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https://github.com/antonblanchard/microwatt.git
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core: Improve timing on bypass control paths
In order to improve timing, the bypass paths now carry the register number being written as well as the tag. The decisions about which bypasses to use for which operands are then made by comparing the register numbers rather than by determining a tag from the register number and then comparing tags. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras
parent
f2166d326c
commit
788f7a1755
@ -420,9 +420,11 @@ package common is
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type bypass_data_t is record
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tag : instr_tag_t;
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reg : gspr_index_t;
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data : std_ulogic_vector(63 downto 0);
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end record;
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constant bypass_data_init : bypass_data_t := (tag => instr_tag_init, data => (others => '0'));
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constant bypass_data_init : bypass_data_t :=
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(tag => instr_tag_init, reg => (others => '0'), data => (others => '0'));
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type cr_bypass_data_t is record
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tag : instr_tag_t;
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107
control.vhdl
107
control.vhdl
@ -32,11 +32,11 @@ entity control is
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gpr_c_read_valid_in : in std_ulogic;
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gpr_c_read_in : in gspr_index_t;
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execute_next_tag : in instr_tag_t;
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execute_next_cr_tag : in instr_tag_t;
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execute2_next_tag : in instr_tag_t;
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execute_next_bypass : in bypass_data_t;
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execute2_next_bypass : in bypass_data_t;
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writeback_bypass : in bypass_data_t;
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execute_next_cr_tag : in instr_tag_t;
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execute2_next_cr_tag : in instr_tag_t;
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writeback_tag : in instr_tag_t;
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cr_read_in : in std_ulogic;
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cr_write_in : in std_ulogic;
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@ -164,109 +164,90 @@ begin
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variable byp_cr : std_ulogic_vector(1 downto 0);
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variable tag_ov : instr_tag_t;
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variable tag_prev : instr_tag_t;
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variable rma : std_ulogic_vector(TAG_COUNT-1 downto 0);
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variable rmb : std_ulogic_vector(TAG_COUNT-1 downto 0);
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variable rmc : std_ulogic_vector(TAG_COUNT-1 downto 0);
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variable tag_a_stall : std_ulogic;
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variable tag_b_stall : std_ulogic;
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variable tag_c_stall : std_ulogic;
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begin
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tag_a := instr_tag_init;
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tag_a_stall := '0';
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rma := (others => '0');
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for i in tag_number_t loop
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if tag_regs(i).valid = '1' and tag_regs(i).wr_gpr = '1' and
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if tag_regs(i).valid = '1' and tag_regs(i).recent = '1' and
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tag_regs(i).reg = gpr_a_read_in and gpr_a_read_valid_in = '1' then
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rma(i) := '1';
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if tag_regs(i).recent = '1' then
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tag_a_stall := '1';
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tag_a.valid := '1';
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tag_a.tag := i;
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if (EX1_BYPASS and tag_match(execute_next_bypass.tag, tag_a)) or
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(EX1_BYPASS and tag_match(execute2_next_bypass.tag, tag_a)) or
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tag_match(complete_in, tag_a) then
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tag_a.valid := '0';
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end if;
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end if;
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end loop;
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byp_a := "0000";
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if EX1_BYPASS and execute_next_tag.valid = '1' and
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rma(execute_next_tag.tag) = '1' then
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if EX1_BYPASS and execute_next_bypass.tag.valid = '1' and
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execute_next_bypass.reg = gpr_a_read_in then
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byp_a(1) := '1';
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tag_a := execute_next_tag;
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elsif EX1_BYPASS and execute2_next_tag.valid = '1' and
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rma(execute2_next_tag.tag) = '1' then
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elsif EX1_BYPASS and execute2_next_bypass.tag.valid = '1' and
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execute2_next_bypass.reg = gpr_a_read_in then
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byp_a(2) := '1';
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tag_a := execute2_next_tag;
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elsif writeback_tag.valid = '1' and rma(writeback_tag.tag) = '1' then
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elsif writeback_bypass.tag.valid = '1' and
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writeback_bypass.reg = gpr_a_read_in then
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byp_a(3) := '1';
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tag_a := writeback_tag;
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end if;
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byp_a(0) := gpr_a_read_valid_in and (byp_a(1) or byp_a(2) or byp_a(3));
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if tag_a.valid = '1' and tag_regs(tag_a.tag).valid = '1' and
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tag_regs(tag_a.tag).recent = '1' then
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tag_a_stall := '0';
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end if;
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tag_b := instr_tag_init;
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tag_b_stall := '0';
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rmb := (others => '0');
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for i in tag_number_t loop
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if tag_regs(i).valid = '1' and tag_regs(i).wr_gpr = '1' and
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if tag_regs(i).valid = '1' and tag_regs(i).recent = '1' and
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tag_regs(i).reg = gpr_b_read_in and gpr_b_read_valid_in = '1' then
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rmb(i) := '1';
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if tag_regs(i).recent = '1' then
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tag_b_stall := '1';
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tag_b.valid := '1';
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tag_b.tag := i;
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if (EX1_BYPASS and tag_match(execute_next_bypass.tag, tag_b)) or
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(EX1_BYPASS and tag_match(execute2_next_bypass.tag, tag_b)) or
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tag_match(complete_in, tag_b) then
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tag_b.valid := '0';
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end if;
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end if;
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end loop;
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byp_b := "0000";
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if EX1_BYPASS and execute_next_tag.valid = '1' and
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rmb(execute_next_tag.tag) = '1' then
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if EX1_BYPASS and execute_next_bypass.tag.valid = '1' and
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execute_next_bypass.reg = gpr_b_read_in then
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byp_b(1) := '1';
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tag_b := execute_next_tag;
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elsif EX1_BYPASS and execute2_next_tag.valid = '1' and
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rmb(execute2_next_tag.tag) = '1' then
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elsif EX1_BYPASS and execute2_next_bypass.tag.valid = '1' and
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execute2_next_bypass.reg = gpr_b_read_in then
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byp_b(2) := '1';
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tag_b := execute2_next_tag;
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elsif writeback_tag.valid = '1' and rmb(writeback_tag.tag) = '1' then
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elsif writeback_bypass.tag.valid = '1' and
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writeback_bypass.reg = gpr_b_read_in then
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byp_b(3) := '1';
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tag_b := writeback_tag;
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end if;
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byp_b(0) := gpr_b_read_valid_in and (byp_b(1) or byp_b(2) or byp_b(3));
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if tag_b.valid = '1' and tag_regs(tag_b.tag).valid = '1' and
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tag_regs(tag_b.tag).recent = '1' then
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tag_b_stall := '0';
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end if;
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tag_c := instr_tag_init;
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tag_c_stall := '0';
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rmc := (others => '0');
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for i in tag_number_t loop
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if tag_regs(i).valid = '1' and tag_regs(i).wr_gpr = '1' and
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if tag_regs(i).valid = '1' and tag_regs(i).recent = '1' and
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tag_regs(i).reg = gpr_c_read_in and gpr_c_read_valid_in = '1' then
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rmc(i) := '1';
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if tag_regs(i).recent = '1' then
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tag_c_stall := '1';
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tag_c.valid := '1';
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tag_c.tag := i;
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if (EX1_BYPASS and tag_match(execute_next_bypass.tag, tag_c)) or
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(EX1_BYPASS and tag_match(execute2_next_bypass.tag, tag_c)) or
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tag_match(complete_in, tag_c) then
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tag_c.valid := '0';
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end if;
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end if;
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end loop;
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byp_c := "0000";
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if EX1_BYPASS and execute_next_tag.valid = '1' and rmc(execute_next_tag.tag) = '1' then
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if EX1_BYPASS and execute_next_bypass.tag.valid = '1' and
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execute_next_bypass.reg = gpr_c_read_in then
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byp_c(1) := '1';
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tag_c := execute_next_tag;
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elsif EX1_BYPASS and execute2_next_tag.valid = '1' and rmc(execute2_next_tag.tag) = '1' then
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elsif EX1_BYPASS and execute2_next_bypass.tag.valid = '1' and
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execute2_next_bypass.reg = gpr_c_read_in then
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byp_c(2) := '1';
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tag_c := execute2_next_tag;
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elsif writeback_tag.valid = '1' and rmc(writeback_tag.tag) = '1' then
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elsif writeback_bypass.tag.valid = '1' and
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writeback_bypass.reg = gpr_c_read_in then
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byp_c(3) := '1';
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tag_c := writeback_tag;
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end if;
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byp_c(0) := gpr_c_read_valid_in and (byp_c(1) or byp_c(2) or byp_c(3));
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if tag_c.valid = '1' and tag_regs(tag_c.tag).valid = '1' and
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tag_regs(tag_c.tag).recent = '1' then
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tag_c_stall := '0';
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end if;
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gpr_bypass_a <= byp_a;
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gpr_bypass_b <= byp_b;
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gpr_bypass_c <= byp_c;
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gpr_tag_stall <= tag_a_stall or tag_b_stall or tag_c_stall;
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gpr_tag_stall <= tag_a.valid or tag_b.valid or tag_c.valid;
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incr_tag := curr_tag;
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instr_tag.tag <= curr_tag;
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@ -279,11 +279,11 @@ begin
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gpr_c_read_valid_in => gpr_c_read_valid,
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gpr_c_read_in => gpr_c_read,
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execute_next_tag => execute_bypass.tag,
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execute_next_bypass => execute_bypass,
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execute_next_cr_tag => execute_cr_bypass.tag,
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execute2_next_tag => execute2_bypass.tag,
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execute2_next_bypass => execute2_bypass,
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execute2_next_cr_tag => execute2_cr_bypass.tag,
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writeback_tag => writeback_bypass.tag,
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writeback_bypass => writeback_bypass,
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cr_read_in => cr_read_valid,
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cr_write_in => cr_write_valid,
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@ -1938,8 +1938,9 @@ begin
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v.fp_exception_next := '0';
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end if;
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bypass_data.tag.valid <= e_in.write_reg_enable and bypass_valid;
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bypass_data.tag.tag <= e_in.instr_tag.tag;
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bypass_data.tag.valid <= v.e.write_enable and bypass_valid;
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bypass_data.tag.tag <= v.e.instr_tag.tag;
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bypass_data.reg <= v.e.write_reg;
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bypass_data.data <= alu_result;
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bypass_cr_data.tag.valid <= e_in.output_cr and bypass_valid;
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@ -2250,6 +2251,7 @@ begin
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bypass2_data.tag.valid <= ex1.e.write_enable and bypass_valid;
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bypass2_data.tag.tag <= ex1.e.instr_tag.tag;
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bypass2_data.reg <= ex1.e.write_reg;
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bypass2_data.data <= ex_result;
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bypass2_cr_data.tag.valid <= (ex1.e.write_cr_enable or (ex1.e.rc and ex1.e.write_enable))
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@ -203,6 +203,7 @@ begin
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-- Register write data bypass to decode2
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wb_bypass.tag.tag <= complete_out.tag;
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wb_bypass.tag.valid <= complete_out.valid and w_out.write_enable;
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wb_bypass.reg <= w_out.write_reg;
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wb_bypass.data <= w_out.write_data;
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end process;
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