C64-dev/vim/mltest.c

/* mltest.c - prove calling machine code from Power C, one marked step at a time.
 * Whatever is left on screen when it hangs is the last step that worked. */

char txt[8];
char rts[4];

main()
{
    char *p;
    char a, x, y;

    p = (char *) 0x0400;
    p[0] = 1;                       /* A: main started */

    rts[0] = 96;                    /* RTS */
    a = 0;
    x = 0;
    y = 0;
    p[1] = 2;                       /* B: about to sys() a bare RTS */
    for (;;) { }
    sys(15, (unsigned) rts, &a, &x, &y);
    p[2] = 3;                       /* C: sys + array address work */

    txt[0] = 72;
    txt[1] = 69;
    txt[2] = 76;
    txt[3] = 76;
    txt[4] = 79;
    mlrow((unsigned) txt, 5, 1104, 2, 0);
    p[3] = 4;                       /* D: the real routine came back */
    for (;;) { }
}