From 043666672d5ebb20945b0b76d3b0ac89c749841c Mon Sep 17 00:00:00 2001
From: Florent Kermarrec <florent@enjoy-digital.fr>
Date: Tue, 24 Mar 2020 14:38:58 +0100
Subject: [PATCH] phy/gensdrphy: sample rddata on sys_clk (assume clk generated
 to sdram is shifted), add cmd_latency parameter and simplify control logic.

---
 litedram/phy/gensdrphy.py | 34 +++++++++++-----------------------
 1 file changed, 11 insertions(+), 23 deletions(-)

diff --git a/litedram/phy/gensdrphy.py b/litedram/phy/gensdrphy.py
index f80c39d..3616726 100644
--- a/litedram/phy/gensdrphy.py
+++ b/litedram/phy/gensdrphy.py
@@ -1,18 +1,7 @@
-# This file is Copyright (c) 2012-2019 Florent Kermarrec <florent@enjoy-digital.fr>
+# This file is Copyright (c) 2012-2020 Florent Kermarrec <florent@enjoy-digital.fr>
 # License: BSD
 
 # 1:1 frequency-ratio Generic SDR PHY
-#
-# The SDR PHY needs 2 Clock domains:
-#  - sys_clk    : The System Clock domain
-#  - sys_clk_ps : The System Clock domain with its phase shifted by -3ns at 100Mhz
-#
-# Assert dfi_wrdata_en and present the data on dfi_wrdata_mask/dfi_wrdata in the
-# same cycle as the write command.
-#
-# Assert dfi_rddata_en in the same cycle as the read command. The data will come
-# back on dfi_rddata 4 cycles later, along with the assertion of dfi_rddata_valid.
-#
 
 from migen import *
 from migen.genlib.record import *
@@ -24,12 +13,13 @@ from litedram.phy.dfi import *
 # Generic SDR PHY ----------------------------------------------------------------------------------
 
 class GENSDRPHY(Module):
-    def __init__(self, pads, cl=2):
+    def __init__(self, pads, cl=2, cmd_latency=1):
         pads        = PHYPadsCombiner(pads)
         addressbits = len(pads.a)
         bankbits    = len(pads.ba)
         nranks      = 1 if not hasattr(pads, "cs_n") else len(pads.cs_n)
         databits    = len(pads.dq)
+        assert cl in [2, 3]
         assert databits%8 == 0
 
         # PHY settings -----------------------------------------------------------------------------
@@ -44,7 +34,7 @@ class GENSDRPHY(Module):
             rdcmdphase    = 0,
             wrcmdphase    = 0,
             cl            = cl,
-            read_latency  = cl + 2,
+            read_latency  = cl + cmd_latency,
             write_latency = 0
         )
 
@@ -80,21 +70,19 @@ class GENSDRPHY(Module):
         if hasattr(pads, "dm"):
             assert len(pads.dm)*8 == databits
             for i in range(len(pads.dm)):
-                self.sync += \
+                self.sync += [
+                    pads.dm[i].eq(0),
                     If(dfi.p0.wrdata_en,
                         pads.dm[i].eq(dfi.p0.wrdata_mask)
-                    ).Else(
-                        pads.dm[i].eq(0)
                     )
-        dq_in = Signal(databits)
-        self.sync.sys_ps += dq_in.eq(dq_i)
-        self.sync += dfi.p0.rddata.eq(dq_in)
+                ]
+        self.sync += dfi.p0.rddata.eq(dq_i)
 
         # DQ/DM Control ----------------------------------------------------------------------------
         wrdata_en = Signal()
         self.sync += wrdata_en.eq(dfi.p0.wrdata_en)
         self.comb += dq_oe.eq(wrdata_en)
 
-        rddata_en = Signal(cl + 2)
-        self.sync += rddata_en.eq(Cat(dfi.p0.rddata_en, rddata_en[:cl + 1]))
-        self.comb += dfi.p0.rddata_valid.eq(rddata_en[cl + 1])
+        rddata_en = Signal(cl + cmd_latency)
+        self.sync += rddata_en.eq(Cat(dfi.p0.rddata_en, rddata_en))
+        self.sync += dfi.p0.rddata_valid.eq(rddata_en[-1])