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xilinx-mult: Move some registers later in the data flow

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This changes s0 to use the P register rather than the A/B/C input
registers, thus improving the timing of the multiplier output.  The
m00, m02 and m03 multipliers now use their P registers rather than the
M registers, moving the addition they do from the second cycle to the
first.

Also, the XOR that inverts the 32 LSBs is moved before the output
register.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras
2021-09-07 09:32:30 +10:00
parent 09bd01a49e
commit 0cdaa2778f
1 changed files with 34 additions and 28 deletions
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62
xilinx-mult.vhdl
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@@ -24,7 +24,6 @@ architecture behaviour of multiply is
signal m11_pc, m12_pc, m13_pc : std_ulogic_vector(47 downto 0);
signal m20_p, m21_p, m22_p, m23_p : std_ulogic_vector(47 downto 0);
signal s0_pc, s1_pc : std_ulogic_vector(47 downto 0);
signal product_lo : std_ulogic_vector(31 downto 0);
signal product : std_ulogic_vector(127 downto 0);
signal addend : std_ulogic_vector(127 downto 0);
signal s0_carry, p0_carry : std_ulogic_vector(3 downto 0);
@@ -33,7 +32,7 @@ architecture behaviour of multiply is
signal p1_pat, p1_patb : std_ulogic;
signal req_32bit, r32_1 : std_ulogic;
signal req_not, rnot_1 : std_ulogic;
signal rnot_1 : std_ulogic;
signal valid_1 : std_ulogic;
signal overflow, ovf_in : std_ulogic;
@@ -49,9 +48,11 @@ begin
BREG => 0,
CARRYINREG => 0,
CARRYINSELREG => 0,
CREG => 0,
INMODEREG => 0,
MREG => 0,
OPMODEREG => 0,
PREG => 0
PREG => 1
)
port map (
A => "0000000" & m_in.data1(22 downto 0),
@@ -69,13 +70,13 @@ begin
CEALUMODE => '0',
CEB1 => '0',
CEB2 => '0',
CEC => '1',
CEC => '0',
CECARRYIN => '0',
CECTRL => '0',
CED => '0',
CEINMODE => '0',
CEM => m_in.valid,
CEP => '0',
CEM => '0',
CEP => m_in.valid,
CLK => clk,
D => (others => '0'),
INMODE => "00000",
@@ -160,9 +161,11 @@ begin
BREG => 0,
CARRYINREG => 0,
CARRYINSELREG => 0,
CREG => 0,
INMODEREG => 0,
MREG => 0,
OPMODEREG => 0,
PREG => 0
PREG => 1
)
port map (
A => "0000000" & m_in.data1(22 downto 0),
@@ -180,13 +183,13 @@ begin
CEALUMODE => '0',
CEB1 => '0',
CEB2 => '0',
CEC => '1',
CEC => '0',
CECARRYIN => '0',
CECTRL => '0',
CED => '0',
CEINMODE => '0',
CEM => m_in.valid,
CEP => '0',
CEM => '0',
CEP => m_in.valid,
CLK => clk,
D => (others => '0'),
INMODE => "00000",
@@ -215,9 +218,11 @@ begin
BREG => 0,
CARRYINREG => 0,
CARRYINSELREG => 0,
CREG => 0,
INMODEREG => 0,
MREG => 0,
OPMODEREG => 0,
PREG => 0
PREG => 1
)
port map (
A => "0000000" & m_in.data1(22 downto 0),
@@ -235,13 +240,13 @@ begin
CEALUMODE => '0',
CEB1 => '0',
CEB2 => '0',
CEC => '1',
CEC => '0',
CECARRYIN => '0',
CECTRL => '0',
CED => '0',
CEINMODE => '0',
CEM => m_in.valid,
CEP => '0',
CEM => '0',
CEP => m_in.valid,
CLK => clk,
D => (others => '0'),
INMODE => "00000",
@@ -709,18 +714,18 @@ begin
s0: DSP48E1
generic map (
ACASCREG => 1,
ACASCREG => 0,
ALUMODEREG => 0,
AREG => 1,
BCASCREG => 1,
BREG => 1,
AREG => 0,
BCASCREG => 0,
BREG => 0,
CARRYINREG => 0,
CARRYINSELREG => 0,
CREG => 1,
CREG => 0,
INMODEREG => 0,
MREG => 0,
OPMODEREG => 0,
PREG => 0,
PREG => 1,
USE_MULT => "none"
)
port map (
@@ -735,18 +740,18 @@ begin
CARRYINSEL => "000",
CARRYOUT => s0_carry,
CEA1 => '0',
CEA2 => valid_1,
CEA2 => '0',
CEAD => '0',
CEALUMODE => '0',
CEB1 => '0',
CEB2 => valid_1,
CEC => valid_1,
CEB2 => '0',
CEC => '0',
CECARRYIN => '0',
CECTRL => '0',
CED => '0',
CEINMODE => '0',
CEM => '0',
CEP => '0',
CEP => valid_1,
CLK => clk,
D => (others => '0'),
INMODE => "00000",
@@ -953,8 +958,6 @@ begin
RSTP => '0'
);
product(31 downto 0) <= product_lo xor (31 downto 0 => req_not);
mult_out: process(all)
variable ov : std_ulogic;
begin
@@ -974,12 +977,15 @@ begin
process(clk)
begin
if rising_edge(clk) then
product_lo <= m10_p(8 downto 0) & m01_p(5 downto 0) & m00_p(16 downto 0);
if rnot_1 = '0' then
product(31 downto 0) <= m10_p(8 downto 0) & m01_p(5 downto 0) & m00_p(16 downto 0);
else
product(31 downto 0) <= not (m10_p(8 downto 0) & m01_p(5 downto 0) & m00_p(16 downto 0));
end if;
m_out.valid <= valid_1;
valid_1 <= m_in.valid;
req_32bit <= r32_1;
r32_1 <= m_in.is_32bit;
req_not <= rnot_1;
rnot_1 <= m_in.not_result;
overflow <= ovf_in;
end if;