From 7492a3533c61a6999d36df687c8d5e6e3603b0d6 Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Wed, 17 Nov 2021 18:01:27 +0000
Subject: [PATCH] reading of regfile bitvector added, which activates on a
 per-FU basis at the regfile read port

this is somewhat complete overkill because strictly speaking the
read should be done at issue time.  fortunately, merging of lots of ORs
results in the exact same thing, just distributed

horribly inefficient though
---
 src/soc/simple/core.py | 45 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 5 deletions(-)

diff --git a/src/soc/simple/core.py b/src/soc/simple/core.py
index a95a7fcd..92d73764 100644
--- a/src/soc/simple/core.py
+++ b/src/soc/simple/core.py
@@ -174,10 +174,12 @@ class NonProductionCore(ControlBase):
         # ssh, cheat: trap uses the main decoder because of the rewriting
         self.des[self.trapunit] = self.i.e.do
 
-        # connect up Function Units, then read/write ports
-        fu_bitdict, fu_selected = self.connect_instruction(m)
-        self.connect_rdports(m, fu_selected)
+        # connect up Function Units, then read/write ports, and hazard conflict
+        issue_conflict = Signal()
+        fu_bitdict, fu_selected = self.connect_instruction(m, issue_conflict)
+        raw_hazard = self.connect_rdports(m, fu_selected)
         self.connect_wrports(m, fu_selected)
+        comb += issue_conflict.eq(raw_hazard)
 
         # note if an exception happened.  in a pipelined or OoO design
         # this needs to be accompanied by "shadowing" (or stalling)
@@ -213,7 +215,7 @@ class NonProductionCore(ControlBase):
                         comb += v.use_svp64_ldst_dec.eq(
                                         self.i.use_svp64_ldst_dec)
 
-    def connect_instruction(self, m):
+    def connect_instruction(self, m, issue_conflict):
         """connect_instruction
 
         uses decoded (from PowerOp) function unit information from CSV files
@@ -351,6 +353,11 @@ class NonProductionCore(ControlBase):
         print("read regfile", rpidx, regfile, regs.rf.keys(),
                               rfile, rfile.unary)
 
+        # for checking if the read port has an outstanding write
+        if self.make_hazard_vecs:
+            wv = regs.wv[regfile.lower()]
+            wvchk = wv.r_ports["issue"] # write-vec bit-level hazard check
+
         fspecs = fspec
         if not isinstance(fspecs, list):
             fspecs = [fspecs]
@@ -425,6 +432,20 @@ class NonProductionCore(ControlBase):
                     # all FUs connect to same port
                     comb += src.eq(rport.o_data)
 
+                if not self.make_hazard_vecs:
+                    continue
+
+                # read the write-hazard bitvector (wv) for any bit that is
+                wvchk_en = Signal(len(wvchk.ren), name="wv_chk_addr_en_"+name)
+                issue_active = Signal(name="rd_iactive_"+name)
+                comb += issue_active.eq(fu.issue_i & rdflags[i])
+                with m.If(issue_active):
+                    if rfile.unary:
+                        comb += wvchk_en.eq(reads[i])
+                    else:
+                        comb += wvchk_en.eq(1<<reads[i])
+                wvens.append(wvchk_en)
+
         # or-reduce the muxed read signals
         if rfile.unary:
             # for unary-addressed
@@ -435,6 +456,16 @@ class NonProductionCore(ControlBase):
             comb += rport.ren.eq(Cat(*rens).bool())
             print ("binary", regfile, rpidx, rport, rport.ren, rens, addrs)
 
+        if not self.make_hazard_vecs:
+            return Const(0) # declare "no hazards"
+
+        # enable the read bitvectors for this issued instruction
+        # and return whether any write-hazard bit is set
+        comb += wvchk.ren.eq(ortreereduce_sig(wvens))
+        hazard_detected = Signal(name="raw_%s_%s" % (regfile, rpidx))
+        comb += hazard_detected.eq(wvchk.o_data.bool())
+        return hazard_detected
+
     def connect_rdports(self, m, fu_bitdict):
         """connect read ports
 
@@ -445,6 +476,7 @@ class NonProductionCore(ControlBase):
         comb, sync = m.d.comb, m.d.sync
         fus = self.fus.fus
         regs = self.regs
+        rd_hazard = []
 
         # dictionary of lists of regfile read ports
         byregfiles_rd, byregfiles_rdspec = self.get_byregfiles(True)
@@ -473,8 +505,11 @@ class NonProductionCore(ControlBase):
             # for each named regfile port, connect up all FUs to that port
             for (regname, fspec) in sort_fuspecs(fuspecs):
                 print("connect rd", regname, fspec)
-                self.connect_rdport(m, fu_bitdict, rdpickers, regfile,
+                rh = self.connect_rdport(m, fu_bitdict, rdpickers, regfile,
                                        regname, fspec)
+                #rd_hazard.append(rh)
+
+        return Cat(*rd_hazard).bool()
 
     def make_hazards(self, m, regfile, rfile, wvclr, wvset,
                     funame, regname, idx,
-- 
2.30.2