[SOLVED] Range in parameter specification of FOR GENERATE must be static

[MSAKARIM]

I'm working on SHA512 algorithm and i have some error in this part of code:

--padding message
mod_val<= (message'length) mod block_size;
padding_length <= ((block_size-129)+(block_size - mod_val));
padded_length <= ( message'length + (1 + padding_length) + length_bits);
message_length <= std_logic_vector(to_unsigned(message'length,length_bits)); 
padding <= "1" & std_logic_vector(to_unsigned(0,padding_length));  
padded_message <= message & padding & message_length; 
block_count<= (padded_message'length)/(block_size);


--assigning block to words
Block_loop: for block_number in 1 to block_count generate
block_block <= padded_message(((block_count - block_number) * block_size) - 1 downto (((block_count - (block_number + 1)) * block_size )))

Error : (vcom-1147) Range in parameter specification of FOR GENERATE must be static.

 

[ads-ee]

block_count isn't a constant at compile time, therefore you get an error.

For loops are NOT the same as software for loops they are unrolled at compile time generating all the iterations of the code.

The range value in a for generate loop (start to end) should both be constants. If all those signal assignments are ultimately based off of some constants make all the computations as constants and use the resulting final calculated constant for block_count instead.

 

[TrickyDicky]

Imagine a generate loop is there to tell the designer how many chips to place on a circuit board.
For one design it may have 6, for another it has 10 (as these may be set from generics)

But it would be impossible for that number to change while the board was switched on and running.