pipeline GW: add buffer error

src/gateware/cxp_pipeline.py

@@ -305,8 +305,10 @@ class RX_Debug_Buffer(Module,AutoCSR):
 class CXP_Data_Packet_Decode(Module):
     def __init__(self):
         self.packet_type = Signal(8)
+
         self.decode_err = Signal()
         self.test_err = Signal()
+        self.buffer_err = Signal()
         # # #
 
         # DEBUG: remove debug
@@ -417,6 +419,8 @@ class CXP_Data_Packet_Decode(Module):
         self.write_ptr_sys = Signal.like(write_ptr)
         self.specials += MultiReg(write_ptr, self.write_ptr_sys),
 
+        self.read_ptr_rx = Signal.like(write_ptr)
+
         self.comb += [
             mem_port.adr[:addr_nbits].eq(addr),
             mem_port.adr[addr_nbits:].eq(write_ptr),
@@ -429,16 +433,32 @@ class CXP_Data_Packet_Decode(Module):
             self.sink.ack.eq(1),
             If(self.sink.stb,
                 If(((self.sink.data == Replicate(KCode["pak_end"], 4)) & (self.sink.k == 0b1111)),
-                    NextValue(write_ptr, write_ptr + 1),
-                    NextState("IDLE"),
+                    NextState("MOVE_BUFFER_PTR"),
                 ).Else(
                     mem_port.we.eq(1),
                     mem_port.dat_w.eq(self.sink.data),
                     NextValue(addr, addr + 1),
+
+                    If(addr == buffer_depth - 1,
+                        # discard the packet
+                        self.buffer_err.eq(1),
+                        NextState("IDLE"),
+                    )
                 )
             )
         )
 
+        fsm.act("MOVE_BUFFER_PTR",
+            self.sink.ack.eq(0),
+            If(write_ptr + 1 == self.read_ptr_rx,
+                # if next one hasn't been read, overwrite the current buffer when new packet comes in
+                self.buffer_err.eq(1),
+            ).Else(
+                NextValue(write_ptr, write_ptr + 1),
+            ),
+            NextState("IDLE"),
+        )
+
 class CXP_Trig_Ack_Checker(Module, AutoCSR):
     def __init__(self):
         self.sink = stream.Endpoint(word_layout)