/*
 * Extended memory overlay demo program.
 *
 * 2012-17-07, Oliver Schmidt (ol.sc@web.de)
 *
 */



#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <dirent.h>
#include <stdlib.h>
#include <em.h>
#include <conio.h>


/* The symbols _OVERLAY?_LOAD__ and _OVERLAY?_SIZE__ were generated by the
 * linker. They contain the overlay area address and size specific to a
 * certain program.
 */
extern void _OVERLAY1_LOAD__, _OVERLAY1_SIZE__;
extern void _OVERLAY2_LOAD__, _OVERLAY2_SIZE__;
extern void _OVERLAY3_LOAD__, _OVERLAY3_SIZE__;
extern void _OVERLAY4_LOAD__, _OVERLAY4_SIZE__;

struct {
    char     *name;
    int      page;
    void     *addr;
    unsigned size;
} overlay[] =
    {{"multdemo.1", -1, &_OVERLAY1_LOAD__, (unsigned)&_OVERLAY1_SIZE__},
     {"multdemo.2", -1, &_OVERLAY2_LOAD__, (unsigned)&_OVERLAY2_SIZE__},
     {"multdemo.3", -1, &_OVERLAY3_LOAD__, (unsigned)&_OVERLAY3_SIZE__},
     {"multdemo.4", -1, &_OVERLAY4_LOAD__, (unsigned)&_OVERLAY4_SIZE__}};

/* Copy overlays into extended memory up to overlay 3. Overlay 4 is known to
 * to be loaded only once for onetime initialization purposes so there's no
 * use in allocating extended memory for it.
 */
#define MAX_EM_OVERLAY 3



/* Functions resident in an overlay can call back functions resident in the
 * main program at any time without any precautions. The function log() is
 * an example for such a function resident in the main program.
 */
void log (char *msg)
{
    /* Functions resident in an overlay can access all program variables and
     * constants at any time without any precautions because those are never
     * placed in overlays. The string constant below is an example for such 
     * a constant resident in the main program.
     */
    printf ("Log: %s\n", msg);
}


/* In a real-world overlay program one would probably not use a #pragma but
 * rather place the all the code of certain source files into the overlay by
 * compiling them with --code-name OVERLAY1.
 */
#pragma code-name (push, "OVERLAY1");

void foo (void)
{
    log ("Calling main from overlay 1");
}

#pragma code-name (pop);


#pragma code-name (push, "OVERLAY2");

void bar (void)
{
    log ("Calling main from overlay 2");
}

#pragma code-name (pop);


#pragma code-name (push, "OVERLAY3");

void foobar (void)
{
    log ("Calling main from overlay 3");
}

#pragma code-name(pop);


#pragma code-name (push, "OVERLAY4");

unsigned char loademdriver (void)
{
    DIR *dir;
    struct dirent *ent;
    char *emd = NULL;
    unsigned char max = 0;
    unsigned char num;

    printf ("Dbg: Searching for emdrivers\n");
    dir = opendir (".");
    if (!dir) {
        log ("Opening directory failed");
        return 0;
    }

    while (ent = readdir (dir)) {
        char *ext;

        if (!_DE_ISREG (ent->d_type)) {
            continue;
        }

        ext = strrchr (ent->d_name, '.');
        if (!ext || strcasecmp (ext, ".emd")) {
            printf ("Dbg: Skipping file %s\n", ent->d_name);
            continue;
        }

        printf ("Dbg: Memorizing file %s\n", ent->d_name);
        emd = realloc (emd, FILENAME_MAX * (max + 1));
        strcpy (emd + FILENAME_MAX * max++, ent->d_name);
    }
    closedir (dir);

    for (num = 0; num < max; ++num) {
        char *drv;

        drv = emd + FILENAME_MAX * num;
        printf ("Dbg: Trying emdriver %s\n", drv);
        if (em_load_driver (drv) == EM_ERR_OK) {
            printf ("Dbg: Loaded emdriver %s\n", drv);
            free (emd);
            return 1;
        }

        printf ("Dbg: Emdriver %s failed\n", drv);
    }

    free (emd);
    return 0;
}

void copyoverlays (void)
{
    unsigned page = 0;
    unsigned char num;

    for (num = 0; num < MAX_EM_OVERLAY; ++num) {
        int file;
        int size;

        if ((overlay[num].size + EM_PAGE_SIZE - 1) / EM_PAGE_SIZE >
             em_pagecount () - page) {
            printf ("Dbg: Not enough memory for overlay %u\n", num + 1);
            continue;
        }

        printf ("Dbg: Reading overlay file %s\n", overlay[num].name);
        file = open (overlay[num].name, O_RDONLY);
        if (file == -1) {
            log ("Opening overlay file failed");
            continue;
        }

        overlay[num].page = page;
        size = overlay[num].size;
        while (size) {
            void *buf;

            /* In general one could as well use em_copyto() to copy a fully
             * loaded overlay into extended memory in one step. However the
             * "streaming" of an overlay from disk to extended memory shown
             * here has two advantages:
             * - It can be done from another overlay (like done here).
             * - It avoids unnecessary double buffering with emdrivers that
             *   provide a hardware memory window.
             */
            buf = em_use (page++);
            size -= read (file, buf, EM_PAGE_SIZE);
            em_commit ();
        }

        printf ("Dbg: Stored overlay %u in pages %u-%u\n",
                num + 1, overlay[num].page, page - 1);

        close (file);
    }
}

#pragma code-name(pop);


unsigned char loadoverlay (unsigned char num)
{
    if (overlay[num - 1].page < 0) {
        int file;

        printf ("Dbg: Loading overlay %u from file\n", num);
        file = open (overlay[num - 1].name, O_RDONLY);
        if (file == -1) {
            log ("Opening overlay file failed");
            return 0;
        }
        read (file, overlay[num - 1].addr,
                    overlay[num - 1].size);
        close (file);
        return 1;
    } else {
        struct em_copy copyinfo;

        printf ("Dbg: Loading overlay %u from memory\n", num);
        copyinfo.offs  = 0;
        copyinfo.page  = overlay[num - 1].page;
        copyinfo.buf   = overlay[num - 1].addr;
        copyinfo.count = overlay[num - 1].size;
        em_copyfrom (&copyinfo);
        return 1;
    }
}

void main (void)
{
    if (loadoverlay (4)) {
        log ("Loading extended memory driver");
        if (loademdriver ()) {
            log ("Copying overlays into ext. memory");
            copyoverlays ();
        } else {
            log ("No extended memory driver found");
        }
    }

    log ("Press any key...");
    cgetc ();

    if (loadoverlay (1)) {
        log ("Calling overlay 1 from main");

        /* The linker makes sure that the call to foo() ends up at the right mem
         * addr. However it's up to user to make sure that the - right - overlay
         * is actually loaded before making the the call.
         */
        foo ();
    }

    /* Replacing one overlay with another one can only happen from the main
     * program. This implies that an overlay can never load another overlay.
     */
    if (loadoverlay (2)) {
        log ("Calling overlay 2 from main");
        bar ();
    }

    if (loadoverlay (3)) {
        log ("Calling overlay 3 from main");
        foobar ();
    }

    log ("Press any key...");
    cgetc ();
}
