source: soft/giet_vm/giet_libs/mwmr_channel.h @ 495

//////////////////////////////////////////////////////////////////////////////////
// File     : mwmr_channel.h         
// Date     : 01/04/2012
// Author   : alain greiner
// Copyright (c) UPMC-LIP6
///////////////////////////////////////////////////////////////////////////////////
// The mwmr_channel.c and mwmr_channel.h files are part of the GIET nano-kernel.
// This  middleware implements a user level Multi-Writers / Multi-Readers
// communication channel, that can be used by parallel multi-tasks applications
// respecting the TCG (Tasks and Communications Graph) formalism.
// 
// The mwmr_read() and mwmr_write() functions do not require a system call.
// The channel must have been allocated in a non cacheable segment,
// if the platform does not provide hardware cache coherence.
//
// An MWMR transaction transfer an integer number of items, and an item is
// an integer number of unsigned int (32 bits words).
// The max number of words that can be stored in a MWMR channel is defined by the
// "depth" parameter, and the "width" parameter define the minimal number of
// word contained in an atomic item. Therefore, the "depth" parameter must be
// a multiple of the "width" parameter.
//
// Both the mwmr_read() and mwmr_write() functions are blocking functions. 
// A queuing lock provides exclusive access to the MWMR channel.
///////////////////////////////////////////////////////////////////////////////////

#ifndef _MWMR_CHANNEL_H_
#define _MWMR_CHANNEL_H_

#include "user_lock.h"

///////////////////////////////////////////////////////////////////////////////////
//  MWMR channel structure
// The data buffer size is defined to obtain sizeof(mwmr_channel_t) = 4096 bytes.
// The actual buffer size cannot be larger than 4072 bytes (1018 words).
///////////////////////////////////////////////////////////////////////////////////

typedef struct mwmr_channel_s 
{
    user_lock_t    lock;       // exclusive access lock
    unsigned int   ptr;        // index of the first valid data word
    unsigned int   ptw;        // index of the first empty slot 
    unsigned int   sts;        // number of words available
    unsigned int   depth;      // max number of words in the channel
    unsigned int   width;      // number of words in an item      
    unsigned int*  data;       // circular buffer base address
} mwmr_channel_t;

//////////////////////////////////////////////////////////////////////////////
//  MWMR access functions
//////////////////////////////////////////////////////////////////////////////

void mwmr_init(  mwmr_channel_t* mwmr,
                 unsigned int*   buffer,    // data buffer base address
                 unsigned int    width,     // number of words per item
                 unsigned int    nitems );  // max number of items

void mwmr_read(  mwmr_channel_t* mwmr,
                 unsigned int*   buffer,
                 unsigned int    items );

void mwmr_write( mwmr_channel_t* mwmr,
                 unsigned int*   buffer,
                 unsigned int    items );

unsigned int nb_mwmr_read ( mwmr_channel_t * mwmr,
                            unsigned int * buffer,
                            unsigned int items );

unsigned int nb_mwmr_write( mwmr_channel_t * mwmr,
                            unsigned int * buffer,
                            unsigned int items );

#endif

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