ASIC/FPGA Design and Verification Out Source Services

VHDL SD CRC16 function.

1. For a test-bench in a SD slave project I needed to calculate CRC16 in VHDL. For that I wrote a function and will describe it in this page.


2. The CRC function receives data and number of bits to work on. The CRC is calculated using a simple for loop. For debug I only print a few results in the start and end of the calculation.


1.   function f_CRC16( data : std_logic_vector; nbits : in std_logic_vector
   
2.   ) return std_logic_vector is
   
3.   variable v_crc_reg : std_logic_vector(15 downto 0);
   
4.   variable v_crc_temp : std_logic_vector(15 downto 0);
   
5.   variable v_this_bit : integer;
   
6.   variable v_tmp : integer;
   
7.   variable my_line : line;
   
8.   variable result : std_logic_vector(15 downto 0);
   
9.   variable data_d : std_logic_vector(data'length-1 downto 0) := data;
   
10.   begin
    
11.     v_crc_reg := (others => '0');
    
12.     for v_this_bit in 1 to f_dbg_conv_i(nbits) loop
    
13.       v_crc_temp := v_crc_reg;
    
14.       v_crc_reg(15 downto 1) := v_crc_temp(14 downto 0);
    
15.       v_crc_reg(0) := (data(f_dbg_conv_i(nbits)-v_this_bit) xor v_crc_temp(15));
    
16.       v_crc_reg(5) := (v_crc_temp( 4) xor v_crc_reg(0));
    
17.       v_crc_reg(12) := (v_crc_temp(11) xor v_crc_reg(0));
    
19.       --dbg pini
    
20.       if(v_this_bit <= 2 or v_this_bit >= f_dbg_conv_i(nbits)-2) then
    
21.         write(my_line, string'("CRC16 dbg reg= "));
    
22.         hwrite(my_line, v_crc_reg);
    
23.         write(my_line, string'(" N= "));
    
24.         v_tmp := f_dbg_conv_i(nbits)-v_this_bit;
    
25.         write(my_line, v_tmp);
    
26.         write(my_line, string'(" di= "));
    
27.         write(my_line, data(v_tmp downto v_tmp));
    
28.         writeline(output, my_line);
    
29.       end if;
    
30.       --dbg pini
    
32.     end loop;
    
33. 
    
34.     result := v_crc_reg;
    
35.     return result;
    
36.   end f_CRC16;
    



3. For more details, please e mail me to bknpk@hotmail.com . Put SD flash in the e mail subject.