From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Wed, 12 Jan 2022 12:11:12 +0000 (+0000)
Subject: dcache 2nd stage (r1) should only indicate not-busy
X-Git-Url: https://git.libre-soc.org/?p=soc.git;a=commitdiff_plain;h=a03aefb1e8ae7d6110a328b57f1336890ebee469

dcache 2nd stage (r1) should only indicate not-busy
(r1.full) when all the ACKs of a cache-line fill have been processed
doing this too early results in r0 being pushed into r1 whilst
ACKs are still outstanding, and their completion corrupts the
operation that should not have been put into r1 in the first place
---

diff --git a/src/soc/experiment/dcache.py b/src/soc/experiment/dcache.py
index 374297ba..e8e0f077 100644
--- a/src/soc/experiment/dcache.py
+++ b/src/soc/experiment/dcache.py
@@ -1550,7 +1550,6 @@ class DCache(Elaboratable):
                               ((r1.dcbz & r1.req.dcbz) |
                                (~r1.dcbz & (r1.req.op == Op.OP_LOAD_MISS))) &
                                 (r1.store_row == get_row(req.real_addr))):
-                        sync += r1.full.eq(0)
                         sync += r1.slow_valid.eq(1)
                         with m.If(r1.mmu_req):
                             sync += r1.mmu_done.eq(1)
@@ -1571,6 +1570,8 @@ class DCache(Elaboratable):
                         comb += cv.bit_select(r1.store_way, 1).eq(1)
                         sync += cache_tags[r1.store_index].valid.eq(cv)
 
+                        # return to idle and indicate r1 stage no longer busy
+                        sync += r1.full.eq(0)
                         sync += r1.state.eq(State.IDLE)
                         sync += Display("cache valid set %x "
                                         "idx %d way %d",
@@ -1613,7 +1614,6 @@ class DCache(Elaboratable):
 
                         with m.If(req.op == Op.OP_STORE_HIT):
                             sync += r1.write_bram.eq(1)
-                        sync += r1.full.eq(0)
                         sync += r1.slow_valid.eq(1)
 
                         # Store requests never come from the MMU
@@ -1629,9 +1629,12 @@ class DCache(Elaboratable):
                                 bus.ack, bus.ack, st_stbs_done, adjust_acks)
                 with m.If(bus.ack):
                     with m.If(st_stbs_done & (adjust_acks == 1)):
+                        # all done, r1 no longer busy, return to idle
+                        sync += r1.full.eq(0)
                         sync += r1.state.eq(State.IDLE)
                         sync += r1.wb.cyc.eq(0)
                         sync += r1.wb.stb.eq(0)
+                    # decrement the number of acks expected
                     sync += r1.dec_acks.eq(1)
 
             with m.Case(State.NC_LOAD_WAIT_ACK):