cores/led: Add initial WS2812/NeoPixel core (MMAPed).
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Florent Kermarrec
parent
c13be522ce
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67431f4109
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@ -1,13 +1,16 @@
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#
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# This file is part of LiteX.
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#
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# Copyright (c) 2020 Florent Kermarrec <florent@enjoy-digital.fr>
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# Copyright (c) 2020-2021 Florent Kermarrec <florent@enjoy-digital.fr>
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# SPDX-License-Identifier: BSD-2-Clause
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import math
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from migen import *
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from migen.genlib.misc import WaitTimer
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from litex.soc.interconnect.csr import *
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from litex.soc.interconnect import wishbone
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# Led Chaser ---------------------------------------------------------------------------------------
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@ -47,3 +50,161 @@ class LedChaser(Module, AutoCSR):
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)
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# Use PWM as Output Enable for pads.
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self.comb += If(~self.pwm.pwm, self.pads.eq(0))
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# WS2812/NeoPixel ----------------------------------------------------------------------------------
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class WS2812(Module):
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"""WS2812/NeoPixel Led Driver.
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Description
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-----------
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┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐
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│DI DO│ │DI DO│ │DI DO│ │DI DO│ │DI DO│ Next leds
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FPGA ───► ├───► ├───► ├───► ├───► ├───► or
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│ LED0 │ │ LED1 │ │ LED2 │ │ LED3 │ │ LED4 │ end of chain.
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└──────┘ └──────┘ └──────┘ └──────┘ └──────┘
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24-bit 24-bit 24-bit 24-bit 24-bit
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WS2812/NeoPixel Leds are smart RGB Leds controlled over a simple one wire protocol:
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- Each Led will "digest" a 24-bit control word: (MSB) G-R-B (LSB).
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- Leds can be chained through DIN->DOUT connection.
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Each control sequence is separated by a reset code: Line low for > 50us.
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Ones are transmitted as:
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┌─────┐
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│ T0H │ │ T0H = 400ns +-150ns
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│ │ T0L │ T0L = 800ns +-150ns
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└───────────┘
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Zeros are transmitted as:
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┌──────────┐
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│ T1H │ │ T1H = 850ns +-150ns
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│ │ T1L │ T1L = 450ns +-150ns
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└──────┘
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Integration
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-----------
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The core handles the WS2812 protocol and exposes the Led chain as an MMAPed peripheral:
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32-bit
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00_GG_RR_BB
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┌───────────┐
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Base + 0 │ LED0 │
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├───────────┤
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Base + 4 │ LED1 │
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├───────────┤
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Base + 8 │ LED2 │
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└───────────┘
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... ...
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It can be simply integrated in a LiteX SoC with:
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self.submodules.ws2812 = WS2812(platform.request("x"), nleds=32, sys_clk_freq=sys_clk_freq)
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self.bus.add_slave(name="ws2812", slave=self.ws2812.bus, region=SoCRegion(
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origin = 0x2000_0000,
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size = 32*4,
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))
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Each Led can then be directly controlled from the Bus of the SoC.
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Parameters
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----------
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pad : Signal, in
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FPGA DOut.
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nleds : int, in
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Number of Leds in the chain.
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sys_clk_freq: int, in
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System Clk Frequency.
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"""
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def __init__(self, pad, nleds, sys_clk_freq):
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# Memory.
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mem = Memory(32, nleds)
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port = mem.get_port()
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self.specials += mem, port
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# Wishone Memory.
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self.submodules.wb_mem = wishbone.SRAM(
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mem_or_size = mem,
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read_only = False,
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bus = wishbone.Interface(data_width=32)
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)
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self.bus = self.wb_mem.bus
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# Internal Signals.
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led_data = Signal(24)
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bit_count = Signal(8)
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led_count = Signal(int(math.log2(nleds)))
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# Timings.
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trst = 75e-6
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t0h = 0.40e-6
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t0l = 0.85e-6
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t1h = 0.80e-6
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t1l = 0.45e-6
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# Timers.
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t0h_timer = WaitTimer(int(t0h*sys_clk_freq))
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t0l_timer = WaitTimer(int(t0l*sys_clk_freq))
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self.submodules += t0h_timer, t0l_timer
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t1h_timer = WaitTimer(int(t1h*sys_clk_freq))
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t1l_timer = WaitTimer(int(t1l*sys_clk_freq))
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self.submodules += t1h_timer, t1l_timer
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trst_timer = WaitTimer(int(trst*sys_clk_freq))
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self.submodules += trst_timer
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# FSM
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self.submodules.fsm = fsm = FSM(reset_state="RST")
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fsm.act("RST",
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trst_timer.wait.eq(1),
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If(trst_timer.done,
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NextValue(led_count, 0),
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NextState("LED-SHIFT")
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)
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)
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self.comb += port.adr.eq(led_count)
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fsm.act("LED-SHIFT",
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NextValue(bit_count, 24-1),
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NextValue(led_data, port.dat_r),
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NextValue(led_count, led_count + 1),
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If(led_count == (nleds-1),
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NextState("RST")
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).Else(
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NextState("BIT-TEST")
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)
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)
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fsm.act("BIT-TEST",
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If(led_data[-1] == 0,
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NextState("ZERO-SEND"),
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),
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If(led_data[-1] == 1,
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NextState("ONE-SEND"),
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),
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)
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fsm.act("ZERO-SEND",
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t0h_timer.wait.eq(1),
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t0l_timer.wait.eq(t0h_timer.done),
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pad.eq(~t0h_timer.done),
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If(t0l_timer.done,
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NextState("BIT-SHIFT")
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)
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)
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fsm.act("ONE-SEND",
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t1h_timer.wait.eq(1),
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t1l_timer.wait.eq(t1h_timer.done),
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pad.eq(~t1h_timer.done),
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If(t1l_timer.done,
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NextState("BIT-SHIFT")
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)
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)
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fsm.act("BIT-SHIFT",
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NextValue(led_data, Cat(Signal(), led_data)),
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NextValue(bit_count, bit_count - 1),
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If(bit_count == 0,
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NextState("LED-SHIFT")
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).Else(
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NextState("BIT-TEST")
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)
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)
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