Compare two byte arrays

Question

I have a list of commands and a command received from UART. 
type commands is array(0 to COM_SIZE) of std_logic_vector(7 downto 0);
signal commands_list : commands(0 to COM_COUNT) := 
(
    x"73746F700000", --stop
    x"667764000000", --fwd
    x"726576000000"  --rev
    
);
type com_str is array (0 to COM_SIZE) of std_logic_vector(7 downto 0);
signal command : com_str;
  I try to compare the hole array  
for i in 0 to COM_COUNT loop
    if (commands_list(i) /=  command) then
        --do something
    end if;
end loop;
  And every byte 
for i in 0 to COM_COUNT loop
    for j in 0 to name_len loop    
        if (commands_list(i)(j) /=  command(j)) then
            --do something
        end if;
    end loop;      
end loop;
  In both cases I get an error Error (10327): VHDL error at parser.vhd(253): can't determine definition of operator ""/="" -- found 0 possible definitions

altera_forum · Answer

In the first case, you're comparing a std_logic_vector to an array of std_logic_vector. Doesn't work.

In the 2nd case, you're comparing a std_logic to a std_logic_vector. Doesn't work either.

I assume the problem is that the type of com_str is wrong. I guess it should really be this:

signal command: std_logic_vector(7 downto 0);

That would, from the context, make more sense to me.

altera_forum · Answer

--- Quote Start ---

In the first case, you're comparing a std_logic_vector to an array of std_logic_vector. Doesn't work.

In the 2nd case, you're comparing a std_logic to a std_logic_vector. Doesn't work either.

I assume the problem is that the type of com_str is wrong. I guess it should really be this:

signal command: std_logic_vector(7 downto 0);

That would, from the context, make more sense to me.

--- Quote End ---

'command' is not a char - it's array of chars. this way - command: std_logic_vector(7 downto 0); - it holds only one char, and I need to get array of chars from terminal.

altera_forum · Answer

Ah, now I understand. So, a "char" in your case is supposed to be a std_logic_vector with 8 bits, right?

But then, "commands" should be an array of array of std_logic_vector(7 downto 0). You're missing one level of arrays. You try to initialize a std_logic_vector(7 downto 0) with "x"73746F700000", where "73746F700000" is 48 bits. I wonder why the compiler doesn't complain, but you have to fix that first.

altera_forum · Answer

--- Quote Start ---  Ah, now I understand. So, a "char" in your case is supposed to be a std_logic_vector with 8 bits, right?  But then, "commands" should be an array of array of std_logic_vector(7 downto 0). You're missing one level of arrays. You try to initialize a std_logic_vector(7 downto 0) with "x"73746F700000", where "73746F700000" is 48 bits. I wonder why the compiler doesn't complain, but you have to fix that first.  --- Quote End ---    Yes. You are right. I need array of array - each member of array is array of chars - a command in the list. But how I should initialize it?  type commands is array(0 to 6) of std_logic_vector(7 downto 0);  signal commands_list : commands(0 to 2) :=  (     x"73746F700000", --stop     x"667764000000", --fwd     x"726576000000"  --rev );  if array(0 to 6) then  x"73746F700000" is 7 elements 73 74 6F 70 00 00 00.  I was trying this way 
signal commands_list : commands_l(2 downto 0) := (
    0 =&gt; (0 =&gt; x"00", 1 =&gt; x"01", 2 =&gt; x"10", 3 =&gt; x"11", 4 =&gt; x"20", 5 =&gt; x"21"), --stop
    1 =&gt; (0 =&gt; x"00", 1 =&gt; x"01", 2 =&gt; x"10", 3 =&gt; x"11", 4 =&gt; x"20", 5 =&gt; x"21"), --fwd
    2 =&gt; (0 =&gt; x"00", 1 =&gt; x"01", 2 =&gt; x"10", 3 =&gt; x"11", 4 =&gt; x"20", 5 =&gt; x"21")  --rev
    );
 But I get an error Error (10515): VHDL type mismatch error at parser.vhd(71): std_ulogic type does not match string literal

altera_forum · Answer

I agree that your approach looks correct now.  However, without seeing the complete code, I cannot tell what's wrong. I have no clue what line 71 is, and I have no clue how the signals and types that are references in that line are declared. Keep that in mind before posting anything else.  Anyway, here's some code that passes synthesis, and should give you the right pointers: type command_type is array(0 to 5) of std_logic_vector(7 downto 0);
type commands_type is array(0 to 2) of command_type;
signal commands: commands_type := (
	0 =&gt; (0 =&gt; x"00", 1 =&gt; x"01", 2 =&gt; x"10", 3 =&gt; x"11", 4 =&gt; x"20", 5 =&gt; x"21"), --stop
	1 =&gt; (0 =&gt; x"00", 1 =&gt; x"01", 2 =&gt; x"10", 3 =&gt; x"11", 4 =&gt; x"20", 5 =&gt; x"21"), --fwd
	2 =&gt; (0 =&gt; x"00", 1 =&gt; x"01", 2 =&gt; x"10", 3 =&gt; x"11", 4 =&gt; x"20", 5 =&gt; x"21")  --rev
);

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Compare two byte arrays

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