cores/lcd/ssd1306: detect bus error (device NAK)

Author: povauboin

lambdalib/cores/lcd/ssd1306.py

@@ -45,6 +45,7 @@ def __init__(self):
             ("data", 8),
         ])
         self.source = stream.Endpoint(i2c_stream_description)
+        self.i2c_error = Signal()
 
     def elaborate(self, platform):
         sink = self.sink
@@ -62,7 +63,10 @@ def elaborate(self, platform):
                     source.valid.eq(sink.valid),
                 ]
                 with m.If(source.valid & source.ready):
-                    m.next = "CONTROL"
+                    with m.If(self.i2c_error):
+                        m.next = "ERROR"
+                    with m.Else():
+                        m.next = "CONTROL"
 
             with m.State("CONTROL"):
                 m.d.comb += [
@@ -85,6 +89,13 @@ def elaborate(self, platform):
                 with m.If(source.valid & source.ready & source.last):
                     m.next = "ADDR"
 
+            with m.State("ERROR"):
+                # The I2C target device is not present on the bus (NAK)
+                # drop the sink until `last`.
+                m.d.comb += sink.ready.eq(1)
+                with m.If(sink.valid & sink.last):
+                    m.next = "ADDR"
+
         return m
 
 
@@ -132,6 +143,7 @@ def __init__(self, width, height, por_init=True):
 
         self.sink   = stream.Endpoint([("data", 8)])
         self.source = stream.Endpoint(i2c_stream_description)
+        self.i2c_error = Signal()
 
     def elaborate(self, platform):
         sink = self.sink
@@ -183,6 +195,7 @@ def elaborate(self, platform):
         # Instanciate the I2C address and control byte wrapper
         m.submodules.wrapper = wrapper = SSD1306_Wrapper()
         m.d.comb += wrapper.source.connect(source)
+        m.d.comb += wrapper.i2c_error.eq(self.i2c_error)
 
         cnt = Signal(range(self._size))