source: liacs/ca/opdr3/memory_dram.c@ 66

/* Author      : Rick van der Zwet
 * S-number    : 0433373
 * Version     : $Id: memory.h 363 2007-12-03 06:07:31Z rick $
 * Copyright   : FreeBSD Licence
 * Description : page-mode DRAM with a page-size of PAGESIZE words, a
 *               random access time of RAS clock cycles and a 'next
 *               access time' of NAT clock cycles.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "common.h"

void
memory_dram(const int PAGESIZE, const int NAT, const int RAS)
{
    struct bus2_t line;
    struct result_t output = {0, 0, 0, 0};

    /* Keep track of which page memory is, cause switching means a lot of
     * extra work/cycles in terms of empty memory, moving to new bank
     */
    int current_page = 0;

    /* Page location needed by new request */
    int page_needed = 0;

    /* Part of page needed by new request */
    int part_needed = 0;

    /* Every page has got 64 entries which all can be busy,
     * by convention 0 means not busy else busy
     */
    int * partbusy = (int *)malloc(sizeof(int) * PAGESIZE);

    int i; /* Temp counter */

    /* Init all parts to be available in the beginning */
    memset(partbusy, FALSE, sizeof(int) * PAGESIZE);

    while (fscanfbus2(&line) != EOF) {
        /* Process the counts */
        setstats(&line, &output);

        /* New request means new cycle as well */
        output.cycles++;

        /* Find proper page, do not take advantage of C div operator on
         * int which is rounding directly, but use more safe/portable
         * approch */
        part_needed = line.address % PAGESIZE;
        page_needed = (line.address - part_needed) / PAGESIZE;

        /* Determine wether we did hit the right page or not */
        if (page_needed == current_page) {
            /* Check whether part is busy, which will result in waiting
             * till part access is granted
             */
            if (partbusy[part_needed] != FALSE) {
                /* Worst case senario on refresh */
                output.cycles += RAS;
                memset(partbusy, FALSE, sizeof(int) * PAGESIZE);
            }
        } else {
            /* Wait till all pending calls in current page are completed
             * 'Abuse' t to be identifier wether some bank was lowered
             */
            /* Worst case senario on refresh */
            output.cycles += RAS;
            memset(partbusy, FALSE, sizeof(int) * PAGESIZE);

            /* Switch to new page */
            current_page = page_needed;
            output.cycles += NAT;
            output.conflicts++;
        }

        /* Set new memory access */
        partbusy[part_needed] = RAS + TRANSFER;

        /* Process all parts to lower cycle count by one */
        for (i = 0; i < PAGESIZE; i++) {
            if (partbusy[i] != FALSE)
                partbusy[i]--;
        }
    }

    /* Make sure remaining data leaves memory safely */

    /* Worst case senario on refresh */
    output.cycles += RAS;

    /* Delete allocated memory */
    free(partbusy);

    printfresult(stdout, &output);
}