How to destuff can frame?

I did not check your vhdl code, but your assumption is wrong. The normal size of a can frame is not 108 bits. There is no normal frame size. The frame size depends on the data length and the can identifier (11 bit or 29 bit identifier) of the transmitted frame. The shortest message can be 47 bits (without any stuff bits, 11 bit identifier, 0 data bytes), the longest message is 129 bits (29 bit identifier, 8 data bytes) + stuffbits.

I think an easier way to detect a stuff bit should be something like that.

process(clk, reset_n)

begin

if(reset_n = '0') then

stuffbit <= '0';

elsif(clk'event and clk = '1') then

-- is next bit a stuff bit ?

if(message_in(4 downto 0) = "11111" or message_in(4 downto 0) = "00000") then

stuffbit <= '1';

else

stuffbit <= '0';

end if;

end if;

end process;