From 8b531b4215decee8f46724deaa7fd6bde0129ae5 Mon Sep 17 00:00:00 2001
From: Florent Kermarrec <florent@enjoy-digital.fr>
Date: Thu, 4 Mar 2021 19:32:41 +0100
Subject: [PATCH] cores: Add code_tmds with TMDS Encoder from Mixxeo/LiteVideo.

---
 litex/soc/cores/code_tmds.py | 99 ++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 litex/soc/cores/code_tmds.py

diff --git a/litex/soc/cores/code_tmds.py b/litex/soc/cores/code_tmds.py
new file mode 100644
index 000000000..70a0994be
--- /dev/null
+++ b/litex/soc/cores/code_tmds.py
@@ -0,0 +1,99 @@
+#
+# This file is part of LiteX
+#
+# Copyright (c) 2015 Sebastien Bourdeauducq <sb@m-labs.hk>
+# Copyright (c) 2016-2021 Florent Kermarrec <florent@enjoy-digital.fr>
+# SPDX-License-Identifier: BSD-2-Clause
+
+from functools import reduce
+from operator import add
+
+from migen import *
+
+# Helpers ------------------------------------------------------------------------------------------
+
+control_tokens = [0b1101010100, 0b0010101011, 0b0101010100, 0b1010101011]
+
+# TMDS Encoder -------------------------------------------------------------------------------------
+
+class TMDSEncoder(Module):
+    def __init__(self):
+        self.d   = Signal(8)
+        self.c   = Signal(2)
+        self.de  = Signal()
+
+        self.out = Signal(10)
+
+        # # #
+
+        # Stage 1 - Count number of 1s in data.
+        d   = Signal(8)
+        n1d = Signal(max=9)
+        self.sync += [
+            n1d.eq(reduce(add, [self.d[i] for i in range(8)])),
+            d.eq(self.d)
+        ]
+
+        # Stage 2 - Add 9th bit.
+        q_m    = Signal(9)
+        q_m8_n = Signal()
+        self.comb += q_m8_n.eq((n1d > 4) | ((n1d == 4) & ~d[0]))
+        for i in range(8):
+            if i:
+                curval = curval ^ d[i] ^ q_m8_n
+            else:
+                curval = d[0]
+            self.sync += q_m[i].eq(curval)
+        self.sync += q_m[8].eq(~q_m8_n)
+
+        # Stage 3 - Count number of 1s and 0s in q_m[:8].
+        q_m_r = Signal(9)
+        n0q_m = Signal(max=9)
+        n1q_m = Signal(max=9)
+        self.sync += [
+            n0q_m.eq(reduce(add, [~q_m[i] for i in range(8)])),
+            n1q_m.eq(reduce(add, [q_m[i] for i in range(8)])),
+            q_m_r.eq(q_m)
+        ]
+
+        # Stage 4 - Final encoding.
+        cnt = Signal((6, True))
+
+        s_c  = self.c
+        s_de = self.de
+        for p in range(3):
+            new_c = Signal(2)
+            new_de = Signal()
+            self.sync += new_c.eq(s_c), new_de.eq(s_de)
+            s_c, s_de = new_c, new_de
+
+        self.sync += [
+            If(s_de,
+                If((cnt == 0) | (n1q_m == n0q_m),
+                    self.out[9].eq(~q_m_r[8]),
+                    self.out[8].eq(q_m_r[8]),
+                    If(q_m_r[8],
+                        self.out[:8].eq(q_m_r[:8]),
+                        cnt.eq(cnt + n1q_m - n0q_m)
+                    ).Else(
+                        self.out[:8].eq(~q_m_r[:8]),
+                        cnt.eq(cnt + n0q_m - n1q_m)
+                    )
+                ).Else(
+                    If((~cnt[5] & (n1q_m > n0q_m)) | (cnt[5] & (n0q_m > n1q_m)),
+                        self.out[9].eq(1),
+                        self.out[8].eq(q_m_r[8]),
+                        self.out[:8].eq(~q_m_r[:8]),
+                        cnt.eq(cnt + Cat(0, q_m_r[8]) + n0q_m - n1q_m)
+                    ).Else(
+                        self.out[9].eq(0),
+                        self.out[8].eq(q_m_r[8]),
+                        self.out[:8].eq(q_m_r[:8]),
+                        cnt.eq(cnt - Cat(0, ~q_m_r[8]) + n1q_m - n0q_m)
+                    )
+                )
+            ).Else(
+                self.out.eq(Array(control_tokens)[s_c]),
+                cnt.eq(0)
+            )
+        ]