execute1: Implement trap instructions properly

This implements the trap instructions (tw, twi, td, tdi) using
much of the same code as is used for the cmp/cmpl instructions.
A 5-bit comparison value is generated, and for cmp/cmpl, the
appropriate 3 bits are used to update the destination CR, and for
trap instructions, the comparison value is ANDed with the TO
field, and an exception is generated if any bit of the result
is 1.

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

execute1.vhdl

@@ -238,6 +238,7 @@ begin
 	variable irq_valid : std_ulogic;
 	variable exception : std_ulogic;
         variable exception_nextpc : std_ulogic;
+        variable trapval : std_ulogic_vector(4 downto 0);
     begin
 	result := (others => '0');
 	result_with_carry := (others => '0');
@@ -446,7 +447,7 @@ begin
 		report "ATTN";
 	    when OP_NOP =>
 		-- Do nothing
-	    when OP_ADD | OP_CMP =>
+	    when OP_ADD | OP_CMP | OP_TRAP =>
 		if e_in.invert_a = '0' then
 		    a_inv := a_in;
 		else
@@ -468,18 +469,18 @@ begin
                     end if;
                     result_en := '1';
                 else
-                    -- CMP and CMPL instructions
+                    -- trap, CMP and CMPL instructions
                     -- Note, we have done RB - RA, not RA - RB
-                    bf := insn_bf(e_in.insn);
+                    if e_in.insn_type = OP_CMP then
                         l := insn_l(e_in.insn);
-                    v.e.write_cr_enable := '1';
+                    else
-                    crnum := to_integer(unsigned(bf));
+                        l := not e_in.is_32bit;
-                    v.e.write_cr_mask := num_to_fxm(crnum);
+                    end if;
                     zerolo := not (or (a_in(31 downto 0) xor b_in(31 downto 0)));
                     zerohi := not (or (a_in(63 downto 32) xor b_in(63 downto 32)));
                     if zerolo = '1' and (l = '0' or zerohi = '1') then
                         -- values are equal
-                        newcrf := "001" & v.e.xerc.so;
+                        trapval := "00100";
                     else
                         if l = '1' then
                             -- 64-bit comparison
@@ -494,19 +495,41 @@ begin
                             -- Subtraction might overflow, but
                             -- comparison is clear from MSB difference.
                             -- for signed, 0 is greater; for unsigned, 1 is greater
-                            a_lt := msb_a xnor e_in.is_signed;
+                            trapval := msb_a & msb_b & '0' & msb_b & msb_a;
                         else
                             -- Subtraction cannot overflow since MSBs are equal.
                             -- carry = 1 indicates RA is smaller (signed or unsigned)
                             a_lt := (not l and carry_32) or (l and carry_64);
+                            trapval := a_lt & not a_lt & '0' & a_lt & not a_lt;
+                        end if;
                     end if;
-                        newcrf := a_lt & not a_lt & '0' & v.e.xerc.so;
+                    if e_in.insn_type = OP_CMP then
+                        if e_in.is_signed = '1' then
+                            newcrf := trapval(4 downto 2) & v.e.xerc.so;
+                        else
+                            newcrf := trapval(1 downto 0) & trapval(2) & v.e.xerc.so;
                         end if;
+                        bf := insn_bf(e_in.insn);
+                        crnum := to_integer(unsigned(bf));
+                        v.e.write_cr_enable := '1';
+                        v.e.write_cr_mask := num_to_fxm(crnum);
                         for i in 0 to 7 loop
                             lo := i*4;
                             hi := lo + 3;
                             v.e.write_cr_data(hi downto lo) := newcrf;
                         end loop;
+                    else
+                        -- trap instructions (tw, twi, td, tdi)
+                        if or (trapval and insn_to(e_in.insn)) = '1' then
+                            -- generate trap-type program interrupt
+                            exception := '1';
+                            ctrl_tmp.irq_nia <= std_logic_vector(to_unsigned(16#700#, 64));
+                            ctrl_tmp.srr1 <= msr_copy(ctrl.msr);
+                            -- set bit 46 to say trap occurred
+                            ctrl_tmp.srr1(63 - 46) <= '1';
+                            report "trap";
+                        end if;
+                    end if;
                 end if;
 	    when OP_AND | OP_OR | OP_XOR =>
 		result := logical_result;
@@ -726,17 +749,6 @@ begin
 		result := x"0000000000000000";
 		result_en := '1';
 
-	    when OP_TRAP =>
-                -- For now, generate a program interrupt if the TO field is all 1s
-                if insn_to(e_in.insn) = "11111" then
-                    exception := '1';
-                    ctrl_tmp.irq_nia <= std_logic_vector(to_unsigned(16#700#, 64));
-                    ctrl_tmp.srr1 <= msr_copy(ctrl.msr);
-                    -- set bit 46 to say a trap occurred
-                    ctrl_tmp.srr1(63 - 46) <= '1';
-                    report "trap";
-                end if;
-
 	    when OP_ISYNC =>
 		f_out.redirect <= '1';
 		f_out.redirect_nia <= next_nia;