Hi Yang,

>  	union {
> +		struct stk_duration duration;
>  		struct stk_command_display_text display_text;
>  		struct stk_command_get_inkey get_inkey;
>  		struct stk_command_get_input get_input;
>

For symmetry / consistency with other commands, can we please make a struct 
stk_command_poll_interval with only duration as a member?

Regards,
-Denis