Floating Point Unit - shifter block

prepared by P. Bakowski (designer G. Ramstein)

back to main text

note : non synthetisable

The following model excecutes the shifter specification.

-- Data inputs :

-- ASX2F(39:0) x-operand input -- ASY2F(39:0) y-operand input -- ASZ2F(31:0) z-operand input

-- -- PS_AV1F ALU overflow flag from ASTAT --

-- Data outputs :

-- -- SR2F(39:0) result operand

-- -- SH_STAT2F(2:0) status output bus -- 0: shifter zero flag -- 1: shifter overflow flag -- 2: shifter sign flag

-- Control inputs :

-- -- RF_SHSD2F selects a shifter operation -- RF_ASOPD2F(7:0) ALU/shifter op code -- PS_T6D1F selects an immediate shifter operation

-- -- CK processor clock -- HLDB processor hold -- RST processor reset -- CEN bus driver enable

use work.DSP21020_pkg.all;

entity SFTR_Nty is port( ASX2F:in BV40_Typ; ASY2F:in BV40_Typ; ASZ2F:in BV32_Typ; RF_SHSD2F:in BIT; RF_ASOPD2F:in BV8_Typ; PS_T6D1F:in BIT; PS_AV1F:in BIT; CK:in BIT; HLDB:in BIT; RST:in BIT; CEN:in BIT; SR2F:out BV40_Typ; SH_STAT2F:out BV3_Typ);

end SFTR_Nty;

architecture SFTR_a of SFTR_Nty is

constant lshift : BV8_Typ := X"00";

constant orlshift : BV8_Typ := X"20";

constant ashift : BV8_Typ := X"04";

constant orashift : BV8_Typ := X"24";

constant rot : BV8_Typ := X"08";

constant bclr : BV8_Typ := X"c4";

constant bset : BV8_Typ := X"c0";

constant btgl : BV8_Typ := X"c8";

constant btst : BV8_Typ := X"cc";

constant fdep : BV8_Typ := X"44";

constant orfdep : BV8_Typ := X"64";

constant fdepse : BV8_Typ := X"4c";

constant orfdepse : BV8_Typ := X"6c";

constant fext : BV8_Typ := X"40";

constant fextse : BV8_Typ := X"48";

constant exp : BV8_Typ := X"80";

constant expex : BV8_Typ := X"84";

constant leftz : BV8_Typ := X"88";

constant lefto : BV8_Typ := X"8c";

begin

SFTR_process : process(Ck)

use WORK.bitvector_pkg.ALL;

use WORK.signvector_pkg.ALL;

use WORK.Float40_Pkg.all;

variable Op : BV8_Typ;

variable Ry, yshf, ylen: Fix_Typ;

variable exe, ovf, zero: BIT;

variable ldrv, lav, lim: BIT;

variable lstat: bit_vector(2 downto 0);

variable xmnt, zmnt, res: BV32_Typ;

variable i : integer;

begin

if Ck='1' then

-- op control

exe := RF_SHSD2F;

if (exe='1') then

lim :=PS_T6D1F; op := RF_ASOPD2F; xmnt:=Asx2f(39 downto 8); Ry:=Fix_Typ(Asy2f(39 downto 8)); zmnt:=Asy2f(31 downto 0);

end if;

if (RST='0') then

ldrv := RF_SHSD2F;

else ldrv :='0';

end if;

lav := PS_AV1F;

--...........................................................................

yshf:=X"00000000"; ylen:=X"00000000";

if ((op = fext) or (op = fextse) or (op = fdep) or (op = orfdep) or (op = fdepse) or (op = orfdepse)) then

yshf(5 downto 0) := Ry(5 downto 0); ylen(5 downto 0) := Ry(11 downto 6);

else

if (lim='0') then

yshf := Ry;

else yshf:= sign_extend(Ry(7 downto 0),32);

end if;

-- logic shifts

if ((op = lshift) or (op = orlshift)) then --...........................................................................

if ((yshf <= X"0000001F") and (yshf >= X"00000000")) then

res := shl(xmnt,to_integer(yshf));

end if;

if ((yshf >=X"FFFFFFE1") and (yshf <X"0000001F") or (yshf >X"00000000") then

ovf :='1'; else ovf :='0';

end if;

-- arithmetic shifts

if ((op = ashift) or (op = orashift)) then --...........................................................................

if ((yshf <= X"0000001F") and (yshf >= X"00000000")) then

res := shl(xmnt,to_integer(yshf));

end if;

if ((yshf >= X"FFFFFFE1") and (yshf < X"00000000")) then

if (xmnt(31)='1') then

res := shr(xmnt, -to_integer(yshf)); res := res or shl(X"ffffffff", 32 + to_integer(yshf));

else res := shr(xmnt, -to_integer(yshf));

end if;

if (yshf > X"0000001F") then

res := X"00000000";

end if;

if (yshf < X"FFFFFFE1") then

if (xmnt(31)='1') then

res := X"ffffffff";

else res := X"00000000";

end if;

end if; --...........................................................................

if (op = orashift) then

res := res or zmnt;

end if; --...........................................................................

i := 1;

while (xmnt(31 - i) = xmnt(31) and (i <= 31)) loop

i:=i+1;

end loop;

if ((to_integer(yshf) >= i) and (xmnt /= X"00000000")) then

ovf:='1';

else ovf:='0';

end if;

-- rotates

if (op = rot) then --...........................................................................

if (yshf >= X"00000000") then

res := shl(xmnt, to_integer(yshf and X"1F")); res := res or shr(xmnt, 32 - to_integer(yshf and X"1F"));

end if;

if (yshf < X"00000000") then

res := shr(xmnt, to_integer((X"00000000"-yshf) and X"1F")); res := res or shl(xmnt,(32 - to_integer((X"00000000"-yshf) and X"1F")));

end if; --...........................................................................

ovf := '0';

end if;

-- bit operations

if ((op = bclr) or (op = bset) or (op = btgl) or (op = btst)) then --...........................................................................

if ((yshf >=X"00000000") and (yshf <= X"0000001F")) then

res :=shl(X"00000001",to_integer(yshf));

if (op = bclr) then

res := xmnt and not res;

end if;

if (op = bset) then

res := xmnt or res;

end if;

if (op = btgl) then

if (xmnt(to_integer(yshf))='1') then

res := xmnt and not res;

else res := xmnt or res;

end if;

if (op = btst) then

res := xmnt and res;

end if;

if ((yshf < X"00000000") or (yshf > X"0000001F")) then

if (op /= btst) then

res := xmnt;

else res := X"00000000";

end if;

end if; --...........................................................................

if (yshf > X"0000001F") or (yshf < X"00000000") then

ovf:='1';

else ovf:='0';

end if;

-- field operations

if ((op = fext) or (op = fextse) or (op = fdep) or (op = fdepse) or (op = orfdep) or (op = orfdepse)) then --...........................................................................

if ((op = fdep) or (op = orfdep)) then

if (yshf <= X"0000001F") then

res := shl(xmnt, to_integer(yshf));

end if;

if (yshf > X"0000001F") then

res := X"00000000";

end if;

if ((yshf + ylen) <= X"0000001F") then

res := res and not shl(X"ffffffff", to_integer(yshf + ylen));

end if;

end if; --...........................................................................

if (op = fext) then

if (yshf <= X"0000001F") then

res := shr(xmnt, to_integer(yshf));

end if;

if (yshf > X"0000001F") then

res := X"00000000";

end if;

if (ylen <= X"0000001F") then

res := res and not shl(X"ffffffff", to_integer(ylen));

end if;

end if; --...........................................................................

if ((op = fdepse) or (op = orfdepse)) then

if (yshf <= X"0000001F") then

res := shl(xmnt, to_integer(yshf));

end if;

if (yshf > X"0000001F") then

res := X"00000000";

end if;

if ((yshf + ylen) <= X"0000001F") then

if (ylen /= X"00000000") then

if (xmnt(to_integer(ylen) - 1)='0') then

res := res and not shl(X"ffffffff", to_integer(yshf + ylen));

else res := res or shl(X"ffffffff", to_integer(yshf + ylen));

end if;

else res := X"00000000";

end if;

end if; --...........................................................................

if ((op = fextse)) then if (yshf <= X"0000001F") then

res := shr(xmnt,to_integer(yshf));

end if;

if (yshf > X"0000001F") then

res := X"00000000";

end if;

if ((to_integer(yshf + ylen) <= 32) and (ylen <= X"0000001F")) then

if (ylen /= X"00000000") then

if (xmnt(to_integer(yshf + ylen) - 1)='0') then

res := shr(xmnt,to_integer(yshf)) and not shl(X"ffffffff", to_integer(ylen));

else res := shr(xmnt,to_integer(yshf)) or shl(X"ffffffff", to_integer(ylen));

end if;

else res := X"00000000";

end if;

end if; --...........................................................................

if ((op = orfdep) or (op = orfdepse)) then

res := res or zmnt;

end if;

if ((yshf + ylen) > X"00000020") then

ovf:='1';

else ovf:='0';

end if;

-- exponent extracts

if ((op = exp) or (op = expex) or (op = leftz) or (op = lefto)) then --...........................................................................

if ((op = exp) or (op = expex)) then

i:= 1;

while (xmnt(31 - i) = xmnt(31) and (i <= 31)) loop

i:=i+1;

end loop;

if (not ((op = expex) and lav='1')) then

res := IToBV(-i + 1,32);

end if;

if ((op = expex) and lav='1') then

res := X"00000001";

end if;

ovf := '0';

end if; --...........................................................................

if (op = leftz) then

i:= 0;

while (xmnt(31 - i) ='0' and (i <= 31)) loop

i:=i+1;

end loop;

res := IToBV(i,32); ovf := res(5);

end if; --...........................................................................

if (op = lefto) then

i:= 0;

while (xmnt(31 - i) ='1' and (i <= 31)) loop

i:=i+1;

end loop;

res := IToBV(i,32); ovf := res(5);

end if;

-- output latches

if (res =X"00000000") then

lstat(0):='1';

else lstat(0):='0';

end if;

lstat(1) := ovf;

if ((op /= exp) and (op /= expex)) then

lstat(2):= '0';

end if;

if ((op =expex) and lav='1') then

lstat(2) := xmnt(31) xor lav;

end if;

if (((op =expex) and lav='0') or (op =exp)) then

lstat(2) := xmnt(31);

end if;

-- output drivers

if (CEN='1' and ldrv='1') then

SR2F(7 downto 0) <= X"00"; SR2F(39 downto 8) <= res;

else

SR2F(i) := RELEASE after RES_CEN_SPD;

end if;

SH_STAT2F <= lstat;

end if;

-- Ck=' '

end process;

end SFTR_a;

back to text