CFREG_BITBLT_SRC_HIGH
cfxga_write_2(sc, CFREG_BITBLT_SRC_HIGH, pos >> 16);
cfxga_write_2(sc, CFREG_BITBLT_SRC_HIGH, srcpos >> 16);
cfxga_write_2(sc, CFREG_BITBLT_SRC_HIGH, 0);