Index: hw/fdc.c
===================================================================
RCS file: /sources/qemu/qemu/hw/fdc.c,v
retrieving revision 1.33
diff -u -d -d -p -r1.33 fdc.c
--- hw/fdc.c	17 Nov 2007 17:14:41 -0000	1.33
+++ hw/fdc.c	17 Dec 2007 14:17:10 -0000
@@ -399,6 +399,8 @@ struct fdctrl_t {
     uint8_t lock;
     /* Power down config (also with status regB access mode */
     uint8_t pwrd;
+    /* Drive status change emulation */
+    uint8_t drstch;
     /* Sun4m quirks? */
     int sun4m;
     /* Floppy drives */
@@ -674,7 +676,7 @@ static void fdctrl_raise_irq (fdctrl_t *
         fdctrl->int_status = status;
         return;
     }
-    if (~(fdctrl->state & FD_CTRL_INTR)) {
+    if (!(fdctrl->state & FD_CTRL_INTR)) {
         qemu_set_irq(fdctrl->irq, 1);
         fdctrl->state |= FD_CTRL_INTR;
     }
@@ -698,6 +700,8 @@ static void fdctrl_reset (fdctrl_t *fdct
     fdctrl->data_dir = FD_DIR_WRITE;
     for (i = 0; i < MAX_FD; i++)
         fd_reset(&fdctrl->drives[i]);
+    /* Initialize the emulated drive status change register */
+    fdctrl->drstch = 0xF;
     fdctrl_reset_fifo(fdctrl);
     if (do_irq)
         fdctrl_raise_irq(fdctrl, 0xc0);
@@ -1410,17 +1414,36 @@ static void fdctrl_write_data (fdctrl_t 
             /* SENSE_INTERRUPT_STATUS */
             FLOPPY_DPRINTF("SENSE_INTERRUPT_STATUS command (%02x)\n",
                            fdctrl->int_status);
-            /* No parameters cmd: returns status if no interrupt */
+            /* No parameters cmd: returns interrupt status */
+            if (!(fdctrl->config & 0x10) && fdctrl->drstch != 0x00) {
+                /* If emulated polling mode is active... */
+                int i;
+                for (i = 0; i < 4; i++) {
+                    if (fdctrl->drstch & (1 << i)) {
+                        /* Emulate 8" drive 'i' status change */
+                        fdctrl->fifo[0] = 0xC0 | i;
+                        fdctrl->drstch &= ~(1 << i);
+                        break;
+                    }
+                }
+            } else if (fdctrl->state & FD_CTRL_INTR) {
 #if 0
-            fdctrl->fifo[0] =
-                fdctrl->int_status | (cur_drv->head << 2) | fdctrl->cur_drv;
+                fdctrl->fifo[0] =
+                    fdctrl->int_status | (cur_drv->head << 2) | fdctrl->cur_drv;
 #else
-            /* XXX: int_status handling is broken for read/write
-               commands, so we do this hack. It should be suppressed
-               ASAP */
-            fdctrl->fifo[0] =
-                0x20 | (cur_drv->head << 2) | fdctrl->cur_drv;
+                /* XXX: int_status handling is broken for read/write
+                   commands, so we do this hack. It should be suppressed
+                   ASAP */
+                fdctrl->fifo[0] =
+                    0x20 | (cur_drv->head << 2) | fdctrl->cur_drv;
 #endif
+            } else {
+                /* When no interrupt is pending, the command is invalid */
+                fdctrl->fifo[0] = 0x80;
+                fdctrl_set_fifo(fdctrl, 1, 0);
+                fdctrl->int_status = 0xC0;
+                return;
+            }
             fdctrl->fifo[1] = cur_drv->track;
             fdctrl_set_fifo(fdctrl, 2, 0);
             fdctrl_reset_irq(fdctrl);