MSYNC_WB0
mbox = (xord & MSYNC_WB0) ? MSYNC_WB1 : MSYNC_WB0;
mbox_page = (mbox == MSYNC_WB0) ? QUEUE_OLD_WB0 : QUEUE_OLD_WB1;
#define MSYNC_WB_MASK (MSYNC_WB0 | MSYNC_WB1)