sprs: Store common SPRs in register file

This stores the most common SPRs in the register file.

This includes CTR and LR and a not yet final list of others.

The register file is set to 64 entries for now. Specific types
are defined that can represent a GPR index (gpr_index_t) or
a GPR/SPR index (gspr_index_t) along with conversion functions
between the two.

On order to deal with some forms of branch updating both LR and
CTR, we introduced a delayed update of LR after a branch link.

Note: We currently stall the pipeline on such a delayed branch,
but we could avoid stalling fetch in that specific case as we
know we have a branch delay. We could also limit that to the
specific case where we need to update both CTR and LR.

This allows us to make bcreg, mtspr and mfspr pipelined. decode1
will automatically force the single issue flag on mfspr/mtspr to
a "slow" SPR.

[paulus@ozlabs.org - fix direction of decode2.stall_in]

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

Makefile

@@ -14,7 +14,7 @@ all: $(all)
 	$(GHDL) -a $(GHDLFLAGS) $<
 
 common.o: decode_types.o
-control.o: gpr_hazard.o cr_hazard.o
+control.o: gpr_hazard.o cr_hazard.o common.o
 sim_jtag.o: sim_jtag_socket.o
 core_tb.o: common.o wishbone_types.o core.o soc.o sim_jtag.o
 core.o: common.o wishbone_types.o fetch1.o fetch2.o icache.o decode1.o decode2.o register_file.o cr_file.o execute1.o loadstore1.o dcache.o multiply.o writeback.o core_debug.o divider.o

common.vhdl

@@ -28,6 +28,12 @@ package common is
     constant SPR_HSPRG0 : spr_num_t := 304;
     constant SPR_HSPRG1 : spr_num_t := 305;
 
+    -- GPR indices in the register file (GPR only)
+    subtype gpr_index_t is std_ulogic_vector(4 downto 0);
+
+    -- Extended GPR indice (can hold an SPR)
+    subtype gspr_index_t is std_ulogic_vector(5 downto 0);
+
     -- Some SPRs are stored in the register file, they use the magic
     -- GPR numbers above 31.
     --
@@ -36,7 +42,13 @@ package common is
     -- indicates if this is indeed a fast SPR. If clear, then
     -- the SPR is not stored in the GPR file.
     --
-    function fast_spr_num(spr: spr_num_t) return std_ulogic_vector;
+    function fast_spr_num(spr: spr_num_t) return gspr_index_t;
+
+    -- Indices conversion functions
+    function gspr_to_gpr(i: gspr_index_t) return gpr_index_t;
+    function gpr_to_gspr(i: gpr_index_t) return gspr_index_t;
+    function gpr_or_spr_to_gspr(g: gpr_index_t; s: gspr_index_t) return gspr_index_t;
+    function is_fast_spr(s: gspr_index_t) return std_ulogic;
 
     -- The XER is split: the common bits (CA, OV, SO, OV32 and CA32) are
     -- in the CR file as a kind of CR extension (with a separate write
@@ -52,8 +64,6 @@ package common is
 
     -- This needs to die...
     type ctrl_t is record
-	lr: std_ulogic_vector(63 downto 0);
-	ctr: std_ulogic_vector(63 downto 0);
 	tb: std_ulogic_vector(63 downto 0);
     end record;
 
@@ -83,6 +93,8 @@ package common is
 	stop_mark : std_ulogic;
 	nia: std_ulogic_vector(63 downto 0);
 	insn: std_ulogic_vector(31 downto 0);
+	ispr1: gspr_index_t; -- (G)SPR used for branch condition (CTR) or mfspr
+	ispr2: gspr_index_t; -- (G)SPR used for branch target (CTR, LR, TAR)
 	decode: decode_rom_t;
     end record;
     constant Decode1ToDecode2Init : Decode1ToDecode2Type := (valid => '0', stop_mark => '0', decode => decode_rom_init, others => (others => '0'));
@@ -91,9 +103,9 @@ package common is
 	valid: std_ulogic;
 	insn_type: insn_type_t;
 	nia: std_ulogic_vector(63 downto 0);
-	write_reg: std_ulogic_vector(4 downto 0);
+	write_reg: gspr_index_t;
-	read_reg1: std_ulogic_vector(4 downto 0);
+	read_reg1: gspr_index_t;
-	read_reg2: std_ulogic_vector(4 downto 0);
+	read_reg2: gspr_index_t;
 	read_data1: std_ulogic_vector(63 downto 0);
 	read_data2: std_ulogic_vector(63 downto 0);
 	read_data3: std_ulogic_vector(63 downto 0);
@@ -121,7 +133,7 @@ package common is
     type Decode2ToMultiplyType is record
 	valid: std_ulogic;
 	insn_type: insn_type_t;
-	write_reg: std_ulogic_vector(4 downto 0);
+	write_reg: gpr_index_t;
 	data1: std_ulogic_vector(64 downto 0);
 	data2: std_ulogic_vector(64 downto 0);
 	rc: std_ulogic;
@@ -135,7 +147,7 @@ package common is
 
     type Decode2ToDividerType is record
 	valid: std_ulogic;
-	write_reg: std_ulogic_vector(4 downto 0);
+	write_reg: gpr_index_t;
 	dividend: std_ulogic_vector(63 downto 0);
 	divisor: std_ulogic_vector(63 downto 0);
 	is_signed: std_ulogic;
@@ -153,11 +165,11 @@ package common is
 
     type Decode2ToRegisterFileType is record
 	read1_enable : std_ulogic;
-	read1_reg : std_ulogic_vector(4 downto 0);
+	read1_reg : gspr_index_t;
 	read2_enable : std_ulogic;
-	read2_reg : std_ulogic_vector(4 downto 0);
+	read2_reg : gspr_index_t;
 	read3_enable : std_ulogic;
-	read3_reg : std_ulogic_vector(4 downto 0);
+	read3_reg : gpr_index_t;
     end record;
 
     type RegisterFileToDecode2Type is record
@@ -187,12 +199,12 @@ package common is
 	addr1 : std_ulogic_vector(63 downto 0);
 	addr2 : std_ulogic_vector(63 downto 0);
 	data : std_ulogic_vector(63 downto 0);		-- data to write, unused for read
-	write_reg : std_ulogic_vector(4 downto 0);	-- read data goes to this register
+	write_reg : gpr_index_t;
 	length : std_ulogic_vector(3 downto 0);
 	byte_reverse : std_ulogic;
 	sign_extend : std_ulogic;			-- do we need to sign extend?
 	update : std_ulogic;				-- is this an update instruction?
-	update_reg : std_ulogic_vector(4 downto 0);	-- if so, the register to update
+	update_reg : gpr_index_t;                      	-- if so, the register to update
 	xerc : xer_common_t;
     end record;
     constant Decode2ToLoadstore1Init : Decode2ToLoadstore1Type := (valid => '0', load => '0', byte_reverse => '0',
@@ -205,19 +217,19 @@ package common is
 	nc : std_ulogic;
 	addr : std_ulogic_vector(63 downto 0);
 	data : std_ulogic_vector(63 downto 0);
-	write_reg : std_ulogic_vector(4 downto 0);
+	write_reg : gpr_index_t;
 	length : std_ulogic_vector(3 downto 0);
 	byte_reverse : std_ulogic;
 	sign_extend : std_ulogic;
 	update : std_ulogic;
-	update_reg : std_ulogic_vector(4 downto 0);
+	update_reg : gpr_index_t;
 	xerc : xer_common_t;
     end record;
 
     type DcacheToWritebackType is record
 	valid : std_ulogic;
 	write_enable: std_ulogic;
-	write_reg : std_ulogic_vector(4 downto 0);
+	write_reg : gpr_index_t;
 	write_data : std_ulogic_vector(63 downto 0);
 	write_len : std_ulogic_vector(3 downto 0);
 	write_shift : std_ulogic_vector(2 downto 0);
@@ -234,7 +246,7 @@ package common is
 	valid: std_ulogic;
 	rc : std_ulogic;
 	write_enable : std_ulogic;
-	write_reg: std_ulogic_vector(4 downto 0);
+	write_reg: gspr_index_t;
 	write_data: std_ulogic_vector(63 downto 0);
 	write_len : std_ulogic_vector(3 downto 0);
 	write_cr_enable : std_ulogic;
@@ -253,7 +265,7 @@ package common is
 	valid: std_ulogic;
 
 	write_reg_enable : std_ulogic;
-	write_reg_nr: std_ulogic_vector(4 downto 0);
+	write_reg_nr: gpr_index_t;
 	write_reg_data: std_ulogic_vector(63 downto 0);
 	write_xerc_enable : std_ulogic;
 	xerc : xer_common_t;
@@ -268,7 +280,7 @@ package common is
 	valid: std_ulogic;
 
 	write_reg_enable : std_ulogic;
-	write_reg_nr: std_ulogic_vector(4 downto 0);
+	write_reg_nr: gpr_index_t;
 	write_reg_data: std_ulogic_vector(63 downto 0);
 	write_xerc_enable : std_ulogic;
 	xerc : xer_common_t;
@@ -280,7 +292,7 @@ package common is
 								 others => (others => '0'));
 
     type WritebackToRegisterFileType is record
-	write_reg : std_ulogic_vector(4 downto 0);
+	write_reg : gspr_index_t;
 	write_data : std_ulogic_vector(63 downto 0);
 	write_enable : std_ulogic;
     end record;
@@ -303,7 +315,7 @@ package body common is
     begin
 	return to_integer(unsigned(insn(15 downto 11) & insn(20 downto 16)));
     end;
-    function fast_spr_num(spr: spr_num_t) return std_ulogic_vector is
+    function fast_spr_num(spr: spr_num_t) return gspr_index_t is
        variable n : integer range 0 to 31;
     begin
        case spr is
@@ -338,4 +350,28 @@ package body common is
        end case;
        return "1" & std_ulogic_vector(to_unsigned(n, 5));
     end;
+
+    function gspr_to_gpr(i: gspr_index_t) return gpr_index_t is
+    begin
+	return i(4 downto 0);
+    end;
+
+    function gpr_to_gspr(i: gpr_index_t) return gspr_index_t is
+    begin
+	return "0" & i;
+    end;
+
+    function gpr_or_spr_to_gspr(g: gpr_index_t; s: gspr_index_t) return gspr_index_t is
+    begin
+	if s(5) = '1' then
+	    return s;
+	else
+	    return gpr_to_gspr(g);
+	end if;
+    end;
+
+    function is_fast_spr(s: gspr_index_t) return std_ulogic is
+    begin
+	return s(5);
+    end;
 end common;

control.vhdl

@@ -1,6 +1,9 @@
 library ieee;
 use ieee.std_logic_1164.all;
 
+library work;
+use work.common.all;
+
 entity control is
     generic (
         PIPELINE_DEPTH : natural := 2
@@ -12,20 +15,21 @@ entity control is
         complete_in         : in std_ulogic;
         valid_in            : in std_ulogic;
         flush_in            : in std_ulogic;
+	stall_in            : in std_ulogic;
         sgl_pipe_in         : in std_ulogic;
         stop_mark_in        : in std_ulogic;
 
         gpr_write_valid_in  : in std_ulogic;
-        gpr_write_in        : in std_ulogic_vector(4 downto 0);
+        gpr_write_in        : in gspr_index_t;
 
         gpr_a_read_valid_in : in std_ulogic;
-        gpr_a_read_in       : in std_ulogic_vector(4 downto 0);
+        gpr_a_read_in       : in gspr_index_t;
 
         gpr_b_read_valid_in : in std_ulogic;
-        gpr_b_read_in       : in std_ulogic_vector(4 downto 0);
+        gpr_b_read_in       : in gspr_index_t;
 
         gpr_c_read_valid_in : in std_ulogic;
-        gpr_c_read_in       : in std_ulogic_vector(4 downto 0);
+        gpr_c_read_in       : in gpr_index_t;
 
         cr_read_in          : in std_ulogic;
         cr_write_in         : in std_ulogic;
@@ -61,6 +65,7 @@ begin
             )
         port map (
             clk                => clk,
+	    stall_in           => stall_in,
 
             gpr_write_valid_in => gpr_write_valid,
             gpr_write_in       => gpr_write_in,
@@ -76,6 +81,7 @@ begin
             )
         port map (
             clk                => clk,
+	    stall_in           => stall_in,
 
             gpr_write_valid_in => gpr_write_valid,
             gpr_write_in       => gpr_write_in,
@@ -91,11 +97,12 @@ begin
             )
         port map (
             clk                => clk,
+	    stall_in           => stall_in,
 
             gpr_write_valid_in => gpr_write_valid,
             gpr_write_in       => gpr_write_in,
             gpr_read_valid_in  => gpr_c_read_valid_in,
-            gpr_read_in        => gpr_c_read_in,
+            gpr_read_in        => "0" & gpr_c_read_in,
 
             stall_out          => stall_c_out
             );
@@ -106,6 +113,7 @@ begin
             )
         port map (
             clk                => clk,
+	    stall_in           => stall_in,
 
             cr_read_in         => cr_read_in,
             cr_write_in        => cr_write_valid,
@@ -129,8 +137,8 @@ begin
         v_int := r_int;
 
         -- asynchronous
-        valid_tmp := valid_in and not flush_in;
+        valid_tmp := valid_in and not flush_in and not stall_in;
-        stall_tmp := '0';
+        stall_tmp := stall_in;
 
         if complete_in = '1' then
             v_int.outstanding := r_int.outstanding - 1;

core.vhdl

@@ -76,8 +76,10 @@ architecture behave of core is
     signal icache_stall_out : std_ulogic;
     signal fetch2_stall_in : std_ulogic;
     signal decode1_stall_in : std_ulogic;
+    signal decode2_stall_in : std_ulogic;
     signal decode2_stall_out : std_ulogic;
     signal ex1_icache_inval: std_ulogic;
+    signal ex1_stall_out: std_ulogic;
 
     signal flush: std_ulogic;
 
@@ -184,6 +186,7 @@ begin
         port map (
             clk => clk,
             rst => core_rst,
+	    stall_in => decode2_stall_in,
             stall_out => decode2_stall_out,
             flush_in => flush,
             complete_in => complete,
@@ -198,6 +201,7 @@ begin
             c_in => cr_file_to_decode2,
             c_out => decode2_to_cr_file
             );
+    decode2_stall_in <= ex1_stall_out;
 
     register_file_0: entity work.register_file
         generic map (
@@ -223,6 +227,7 @@ begin
         port map (
             clk => clk,
             flush_out => flush,
+	    stall_out => ex1_stall_out,
             e_in => decode2_to_execute1,
             f_out => execute1_to_fetch1,
             e_out => execute1_to_writeback,

cr_hazard.vhdl

@@ -7,7 +7,8 @@ entity cr_hazard is
         PIPELINE_DEPTH : natural := 2
         );
     port(
-        clk         : in std_logic;
+        clk         : in std_ulogic;
+	stall_in    : in std_ulogic;
 
         cr_read_in  : in std_ulogic;
         cr_write_in : in std_ulogic;
@@ -29,7 +30,9 @@ begin
     cr_hazard0: process(clk)
     begin
         if rising_edge(clk) then
-            r <= rin;
+	    if stall_in = '0' then
+		r <= rin;
+	    end if;
         end if;
     end process;
 

decode1.vhdl

@@ -43,7 +43,7 @@ architecture behaviour of decode1 is
 		28 =>       (ALU,    OP_AND,       NONE,       CONST_UI,    RS,   RA,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', ONE,  '0', '0'), -- andi.
 		29 =>       (ALU,    OP_AND,       NONE,       CONST_UI_HI, RS,   RA,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', ONE,  '0', '0'), -- andis.
 		18 =>       (ALU,    OP_B,         NONE,       CONST_LI,    NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '1', '0'), -- b
-		16 =>       (ALU,    OP_BC,        NONE,       CONST_BD,    NONE, NONE, '1', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '1', '0'), -- bc
+		16 =>       (ALU,    OP_BC,        SPR,        CONST_BD,    NONE, SPR , '1', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '1', '0'), -- bc
 		11 =>       (ALU,    OP_CMP,       RA,         CONST_SI,    NONE, NONE, '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- cmpi
 		10 =>       (ALU,    OP_CMPL,      RA,         CONST_UI,    NONE, NONE, '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- cmpli
 		34 =>       (LDST,   OP_LOAD,      RA_OR_ZERO, CONST_SI,    NONE, RT,   '0', '0', '0', '0', ZERO, '0', is1B, '0', '0', '0', '0', '0', '0', NONE, '0', '1'), -- lbz
@@ -106,7 +106,7 @@ architecture behaviour of decode1 is
 		-- addpcis not implemented yet
 		2#001#    =>       (ALU,    OP_ILLEGAL,   NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '1'),
                 -- bclr, bcctr, bctar
-		2#100#    =>       (ALU,    OP_BCREG,     NONE,       NONE,        NONE, NONE, '1', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '1', '1'),
+		2#100#    =>       (ALU,    OP_BCREG,     SPR,        SPR,         NONE, SPR,  '1', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '1', '0'),
                 -- isync
 		2#111#    =>       (ALU,    OP_ISYNC,     NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'),
 		others   => illegal_inst
@@ -237,13 +237,13 @@ architecture behaviour of decode1 is
 		-- 2#1000000000# mcrxr
 		-- 2#1001000000# mcrxrx
 		2#0000010011#  =>       (ALU,    OP_MFCR,      NONE,       NONE,        NONE, RT,   '1', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- mfcr/mfocrf
-		2#0101010011#  =>       (ALU,    OP_MFSPR,     NONE,       NONE,        NONE, RT,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'), -- mfspr
+		2#0101010011#  =>       (ALU,    OP_MFSPR,     SPR,        NONE,        NONE, RT,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- mfspr
 		2#0100001001#  =>       (DIV,    OP_MOD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'), -- modud
 		2#0100001011#  =>       (DIV,    OP_MOD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'), -- moduw
 		2#1100001001#  =>       (DIV,    OP_MOD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'), -- modsd
 		2#1100001011#  =>       (DIV,    OP_MOD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'), -- modsw
 		2#0010010000#  =>       (ALU,    OP_MTCRF,     NONE,       NONE,        RS,   NONE, '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- mtcrf/mtocrf
-		2#0111010011#  =>       (ALU,    OP_MTSPR,     NONE,       NONE,        RS,   NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'), -- mtspr
+		2#0111010011#  =>       (ALU,    OP_MTSPR,     NONE,       NONE,        RS,   SPR,  '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- mtspr
 		2#0001001001#  =>       (MUL,    OP_MUL_H64,   RA,         RB,          NONE, RT,   '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '1', RC,   '0', '1'), -- mulhd
 		2#0000001001#  =>       (MUL,    OP_MUL_H64,   RA,         RB,          NONE, RT,   '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '1'), -- mulhdu
 		2#0001001011#  =>       (MUL,    OP_MUL_H32,   RA,         RB,          NONE, RT,   '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '1', RC,   '0', '1'), -- mulhw
@@ -355,6 +355,8 @@ begin
 		v.nia  := f_in.nia;
 		v.insn := f_in.insn;
 		v.stop_mark := f_in.stop_mark;
+		v.ispr1 := (others => '0');
+		v.ispr2 := (others => '0');
 
 		if f_in.valid = '1' then
 			report "Decode insn " & to_hstring(f_in.insn) & " at " & to_hstring(f_in.nia);
@@ -398,6 +400,33 @@ begin
                         v.decode := major_decode_rom_array(to_integer(majorop));
 		end if;
 
+		-- Set ISPR1/ISPR2 when needed
+		if v.decode.insn_type = OP_BC or v.decode.insn_type = OP_BCREG then
+		    -- Branch uses CTR as condition when BO(2) is 0. This is
+		    -- also used to indicate that CTR is modified (they go
+		    -- together).
+		    --
+		    if f_in.insn(23) = '0' then
+			v.ispr1 := fast_spr_num(SPR_CTR);
+		    end if;
+
+		    -- Branch source register is an SPR
+		    if v.decode.insn_type = OP_BCREG then
+			-- TODO: Add TAR
+			if f_in.insn(10) = '0' then
+			    v.ispr2 := fast_spr_num(SPR_LR);
+			else
+			    v.ispr2 := fast_spr_num(SPR_CTR);
+			end if;
+		    end if;
+		elsif v.decode.insn_type = OP_MFSPR or v.decode.insn_type = OP_MTSPR then
+		    v.ispr1 := fast_spr_num(decode_spr_num(f_in.insn));
+		    -- Make slow SPRs single issue
+		    if is_fast_spr(v.ispr1) = '0' then
+			v.decode.sgl_pipe := '1';
+		    end if;
+		end if;
+
 		if flush_in = '1' then
 			v.valid := '0';
 		end if;

decode2.vhdl

@@ -14,6 +14,7 @@ entity decode2 is
 		rst   : in std_ulogic;
 
 		complete_in : in std_ulogic;
+		stall_in : in std_ulogic;
 		stall_out : out std_ulogic;
 
 		stopped_out : out std_ulogic;
@@ -47,30 +48,49 @@ architecture behaviour of decode2 is
 
 	type decode_input_reg_t is record
 		reg_valid : std_ulogic;
-		reg       : std_ulogic_vector(4 downto 0);
+		reg       : gspr_index_t;
 		data      : std_ulogic_vector(63 downto 0);
 	end record;
 
+	type decode_output_reg_t is record
+		reg_valid : std_ulogic;
+		reg       : gspr_index_t;
+	end record;
+
 	function decode_input_reg_a (t : input_reg_a_t; insn_in : std_ulogic_vector(31 downto 0);
-				     reg_data : std_ulogic_vector(63 downto 0)) return decode_input_reg_t is
+				     reg_data : std_ulogic_vector(63 downto 0);
+				     ispr : gspr_index_t) return decode_input_reg_t is
 		variable is_reg : std_ulogic;
 	begin
 		is_reg := '0' when insn_ra(insn_in) = "00000" else '1';
 
 		if t = RA or (t = RA_OR_ZERO and insn_ra(insn_in) /= "00000") then
-			--return (is_reg, insn_ra(insn_in), reg_data);
+		    assert is_fast_spr(ispr) = '0' report "Decode A says GPR but ISPR says SPR:" &
-			return ('1', insn_ra(insn_in), reg_data);
+			to_hstring(ispr) severity failure;
+		    return ('1', gpr_to_gspr(insn_ra(insn_in)), reg_data);
+		elsif t = SPR then
+		    -- ISPR must be either a valid fast SPR number or all 0 for a slow SPR.
+		    -- If it's all 0, we don't treat it as a dependency as slow SPRs
+		    -- operations are single issue.
+		    --
+		    assert is_fast_spr(ispr) =  '1' or ispr = "000000"
+			report "Decode A says SPR but ISPR is invalid:" &
+			to_hstring(ispr) severity failure;
+		    return (is_fast_spr(ispr), ispr, reg_data);
 		else
 			return ('0', (others => '0'), (others => '0'));
 		end if;
 	end;
 
 	function decode_input_reg_b (t : input_reg_b_t; insn_in : std_ulogic_vector(31 downto 0);
-				     reg_data : std_ulogic_vector(63 downto 0)) return decode_input_reg_t is
+				     reg_data : std_ulogic_vector(63 downto 0);
+				     ispr : gspr_index_t) return decode_input_reg_t is
 	begin
 		case t is
 		when RB =>
-			return ('1', insn_rb(insn_in), reg_data);
+		    assert is_fast_spr(ispr) = '0' report "Decode B says GPR but ISPR says SPR:" &
+			to_hstring(ispr) severity failure;
+		    return ('1', gpr_to_gspr(insn_rb(insn_in)), reg_data);
 		when CONST_UI =>
 			return ('0', (others => '0'), std_ulogic_vector(resize(unsigned(insn_ui(insn_in)), 64)));
 		when CONST_SI =>
@@ -91,6 +111,14 @@ architecture behaviour of decode2 is
 			return ('0', (others => '0'), x"00000000000000" & "00" & insn_in(1) & insn_in(15 downto 11));
 		when CONST_SH32 =>
 			return ('0', (others => '0'), x"00000000000000" & "000" & insn_in(15 downto 11));
+		when SPR =>
+		    -- ISPR must be either a valid fast SPR number or all 0 for a slow SPR.
+		    -- If it's all 0, we don't treat it as a dependency as slow SPRs
+		    -- operations are single issue.
+		    assert is_fast_spr(ispr) = '1' or ispr = "000000"
+			report "Decode B says SPR but ISPR is invalid:" &
+			to_hstring(ispr) severity failure;
+		    return (is_fast_spr(ispr), ispr, reg_data);
 		when NONE =>
 			return ('0', (others => '0'), (others => '0'));
 		end case;
@@ -101,21 +129,30 @@ architecture behaviour of decode2 is
 	begin
 		case t is
 		when RS =>
-			return ('1', insn_rs(insn_in), reg_data);
+			return ('1', gpr_to_gspr(insn_rs(insn_in)), reg_data);
 		when NONE =>
 			return ('0', (others => '0'), (others => '0'));
 		end case;
 	end;
 
-	function decode_output_reg (t : output_reg_a_t; insn_in : std_ulogic_vector(31 downto 0)) return std_ulogic_vector is
+	function decode_output_reg (t : output_reg_a_t; insn_in : std_ulogic_vector(31 downto 0);
+				    ispr : gspr_index_t) return decode_output_reg_t is
 	begin
 		case t is
 		when RT =>
-			return insn_rt(insn_in);
+		    return ('1', gpr_to_gspr(insn_rt(insn_in)));
 		when RA =>
-			return insn_ra(insn_in);
+		    return ('1', gpr_to_gspr(insn_ra(insn_in)));
+		when SPR =>
+		    -- ISPR must be either a valid fast SPR number or all 0 for a slow SPR.
+		    -- If it's all 0, we don't treat it as a dependency as slow SPRs
+		    -- operations are single issue.
+		    assert is_fast_spr(ispr) = '1' or ispr = "000000"
+			report "Decode B says SPR but ISPR is invalid:" &
+			to_hstring(ispr) severity failure;
+		    return (is_fast_spr(ispr), ispr);
 		when NONE =>
-			return "00000";
+		    return ('0', "000000");
 		end case;
 	end;
 
@@ -153,16 +190,16 @@ architecture behaviour of decode2 is
 	signal control_sgl_pipe : std_logic;
 
 	signal gpr_write_valid : std_ulogic;
-	signal gpr_write : std_ulogic_vector(4 downto 0);
+	signal gpr_write : gspr_index_t;
 
 	signal gpr_a_read_valid : std_ulogic;
-	signal gpr_a_read : std_ulogic_vector(4 downto 0);
+	signal gpr_a_read :gspr_index_t;
 
 	signal gpr_b_read_valid : std_ulogic;
-	signal gpr_b_read : std_ulogic_vector(4 downto 0);
+	signal gpr_b_read : gspr_index_t;
 
 	signal gpr_c_read_valid : std_ulogic;
-	signal gpr_c_read : std_ulogic_vector(4 downto 0);
+	signal gpr_c_read : gpr_index_t;
 
 	signal cr_write_valid : std_ulogic;
 begin
@@ -176,6 +213,7 @@ begin
 
 		complete_in => complete_in,
 		valid_in    => control_valid_in,
+		stall_in    => stall_in,
 		flush_in    => flush_in,
 		sgl_pipe_in => control_sgl_pipe,
 		stop_mark_in => d_in.stop_mark,
@@ -210,8 +248,8 @@ begin
 		end if;
 	end process;
 
-	r_out.read1_reg <= insn_ra(d_in.insn);
+	r_out.read1_reg <= gpr_or_spr_to_gspr(insn_ra(d_in.insn), d_in.ispr1);
-	r_out.read2_reg <= insn_rb(d_in.insn);
+	r_out.read2_reg <= gpr_or_spr_to_gspr(insn_rb(d_in.insn), d_in.ispr2);
 	r_out.read3_reg <= insn_rs(d_in.insn);
 
 	c_out.read <= d_in.decode.input_cr;
@@ -223,6 +261,7 @@ begin
 		variable decoded_reg_a : decode_input_reg_t;
 		variable decoded_reg_b : decode_input_reg_t;
 		variable decoded_reg_c : decode_input_reg_t;
+		variable decoded_reg_o : decode_output_reg_t;
                 variable signed_division: std_ulogic;
                 variable length : std_ulogic_vector(3 downto 0);
 	begin
@@ -240,9 +279,10 @@ begin
 		--v.m.input_cr := d_in.decode.input_cr;
 		--v.e.output_cr := d_in.decode.output_cr;
     
-		decoded_reg_a := decode_input_reg_a (d_in.decode.input_reg_a, d_in.insn, r_in.read1_data);
+		decoded_reg_a := decode_input_reg_a (d_in.decode.input_reg_a, d_in.insn, r_in.read1_data, d_in.ispr1);
-		decoded_reg_b := decode_input_reg_b (d_in.decode.input_reg_b, d_in.insn, r_in.read2_data);
+		decoded_reg_b := decode_input_reg_b (d_in.decode.input_reg_b, d_in.insn, r_in.read2_data, d_in.ispr2);
 		decoded_reg_c := decode_input_reg_c (d_in.decode.input_reg_c, d_in.insn, r_in.read3_data);
+		decoded_reg_o := decode_output_reg (d_in.decode.output_reg_a, d_in.insn, d_in.ispr1);
 
 		r_out.read1_enable <= decoded_reg_a.reg_valid;
 		r_out.read2_enable <= decoded_reg_b.reg_valid;
@@ -269,7 +309,7 @@ begin
 		v.e.read_reg2 := decoded_reg_b.reg;
 		v.e.read_data2 := decoded_reg_b.data;
                 v.e.read_data3 := decoded_reg_c.data;
-		v.e.write_reg := decode_output_reg(d_in.decode.output_reg_a, d_in.insn);
+		v.e.write_reg := decoded_reg_o.reg;
 		v.e.rc := decode_rc(d_in.decode.rc, d_in.insn);
 		v.e.oe := decode_oe(d_in.decode.rc, d_in.insn);
 		v.e.cr := c_in.read_cr_data;
@@ -290,7 +330,7 @@ begin
 		v.m.insn_type := d_in.decode.insn_type;
 		mul_a := decoded_reg_a.data;
 		mul_b := decoded_reg_b.data;
-		v.m.write_reg := decode_output_reg(d_in.decode.output_reg_a, d_in.insn);
+		v.m.write_reg := gspr_to_gpr(decoded_reg_o.reg);
 		v.m.rc := decode_rc(d_in.decode.rc, d_in.insn);
 		v.m.xerc := c_in.read_xerc_data;
 		if v.m.insn_type = OP_MUL_L64 then
@@ -327,7 +367,7 @@ begin
                 --       s = 1 for signed, 0 for unsigned (for div*)
                 --       t = 1 for 32-bit, 0 for 64-bit
                 --       r = RC bit (record condition code)
-		v.d.write_reg := decode_output_reg(d_in.decode.output_reg_a, d_in.insn);
+		v.d.write_reg := gspr_to_gpr(decoded_reg_o.reg);
                 v.d.is_modulus := not d_in.insn(8);
                 v.d.is_32bit := d_in.insn(2);
                 if d_in.insn(8) = '1' then
@@ -364,11 +404,11 @@ begin
 		v.d.oe := decode_oe(d_in.decode.rc, d_in.insn);
 
 		-- load/store unit
-		v.l.update_reg := decoded_reg_a.reg;
+		v.l.update_reg := gspr_to_gpr(decoded_reg_a.reg);
 		v.l.addr1 := decoded_reg_a.data;
 		v.l.addr2 := decoded_reg_b.data;
 		v.l.data := decoded_reg_c.data;
-		v.l.write_reg := decode_output_reg(d_in.decode.output_reg_a, d_in.insn);
+		v.l.write_reg := gspr_to_gpr(decoded_reg_o.reg);
 
 		if d_in.decode.insn_type = OP_LOAD then
 			v.l.load := '1';
@@ -386,8 +426,8 @@ begin
 		control_valid_in <= d_in.valid;
 		control_sgl_pipe <= d_in.decode.sgl_pipe;
 
-		gpr_write_valid <= '1' when d_in.decode.output_reg_a /= NONE else '0';
+		gpr_write_valid <= decoded_reg_o.reg_valid;
-		gpr_write <= decode_output_reg(d_in.decode.output_reg_a, d_in.insn);
+		gpr_write <= decoded_reg_o.reg;
 
 		gpr_a_read_valid <= decoded_reg_a.reg_valid;
 		gpr_a_read <= decoded_reg_a.reg;
@@ -396,7 +436,7 @@ begin
 		gpr_b_read <= decoded_reg_b.reg;
 
 		gpr_c_read_valid <= decoded_reg_c.reg_valid;
-		gpr_c_read <= decoded_reg_c.reg;
+		gpr_c_read <= gspr_to_gpr(decoded_reg_c.reg);
 
                 cr_write_valid <= d_in.decode.output_cr or decode_rc(d_in.decode.rc, d_in.insn);
 

decode_types.vhdl

@@ -21,10 +21,10 @@ package decode_types is
 			 OP_TWI, OP_XOR, OP_SIM_CONFIG
 			 );
 
-    type input_reg_a_t is (NONE, RA, RA_OR_ZERO);
+    type input_reg_a_t is (NONE, RA, RA_OR_ZERO, SPR);
-    type input_reg_b_t is (NONE, RB, CONST_UI, CONST_SI, CONST_SI_HI, CONST_UI_HI, CONST_LI, CONST_BD, CONST_DS, CONST_M1, CONST_SH, CONST_SH32);
+    type input_reg_b_t is (NONE, RB, CONST_UI, CONST_SI, CONST_SI_HI, CONST_UI_HI, CONST_LI, CONST_BD, CONST_DS, CONST_M1, CONST_SH, CONST_SH32, SPR);
     type input_reg_c_t is (NONE, RS);
-    type output_reg_a_t is (NONE, RT, RA);
+    type output_reg_a_t is (NONE, RT, RA, SPR);
     type rc_t is (NONE, ONE, RC);
     type carry_in_t is (ZERO, CA, ONE);
 

execute1.vhdl

@@ -12,10 +12,11 @@ use work.ppc_fx_insns.all;
 
 entity execute1 is
     port (
-	clk   : in std_logic;
+	clk   : in std_ulogic;
 
 	-- asynchronous
 	flush_out : out std_ulogic;
+	stall_out : out std_ulogic;
 
 	e_in  : in Decode2ToExecute1Type;
 
@@ -32,6 +33,8 @@ end entity execute1;
 architecture behaviour of execute1 is
     type reg_type is record
 	e : Execute1ToWritebackType;
+	lr_update : std_ulogic;
+	next_lr : std_ulogic_vector(63 downto 0);
     end record;
 
     signal r, rin : reg_type;
@@ -125,6 +128,12 @@ begin
 	if rising_edge(clk) then
 	    r <= rin;
 	    ctrl <= ctrl_tmp;
+	    assert not (r.lr_update = '1' and e_in.valid = '1')
+		report "LR update collision with valid in EX1"
+		severity failure;
+	    if r.lr_update = '1' then
+		report "LR update to " & to_hstring(r.next_lr);
+	    end if;
 	end if;
     end process;
 
@@ -190,12 +199,15 @@ begin
 	    v.e.xerc := e_in.xerc;
 	end if;
 
+	v.lr_update := '0';
+
 	ctrl_tmp <= ctrl;
 	-- FIXME: run at 512MHz not core freq
 	ctrl_tmp.tb <= std_ulogic_vector(unsigned(ctrl.tb) + 1);
 
 	terminate_out <= '0';
 	icache_inval <= '0';
+	stall_out <= '0';
 	f_out <= Execute1ToFetch1TypeInit;
 
 	-- Next insn adder used in a couple of places
@@ -251,12 +263,15 @@ begin
 		    f_out.redirect_nia <= std_ulogic_vector(signed(e_in.nia) + signed(e_in.read_data2));
 		end if;
 	    when OP_BC =>
+		-- read_data1 is CTR
 		bo := insn_bo(e_in.insn);
 		bi := insn_bi(e_in.insn);
 		if bo(4-2) = '0' then
-		    ctrl_tmp.ctr <= std_ulogic_vector(unsigned(ctrl.ctr) - 1);
+		    result := std_ulogic_vector(unsigned(e_in.read_data1) - 1);
+		    result_en := '1';
+		    v.e.write_reg := fast_spr_num(SPR_CTR);
 		end if;
-		if ppc_bc_taken(bo, bi, e_in.cr, ctrl.ctr) = 1 then
+		if ppc_bc_taken(bo, bi, e_in.cr, e_in.read_data1) = 1 then
 		    f_out.redirect <= '1';
 		    if (insn_aa(e_in.insn)) then
 			f_out.redirect_nia <= std_ulogic_vector(signed(e_in.read_data2));
@@ -265,19 +280,18 @@ begin
 		    end if;
 		end if;
 	    when OP_BCREG =>
-                -- bits 10 and 6 distinguish between bclr, bcctr and bctar
+		-- read_data1 is CTR
+		-- read_data2 is target register (CTR, LR or TAR)
 		bo := insn_bo(e_in.insn);
 		bi := insn_bi(e_in.insn);
 		if bo(4-2) = '0' and e_in.insn(10) = '0' then
-		    ctrl_tmp.ctr <= std_ulogic_vector(unsigned(ctrl.ctr) - 1);
+		    result := std_ulogic_vector(unsigned(e_in.read_data1) - 1);
+		    result_en := '1';
+		    v.e.write_reg := fast_spr_num(SPR_CTR);
 		end if;
-		if ppc_bc_taken(bo, bi, e_in.cr, ctrl.ctr) = 1 then
+		if ppc_bc_taken(bo, bi, e_in.cr, e_in.read_data1) = 1 then
 		    f_out.redirect <= '1';
-		    if e_in.insn(10) = '0' then
+		    f_out.redirect_nia <= e_in.read_data2(63 downto 2) & "00";
-			f_out.redirect_nia <= ctrl.lr(63 downto 2) & "00";
-		    else
-			f_out.redirect_nia <= ctrl.ctr(63 downto 2) & "00";
-		    end if;
 		end if;
 	    when OP_CMPB =>
 		result := ppc_cmpb(e_in.read_data3, e_in.read_data2);
@@ -340,23 +354,24 @@ begin
 		    v.e.write_cr_data(hi downto lo) := newcrf;
 		end loop;
 	    when OP_MFSPR =>
-		case decode_spr_num(e_in.insn) is
+		if is_fast_spr(e_in.read_reg1) then
-		when SPR_XER =>
+		    result := e_in.read_data1;
-		    result := ( 63-32 => v.e.xerc.so,
+		    if decode_spr_num(e_in.insn) = SPR_XER then
-				63-33 => v.e.xerc.ov,
+			result(63-32) := v.e.xerc.so;
-				63-34 => v.e.xerc.ca,
+			result(63-33) := v.e.xerc.ov;
-				63-44 => v.e.xerc.ov32,
+			result(63-34) := v.e.xerc.ca;
-				63-45 => v.e.xerc.ca32,
+			result(63-35 downto 63-43) := "000000000";
-				others => '0');
+			result(63-44) := v.e.xerc.ov32;
-		when SPR_CTR =>
+			result(63-45) := v.e.xerc.ca32;
-		    result := ctrl.ctr;
+		    end if;
-		when SPR_LR =>
+		else
-		    result := ctrl.lr;
+		    case decode_spr_num(e_in.insn) is
-		when SPR_TB =>
+		    when SPR_TB =>
-		    result := ctrl.tb;
+			result := ctrl.tb;
-		when others =>
+		    when others =>
-		    result := (others => '0');
+			result := (others => '0');
-		end case;
+		    end case;
+		end if;
 		result_en := '1';
 	    when OP_MFCR =>
 		if e_in.insn(20) = '0' then
@@ -387,20 +402,25 @@ begin
 		end if;
 		v.e.write_cr_data := e_in.read_data3(31 downto 0);
 	    when OP_MTSPR =>
-		case decode_spr_num(e_in.insn) is
+		report "MTSPR to SPR " & integer'image(decode_spr_num(e_in.insn)) &
-		when SPR_XER =>
+		    "=" & to_hstring(e_in.read_data3);
-		    v.e.xerc.so := e_in.read_data3(63-32);
+		if is_fast_spr(e_in.write_reg) then
-		    v.e.xerc.ov := e_in.read_data3(63-33);
+		    result := e_in.read_data3;
-		    v.e.xerc.ca := e_in.read_data3(63-34);
+		    result_en := '1';
-		    v.e.xerc.ov32 := e_in.read_data3(63-44);
+		    if decode_spr_num(e_in.insn) = SPR_XER then
-		    v.e.xerc.ca32 := e_in.read_data3(63-45);
+			v.e.xerc.so := e_in.read_data3(63-32);
-		    v.e.write_xerc_enable := '1';
+			v.e.xerc.ov := e_in.read_data3(63-33);
-		when SPR_CTR =>
+			v.e.xerc.ca := e_in.read_data3(63-34);
-		    ctrl_tmp.ctr <= e_in.read_data3;
+			v.e.xerc.ov32 := e_in.read_data3(63-44);
-		when SPR_LR =>
+			v.e.xerc.ca32 := e_in.read_data3(63-45);
-		    ctrl_tmp.lr <= e_in.read_data3;
+			v.e.write_xerc_enable := '1';
-		when others =>
+		    end if;
-		end case;
+		else
+-- TODO: Implement slow SPRs	    
+--		    case decode_spr_num(e_in.insn) is
+--		    when others =>
+--		    end case;
+		end if;
 	    when OP_POPCNTB =>
 		result := ppc_popcntb(e_in.read_data3);
 		result_en := '1';
@@ -444,15 +464,36 @@ begin
 		report "illegal";
 	    end case;
 
+	    -- Update LR on the next cycle after a branch link
+	    --
+	    -- WARNING: The LR update isn't tracked by our hazard tracker. This
+	    --          will work (well I hope) because it only happens on branches
+	    --          which will flush all decoded instructions. By the time
+	    --          fetch catches up, we'll have the new LR. This will
+	    --          *not* work properly however if we have a branch predictor,
+	    --          in which case the solution would probably be to keep a
+	    --          local cache of the updated LR in execute1 (flushed on
+	    --          exceptions) that is used instead of the value from
+	    --          decode when its content is valid.
 	    if e_in.lr = '1' then
-		ctrl_tmp.lr <= next_nia;
+		v.lr_update := '1';
+		v.next_lr := next_nia;
+		v.e.valid := '0';
+		report "Delayed LR update to " & to_hstring(next_nia);
+		stall_out <= '1';
 	    end if;
-
+	elsif r.lr_update = '1' then
+	    result_en := '1';
+	    result := r.next_lr;
+	    v.e.write_reg := fast_spr_num(SPR_LR);
+	    v.e.write_len := x"8";
+	    v.e.sign_extend := '0';
+	    v.e.valid := '1';
 	end if;
 
 	v.e.write_data := result;
 	v.e.write_enable := result_en;
-	v.e.rc := e_in.rc;
+	v.e.rc := e_in.rc and e_in.valid;
 
 	-- Update registers
 	rin <= v;

gpr_hazard.vhdl

@@ -7,12 +7,13 @@ entity gpr_hazard is
         PIPELINE_DEPTH : natural := 2
         );
     port(
-        clk                : in std_logic;
+        clk                : in std_ulogic;
+	stall_in           : in std_ulogic;
 
         gpr_write_valid_in : in std_ulogic;
-        gpr_write_in       : in std_ulogic_vector(4 downto 0);
+        gpr_write_in       : in std_ulogic_vector(5 downto 0);
         gpr_read_valid_in  : in std_ulogic;
-        gpr_read_in        : in std_ulogic_vector(4 downto 0);
+        gpr_read_in        : in std_ulogic_vector(5 downto 0);
 
         stall_out          : out std_ulogic
         );
@@ -20,7 +21,7 @@ end entity gpr_hazard;
 architecture behaviour of gpr_hazard is
     type pipeline_entry_type is record
         valid : std_ulogic;
-        gpr   : std_ulogic_vector(4 downto 0);
+        gpr   : std_ulogic_vector(5 downto 0);
     end record;
     constant pipeline_entry_init : pipeline_entry_type := (valid => '0', gpr => (others => '0'));
 
@@ -32,7 +33,9 @@ begin
     gpr_hazard0: process(clk)
     begin
         if rising_edge(clk) then
-            r <= rin;
+	    if stall_in = '0' then
+		r <= rin;
+	    end if;
         end if;
     end process;
 

ppc_fx_insns.vhdl

@@ -94,7 +94,6 @@ package ppc_fx_insns is
 	function ppc_divwu (ra, rb: std_ulogic_vector(63 downto 0)) return std_ulogic_vector;
 
 	function ppc_bc_taken(bo, bi: std_ulogic_vector(4 downto 0); cr: std_ulogic_vector(31 downto 0); ctr: std_ulogic_vector(63 downto 0)) return integer;
-	function ppc_bcctr_taken(bo, bi: std_ulogic_vector(4 downto 0); cr: std_ulogic_vector(31 downto 0)) return integer;
 end package ppc_fx_insns;
 
 package body ppc_fx_insns is
@@ -809,21 +808,4 @@ package body ppc_fx_insns is
 		return ret;
 	end;
 
-	function ppc_bcctr_taken(bo, bi: std_ulogic_vector(4 downto 0); cr: std_ulogic_vector(31 downto 0)) return integer is
-		variable crfield: integer;
-		variable crbit_match: std_ulogic;
-		variable cond_ok: std_ulogic;
-		variable ret: integer;
-	begin
-		crfield := to_integer(unsigned(bi));
-		-- BE bit numbering
-		crbit_match := '1' when cr(31-crfield) = bo(4-1) else '0';
-		cond_ok := bo(4-0) or crbit_match;
-		if cond_ok = '1' then
-			ret := 1;
-		else
-			ret := 0;
-		end if;
-		return ret;
-	end;
 end package body ppc_fx_insns;

register_file.vhdl

@@ -23,7 +23,7 @@ entity register_file is
 end entity register_file;
 
 architecture behaviour of register_file is
-    type regfile is array(0 to 31) of std_ulogic_vector(63 downto 0);
+    type regfile is array(0 to 63) of std_ulogic_vector(63 downto 0);
     signal registers : regfile := (others => (others => '0'));
 begin
     -- synchronous writes
@@ -32,7 +32,11 @@ begin
         if rising_edge(clk) then
             if w_in.write_enable = '1' then
                 assert not(is_x(w_in.write_data)) and not(is_x(w_in.write_reg)) severity failure;
-                report "Writing GPR " & to_hstring(w_in.write_reg) & " " & to_hstring(w_in.write_data);
+		if w_in.write_reg(5) = '0' then
+		    report "Writing GPR " & to_hstring(w_in.write_reg) & " " & to_hstring(w_in.write_data);
+		else
+		    report "Writing GSPR " & to_hstring(w_in.write_reg) & " " & to_hstring(w_in.write_data);
+		end if;
                 registers(to_integer(unsigned(w_in.write_reg))) <= w_in.write_data;
             end if;
         end if;
@@ -52,7 +56,7 @@ begin
         end if;
         d_out.read1_data <= registers(to_integer(unsigned(d_in.read1_reg)));
         d_out.read2_data <= registers(to_integer(unsigned(d_in.read2_reg)));
-        d_out.read3_data <= registers(to_integer(unsigned(d_in.read3_reg)));
+        d_out.read3_data <= registers(to_integer(unsigned(gpr_to_gspr(d_in.read3_reg))));
 
         -- Forward any written data
         if w_in.write_enable = '1' then
@@ -62,7 +66,7 @@ begin
             if d_in.read2_reg = w_in.write_reg then
                 d_out.read2_data <= w_in.write_data;
             end if;
-            if d_in.read3_reg = w_in.write_reg then
+            if gpr_to_gspr(d_in.read3_reg) = w_in.write_reg then
                 d_out.read3_data <= w_in.write_data;
             end if;
         end if;

writeback.vhdl

@@ -126,7 +126,7 @@ begin
 	end if;
 
 	if l_in.write_enable = '1' then
-            w_out.write_reg <= l_in.write_reg;
+            w_out.write_reg <= gpr_to_gspr(l_in.write_reg);
             data_in <= l_in.write_data;
             data_len <= unsigned(l_in.write_len);
             byte_offset <= unsigned(l_in.write_shift);
@@ -144,7 +144,7 @@ begin
 
         if m_in.write_reg_enable = '1' then
             w_out.write_enable <= '1';
-            w_out.write_reg <= m_in.write_reg_nr;
+            w_out.write_reg <= gpr_to_gspr(m_in.write_reg_nr);
             data_in <= m_in.write_reg_data;
             rc <= m_in.rc;
 	    xe := m_in.xerc;
@@ -157,7 +157,7 @@ begin
 
         if d_in.write_reg_enable = '1' then
             w_out.write_enable <= '1';
-            w_out.write_reg <= d_in.write_reg_nr;
+            w_out.write_reg <= gpr_to_gspr(d_in.write_reg_nr);
             data_in <= d_in.write_reg_data;
             rc <= d_in.rc;
 	    xe := d_in.xerc;