Constraint Error warning using Enum in ADA -

i'd know why constraint errors warnings prompted in ada when enums used in example below. i've been using enums can replace them better implementation.

type uart_instance_type (com1, com2, com3);  uart_instance_type use   ( com1   =>    16#0001# ,     com2   =>    16#0002# ,     com3   =>    16#0003#    );    type uart_register_type record     sr         : half_word; -- usart status register     reserved_0 : half_word;     dr         : half_word; -- usart data register     reserved_1 : half_word;     brr        : half_word; -- usart baud rate register     reserved_2 : half_word;   end record   volatile;    uart_register_type use record     sr           @  0  range 0 .. 15;     reserved_0   @  2  range 0 .. 15;     dr           @  4  range 0 .. 15;     reserved_1   @  6  range 0 .. 15;     brr          @  8  range 0 .. 15;     reserved_2   @ 10  range 0 .. 15;   end record;  type uart_register_access access uart_register_type;  uarts: array (uart_instance_type range com1 .. com3) of aliased uart_register_access; 

the compiler prompt @ last line ("uarts: ...) , shows:

  warning: "constraint error" may call last_chance_handler 

is there better implementation avoid these warnings when using enums?

thanks in advance! :)

i think must compiling restricted (ravenscar?) runtime, why any exception result in call last_chance_handler.

i encountered lot of irritating warnings this, , traced compiling with
-gnatwa (“turn on info/warnings marked below +”) enables
-gnatw.x ("turn on warnings non-local exception”).

you can suppress warnings -gnatw.x.

(for info, can see command line options saying gnatmake -h (or arm-eabi-gnatmake -h). there lot.)