Decode sc in the major opcode decode table

This decodes sc using entry 17 of the major_decode_rom_array table
instead of a special case in the decode1_1 process.  This means that
only the major opcode (the top 6 bits) is checked at decode time.
To make sure that the instruction is sc not scv, we now check bit
1 of the instruction at execute time and generate an illegal
instruction interrupt if it is 0 (indicating scv).  The level field
of the sc instruction is now ignored.

This reduces LUT consumption by 31 LUTs on the Arty A7-100.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

decode1.vhdl

@@ -60,6 +60,7 @@ architecture behaviour of decode1 is
 		20 =>       (ALU,    OP_RLC,       RA,         CONST_SH32,  RS,   RA,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC,   '0', '0'), -- rlwimi
 		21 =>       (ALU,    OP_RLC,       NONE,       CONST_SH32,  RS,   RA,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC,   '0', '0'), -- rlwinm
 		23 =>       (ALU,    OP_RLC,       NONE,       RB,          RS,   RA,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC,   '0', '0'), -- rlwnm
+                17 =>       (ALU,    OP_SC,        NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- sc
 		38 =>       (LDST,   OP_STORE,     RA_OR_ZERO, CONST_SI,    RS,   NONE, '0', '0', '0', '0', ZERO, '0', is1B, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- stb
 		39 =>       (LDST,   OP_STORE,     RA_OR_ZERO, CONST_SI,    RS,   NONE, '0', '0', '0', '0', ZERO, '0', is1B, '0', '0', '1', '0', '0', '0', NONE, '0', '0'), -- stbu
 		44 =>       (LDST,   OP_STORE,     RA_OR_ZERO, CONST_SI,    RS,   NONE, '0', '0', '0', '0', ZERO, '0', is2B, '0', '0', '0', '0', '0', '0', NONE, '0', '0'), -- sth
@@ -344,7 +345,6 @@ architecture behaviour of decode1 is
         --                                                      op                                           in   out   A   out  in    out  len        ext                                 pipe
         constant attn_instr    : decode_rom_t := (ALU,    OP_ATTN,      NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1');
 	constant nop_instr     : decode_rom_t := (ALU,    OP_NOP,       NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0');
-	constant sc_instr     :  decode_rom_t := (ALU,    OP_SC,        NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '0');
 
 begin
 	decode1_0: process(clk)
@@ -402,9 +402,6 @@ begin
                 elsif std_match(f_in.insn, "01100000000000000000000000000000") then
                         report "PPC_nop";
                         v.decode := nop_instr;
-                elsif std_match(f_in.insn, "010001--------------0000000---1-") then
-                        report "PPC_sc";
-                        v.decode := sc_instr;
                 elsif std_match(f_in.insn, "000000---------------0100000000-") then
                         report "PPC_attn";
                         v.decode := attn_instr;

execute1.vhdl

@@ -239,6 +239,7 @@ begin
 	variable exception : std_ulogic;
         variable exception_nextpc : std_ulogic;
         variable trapval : std_ulogic_vector(4 downto 0);
+        variable illegal : std_ulogic;
     begin
 	result := (others => '0');
 	result_with_carry := (others => '0');
@@ -388,6 +389,7 @@ begin
 
 	ctrl_tmp.irq_state <= WRITE_SRR0;
 	exception := '0';
+        illegal := '0';
         exception_nextpc := '0';
         v.e.exc_write_enable := '0';
         v.e.exc_write_reg := fast_spr_num(SPR_SRR0);
@@ -426,22 +428,21 @@ begin
 	    when OP_ILLEGAL =>
 		-- we need two cycles to write srr0 and 1
 		-- will need more when we have to write DSISR, DAR and HIER
-		exception := '1';
+		illegal := '1';
-		ctrl_tmp.irq_nia <= std_logic_vector(to_unsigned(16#700#, 64));
-		ctrl_tmp.srr1 <= msr_copy(ctrl.msr);
-		-- Since we aren't doing Hypervisor emulation assist (0xe40) we
-		-- set bit 44 to indicate we have an illegal
-		ctrl_tmp.srr1(63 - 44) <= '1';
-		report "illegal";
 	    when OP_SC =>
-		-- FIXME Assume everything is SC (not SCV) for now
+		-- check bit 1 of the instruction is 1 so we know this is sc;
+                -- 0 would mean scv, so generate an illegal instruction interrupt
 		-- we need two cycles to write srr0 and 1
 		-- will need more when we have to write DSISR, DAR and HIER
+                if e_in.insn(1) = '1' then
                     exception := '1';
                     exception_nextpc := '1';
                     ctrl_tmp.irq_nia <= std_logic_vector(to_unsigned(16#C00#, 64));
                     ctrl_tmp.srr1 <= msr_copy(ctrl.msr);
                     report "sc";
+                else
+                    illegal := '1';
+                end if;
 	    when OP_ATTN =>
 		terminate_out <= '1';
 		report "ATTN";
@@ -836,6 +837,15 @@ begin
 	    end if;
 	end if;
 
+        if illegal = '1' then
+            exception := '1';
+            ctrl_tmp.irq_nia <= std_logic_vector(to_unsigned(16#700#, 64));
+            ctrl_tmp.srr1 <= msr_copy(ctrl.msr);
+            -- Since we aren't doing Hypervisor emulation assist (0xe40) we
+            -- set bit 44 to indicate we have an illegal
+            ctrl_tmp.srr1(63 - 44) <= '1';
+            report "illegal";
+        end if;
 	if exception = '1' then
             v.e.exc_write_enable := '1';
             if exception_nextpc = '1' then