From 48f260761b72924030abc8ff6bc1a727f2dbf331 Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Mon, 21 Oct 2019 15:11:47 +1100 Subject: [PATCH] writeback: Slightly improve timing The CR update currently depends on the complete data formatting mux chain. This makes it source its inputs from a bit earlier in the chian, thus improving timing a bit Signed-off-by: Benjamin Herrenschmidt --- writeback.vhdl | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/writeback.vhdl b/writeback.vhdl index 0d9397c..e2b74f8 100644 --- a/writeback.vhdl +++ b/writeback.vhdl @@ -44,6 +44,7 @@ architecture behaviour of writeback is signal sign_extend : std_ulogic; signal negative : std_ulogic; signal second_word : std_ulogic; + signal zero : std_ulogic; begin writeback_0: process(clk) begin @@ -155,7 +156,9 @@ begin -- If the data can arrive split over two cycles, this will be correct -- provided we don't have both sign extension and byte reversal. - negative <= (data_len(2) and data_permuted(31)) or (data_len(1) and data_permuted(15)) or + negative <= (data_len(3) and data_permuted(63)) or + (data_len(2) and data_permuted(31)) or + (data_len(1) and data_permuted(15)) or (data_len(0) and data_permuted(7)); -- trim and sign-extend @@ -170,12 +173,16 @@ begin trim_ctl(i) <= '0' & (negative and sign_extend); end if; end loop; + zero <= not negative; for i in 0 to 7 loop case trim_ctl(i) is when "11" => data_trimmed(i * 8 + 7 downto i * 8) <= data_latched(i * 8 + 7 downto i * 8); when "10" => data_trimmed(i * 8 + 7 downto i * 8) <= data_permuted(i * 8 + 7 downto i * 8); + if or data_permuted(i * 8 + 7 downto i * 8) /= '0' then + zero <= '0'; + end if; when "01" => data_trimmed(i * 8 + 7 downto i * 8) <= x"FF"; when others => @@ -190,9 +197,9 @@ begin if rc = '1' then c_out.write_cr_enable <= '1'; c_out.write_cr_mask <= num_to_fxm(0); - if data_trimmed(63) = '1' then + if negative = '1' then c_out.write_cr_data <= x"80000000"; - elsif or (data_trimmed(62 downto 0)) = '1' then + elsif zero = '0' then c_out.write_cr_data <= x"40000000"; else c_out.write_cr_data <= x"20000000"; -- 2.30.2