Re: String operation

Altera_Forum · ‎07-11-2017

I have a string


signal rx_uart_buf : string (0 to 127);

Now I want to test every char value


when ST_PARSE_COM =>
if (idx < RX_BUF_SIZE) then
    case character'pos(rx_uart_buf(idx)) is
        when 0  => ParseState <= ST_PARSE_IDLE;
        when 32 => ParseState <= ST_PARSE_ARG1;
    end case;
    idx := idx + 1;
 end if;

Is it right way to do it?

Altera_Forum · ‎07-11-2017

In what context? Strings are not suitable for synthesis, so I assume this is simulation only code?

Also, strings can only have a positive range, so cannot start at 0 - it must start at 1 or above?

Why bother coverting the char to an integer? why not just use the chars directly?


if (idx < RX_BUF_SIZE) then
    case rx_uart_buf(idx) is
        when NUL  => ParseState <= ST_PARSE_IDLE;
        when ' ' => ParseState <= ST_PARSE_ARG1;
    end case;
    idx := idx + 1;
 end if;

Altera_Forum · ‎07-11-2017

--- Quote Start ---

In what context? Strings are not suitable for synthesis, so I assume this is simulation only code?

Also, strings can only have a positive range, so cannot start at 0 - it must start at 1 or above?

Why bother coverting the char to an integer? why not just use the chars directly?


if (idx < RX_BUF_SIZE) then
    case rx_uart_buf(idx) is
        when NUL  => ParseState <= ST_PARSE_IDLE;
        when ' ' => ParseState <= ST_PARSE_ARG1;
    end case;
    idx := idx + 1;
 end if;

--- Quote End ---

I see. Thank you. So it doesn't work in real life? I was planning to accumulate chars from terminal to rx_uart_buf and then parse the string.

Altera_Forum · ‎07-11-2017

A string is just an abstract concept. At hardware level they are just a set of integers.

You could try using a string, and qartus may compile it (Ive done it as a proof of concept to myself) but I wouldnt trust it.

Altera_Forum · ‎07-11-2017

I see. Thank you. Quartus compiles it. But to be on safety side I've decided to define a string as array of bytes

type byte_array is array (0 to RX_BUF_SIZE) of std_logic_vector(7 downto 0);

signal rx_uart_buf : byte_array;

Altera_Forum · ‎07-11-2017

I think you mean:

type byte_array is array (0 to RX_BUF_SIZE-1) of std_logic_vector(7 downto 0);