From 8ba7793b245c0d2c3cf1c475521443716575fc1f Mon Sep 17 00:00:00 2001
From: morgan <mc@m-labs.hk>
Date: Fri, 28 Jun 2024 12:46:35 +0800
Subject: [PATCH] cxp upconn: fix word count issue

---
 src/gateware/cxp_upconn.py | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/src/gateware/cxp_upconn.py b/src/gateware/cxp_upconn.py
index ae8f9ba..3aa09b5 100644
--- a/src/gateware/cxp_upconn.py
+++ b/src/gateware/cxp_upconn.py
@@ -10,12 +10,9 @@ from misoc.interconnect.csr import *
 IDLE_CHARS = [
     #[data, k]
     [0b10111100, 1], #K28.5
-    [0b10111100, 1], #K28.5
-    [0b10111100, 1], #K28.5
-    [0b10111100, 1], #K28.5
-    # [0b00111100, 1], #K28.1
-    # [0b00111100, 1], #K28.1
-    # [0b10111100, 0], #D28.5
+    [0b00111100, 1], #K28.1
+    [0b00111100, 1], #K28.1
+    [0b10111100, 0], #D28.5
 ]
 
 
@@ -82,7 +79,7 @@ class CXP_UpConn(Module, AutoCSR):
                 NextValue(self.encoder.d, IDLE_CHARS[0][0]),
                 NextValue(self.encoder.k, IDLE_CHARS[0][1]),
                 NextValue(self.encoder.disp_in, 0),
-                NextValue(tx_wordcount, 0),
+                NextValue(tx_wordcount, 1),
                 NextValue(tx_bitcount, 0),
                 NextState("LOAD_CHAR")
             )
@@ -103,6 +100,9 @@ class CXP_UpConn(Module, AutoCSR):
         )
 
         # CXP 2.1 section 9.2.4 
+        # Higher priority packet can be inserted into a lower priority packet during transmission
+        # Priority lv 0 can be inserted in char boundary of the packet 
+        # Priority lv 1-2 need to be inserted in word boundary of the packet
         self.sync.cxp_upconn += [
             self.tx_fifos.disp_in.eq(disp),
             self.encoder.disp_in.eq(disp),
@@ -122,10 +122,15 @@ class CXP_UpConn(Module, AutoCSR):
                         self.tx_fifos.source_ack[0].eq(1),
                         disp.eq(self.tx_fifos.disp_out[0]),
                     ).Else(
-                        # at word boundary
-                        If(tx_wordcount == 3,
+                        # priority zero doesn't contribute to word count
+                        If(tx_wordcount != 3,
+                            tx_wordcount.eq(tx_wordcount + 1),
+                        ).Else(
                             tx_wordcount.eq(0),
-                            # at word boundary
+                        ),
+
+                        # word boundary
+                        If(tx_wordcount == 0,
                             If(~self.tx_fifos.pe.n,
                                 idling.eq(0),
                                 priority.eq(self.tx_fifos.pe.o),
@@ -138,8 +143,6 @@ class CXP_UpConn(Module, AutoCSR):
                                 disp.eq(self.encoder.disp_out),
                             )
                         ).Else(
-                            # priority zero doesn't contribute to word count
-                            tx_wordcount.eq(tx_wordcount + 1),
                             If(~idling,
                                 self.tx_fifos.source_ack[priority].eq(1),
                                 tx_reg.eq(self.tx_fifos.source_data[priority]),
@@ -171,7 +174,7 @@ class CXP_UpConn(Module, AutoCSR):
         p2 = Signal()
         self.comb += [
            ninth_bit.eq(tx_bitcount == 9),
-           word_bound.eq(tx_wordcount == 3),
+           word_bound.eq(tx_wordcount == 0),
            p1.eq(priority == 1),
            p2.eq(priority == 2),
         ]