From c867d5647b41cdfb826ccd8d93ddec73d1e4791a Mon Sep 17 00:00:00 2001
From: Andrew Dennison <andrew@motec.com.au>
Date: Fri, 25 Aug 2023 15:24:03 +1000
Subject: [PATCH] soc/cores/i2c: only change SDA when SCL is stable

Avoid changing SDA immediately in states WRITE0 and READ0 to guarantee SDA hold is > 0
---
 litex/soc/cores/i2c.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/litex/soc/cores/i2c.py b/litex/soc/cores/i2c.py
index 8d2fb50ad..6a7fbd331 100644
--- a/litex/soc/cores/i2c.py
+++ b/litex/soc/cores/i2c.py
@@ -232,11 +232,19 @@ class I2CMaster(Module, AutoCSR):
         self.sda_t = TSTriple()
         self.specials += self.sda_t.get_tristate(pads.sda)
         self.comb += [
-            self.sda_t.oe.eq(~i2c.sda_o),
             self.sda_t.o.eq(0),
             i2c.sda_i.eq(self.sda_t.i),
         ]
 
+        # only change SDA when SCL is stable
+        self.scl_i_n = Signal() # previous scl_i
+        self.sync += [
+            self.scl_i_n.eq(self.scl_t.i),
+            If(self.scl_i_n == i2c.scl_o,
+                self.sda_t.oe.eq(~i2c.sda_o),
+            ),
+        ]
+
         # Event Manager.
         self.submodules.ev = EventManager()
         self.ev.idle       = EventSourceProcess(edge="rising")