source: mainline/uspace/drv/char/i8042/buffer.h@ c657bd7

/*
 * Copyright (c) 2011 Jan Vesely
 * 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 kbd
 * @{
 */

/** @file
 * @brief Cyclic buffer structure.
 */

#ifndef BUFFER_H_
#define BUFFER_H_

#include <assert.h>
#include <fibril_synch.h>

/** Cyclic buffer that blocks on full/empty.
 *
 * read_head == write_head means that the buffer is empty.
 * write_head + 1 == read_head means that the buffer is full.
 * Attempt to insert byte into the full buffer will block until it can succeed.
 * Attempt to read from empty buffer will block until it can succeed.
 *
 */
typedef struct {
        uint8_t *buffer;          /**< Storage space. */
        uint8_t *buffer_end;      /**< End of storage place. */
        fibril_mutex_t guard;     /**< Protects buffer structures. */
        fibril_condvar_t change;  /**< Indicates change (empty/full). */
        uint8_t *read_head;       /**< Place of the next readable element. */
        uint8_t *write_head;      /**< Pointer to the next writable place. */
} buffer_t;

/** Initialize cyclic buffer using provided memory space.
 *
 * @param buffer Cyclic buffer structure to initialize.
 * @param data   Memory space to use.
 * @param size   Size of the memory place.
 *
 */
static inline void buffer_init(buffer_t *buffer, uint8_t *data, size_t size)
{
        assert(buffer);
        
        fibril_mutex_initialize(&buffer->guard);
        fibril_condvar_initialize(&buffer->change);
        buffer->buffer = data;
        buffer->buffer_end = data + size;
        buffer->read_head = buffer->buffer;
        buffer->write_head = buffer->buffer;
        memset(buffer->buffer, 0, size);
}

/** Write byte to cyclic buffer.
 *
 * @param buffer Cyclic buffer to write to.
 * @param data   Data to write.
 *
 */
static inline void buffer_write(buffer_t *buffer, uint8_t data)
{
        fibril_mutex_lock(&buffer->guard);
        
        /* Next position. */
        uint8_t *new_head = buffer->write_head + 1;
        if (new_head == buffer->buffer_end)
                new_head = buffer->buffer;
        
        /* Buffer full. */
        while (new_head == buffer->read_head)
                fibril_condvar_wait(&buffer->change, &buffer->guard);
        
        /* Write data. */
        *buffer->write_head = data;
        
        /* Buffer was empty. */
        if (buffer->write_head == buffer->read_head)
                fibril_condvar_broadcast(&buffer->change);
        
        /* Move head */
        buffer->write_head = new_head;
        fibril_mutex_unlock(&buffer->guard);
}

/** Read byte from cyclic buffer.
 *
 * @param buffer Cyclic buffer to read from.
 * @param rb Place to store byte read
 * @param wait @c True to wait until byte is available
 *
 * @return EOK on success, EAGAIN if @c wait is false and no data is available
 *
 */
static inline int buffer_read(buffer_t *buffer, uint8_t *rb, bool wait)
{
        fibril_mutex_lock(&buffer->guard);
        
        /* Buffer is empty. */
        while (wait && buffer->write_head == buffer->read_head)
                fibril_condvar_wait(&buffer->change, &buffer->guard);
        
        if (buffer->write_head == buffer->read_head) {
                fibril_mutex_unlock(&buffer->guard);
                return EAGAIN;
        }
        
        /* Next position. */
        uint8_t *new_head = buffer->read_head + 1;
        if (new_head == buffer->buffer_end)
                new_head = buffer->buffer;
        
        /* Read data. */
        const uint8_t data = *buffer->read_head;
        
        /* Buffer was full. */
        uint8_t *new_write_head = buffer->write_head + 1;
        if (new_write_head == buffer->buffer_end)
                new_write_head = buffer->buffer;
        if (new_write_head == buffer->read_head)
                fibril_condvar_broadcast(&buffer->change);
        
        /* Move head */
        buffer->read_head = new_head;
        
        fibril_mutex_unlock(&buffer->guard);
        *rb = data;
        return EOK;
}

#endif

/**
 * @}
 */