litex/misoclib/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 _EncoderSerializer(Module):
	def __init__(self, serdesstrobe, pad_p, pad_n):
		self.submodules.encoder = RenameClockDomains(Encoder(), "pix")
		self.d, self.c, self.de = self.encoder.d, self.encoder.c, self.encoder.de

		###

		# 2X soft serialization
		ed_2x = Signal(5)
		self.sync.pix2x += ed_2x.eq(Mux(ClockSignal("pix"), self.encoder.out[:5], self.encoder.out[5:]))

		# 5X hard serialization
		cascade_di = Signal()
		cascade_do = Signal()
		cascade_ti = Signal()
		cascade_to = Signal()
		pad_se = Signal()
		self.specials += [
			Instance("OSERDES2",
				p_DATA_WIDTH=5, p_DATA_RATE_OQ="SDR", p_DATA_RATE_OT="SDR",
				p_SERDES_MODE="MASTER", p_OUTPUT_MODE="DIFFERENTIAL",

				o_OQ=pad_se,
				i_OCE=1, i_IOCE=serdesstrobe, i_RST=0,
				i_CLK0=ClockSignal("pix10x"), i_CLK1=0, i_CLKDIV=ClockSignal("pix2x"),
				i_D1=ed_2x[4], i_D2=0, i_D3=0, i_D4=0,
				i_T1=0, i_T2=0, i_T3=0, i_T4=0,
				i_TRAIN=0, i_TCE=1,
				i_SHIFTIN1=1, i_SHIFTIN2=1,
				i_SHIFTIN3=cascade_do, i_SHIFTIN4=cascade_to,
				o_SHIFTOUT1=cascade_di, o_SHIFTOUT2=cascade_ti),
			Instance("OSERDES2",
				p_DATA_WIDTH=5, p_DATA_RATE_OQ="SDR", p_DATA_RATE_OT="SDR",
				p_SERDES_MODE="SLAVE", p_OUTPUT_MODE="DIFFERENTIAL",

				i_OCE=1, i_IOCE=serdesstrobe, i_RST=0,
				i_CLK0=ClockSignal("pix10x"), i_CLK1=0, i_CLKDIV=ClockSignal("pix2x"),
				i_D1=ed_2x[0], i_D2=ed_2x[1], i_D3=ed_2x[2], i_D4=ed_2x[3],
				i_T1=0, i_T2=0, i_T3=0, i_T4=0,
				i_TRAIN=0, i_TCE=1,
				i_SHIFTIN1=cascade_di, i_SHIFTIN2=cascade_ti,
				i_SHIFTIN3=1, i_SHIFTIN4=1,
				o_SHIFTOUT3=cascade_do, o_SHIFTOUT4=cascade_to),
			Instance("OBUFDS", i_I=pad_se, o_O=pad_p, o_OB=pad_n)
		]


class PHY(Module):
	def __init__(self, serdesstrobe, pads):
		self.hsync = Signal()
		self.vsync = Signal()
		self.de = Signal()
		self.r = Signal(8)
		self.g = Signal(8)
		self.b = Signal(8)

		###

		self.submodules.es0 = _EncoderSerializer(serdesstrobe, pads.data0_p, pads.data0_n)
		self.submodules.es1 = _EncoderSerializer(serdesstrobe, pads.data1_p, pads.data1_n)
		self.submodules.es2 = _EncoderSerializer(serdesstrobe, pads.data2_p, pads.data2_n)
		self.comb += [
			self.es0.d.eq(self.r),
			self.es1.d.eq(self.g),
			self.es2.d.eq(self.b),
			self.es0.c.eq(Cat(self.hsync, self.vsync)),
			self.es1.c.eq(0),
			self.es2.c.eq(0),
			self.es0.de.eq(self.de),
			self.es1.de.eq(self.de),
			self.es2.de.eq(self.de),
		]

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, selfp):
		if self._end_cycle is None:
			try:
				nv = next(self._iter_inputs)
			except StopIteration:
				self._end_cycle = selfp.simulator.cycle_counter + 4
			else:
				selfp.dut.d = nv
		if selfp.simulator.cycle_counter == self._end_cycle:
			raise StopSimulation
		if selfp.simulator.cycle_counter > 4:
			self.outs.append(selfp.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 run_simulation
	from random import Random

	rng = Random(788)
	test_list = [rng.randrange(256) for i in range(500)]
	tb = _EncoderTB(test_list)
	run_simulation(tb)

	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))