From 0212cec833e9b0e72192ea96c69ccf9f7b3cec6d Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Tue, 30 Nov 2021 14:05:38 +0000
Subject: [PATCH] fix read-decode information by latching not just the read reg
 number but *whether it is valid or not*. not only the register *number* from
 regspec_decode_read() needs to be captured but its ok (valid) flag as well

this error only showed up when a mul (2-operand) was followed by addi
(1-operand).  the mul had its 2nd operand dropped on the floor because
the *addi* only has one operand.
---
 src/soc/simple/core.py | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/soc/simple/core.py b/src/soc/simple/core.py
index debff9da..f24bcaa8 100644
--- a/src/soc/simple/core.py
+++ b/src/soc/simple/core.py
@@ -482,10 +482,10 @@ class NonProductionCore(ControlBase):
                 (fspec.rdport, fspec.wrport, fspec.read, fspec.write,
                  fspec.wid, fspec.specs)
             print ("fpsec", i, fspec, len(fuspecs))
+            name = "%s_%s_%d" % (regfile, regname, i)
             ppoffs.append(pplen) # record offset for picker
             pplen += len(fspec.specs)
-            name = "rdflag_%s_%s_%d" % (regfile, regname, i)
-            rdflag = Signal(name=name, reset_less=True)
+            rdflag = Signal(name="rdflag_"+name, reset_less=True)
             comb += rdflag.eq(fspec.rdport)
             rdflags.append(rdflag)
 
@@ -513,21 +513,29 @@ class NonProductionCore(ControlBase):
                 fu_issued = fu_bitdict[funame]
 
                 # get (or set up) a latched copy of read register number
+                # and (sigh) also the read-ok flag
                 rname = "%s_%s_%s_%d" % (funame, regfile, regname, pi)
                 read = Signal.like(_read, name="read_"+name)
+                rdflag = Signal(name="rdflag_"+rname, reset_less=True)
                 if rname not in fu.rd_latches:
                     rdl = Signal.like(_read, name="rdlatch_"+rname)
+                    rfl = Signal(name="rdflag_latch_"+rname)
                     fu.rd_latches[rname] = rdl
+                    fu.rf_latches[rname] = rfl
                     with m.If(fu.issue_i):
                         sync += rdl.eq(_read)
+                        sync += rfl.eq(rdflags[i])
                 else:
                     rdl = fu.rd_latches[rname]
+                    rfl = fu.rf_latches[rname]
                 # latch to make the read immediately available on issue cycle
                 # after the read cycle, use the latched copy
                 with m.If(fu.issue_i):
                     comb += read.eq(_read)
+                    comb += rdflag.eq(rdflags[i])
                 with m.Else():
                     comb += read.eq(rdl)
+                    comb += rdflag.eq(rfl)
 
                 # connect request-read to picker input, and output to go-rd
                 addr_en = Signal.like(read, name="addr_en_"+name)
@@ -538,7 +546,7 @@ class NonProductionCore(ControlBase):
 
                 # exclude any currently-enabled read-request (mask out active)
                 # entirely block anything hazarded from being picked
-                comb += pick.eq(fu.rd_rel_o[idx] & fu_active & rdflags[i] &
+                comb += pick.eq(fu.rd_rel_o[idx] & fu_active & rdflag &
                                 ~delay_pick & ~rhazard)
                 comb += rdpick.i[pi].eq(pick)
                 comb += fu.go_rd_i[idx].eq(delay_pick) # pass in *delayed* pick
@@ -1022,7 +1030,8 @@ class NonProductionCore(ControlBase):
             # the issue there is that this function is actually better
             # suited at the moment
             if readmode:
-                fu.rd_latches = {}
+                fu.rd_latches = {} # read reg number latches
+                fu.rf_latches = {} # read flag latches
             else:
                 fu.wr_latches = {}
 
-- 
2.30.2