A Greatest Common Divisor(GCD) Processor

Euclid’s GCD algorithm

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

GCD(9,15)x = 9y = 15y = 15 – 9 = 6x = 9 – 6 = 3y = 6 – 3 = 3

GCD(9,15) = 3

ALU

Alusel(2:0) Function Output 0 0 0 Pass A A 0 0 1 Addition A + B 0 1 0 Subtraction-1 A – B 0 1 1 Subtraction-2 B – A 1 0 0 Invert NOT A 1 0 1 And A AND B 1 1 0 Or A OR B 1 1 1 Xor A XOR B

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

000

0

00

1

0

1111

1001

ALU: Pass AR0 1001

clrclk

stld N Z V C

40

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

1111 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

000

0

01

0

1

1111

1001

ALU: Pass AR1 1111

clrclk

stld N Z V C

40

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

1111 clrclkr1ld

1001 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

000

1

11

0

0

xxxx

xxxx

ALU: Pass AW R0

clrclk

stld N Z V C

40

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

1111 clrclkr1ld

0110 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

010

1

10

0

0

xxxx

xxxx

ALU: A - BW R1 - W

clrclk

stld N Z V C

41

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

1111 clrclkr1ld

0110 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

010

1

10

0

0

xxxx

xxxx

ALU: A - BW R1 - W

clrclk

stld N Z V C

41

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

1111 clrclkr1ld

1001 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

000

1

11

0

0

xxxx

xxxx

ALU: Pass AW R0

clrclk

stld N Z V C

40

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

0110 clrclkr1ld

1001 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

010

0

10

0

1

xxxx

xxxx

ALU: A - BR1 R1 - W

clrclk

stld N Z V C

41

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

1001 clrclkr0ld

0110 clrclkr1ld

1001 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

000

1

11

0

0

xxxx

xxxx

ALU: Pass AW R0

clrclk

stld N Z V C

40

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

0011clr

clkr0ld

0110clr

clkr1ld

1001clr

clkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

011

0

10

1

0

xxxx

xxxx

ALU: B - AR0 W - R1

clr

clkstld N Z V C

41

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

0011 clrclkr0ld

0110 clrclkr1ld

0011 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

000

1

11

0

0

xxxx

xxxx

ALU: Pass AW R0

clrclk

stld N Z V C

40

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

0011 clrclkr0ld

0011 clrclkr1ld

0011 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

010

1

10

0

1

xxxx

xxxx

ALU: A - BR1 R1 - W

clrclk

stld N Z V C

41

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

msel(1:0)

0011 clrclkr0ld

0011 clrclkr1ld

0011 clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

000

1

11

0

0

xxxx

xxxx

ALU: Pass AW R0

clrclk

stld N Z V C

40

GCD

GCDDatapath

GCDControl Unit

ZC

clr clk clr clk

r0ldr1ldwldstldmsel(1:0)alusel(2:0)

PE

PA

PB

gcdpath.vhd-- Title: GCD Datapathlibrary IEEE;use IEEE.STD_LOGIC_1164.all;use IEEE.std_logic_unsigned.all;use work.gcd_components.all;

entity GCDpath is generic(width:positive); port(

PA: in STD_LOGIC_VECTOR (width-1 downto 0); PB: in STD_LOGIC_VECTOR (width-1 downto 0); alusel: in STD_LOGIC_VECTOR (2 downto 0);

msel: in STD_LOGIC_VECTOR (1 downto 0);r0ld, r1ld, stld, wld: in STD_LOGIC;clr, clk: in STD_LOGIC;C, Z: out STD_LOGIC;

PE: out STD_LOGIC_VECTOR (width-1 downto 0)

);end GCDpath;

architecture GCDpath_arch of GCDpath is

signal y, a, PEs, PCs, PDs: std_logic_vector(width-1 downto 0);signal s, status: std_logic_vector(3 downto 0);constant bus_width: integer := 4;constant status_width: integer := 4;

begin

gcdpath.vhd (cont.)

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

y

as

alu1: alu generic map(width => bus_width) port map (a => a, b => PEs, alusel => alusel, status => s, y => y); R0: reg generic map(width => bus_width) port map (d => y, load =>r0ld, clr => clr, clk =>clk, q => PDs); R1: reg generic map(width => bus_width) port map (d => y, load => r1ld, clr => clr, clk =>clk, q => PCs);

stat: reg generic map(width => status_width) port map (d => s, load =>stld, clr => clr, clk =>clk, q => status);

gcdpath.vhd (cont.)

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

a

y

s

W: reg generic map(width => bus_width) port map (d => y, load => wld, clr => clr, clk =>clk, q => PEs);

M1: mux4g generic map(width => bus_width) port map (a => PA, b => PB, c => PCs, d => PDs, sel => msel, y => a); C <= status(0); Z <= status(2); PE <= PEs; end GCDpath_arch;

gcdpath.vhd (cont.)

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

a

y

s

GCD

GCDDatapath

GCDControl Unit

ZC

clr clk clr clk

r0ldr1ldwldstldmsel(1:0)alusel(2:0)

PE

PA

PB

s0

s1

s2

s3

s4

s5 s6

s7

R0 x

R1 y

W R0

W R1 - W

C = 1W R0

R1 R1 - W

Z = 1

C = 0W R0

W R0

R0 W - R1

W R0

Done

1: int x, y;2: x = x_input;3: y = y_input;4: while (x != y) 5: {6: if (x<y)7: y = y-x;8: else9: x = x-y;10: }11: output = x;

VHDLMealy Machine

Stat

e R

egis

ter

C1

x(t)

s(t+1)

s(t)z(t)

clk

init

present statepresent

input

nextstate

C2

process(clk, init)

process(present_state, x)

process(present_state, x)

gcd_control.vhd

-- Title: GCD Control Unitlibrary IEEE;use IEEE.std_logic_1164.all;use IEEE.std_logic_unsigned.all;

entity gcd_control is port ( clr: in STD_LOGIC; clk: in STD_LOGIC; Z: in STD_LOGIC; C: in STD_LOGIC; alusel: out STD_LOGIC_VECTOR (2 downto 0); msel: out STD_LOGIC_VECTOR (1 downto 0); r0ld, r1ld, stld, wld: out STD_LOGIC );end gcd_control;

architecture gcd_control_arch of gcd_control is

type state_type is (s0, s1, s2, s3, s4, s5, s6, s7);

signal current_state, next_state: state_type;

begin statereg: process(clk, clr) -- the state register begin if clr = '1' then current_state <= s0; elsif (clk'event and clk = '1') then current_state <= next_state;

end if; end process statereg;

gcd_control.vhd (cont.)

gcd_control.vhd (cont.)

s0

s1

s2

s3

s4

s5 s6

s7

R0 x

R1 y

W R0

W R1 - W

C = 1W R0

R1 R1 - W

Z = 1

C = 0W R0

W R0

R0 W - R1

W R0

Done

C1: process(current_state, Z, C) begin case current_state is when s0 =>

next_state <= s1; when s1 =>

next_state <= s2; when s2 =>

next_state <= s3; when s3 =>

next_state <= s4; when s4 =>

if Z = '1' then next_state <= s7; elsif C = '1' then

next_state <= s5;else next_state <= s6;

end if;

gcd_control.vhd (cont.)s0

s1

s2

s3

s4

s5 s6

s7

R0 x

R1 y

W R0

W R1 - W

C = 1W R0

R1 R1 - W

Z = 1

C = 0W R0

W R0

R0 W - R1

W R0

Done

when s5 => next_state <= s2;

when s6 => next_state <= s2;

when s7 => next_state <= s7;

end case;end process C1;

gcd_control.vhd (cont.)C2: process(current_state) begin -- Initialize all outputs alusel <= "000"; msel <= "00"; r0ld <= '0'; r1ld <= '0'; stld <= '0'; wld <= '0';

case current_state is when s0 => -- R0 <- x r0ld <= '1' ; r1ld <= '0';

stld <= '1'; wld <= '0'; msel <= "00";

alusel <= "000";

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

a

y

s

gcd_control.vhd (cont.)

when s1 => -- R1 <- Y r0ld <= '0' ; r1ld <= '1';

stld <= '1'; wld <= '0'; msel <= "01";

alusel <= "000";

when s2 => -- W <- R0 r0ld <= '0' ; r1ld <= '0';

stld <= '1'; wld <= '1'; msel <= "11";

alusel <= "000";

when s3 => -- W <- R1 - W r0ld <= '0' ; r1ld <= '0';

stld <= '1'; wld <= '1'; msel <= "10";

alusel <= "010";

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

a

y

s

gcd_control.vhd (cont.)

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

a

y

s

when s4 => -- W <- R0 r0ld <= '0' ; r1ld <= '0';

stld <= '1'; wld <= '1'; msel <= "11";

alusel <= "000";

when s5 => -- R0 <- W - R1 r0ld <= '1' ; r1ld <= '0';

stld <= '1'; wld <= '0'; msel <= "10";

alusel <= "011";

when s6 => -- R1 <- R1 - W r0ld <= '0' ; r1ld <= '1';

stld <= '1'; wld <= '0'; msel <= "10";

alusel <= "010";

gcd_control.vhd (cont.)

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

a

y

s

when s7 => -- W <- R0 r0ld <= '0' ; r1ld <= '0';

stld <= '1'; wld <= '1'; msel <= "11";

alusel <= "000";

when others => null;

end case; end process C2; end gcd_control_arch;

GCD

GCDDatapath

GCDControl Unit

ZC

clr clk clr clk

r0ldr1ldwldstldmsel(1:0)alusel(2:0)

PE

PA

PB

GCDDatapath

GCDControl Unit

ZC

clr clk clr clk

r0ldr1ldwldstld

msel(1:0)alusel(2:0)

PE

PA

PB

-- Title: Greatest Common Divisorlibrary IEEE;use IEEE.STD_LOGIC_1164.all;use IEEE.std_logic_unsigned.all;use work.GCD_components.all;

entity GCD isgeneric(width:positive);port( PA: in STD_LOGIC_VECTOR ((width-1) downto 0); PB: in STD_LOGIC_VECTOR ((width-1) downto 0); clr, clk: in STD_LOGIC;

PE: out STD_LOGIC_VECTOR ((width-1) downto 0)

);end GCD;

GCD.vhd

GCD.vhd (cont.)architecture GCD_arch of GCD is

signal alusel: std_logic_vector(2 downto 0);signal msel: std_logic_vector(1 downto 0);signal C, Z: std_logic;signal r0ld, r1ld, stld, wld: std_logic;

GCDDatapath

GCDControl Unit

ZC

clr clk clr clk

r0ldr1ldwldstld

msel(1:0)alusel(2:0)

PE

PA

PB

GCD.vhd (cont.)

GCDDatapath

GCDControl Unit

ZC

clr clk clr clk

r0ldr1ldwldstld

msel(1:0)alusel(2:0)

PE

PA

PB

begin

U1: gcdpath generic map(width => width) port map (PA => PA, PB => PB, alusel => alusel, msel => msel, r0ld => r0ld, r1ld => r1ld, stld => stld, wld => wld,

clr => clr, clk =>clk, PE => PE, C => C, Z => Z); U2: gcd_control port map (alusel => alusel, msel => msel, C => C, Z => Z, r0ld => r0ld, r1ld => r1ld, stld => stld, wld => wld,

clr => clr, clk => clk);

end GCD_arch;

-- Title: GCD Testlibrary IEEE;use IEEE.STD_LOGIC_1164.all;use IEEE.std_logic_unsigned.all;use work.GCD_components.all;

entity GCDtest is port(

mclk : in STD_LOGIC; SW : in STD_LOGIC_VECTOR(7 downto 0);

BTN: in STD_LOGIC_VECTOR(3 downto 0); LD : out STD_LOGIC_VECTOR(7 downto 0); AtoG : out STD_LOGIC_VECTOR(6 downto 0); AN : out STD_LOGIC_VECTOR(3 downto 0)

);end GCDtest;

GCDtest.vhd

GCDtest.vhd (cont.)

architecture GCDtest_arch of GCDtest is

signal r, p: std_logic_vector(15 downto 0);signal clr, clk, cclk, bnbuf: std_logic;signal clkdiv: std_logic_vector(26 downto 0);

constant bus_width: positive := 4;

begin clr <= BTN(3);

GCDtest.vhd (cont.)

-- Divide the master clock (50Mhz) process (mclk)

begin if mclk = '1' and mclk'Event then

clkdiv <= clkdiv + 1; end if;

end process;

clk <= clkdiv(0); -- 25 MHz

cclk <= clkdiv(17); -- 190 Hz

r(15 downto 4) <= "000000000000";

GCDtest.vhd (cont.)

U1: GCD generic map(width => bus_width) port map (PA => SW(7 downto 4), PB =>SW(3 downto 0),

clr => clr, clk =>clk, PE => r(3 downto 0)); U2: binbcd port map (B => r, P => p); U3: x7segb port map (x => p, cclk => cclk, clr => clr, AtoG => AtoG,

AN => AN);

LD <= SW;

end GCDtest_arch;

s0

s1

s2

s3

s4

s5 s6

s7

R0 x

R1 y

W R0

W R1 - W

C = 1W R0

R1 R1 - W

Z = 1

C = 0W R0

W R0

R0 W - R1

W R0

Done

msel(1:0)

R0 clrclkr0ld

R1 clrclkr1ld

W clrclkwld

ALU alusel(2:0)B A

Y

PAPB

M10123

PDPC

PE

Input

Input

clrclk

stld N Z V C

4

a

y

s