NCT_MAX_GROUP
uint8_t ior[NCT_MAX_GROUP + 1]; /* direction, 1: input 0: output */
uint8_t out[NCT_MAX_GROUP + 1]; /* output value */
uint8_t out_known[NCT_MAX_GROUP + 1]; /* whether out is valid */
uint8_t inv[NCT_MAX_GROUP + 1]; /* inversion, 1: inverted */
struct nct_gpio_group *grpmap[NCT_MAX_GROUP+1];
struct nct_gpio_group groups[NCT_MAX_GROUP + 1];