source: soft/giet_vm/libs/mwmr_channel.c @ 240

//////////////////////////////////////////////////////////////////////////////////
// File     : mwmr_channel_.c         
// 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 itself must have been allocated in a non cacheable segment,
// if the platform does not provide hardware cache coherence.
//
// ALL MWMR channels must be defined in the mapping_info data structure, 
// to be initialised by the GIET in the boot phase.
// The vobj_get_vbase() system call (defined in stdio.c and stdio.h files)
// can be used to get the virtual base address of the channel from it's name.
//
// 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 private lock provides exclusive access to the MWMR channel, that can have
// a variable number of producers and a variable number of consumers.
///////////////////////////////////////////////////////////////////////////////////

#include <mwmr_channel.h>
#include <stdio.h>

//////////////////////////////////////////////////////////////////////////////
//  mwmr_lock_aquire()
// This blocking function returns only when the lock has been taken.
// If the lock is already taken a fixed delay is introduced before retry.
//////////////////////////////////////////////////////////////////////////////
void mwmr_lock_acquire(unsigned int * lock_address) {
    register unsigned int * plock = lock_address;
    register unsigned int delay = 100;
    asm volatile (
            "mwmr_lock_try:                    \n"
            "ll   $2,    0(%0)                \n" /* $2 <= lock current value */
            "bnez $2,    mwmr_lock_delay    \n" /* retry after delay if lock busy */
            "li   $3,    1                    \n" /* $3 <= argument for sc */
            "sc   $3,    0(%0)                \n" /* try to get lock */
            "bnez $3,    mwmr_lock_ok        \n" /* exit if atomic */
            "mwmr_lock_delay:                \n"
            "move $4,    %1                 \n" /* $4 <= delay */
            "mwmr_lock_loop:                \n"
            "beqz $4,    mwmr_lock_loop        \n" /* test end delay */
            "addi $4,    $4,  -1            \n" /* $4 <= $4 - 1 */
            "j           mwmr_lock_try        \n" /* retry ll */
            "nop                            \n"
            "mwmr_lock_ok:                    \n"
            :
            :"r"(plock), "r"(delay)
            :"$2", "$3", "$4");
} 


//////////////////////////////////////////////////////////////////////////////
//       nb_mwmr_write()
// This is a non-blocking function.
// The nitems parameter is the number of items to be transfered.
// The requested transfer is therefore (nitems * width) words.
// It takes the lock for exclusive access before testing the channel state.
// If there is not enough data in mwmr channel to read nitems,
// it reads as many items as possible, releases the lock, and returns 
// the number of read items (it can be 0).
//////////////////////////////////////////////////////////////////////////////
unsigned int nb_mwmr_write(mwmr_channel_t * mwmr, unsigned int * buffer, unsigned int nitems) {
    unsigned int x;
    unsigned int spaces; // number of empty slots (in words)
    unsigned int nwords; // requested transfer length (in words)
    unsigned int depth;  // channel depth (in words)
    unsigned int width;  // channel width (in words)
    unsigned int sts;    // channel sts
    unsigned int ptw;    // channel ptw

    if (nitems == 0) {
        return 0;
    }

    // get the lock
    mwmr_lock_acquire(&mwmr->lock);

    // access fifo status
    depth = mwmr->depth;
    width = mwmr->width;
    sts = mwmr->sts;
    ptw = mwmr->ptw;
    spaces = depth - sts;
    nwords = width * nitems;

    if (spaces >= nwords) { // transfer nitems, release lock and return 
        for (x = 0; x < nwords; x++) {
            mwmr->data[ptw] = buffer[x];
            if ((ptw + 1) == depth) {
                ptw = 0;
            }
            else {
                ptw = ptw + 1;
            }
        }
        mwmr->sts = mwmr->sts + nwords;
        mwmr->ptw = ptw;
        mwmr->lock = 0;
        return nitems;
    }
    else if (spaces < width) {
        // release lock and return 
        mwmr->lock = 0;
        return 0;
    }
    else {
        // transfer as many items as possible, release lock and return 
        nwords = (spaces / width) * width;    // integer number of items
        for (x = 0; x < nwords; x++) {
            mwmr->data[ptw] = buffer[x];
            if ((ptw + 1) == depth) {
                ptw = 0;
            }
            else {
                ptw = ptw + 1;
            }
        }
        mwmr->sts = sts + nwords;
        mwmr->ptw = ptw;
        mwmr->lock = 0;
        return (nwords / width);
    }
} // end nb_mwmr_write()


//////////////////////////////////////////////////////////////////////////////
//    mwmr_write()
// This blocking function returns only when the transfer is completed.
// The nitems parameter is the number of items to be transfered.
// The requested transfer is therefore (nitems * width) words.
// It takes the lock for exclusive access before testing the channel state.
// If there is not enough space in mwmr channel to write nitems,
// it writes as many items as possible, releases the lock, and retry 
// after a random delay.
//////////////////////////////////////////////////////////////////////////////
void mwmr_write(mwmr_channel_t * mwmr, unsigned int * buffer, unsigned int nitems) {
    unsigned int x;
    unsigned int spaces; // number of empty slots (in words)
    unsigned int nwords; // requested transfer length (in words)
    unsigned int depth;  // channel depth (in words)
    unsigned int width;  // channel width (in words)
    unsigned int sts;    // channel sts
    unsigned int ptw;    // channel ptw

    if (nitems == 0) {
        return;
    }

    while (1) {
        // get the lock
        mwmr_lock_acquire(&mwmr->lock);

        // compute spaces and nwords
        depth = mwmr->depth;
        width = mwmr->width;
        sts  = mwmr->sts;
        ptw  = mwmr->ptw;
        spaces = depth - sts;
        nwords = width * nitems;

        if (spaces >= nwords) {
            // write nwords, release lock and return
            for (x = 0; x < nwords; x++) {
                mwmr->data[ptw] = buffer[x];
                if ((ptw + 1) == depth) {
                    ptw = 0;
                }
                else {
                    ptw = ptw + 1;
                }
            }
            mwmr->ptw = ptw;
            mwmr->sts = sts + nwords;
            mwmr->lock = 0;
            return;
        }
        else if (spaces < width) {
            // release lock and retry after delay
            mwmr->lock = 0;
        }
        else {
            // write as many items as possible, release lock and retry after delay
            nwords = (spaces / width) * width;  // integer number of items
            for (x = 0; x < nwords; x++) {
                mwmr->data[ptw] = buffer[x];
                if ((ptw + 1) == depth) {
                    ptw = 0;
                }
                else {
                    ptw = ptw + 1;
                }
            }
            mwmr->sts = sts + nwords;
            mwmr->ptw = ptw;
            buffer = buffer + nwords;
            nitems = nitems - (nwords/width);
            mwmr->lock = 0;
        }
        giet_context_switch();
    }
} // end mwmr_write()


//////////////////////////////////////////////////////////////////////////////
//       nb_mwmr_read()
// This is a non-blocking function.
// The nitems parameter is the number of items to be transfered.
// The requested transfer is therefore (nitems * width) words.
// It takes the lock for exclusive access before testing the channel state.
// If there is not enough data in mwmr channel to read nitems,
// it reads as many items as possible, releases the lock, and returns 
// the number of read items (it can be 0).
//////////////////////////////////////////////////////////////////////////////
unsigned int nb_mwmr_read(mwmr_channel_t * mwmr, unsigned int * buffer, unsigned int nitems) {
    unsigned int x;
    unsigned int nwords; // requested transfer length (in words)
    unsigned int depth;  // channel depth (in words)
    unsigned int width;  // channel width (in words)
    unsigned int sts;    // channel sts
    unsigned int ptr;    // channel ptr

    if (nitems == 0) {
        return 0;
    }

    // get the lock
    mwmr_lock_acquire(&mwmr->lock);

    // access fifo status
    depth = mwmr->depth;
    width = mwmr->width;
    sts = mwmr->sts;
    ptr = mwmr->ptr;
    nwords = width * nitems;

    if (sts >= nwords) {
        // transfer nitems, release lock and return 
        for (x = 0; x < nwords; x++) {
            buffer[x] = mwmr->data[ptr];
            if ((ptr + 1) == depth) {
                ptr = 0;
            }
            else {
                ptr = ptr + 1;
            }
        }
        mwmr->sts = mwmr->sts - nwords;
        mwmr->ptr = ptr;
        mwmr->lock = 0;
        return nitems;
    }
    else if (sts < width) {
        // release lock and return 
        mwmr->lock = 0;
        return 0;
    }
    else {
        // transfer as many items as possible, release lock and return 
        nwords = (sts / width) * width; // integer number of items
        for (x = 0 ; x < nwords ; x++) {
            buffer[x] = mwmr->data[ptr];
            if ((ptr + 1) == depth) {
                ptr = 0;
            }
            else {
                ptr = ptr + 1;
            }
        }
        mwmr->sts = sts - nwords;
        mwmr->ptr = ptr;
        mwmr->lock = 0;
        return (nwords / width);
    }
} // nb_mwmr_read()


//////////////////////////////////////////////////////////////////////////////
//    mwmr_read()
// This blocking function returns only when the transfer is completed.
// The nitems parameter is the number of items to be transfered.
// The requested transfer is therefore (nitems * width) words.
// It takes the lock for exclusive access before testing the channel state.
// If there is not enough data in mwmr channel to read nitems,
// it reads as many items as possible, releases the lock, and retry 
// after a random delay.
//////////////////////////////////////////////////////////////////////////////
void mwmr_read( mwmr_channel_t * mwmr, unsigned int * buffer, unsigned int nitems) {
    unsigned int x;
    unsigned int nwords; // requested transfer length (in words)
    unsigned int depth;  // channel depth (in words)
    unsigned int width;  // channel width (in words)
    unsigned int sts;    // channel sts
    unsigned int ptr;    // channel ptr

    if (nitems == 0) {
        return;
    }

    while (1) {
        // get the lock
        mwmr_lock_acquire(&mwmr->lock);

        // compute nwords
        depth = mwmr->depth;
        width = mwmr->width;
        sts = mwmr->sts;
        ptr = mwmr->ptr;
        nwords = width * nitems;

        if (sts >= nwords) {
            // read nwords, release lock and return
            for (x = 0; x < nwords; x++) {
                buffer[x] = mwmr->data[ptr];
                if ((ptr + 1) == depth) {
                    ptr = 0;
                }
                else {
                    ptr = ptr + 1;
                }
            }
            mwmr->sts = mwmr->sts - nwords;
            mwmr->ptr = ptr;
            mwmr->lock = 0;
            return;
        }
        else if (sts < width) {
            // release lock and retry after delay
            mwmr->lock = 0;
        }
        else {   // read as many items as possible, release lock and retry after delay
            nwords = (sts / width) * width; // integer number of items
            for (x = 0; x < nwords; x++) {
                buffer[x] = mwmr->data[ptr];
                if ((ptr + 1) == depth) {
                    ptr = 0;
                }
                else {
                    ptr = ptr + 1;
                }
            }
            mwmr->sts = sts - nwords;
            mwmr->ptr = ptr;
            buffer = buffer + nwords;
            nitems = nitems - (nwords/width);
            mwmr->lock = 0;
        }
        giet_context_switch();
    }
} // end mwmr_read() 


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