From 78587d1eaabd60008abfb570567631eb58c79862 Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sebastien@milkymist.org>
Date: Mon, 16 Sep 2013 23:51:37 +0200
Subject: [PATCH] framebuffer/dvi: add TMDS encoder (untested)

---
 milkymist/framebuffer/dvi.py | 88 ++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 milkymist/framebuffer/dvi.py

diff --git a/milkymist/framebuffer/dvi.py b/milkymist/framebuffer/dvi.py
new file mode 100644
index 000000000..7f4b2ac74
--- /dev/null
+++ b/milkymist/framebuffer/dvi.py
@@ -0,0 +1,88 @@
+from migen.fhdl.std import *
+from migen.genlib.misc import optree
+
+control_tokens = [0b1101010100, 0b0010101011, 0b0101010100, 0b1010101011]
+
+class Encoder(Module):
+	def __init__(self):
+		self.d = Signal(8)
+		self.c = Signal(2)
+		self.de = Signal()
+
+		self.output = Signal(10)
+
+		###
+
+		# stage 1 - count number of 1s in data
+		d = Signal(8)
+		n1d = Signal(max=9)
+		self.sync += [
+			n1d.eq(optree("+", [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(optree("+", [~q_m[i] for i in range(8)])),
+			n1q_m.eq(optree("+", [q_m[i] for i in range(8)])),
+			q_m_r.eq(q_m)
+		]
+
+		# stage 4 - final encoding
+		cnt = Signal((5, 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.output[9].eq(~q_m_r[8]),
+					self.output[8].eq(q_m_r[8]),
+					If(q_m_r[8],
+						self.output[:8].eq(q_m_r[:8]),
+						cnt.eq(cnt + n1q_m - n0q_m)
+					).Else(
+						self.output[:8].eq(~q_m_r[:8]),
+						cnt.eq(cnt + n0q_m - n1q_m)
+					)
+				).Else(
+					If((~cnt[4] & (n1q_m > n0q_m)) | (cnt[4] & (n0q_m > n1q_m)),
+						self.output[9].eq(1),
+						self.output[8].eq(q_m_r[8]),
+						self.output[:8].eq(~q_m_r[:8]),
+						cnt.eq(cnt + Cat(0, q_m_r[8]) + n0q_m - n1q_m)
+					).Else(
+						self.output[9].eq(0),
+						self.output[8].eq(q_m_r[8]),
+						self.output[:8].eq(q_m_r[:8]),
+						cnt.eq(cnt - Cat(0, ~q_m_r[8]) + n1q_m - n0q_m)
+					)
+				)
+			).Else(
+				self.output.eq(Array(control_tokens)[s_c]),
+				cnt.eq(0)
+			)
+
+if __name__ == "__main__":
+	from migen.fhdl import verilog
+	print(verilog.convert(Encoder()))