET_INTLEVEL(XCHAL_EXCM_LEVEL);

    RSR(PRID, core_id);
    assert(core_id == lock->owner); // This is a mutex we didn't lock, or it's corrupt
    lock->count--;

    if(!lock->count) {
        lock->owner = SPINLOCK_FREE;
    } else {
        assert(lock->count < 0x100); // Indicates memory corruption
    }

    XTOS_RESTORE_INTLEVEL(irq_status);
#endif
}

#ifdef __cplusplus
}
#endif