ECE 448: Spring 11Lab 3

Sequential Logic for Synthesis

FPGA Design Flow Based on Aldec Active-HDL

Part 1: Introduction to the new Lab Assignment: Square Root Unit based on CORDIC

Part 2: FPGA Design Flow based on Aldec Active-HDL - using Xilinx XST - using Synplify Premier DP

Part 3: Demos of Lab 2

Agenda for today

Part 1

Introduction to the new Lab AssignmentSquare Root Unit based on CORDIC

CORDIC Algorithms - Motivation• Operations such as trigonometric functions, division,

and logarithms are not synthesizable.• Some alternative methods

• Lookup tables• Can require large amounts of memory.

• Taylor/Maclaurin series• Requires multipliers

• CORDIC algorithms• Small area = Inexpensive in hardware• High latency

CORDIC Algorithm for Square Root

y = 0for i=N/2-1 downto 0 do temp = (y + 2i)2

if temp ≤ x theny = y + 2i

end ifend forsqrt_x = y

• Calculates • Pseudocode

• (y + 2i)2 = y2 + (2i+1)y + 22i

y = 0y_sq = 0for i=N/2-1 downto 0 dotemp = y_sq + (2i+1)y + 22i

if temp ≤ x theny = y + 2i

y_sq = tempend if

end forsqrt_x = y

Modified Pseudocode

• All computations performed using only addition, bit shifts, and comparisons.

ExampleN = 8, x = 26

• i = 3, temp = 0 + 2(0)(8) + 82 = 64, y = 0, y_sq = 0

• i = 2, temp = 0 + 2(0)(4) + 42 = 16, y = 4, y_sq = 16

• i = 1, temp = 16 + 2(4)(2)+ 22 = 36, y = 4, y_sq = 16

• i = 0, temp = 16 + 2(4)(1) + 12 = 25, y = 5, y_sq = 25

• Done! sqrt_x = 5

in_validShift Reg.ld_en

load

Qs_in Q(0)‘0’

+1

Q

A << BA

B

A << BA

B +A ≥ B

A

B

QDrst

en

xD Q out_valid

sqrt_x

QDrst

enN

N

N

N

N

L-1

L

N/2

N/2

N/2

“1000…..000”

L = ceil(log2(N))

+

N/2

Down counterld_en

QN/2 -1 loadL-1

Block Diagram

temp

y_sq

y

(2i+1)y i+1

i(2i )(2i)=22i

2i

Bonus

• Make output with M variable.

• Allows greater output precision

• Output is of form:

y = 0y_sq = 0x_shifted = x << (2M – N)for i=M-1 downto 0 do

temp = y_sq + (2i+1)y + 22i

if temp ≤ x_shifted theny = y + 2i

y_sq = tempend if

end forsqrt_x = y

Bonus Pseudocode

ExampleN = 8, M = 6, x = 42

• x_shifted = 42 << (2(6) – 8) = 42 << 4 = 672.

• i = 5, temp = 0 + 2(0)(32) + 322 = 1024, y = 0, y_sq = 0• i = 4, temp = 0 + 2(0)(16) + 162 = 256, y = 16, y_sq = 256• i = 3, temp = 256 + 2(16)(8) + 82 = 576, y = 24, y_sq = 576• i = 2, temp = 576 + 2(24)(4) + 42 = 784, y = 24, y_sq = 576• i = 1, temp = 576 + 2(24)(2) + 22 = 676, y = 24, y_sq = 576• i = 0, temp = 576 + 2(24)(1) + 12 = 625, y = 25, y_sq = 625

• Done! x_sqrt = 25. • 25/22 = 6.25• Check : sqrt(42) = 6.481

in_validShift Reg.ld_en

load

Qs_in Q(0)‘0’

+1

Q

A << BA

B

A << BA

B +A ≥ B

A

B

QDrst

en

x

D Q out_valid

sqrt_x

QDrst

en

2M

2M

2M

2M

L-1

L

M

M

M

“1000…..000”

L = ceil(log2(2M))

+

M

Down counterld_en

QM -1 loadL-1

<< (2M-N)

N

2M

Bonus Diagram

temp

y_sq

y(2i+1)y

i+1

i (2i )(2i)=22i

2i

Part 2

FPGA Design Flow based on Aldec Active-HDL

FPGA Design process (1)Design and implement a simple unit permitting to speed up encryption with RC5-similar cipher with fixed key set on 8031 microcontroller. Unlike in the experiment 5, this time your unit has to be able to perform an encryption algorithm by itself, executing 32 rounds…..

Library IEEE;use ieee.std_logic_1164.all;use ieee.std_logic_unsigned.all;

entity RC5_core is port( clock, reset, encr_decr: in std_logic; data_input: in std_logic_vector(31 downto 0); data_output: out std_logic_vector(31 downto 0); out_full: in std_logic; key_input: in std_logic_vector(31 downto 0); key_read: out std_logic; );end AES_core;

Specification (Lab Assignments)

VHDL description (Your Source Files)

Functional simulation

Post-synthesis simulationSynthesis

On-paper hardware design (Block diagram & ASM chart)

FPGA Design process (2)

Implementation

Configuration

Timing simulation

On chip testing

Design Process control from Active-HDL

17

Synthesis Tools

Synplify Premier DPXilinx XST

18

architecture MLU_DATAFLOW of MLU is

signal A1:STD_LOGIC;signal B1:STD_LOGIC;signal Y1:STD_LOGIC;signal MUX_0, MUX_1, MUX_2, MUX_3: STD_LOGIC;

beginA1<=A when (NEG_A='0') else

not A;B1<=B when (NEG_B='0') else

not B;Y<=Y1 when (NEG_Y='0') else

not Y1;

MUX_0<=A1 and B1;MUX_1<=A1 or B1;MUX_2<=A1 xor B1;MUX_3<=A1 xnor B1;

with (L1 & L0) selectY1<=MUX_0 when "00",

MUX_1 when "01",MUX_2 when "10",MUX_3 when others;

end MLU_DATAFLOW;

VHDL description Circuit netlist

Logic Synthesis

19

Implementation

• After synthesis the entire implementation process is performed by FPGA vendor tools

Xilinx ISE/WebPACK