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

@@ -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")