Implement data storage interrupts

This adds a path from loadstore1 back to execute1 for reporting
errors, and machinery in execute1 for generating data storage
interrupts at vector 0x300.

If dcache is given two requests in successive cycles and the
first encounters an error (e.g. a TLB miss), it will now cancel
the second request.

Loadstore1 now responds to errors reported by dcache by sending
an exception signal to execute1 and returning to the idle state.
Execute1 then writes SRR0 and SRR1 and jumps to the 0x300 Data
Storage Interrupt vector.  DAR and DSISR are held in loadstore1.

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

common.vhdl

@@ -238,6 +238,10 @@ package common is
                                                                      reserve => '0', rc => '0', virt_mode => '0',
                                                                      spr_num => 0, others => (others => '0'));
 
+    type Loadstore1ToExecute1Type is record
+        exception : std_ulogic;
+    end record;
+
     type Loadstore1ToDcacheType is record
 	valid : std_ulogic;
 	load : std_ulogic;				-- is this a load

core.vhdl

@@ -63,6 +63,7 @@ architecture behave of core is
 
     -- load store signals
     signal execute1_to_loadstore1: Execute1ToLoadstore1Type;
+    signal loadstore1_to_execute1: Loadstore1ToExecute1Type;
     signal loadstore1_to_writeback: Loadstore1ToWritebackType;
 
     -- dcache signals
@@ -251,6 +252,7 @@ begin
 	    stall_out => ex1_stall_out,
             e_in => decode2_to_execute1,
             i_in => xics_in,
+            l_in => loadstore1_to_execute1,
             l_out => execute1_to_loadstore1,
             f_out => execute1_to_fetch1,
             e_out => execute1_to_writeback,
@@ -264,6 +266,7 @@ begin
             clk => clk,
             rst => core_rst,
             l_in => execute1_to_loadstore1,
+            e_out => loadstore1_to_execute1,
             l_out => loadstore1_to_writeback,
             d_out => loadstore1_to_dcache,
             d_in => dcache_to_loadstore1,

dcache.vhdl

@@ -147,6 +147,7 @@ architecture rtl of dcache is
     attribute ram_style of dtlb_ptes : signal is "distributed";
 
     signal r0 : Loadstore1ToDcacheType;
+    signal r0_valid : std_ulogic;
 
     -- Type of operation on a "valid" input
     type op_t is (OP_NONE,
@@ -406,6 +407,10 @@ begin
         end if;
     end process;
 
+    -- Hold off the request in r0 when stalling,
+    -- and cancel it if we get an error in a previous request.
+    r0_valid <= r0.valid and not stall_out and not r1.error_done;
+
     -- TLB
     -- Operates in the second cycle on the request latched in r0.
     -- TLB updates write the entry at the end of the second cycle.
@@ -478,7 +483,7 @@ begin
                 hit := '1';
             end if;
         end loop;
-        tlb_hit <= hit and r0.valid;
+        tlb_hit <= hit and r0_valid;
         tlb_hit_way <= hitway;
         pte <= read_tlb_pte(hitway, tlb_pte_way);
         valid_ra <= tlb_hit or not r0.virt_mode;
@@ -503,7 +508,7 @@ begin
             tlbie := '0';
             tlbia := '0';
             tlbwe := '0';
-            if r0.valid = '1' and stall_out = '0' and r0.tlbie = '1' then
+            if r0_valid = '1' and r0.tlbie = '1' then
                 if r0.addr(11 downto 10) /= "00" then
                     tlbia := '1';
                 elsif r0.addr(9) = '1' then
@@ -596,7 +601,7 @@ begin
         req_tag <= get_tag(ra);
 
         -- Only do anything if not being stalled by stage 1
-        go := r0.valid and not stall_out and not r0.tlbie;
+        go := r0_valid and not r0.tlbie;
 
         -- Calculate address of beginning of cache line, will be
         -- used for cache miss processing if needed
@@ -697,7 +702,7 @@ begin
         cancel_store <= '0';
         set_rsrv <= '0';
         clear_rsrv <= '0';
-        if stall_out = '0' and r0.valid = '1' and r0.reserve = '1' then
+        if r0_valid = '1' and r0.reserve = '1' then
             -- XXX generate alignment interrupt if address is not aligned
             -- XXX or if r0.nc = '1'
             if r0.load = '1' then
@@ -920,7 +925,7 @@ begin
             end if;
 
             -- complete tlbies in the third cycle
-            r1.tlbie_done <= r0.valid and r0.tlbie and not stall_out;
+            r1.tlbie_done <= r0_valid and r0.tlbie;
 	end if;
     end process;
 

execute1.vhdl

@@ -23,6 +23,7 @@ entity execute1 is
 	stall_out : out std_ulogic;
 
 	e_in  : in Decode2ToExecute1Type;
+        l_in  : in Loadstore1ToExecute1Type;
 
 	i_in : in XicsToExecute1Type;
 
@@ -51,6 +52,7 @@ architecture behaviour of execute1 is
 	slow_op_rc : std_ulogic;
 	slow_op_oe : std_ulogic;
 	slow_op_xerc : xer_common_t;
+        ldst_nia : std_ulogic_vector(63 downto 0);
     end record;
     constant reg_type_init : reg_type :=
         (e => Execute1ToWritebackInit, lr_update => '0',
@@ -446,9 +448,9 @@ begin
         v.e.exc_write_reg := fast_spr_num(SPR_SRR0);
         v.e.exc_write_data := e_in.nia;
 
-	if ctrl.irq_state = WRITE_SRR1 then
-	    v.e.exc_write_reg := fast_spr_num(SPR_SRR1);
-	    v.e.exc_write_data := ctrl.srr1;
+ 	if ctrl.irq_state = WRITE_SRR1 then
+ 	    v.e.exc_write_reg := fast_spr_num(SPR_SRR1);
+ 	    v.e.exc_write_data := ctrl.srr1;
             v.e.exc_write_enable := '1';
             ctrl_tmp.msr(MSR_SF) <= '1';
             ctrl_tmp.msr(MSR_EE) <= '0';
@@ -899,6 +901,7 @@ begin
 
         elsif e_in.valid = '1' then
             -- instruction for other units, i.e. LDST
+            v.ldst_nia := e_in.nia;
             v.e.valid := '0';
             if e_in.unit = LDST then
                 lv.valid := '1';
@@ -969,6 +972,17 @@ begin
 	v.e.write_data := result;
 	v.e.write_enable := result_en;
 
+        -- generate DSI for load/store exceptions
+        if l_in.exception = '1' then
+            ctrl_tmp.irq_nia <= std_logic_vector(to_unsigned(16#300#, 64));
+            ctrl_tmp.srr1 <= msr_copy(ctrl.msr);
+            v.e.exc_write_enable := '1';
+            v.e.exc_write_reg := fast_spr_num(SPR_SRR0);
+            v.e.exc_write_data := r.ldst_nia;
+            ctrl_tmp.irq_state <= WRITE_SRR1;
+            v.e.valid := '1';   -- complete the original load or store
+        end if;
+
         -- Outputs to loadstore1 (async)
         lv.op := e_in.insn_type;
         lv.addr1 := a_in;

loadstore1.vhdl

@@ -16,6 +16,7 @@ entity loadstore1 is
         rst   : in std_ulogic;
 
         l_in  : in Execute1ToLoadstore1Type;
+        e_out : out Loadstore1ToExecute1Type;
         l_out : out Loadstore1ToWritebackType;
 
         d_out : out Loadstore1ToDcacheType;
@@ -142,6 +143,9 @@ begin
         variable mfspr : std_ulogic;
         variable sprn : std_ulogic_vector(9 downto 0);
         variable sprval : std_ulogic_vector(63 downto 0);
+        variable exception : std_ulogic;
+        variable next_addr : std_ulogic_vector(63 downto 0);
+        variable dsisr : std_ulogic_vector(31 downto 0);
     begin
         v := r;
         req := '0';
@@ -151,6 +155,8 @@ begin
         addr := lsu_sum;
         mfspr := '0';
         sprval := (others => '0');      -- avoid inferred latches
+        exception := '0';
+        dsisr := (others => '0');
 
         write_enable := '0';
         do_update := '0';
@@ -204,6 +210,9 @@ begin
             end case;
         end loop;
 
+        -- compute (addr + 8) & ~7 for the second doubleword when unaligned
+        next_addr := std_ulogic_vector(unsigned(r.addr(63 downto 3)) + 1) & "000";
+
         case r.state is
         when IDLE =>
             if l_in.valid = '1' then
@@ -301,8 +310,7 @@ begin
             end if;
 
         when SECOND_REQ =>
-            -- compute (addr + 8) & ~7 for the second doubleword when unaligned
-            addr := std_ulogic_vector(unsigned(r.addr(63 downto 3)) + 1) & "000";
+            addr := next_addr;
             byte_sel := r.second_bytes;
             req := '1';
             stall := '1';
@@ -311,25 +319,43 @@ begin
         when FIRST_ACK_WAIT =>
             stall := '1';
             if d_in.valid = '1' then
-                v.state := LAST_ACK_WAIT;
-                if r.load = '1' then
-                    v.load_data := data_permuted;
+                if d_in.error = '1' then
+                    -- dcache will discard the second request
+                    exception := '1';
+                    dsisr(30) := d_in.tlb_miss;
+                    v.state := IDLE;
+                else
+                    v.state := LAST_ACK_WAIT;
+                    if r.load = '1' then
+                        v.load_data := data_permuted;
+                    end if;
                 end if;
             end if;
 
         when LAST_ACK_WAIT =>
             stall := '1';
             if d_in.valid = '1' then
-                write_enable := r.load;
-                if r.load = '1' and r.update = '1' then
-                    -- loads with rA update need an extra cycle
-                    v.state := LD_UPDATE;
-                else
-                    -- stores write back rA update in this cycle
-                    do_update := r.update;
-                    stall := '0';
-                    done := '1';
+                if d_in.error = '1' then
+                    if two_dwords = '1' then
+                        addr := next_addr;
+                    else
+                        addr := r.addr;
+                    end if;
+                    exception := '1';
+                    dsisr(30) := d_in.tlb_miss;
                     v.state := IDLE;
+                else
+                    write_enable := r.load;
+                    if r.load = '1' and r.update = '1' then
+                        -- loads with rA update need an extra cycle
+                        v.state := LD_UPDATE;
+                    else
+                        -- stores write back rA update in this cycle
+                        do_update := r.update;
+                        stall := '0';
+                        done := '1';
+                        v.state := IDLE;
+                    end if;
                 end if;
             end if;
 
@@ -372,6 +398,13 @@ begin
         l_out.rc <= r.rc and done;
         l_out.store_done <= d_in.store_done;
 
+        -- update exception info back to execute1
+        e_out.exception <= exception;
+        if exception = '1' then
+            v.dar := addr;
+            v.dsisr := dsisr;
+        end if;
+
         stall_out <= stall;
 
         -- Update registers