Cryptographic applications commonly require circular shifts. Whereas these shifts can be accomplished using a shift register, combinational shifting is required to complete these operations in a reasonable amount of time. Design an 8 bit barrel shifter that has 8 data inputs and 8 data outputs, and 3 control inputs that determine the shift amount (0-7). An additional enable input controls whether the outputs are tri-state or not. Use the truth table below as the functionality and use the entity declaration given.
en s2 s1 s0 c7 c6 c5 c4 c3 c2 c1 c0
| 0 0 0 0 | a7 a6 a5 a4 a3 a2 a1 a0 |
| 0 0 0 1 | a0 a7 a6 a5 a4 a3 a2 a1 |
| 0 0 1 0 | a1 a0 a7 a6 a5 a4 a3 a2 |
| 0 0 1 1 | a2 a1 a0 a7 a6 a5 a4 a3 |
| 0 1 0 0 | a3 a2 a1 a0 a7 a6 a5 a4 |
| 0 1 0 1 | a4 a3 a2 a1 a0 a7 a6 a5 |
| 0 1 1 0 | a5 a4 a3 a2 a1 a0 a7 a6 |
| 0 1 1 1 | a6 a5 a4 a3 a2 a1 a0 a7 |
| 1 0 0 0 | Z Z Z Z Z Z Z Z |
| 1 0 0 1 | Z Z Z Z Z Z Z Z |
| 1 0 1 0 | Z Z Z Z Z Z Z Z |
| 1 0 1 1 | Z Z Z Z Z Z Z Z |
| 1 1 0 0 | Z Z Z Z Z Z Z Z |
| 1 1 0 1 | Z Z Z Z Z Z Z Z |
| 1 1 1 0 | Z Z Z Z Z Z Z Z |
| 1 1 1 1 | Z Z Z Z Z Z Z Z |
Use the following entity
entity barrel is
port (a : in std_logic_vector (7 downto 0); s : in std_logic (2 downto 0; en : in std_logic;
c : out std_logic_vector (7 downto 0)); end entity barrel;
Develop a behavioral architecture for the system.
Perform the following steps
- Modify the test bench given in homework #1 to test this circuit.
- Compile all of the files
- Simulate to verify correctness.
Turn in all VHDL files.
