From: Paul Mackerras <paulus@ozlabs.org>
Date: Mon, 13 Jul 2020 07:43:52 +0000 (+1000)
Subject: loadstore1: Separate address calculation for MMU to ease timing
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=b80e81e1234022c9c22725489b5031dc6e6b06ab;p=microwatt.git

loadstore1: Separate address calculation for MMU to ease timing

This computes the address sent to the MMU separately from that sent
to the dcache.  This means that the address sent to the MMU doesn't
have the delay through the lsu_sum adder, making it available earlier.
The path through the lsu_sum adder and through the MMU to the MMU
done and err outputs showed up as a critical path on some builds.

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

diff --git a/loadstore1.vhdl b/loadstore1.vhdl
index 660e6c0..16df9b1 100644
--- a/loadstore1.vhdl
+++ b/loadstore1.vhdl
@@ -152,6 +152,7 @@ begin
         variable req : std_ulogic;
         variable busy : std_ulogic;
         variable addr : std_ulogic_vector(63 downto 0);
+        variable maddr : std_ulogic_vector(63 downto 0);
         variable wdata : std_ulogic_vector(63 downto 0);
         variable write_enable : std_ulogic;
         variable do_update : std_ulogic;
@@ -173,6 +174,7 @@ begin
         req := '0';
         byte_sel := (others => '0');
         addr := lsu_sum;
+        maddr := l_in.addr2;    -- address from RB for tlbie
         v.mfspr := '0';
         mmu_mtspr := '0';
         itlb_fault := '0';
@@ -260,9 +262,9 @@ begin
                 -- dcache will discard the second request if it
                 -- gets an error on the 1st of two requests
                 if r.dwords_done = '1' then
-                    addr := next_addr;
+                    maddr := next_addr;
                 else
-                    addr := r.addr;
+                    maddr := r.addr;
                 end if;
                 if d_in.cache_paradox = '1' then
                     -- signal an interrupt straight away
@@ -427,8 +429,7 @@ begin
                     end if;
                 when OP_FETCH_FAILED =>
                     -- send it to the MMU to do the radix walk
-                    addr := l_in.nia;
-                    v.addr := l_in.nia;
+                    maddr := l_in.nia;
                     v.instr_fault := '1';
                     mmureq := '1';
                     v.state := MMU_LOOKUP;
@@ -490,7 +491,7 @@ begin
         m_out.tlbie <= v.tlbie;
         m_out.mtspr <= mmu_mtspr;
         m_out.sprn <= sprn;
-        m_out.addr <= addr;
+        m_out.addr <= maddr;
         m_out.slbia <= l_in.insn(7);
         m_out.rs <= l_in.data;