GPXADDR
ioaccess(tmp, vax_trunc_page(GPXADDR + GPX_ADDER_OFFSET), 1);
ioaccess(tmp, vax_trunc_page(GPXADDR + GPX_READBACK_OFFSET), 1);
vax_trunc_page(GPXADDR + GPX_READBACK_OFFSET), 1);
ioaccess(virtual_avail, GPXADDR + GPX_ADDER_OFFSET, 1);
ioaccess(virtual_avail, vax_trunc_page(GPXADDR + GPX_VDAC_OFFSET), 1);
ioaccess(virtual_avail, GPXADDR + GPX_CURSOR_OFFSET, 1);
if (va->va_paddr != GPXADDR)