litex/milkymist/framebuffer/dvi.py

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.out = 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((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)
			)

class _EncoderTB(Module):
	def __init__(self, inputs):
		self.outs = []
		self._iter_inputs = iter(inputs)
		self._end_cycle = None
		self.submodules.dut = Encoder()
		self.comb += self.dut.de.eq(1)

	def do_simulation(self, s):
		if self._end_cycle is None:
			try:
				nv = next(self._iter_inputs)
			except StopIteration:
				self._end_cycle = s.cycle_counter + 4
			else:
				s.wr(self.dut.d, nv)
		if s.cycle_counter == self._end_cycle:
			s.interrupt = True
		if s.cycle_counter > 4:
			self.outs.append(s.rd(self.dut.out))

def _bit(i, n):
	return (i >> n) & 1

def _decode_tmds(b):
	try:
		c = control_tokens.index(b)
		de = False
	except ValueError:
		c = 0
		de = True
	vsync = bool(c & 2)
	hsync = bool(c & 1)

	value = _bit(b, 0) ^ _bit(b, 9)
	for i in range(1, 8):
		value |= (_bit(b, i) ^ _bit(b, i-1) ^ (~_bit(b, 8) & 1)) << i

	return de, hsync, vsync, value

if __name__ == "__main__":
	from migen.sim.generic import Simulator
	from random import Random
	
	rng = Random(788)
	test_list = [rng.randrange(256) for i in range(500)]
	tb = _EncoderTB(test_list)
	Simulator(tb).run()

	check = [_decode_tmds(out)[3] for out in tb.outs]
	assert(check == test_list)
	
	nb0 = 0
	nb1 = 0
	for out in tb.outs:
		for i in range(10):
			if _bit(out, i):
				nb1 += 1
			else:
				nb0 += 1
	print("0/1: {}/{} ({:.2f})".format(nb0, nb1, nb0/nb1))