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no more writes to dummy register x0 - not really relevant, but maybe saves some energy

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stnolting 2020-07-21 19:39:21 +02:00
parent 819f0488c3
commit 3786bfe06f
1 changed files with 8 additions and 3 deletions
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11
rtl/core/neorv32_cpu_regfile.vhd
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@ -2,7 +2,7 @@
-- # << NEORV32 - CPU Register File >> #
-- # ********************************************************************************************* #
-- # General purpose data registers. 32 entries for normal mode, 16 entries for embedded mode when #
-- # RISC-V M extension is enabled. R0 output is hardwired to zero. #
-- # RISC-V M extension is enabled. x0 output is allways set to zero. #
-- # ********************************************************************************************* #
-- # BSD 3-Clause License #
-- # #
@ -69,6 +69,7 @@ architecture neorv32_cpu_regfile_rtl of neorv32_cpu_regfile is
signal reg_file : reg_file_t;
signal reg_file_emb : reg_file_emb_t;
signal rf_write_data : std_ulogic_vector(data_width_c-1 downto 0); -- actual write-back data
signal valid_wr : std_ulogic; -- writing not to r0
signal rs1_read : std_ulogic_vector(data_width_c-1 downto 0); -- internal operand rs1
signal rs2_read : std_ulogic_vector(data_width_c-1 downto 0); -- internal operand rs2
@ -103,6 +104,10 @@ begin
end case;
end process input_mux;
-- only write if destination is not x0 (pretty irrelevant, but might save some power) --
valid_wr <= or_all_f(ctrl_i(ctrl_rf_rd_adr4_c downto ctrl_rf_rd_adr0_c)) when (CPU_EXTENSION_RISCV_E = false) else
or_all_f(ctrl_i(ctrl_rf_rd_adr3_c downto ctrl_rf_rd_adr0_c));
-- Register file read/write access --------------------------------------------------------
-- -------------------------------------------------------------------------------------------
@ -120,7 +125,7 @@ begin
rs2_clear <= '1';
end if;
-- write --
if (ctrl_i(ctrl_rf_wb_en_c) = '1') then -- valid write-back
if (ctrl_i(ctrl_rf_wb_en_c) = '1') and (valid_wr = '1') then -- valid write-back
reg_file(to_integer(unsigned(ctrl_i(ctrl_rf_rd_adr4_c downto ctrl_rf_rd_adr0_c)))) <= rf_write_data;
end if;
-- read --
@ -138,7 +143,7 @@ begin
rs2_clear <= '1';
end if;
-- write --
if (ctrl_i(ctrl_rf_wb_en_c) = '1') then -- valid write-back
if (ctrl_i(ctrl_rf_wb_en_c) = '1') and (valid_wr = '1') then -- valid write-back
reg_file_emb(to_integer(unsigned(ctrl_i(ctrl_rf_rd_adr3_c downto ctrl_rf_rd_adr0_c)))) <= rf_write_data;
end if;
-- read --