grts_map_channel
error = grts_map_channel(st, dev, GRTS_CH_X, "x", false);
error = grts_map_channel(st, dev, GRTS_CH_Y, "y", false);
error = grts_map_channel(st, dev, GRTS_CH_PRESSURE, "pressure", true);
error = grts_map_channel(st, dev, GRTS_CH_Z1, "z1", true);
error = grts_map_channel(st, dev, GRTS_CH_Z2, "z2", true);