GR2_REVISION_RD1
dc->zbuffer = !(bus_space_read_4(dc->iot, dc->ioh, GR2_REVISION_RD1) & GR2_REVISION_RD1_ZBUFFER);
(bus_space_read_4(dc->iot, dc->ioh, GR2_REVISION_RD1) & 0x01);
dc->backendrev = ~(bus_space_read_4(dc->iot, dc->ioh, GR2_REVISION_RD1)) & 0x03;
dc->zbuffer = bus_space_read_4(dc->iot, dc->ioh, GR2_REVISION_RD1) & GR2_REVISION4_RD1_ZBUFFER;
dc->depth = ((bus_space_read_4(dc->iot, dc->ioh, GR2_REVISION_RD1) & GR2_REVISION4_RD1_24BPP) >> 4) ? 24 : 8;