xp —
HD647180X I/O processor
xpbus0 at mainbus0
xp0 at xpbus0
The file /dev/xp is an
  mmap(2) capable interface to
  the memory area of the HD647180X I/O processor (so-called "XP") on
  LUNA-I and LUNA-II. Byte offsets in this file are interpreted as relative
  memory addresses of the I/O processor. The range should be between 0x0 and
  0xffff.
The following
    ioctl(2) call applies to
    /dev/xp:
  - XPIOCDOWNLDstruct xp_download
- Load binary and reset I/O processor.
    
    
struct xp_download {
        u_int    size;
	u_int8_t *data;
};
    
 The size member specifies the loading
        binary size, in bytes. The data member points to
        the binary image. 
  - [EACCES]
- The device is opened without write permission.
- [EINVAL]
- The specified size is 0 or more than the I/O processor's memory size.
The /dev/xp file first appeared in
  NetBSD 7.1.