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microwatt/cr_file.vhdl

75 lines
2.0 KiB
VHDL

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
library work;
use work.common.all;
entity cr_file is
port(
clk : in std_logic;
d_in : in Decode2ToCrFileType;
d_out : out CrFileToDecode2Type;
w_in : in WritebackToCrFileType
);
end entity cr_file;
architecture behaviour of cr_file is
signal crs : std_ulogic_vector(31 downto 0) := (others => '0');
Add basic XER support The carry is currently internal to execute1. We don't handle any of the other XER fields. This creates type called "xer_common_t" that contains the commonly used XER bits (CA, CA32, SO, OV, OV32). The value is stored in the CR file (though it could be a separate module). The rest of the bits will be implemented as a separate SPR and the two parts reconciled in mfspr/mtspr in latter commits. We always read XER in decode2 (there is little point not to) and send it down all pipeline branches as it will be needed in writeback for all type of instructions when CR0:SO needs to be updated (such forms exist for all pipeline branches even if we don't yet implement them). To avoid having to track XER hazards, we forward it back in EX1. This assumes that other pipeline branches that can modify it (mult and div) are running single issue for now. One additional hazard to beware of is an XER:SO modifying instruction in EX1 followed immediately by a store conditional. Due to our writeback latency, the store will go down the LSU with the previous XER value, thus the stcx. will set CR0:SO using an obsolete SO value. I doubt there exist any code relying on this behaviour being correct but we should account for it regardless, possibly by ensuring that stcx. remain single issue initially, or later by adding some minimal tracking or moving the LSU into the same pipeline as execute. Missing some obscure XER affecting instructions like addex or mcrxrx. [paulus@ozlabs.org - fix CA32 and OV32 for OP_ADD, fix order of arguments to set_ov] Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
signal crs_updated : std_ulogic_vector(31 downto 0);
signal xerc : xer_common_t := xerc_init;
signal xerc_updated : xer_common_t;
begin
cr_create_0: process(all)
variable hi, lo : integer := 0;
variable cr_tmp : std_ulogic_vector(31 downto 0) := (others => '0');
begin
cr_tmp := crs;
for i in 0 to 7 loop
if w_in.write_cr_mask(i) = '1' then
lo := i*4;
hi := lo + 3;
cr_tmp(hi downto lo) := w_in.write_cr_data(hi downto lo);
end if;
end loop;
crs_updated <= cr_tmp;
Add basic XER support The carry is currently internal to execute1. We don't handle any of the other XER fields. This creates type called "xer_common_t" that contains the commonly used XER bits (CA, CA32, SO, OV, OV32). The value is stored in the CR file (though it could be a separate module). The rest of the bits will be implemented as a separate SPR and the two parts reconciled in mfspr/mtspr in latter commits. We always read XER in decode2 (there is little point not to) and send it down all pipeline branches as it will be needed in writeback for all type of instructions when CR0:SO needs to be updated (such forms exist for all pipeline branches even if we don't yet implement them). To avoid having to track XER hazards, we forward it back in EX1. This assumes that other pipeline branches that can modify it (mult and div) are running single issue for now. One additional hazard to beware of is an XER:SO modifying instruction in EX1 followed immediately by a store conditional. Due to our writeback latency, the store will go down the LSU with the previous XER value, thus the stcx. will set CR0:SO using an obsolete SO value. I doubt there exist any code relying on this behaviour being correct but we should account for it regardless, possibly by ensuring that stcx. remain single issue initially, or later by adding some minimal tracking or moving the LSU into the same pipeline as execute. Missing some obscure XER affecting instructions like addex or mcrxrx. [paulus@ozlabs.org - fix CA32 and OV32 for OP_ADD, fix order of arguments to set_ov] Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
if w_in.write_xerc_enable = '1' then
xerc_updated <= w_in.write_xerc_data;
else
xerc_updated <= xerc;
end if;
end process;
-- synchronous writes
cr_write_0: process(clk)
begin
if rising_edge(clk) then
if w_in.write_cr_enable = '1' then
report "Writing " & to_hstring(w_in.write_cr_data) & " to CR mask " & to_hstring(w_in.write_cr_mask);
crs <= crs_updated;
end if;
Add basic XER support The carry is currently internal to execute1. We don't handle any of the other XER fields. This creates type called "xer_common_t" that contains the commonly used XER bits (CA, CA32, SO, OV, OV32). The value is stored in the CR file (though it could be a separate module). The rest of the bits will be implemented as a separate SPR and the two parts reconciled in mfspr/mtspr in latter commits. We always read XER in decode2 (there is little point not to) and send it down all pipeline branches as it will be needed in writeback for all type of instructions when CR0:SO needs to be updated (such forms exist for all pipeline branches even if we don't yet implement them). To avoid having to track XER hazards, we forward it back in EX1. This assumes that other pipeline branches that can modify it (mult and div) are running single issue for now. One additional hazard to beware of is an XER:SO modifying instruction in EX1 followed immediately by a store conditional. Due to our writeback latency, the store will go down the LSU with the previous XER value, thus the stcx. will set CR0:SO using an obsolete SO value. I doubt there exist any code relying on this behaviour being correct but we should account for it regardless, possibly by ensuring that stcx. remain single issue initially, or later by adding some minimal tracking or moving the LSU into the same pipeline as execute. Missing some obscure XER affecting instructions like addex or mcrxrx. [paulus@ozlabs.org - fix CA32 and OV32 for OP_ADD, fix order of arguments to set_ov] Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
if w_in.write_xerc_enable = '1' then
report "Writing XERC";
xerc <= xerc_updated;
end if;
end if;
end process;
-- asynchronous reads
cr_read_0: process(all)
begin
-- just return the entire CR to make mfcrf easier for now
if d_in.read = '1' then
report "Reading CR " & to_hstring(crs_updated);
end if;
d_out.read_cr_data <= crs_updated;
Add basic XER support The carry is currently internal to execute1. We don't handle any of the other XER fields. This creates type called "xer_common_t" that contains the commonly used XER bits (CA, CA32, SO, OV, OV32). The value is stored in the CR file (though it could be a separate module). The rest of the bits will be implemented as a separate SPR and the two parts reconciled in mfspr/mtspr in latter commits. We always read XER in decode2 (there is little point not to) and send it down all pipeline branches as it will be needed in writeback for all type of instructions when CR0:SO needs to be updated (such forms exist for all pipeline branches even if we don't yet implement them). To avoid having to track XER hazards, we forward it back in EX1. This assumes that other pipeline branches that can modify it (mult and div) are running single issue for now. One additional hazard to beware of is an XER:SO modifying instruction in EX1 followed immediately by a store conditional. Due to our writeback latency, the store will go down the LSU with the previous XER value, thus the stcx. will set CR0:SO using an obsolete SO value. I doubt there exist any code relying on this behaviour being correct but we should account for it regardless, possibly by ensuring that stcx. remain single issue initially, or later by adding some minimal tracking or moving the LSU into the same pipeline as execute. Missing some obscure XER affecting instructions like addex or mcrxrx. [paulus@ozlabs.org - fix CA32 and OV32 for OP_ADD, fix order of arguments to set_ov] Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
d_out.read_xerc_data <= xerc_updated;
end process;
end architecture behaviour;