dcache: Ease timing on calculation of acks remaining

This moves the incrementing or decrementing of r1.acks_pending
to the cycle after a strobe is output or an ack is seen on the
wishbone, and simplifies the logic that determines whether the
cycle is now complete.  This means that the path from seeing
req_op equal to OP_STORE_HIT or OP_STORE_MISS to setting r1.state
and r1.cyc now just involves the stbs_done bit rather than a more
complex calculation involving the possibly incremented r1.acks_pending.

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

diff --git a/dcache.vhdl b/dcache.vhdl
index 5cbc9100a2f724916c37f378ff014290878b7f36..a24dc15af28a403671133f9c3dede98d2d838019 100644 (file)
--- a/dcache.vhdl
+++ b/dcache.vhdl
@@ -282,6 +282,8 @@ architecture rtl of dcache is
         end_row_ix       : row_in_line_t;
         rows_valid       : row_per_line_valid_t;
         acks_pending     : unsigned(2 downto 0);
+        inc_acks         : std_ulogic;
+        dec_acks         : std_ulogic;
 
         -- Signals to complete (possibly with error)
         ls_valid         : std_ulogic;
@@ -1209,6 +1211,8 @@ begin
                -- One cycle pulses reset
                r1.slow_valid <= '0';
                 r1.write_bram <= '0';
+                r1.inc_acks <= '0';
+                r1.dec_acks <= '0';
 
                 r1.ls_valid <= '0';
                 -- complete tlbies and TLB loads in the third cycle
@@ -1409,6 +1413,14 @@ begin
                 when STORE_WAIT_ACK =>
                    stbs_done := r1.wb.stb = '0';
                     acks := r1.acks_pending;
+                    if r1.inc_acks /= r1.dec_acks then
+                        if r1.inc_acks = '1' then
+                            acks := acks + 1;
+                        else
+                            acks := acks - 1;
+                        end if;
+                    end if;
+                    r1.acks_pending <= acks;
                    -- Clear stb when slave accepted request
                     if wishbone_in.stall = '0' then
                         -- See if there is another store waiting to be done
@@ -1430,7 +1442,8 @@ begin
                             r1.slow_valid <= '1';
                             -- Store requests never come from the MMU
                             r1.ls_valid <= '1';
-                            acks := acks + 1;
+                            stbs_done := false;
+                            r1.inc_acks <= '1';
                         else
                             r1.wb.stb <= '0';
                             stbs_done := true;
@@ -1444,9 +1457,8 @@ begin
                             r1.wb.cyc <= '0';
                             r1.wb.stb <= '0';
                         end if;
-                        acks := acks - 1;
+                        r1.dec_acks <= '1';
                    end if;
-                    r1.acks_pending <= acks;
 
                 when NC_LOAD_WAIT_ACK =>
                    -- Clear stb when slave accepted request