diff --git a/litex/build/xilinx/platform.py b/litex/build/xilinx/platform.py
index c2b769ffa..57d9ef50b 100644
--- a/litex/build/xilinx/platform.py
+++ b/litex/build/xilinx/platform.py
@@ -5,7 +5,7 @@
 import os
 
 from litex.build.generic_platform import GenericPlatform
-from litex.build.xilinx import common, vivado, ise
+from litex.build.xilinx import common, vivado, ise, symbiflow
 
 # XilinxPlatform -----------------------------------------------------------------------------------
 
@@ -20,6 +20,8 @@ class XilinxPlatform(GenericPlatform):
             self.toolchain = ise.XilinxISEToolchain()
         elif toolchain == "vivado":
             self.toolchain = vivado.XilinxVivadoToolchain()
+        elif toolchain == "symbiflow":
+            self.toolchain = symbiflow.SymbiflowToolchain()
         else:
             raise ValueError("Unknown toolchain")
 
diff --git a/litex/build/xilinx/symbiflow.py b/litex/build/xilinx/symbiflow.py
new file mode 100644
index 000000000..c8653b9ea
--- /dev/null
+++ b/litex/build/xilinx/symbiflow.py
@@ -0,0 +1,321 @@
+# This file is Copyright (c) 2014-2020 Florent Kermarrec <florent@enjoy-digital.fr>
+# This file is Copyright (c) 2020 Antmicro <www.antmicro.com>
+# License: BSD
+
+import os
+import subprocess
+import sys
+import math
+from typing import NamedTuple, Union, List
+import re
+
+from migen.fhdl.structure import _Fragment, wrap, Constant
+from migen.fhdl.specials import Instance
+
+from litex.build.generic_platform import *
+from litex.build import tools
+
+
+def _unwrap(value):
+    return value.value if isinstance(value, Constant) else value
+
+# Constraints (.xdc) -------------------------------------------------------------------------------
+
+def _xdc_separator(msg):
+    r =  "#"*80 + "\n"
+    r += "# " + msg + "\n"
+    r += "#"*80 + "\n"
+    return r
+
+
+def _format_xdc_constraint(c):
+    if isinstance(c, Pins):
+        return "set_property LOC " + c.identifiers[0]
+    elif isinstance(c, IOStandard):
+        return "set_property IOSTANDARD " + c.name
+    elif isinstance(c, Drive):
+        return "set_property DRIVE " + str(c.strength)
+    elif isinstance(c, Misc):
+        return "set_property " + c.misc.replace("=", " ")
+    elif isinstance(c, Inverted):
+        return None
+    else:
+        raise ValueError("unknown constraint {}".format(c))
+
+
+def _format_xdc(signame, resname, *constraints):
+    fmt_c = [_format_xdc_constraint(c) for c in constraints]
+    fmt_r = resname[0] + ":" + str(resname[1])
+    if resname[2] is not None:
+        fmt_r += "." + resname[2]
+    r = "# {}\n".format(fmt_r)
+    for c in fmt_c:
+        if c is not None:
+            r += c + " [get_ports {" + signame + "}]\n"
+    r += "\n"
+    return r
+
+
+def _build_xdc(named_sc):
+    r = ""
+    for sig, pins, others, resname in named_sc:
+        if len(pins) > 1:
+            for i, p in enumerate(pins):
+                r += _format_xdc(sig + "[" + str(i) + "]", resname, Pins(p), *others)
+        elif pins:
+            r += _format_xdc(sig, resname, Pins(pins[0]), *others)
+        else:
+            r += _format_xdc(sig, resname, *others)
+    return r
+
+# PCF ----------------------------------------------------------------------------------------------
+
+def _build_pcf(named_sc):
+    r = ""
+    current_resname = ""
+    for sig, pins, _, resname in named_sc:
+        if current_resname != resname[0]:
+            if current_resname:
+                r += "\n"
+            current_resname = resname[0]
+            r += f"# {current_resname}\n"
+        if len(pins) > 1:
+            for i, p in enumerate(pins):
+                r += f"set_io {sig}[{i}] {Pins(p).identifiers[0]}\n"
+        elif pins:
+            r += f"set_io {sig} {Pins(pins[0]).identifiers[0]}\n"
+    return r
+
+# SDC ----------------------------------------------------------------------------------------------
+
+def _build_sdc(named_pc):
+    return "\n".join(named_pc) if named_pc else ""
+
+# Makefile -----------------------------------------------------------------------------------------
+
+class _MakefileGenerator:
+    class Var(NamedTuple):
+        name: str
+        value: Union[str, List[str]] = ""
+
+    class Rule(NamedTuple):
+        target: str
+        prerequisites: List[str] = []
+        commands: List[str] = []
+        phony: bool = False
+
+    def __init__(self, ast):
+        self.ast = ast
+
+    def generate(self):
+        makefile = []
+        for entry in self.ast:
+            if isinstance(entry, str):
+                makefile.append(entry)
+            elif isinstance(entry, self.Var):
+                if not entry.value:
+                    makefile.append(f"{entry.name} :=")
+                elif isinstance(entry.value, list):
+                    indent = " " * (len(entry.name) + len(" := "))
+                    line = f"{entry.name} := {entry.value[0]}"
+                    for value in entry.value[1:]:
+                        line += " \\"
+                        makefile.append(line)
+                        line = indent + value
+                    makefile.append(line)
+                elif isinstance(entry.value, str):
+                    makefile.append(f"{entry.name} := {entry.value}")
+                else:
+                    raise
+            elif isinstance(entry, self.Rule):
+                makefile.append("")
+                if entry.phony:
+                    makefile.append(f".PHONY: {entry.target}")
+                makefile.append(" ".join([f"{entry.target}:", *entry.prerequisites]))
+                for cmd in entry.commands:
+                    makefile.append(f"\t{cmd}")
+
+        return "\n".join(makefile)
+
+
+def _run_make():
+    if tools.subprocess_call_filtered("make", []) != 0:
+        raise OSError("Subprocess failed")
+
+# SymbiflowToolchain -------------------------------------------------------------------------------
+
+class SymbiflowToolchain:
+    attr_translate = {
+        "keep":            ("dont_touch", "true"),
+        "no_retiming":     ("dont_touch", "true"),
+        "async_reg":       ("async_reg",  "true"),
+        "mr_ff":           ("mr_ff",      "true"), # user-defined attribute
+        "ars_ff1":         ("ars_ff1",    "true"), # user-defined attribute
+        "ars_ff2":         ("ars_ff2",    "true"), # user-defined attribute
+        "no_shreg_extract": None
+    }
+
+    def __init__(self):
+        self.clocks = dict()
+        self.false_paths = set()
+        self.symbiflow_device = None
+        self.bitstream_device = None
+
+    def _check_properties(self, platform):
+        if not self.symbiflow_device:
+            raise ValueError(f"symbiflow_device is not specified")
+        if not self.bitstream_device:
+            try:
+                self.bitstream_device = {
+                    "xc7a": "artix7"
+                }[platform.device[:4]]
+            except KeyError:
+                raise ValueError(f"Unsupported device: {platform.device}")
+
+    def _generate_makefile(self, platform, build_name):
+        Var = _MakefileGenerator.Var
+        Rule = _MakefileGenerator.Rule
+
+        makefile = _MakefileGenerator([
+            "# Autogenerated by LiteX / git: " + tools.get_litex_git_revision() + "\n",
+            Var("TOP", build_name),
+            Var("PARTNAME", platform.device),
+            Var("DEVICE", self.symbiflow_device),
+            Var("BITSTREAM_DEVICE", self.bitstream_device),
+            "",
+            Var("VERILOG", [f for f,language,_ in platform.sources if language in ["verilog", "system_verilog"]]),
+            Var("MEM_INIT", [f"{name}" for name in os.listdir() if name.endswith(".init")]),
+            Var("PCF", f"{build_name}.pcf"),
+            Var("SDC", f"{build_name}.sdc"),
+            Var("XDC", f"{build_name}.xdc"),
+            Var("ARTIFACTS", [
+                    "$(TOP).eblif", "$(TOP).frames", "$(TOP).ioplace", "$(TOP).net",
+                    "$(TOP).place", "$(TOP).route", "$(TOP)_synth.*",
+                    "*.bit", "*.fasm", "*.json", "*.log", "*.rpt",
+                    "constraints.place"
+                ]),
+
+            Rule("all", ["$(TOP).bit"], phony=True),
+            Rule("$(TOP).eblif", ["$(VERILOG)", "$(MEM_INIT)", "$(XDC)"], commands=[
+                    "synth -t $(TOP) -v $(VERILOG) -d $(BITSTREAM_DEVICE) -p $(PARTNAME) -x $(XDC) > /dev/null"
+                ]),
+            Rule("$(TOP).net", ["$(TOP).eblif", "$(SDC)"], commands=[
+                    "pack -e $(TOP).eblif -d $(DEVICE) -s $(SDC) > /dev/null"
+                ]),
+            Rule("$(TOP).place", ["$(TOP).net", "$(PCF)"], commands=[
+                    "place -e $(TOP).eblif -d $(DEVICE) -p $(PCF) -n $(TOP).net -P $(PARTNAME) -s $(SDC) > /dev/null"
+                ]),
+            Rule("$(TOP).route", ["$(TOP).place"], commands=[
+                    "route -e $(TOP).eblif -d $(DEVICE) -s $(SDC) > /dev/null"
+                ]),
+            Rule("$(TOP).fasm", ["$(TOP).route"], commands=[
+                    "write_fasm -e $(TOP).eblif -d $(DEVICE) > /dev/null"
+                ]),
+            Rule("$(TOP).bit", ["$(TOP).fasm"], commands=[
+                    "write_bitstream -d $(BITSTREAM_DEVICE) -f $(TOP).fasm -p $(PARTNAME) -b $(TOP).bit > /dev/null"
+                ]),
+            Rule("clean", phony=True, commands=[
+                    "rm -f $(ARTIFACTS)"
+                ]),
+        ])
+
+        tools.write_to_file("Makefile", makefile.generate())
+
+    def _build_clock_constraints(self, platform):
+        for clk, (period, phase) in sorted(self.clocks.items(), key=lambda x: x[0].duid):
+            rising_edge = math.floor(period/360.0 * phase * 1e3)/1e3
+            falling_edge = math.floor(((rising_edge + period/2) % period) * 1.e3)/1e3
+            platform.add_platform_command(f"create_clock -period {period} {{clk}} -waveform {{{{{rising_edge} {falling_edge}}}}}", clk=clk)
+        for from_, to in sorted(self.false_paths, key=lambda x: (x[0].duid, x[1].duid)):
+           platform.add_platform_command("set_clock_groups -exclusive -group {{{from_}}} -group {{{to}}}", from_=from_, to=to)
+        # Make sure add_*_constraint cannot be used again
+        del self.clocks
+        del self.false_paths
+
+    # Yosys has limited support for real type. It requires that some values be multiplied
+    # by 1000 and passed as integers. For details, see:
+    # https://github.com/SymbiFlow/symbiflow-arch-defs/blob/master/xc/xc7/techmap/cells_map.v
+    def _fix_instance(self, instance):
+        if instance.of == "PLLE2_ADV":
+            for item in instance.items:
+                if isinstance(item, Instance.Parameter) and re.fullmatch("CLKOUT[0-9]_(PHASE|DUTY_CYCLE)", item.name):
+                    item.value = wrap(math.floor(_unwrap(item.value) * 1000))
+
+    def build(self, platform, fragment,
+        build_dir  = "build",
+        build_name = "top",
+        run        = True,
+        enable_xpm = False,
+        **kwargs):
+
+        self._check_properties(platform)
+
+        # Create build directory
+        os.makedirs(build_dir, exist_ok=True)
+        cwd = os.getcwd()
+        os.chdir(build_dir)
+
+        # Finalize design
+        if not isinstance(fragment, _Fragment):
+            fragment = fragment.get_fragment()
+        platform.finalize(fragment)
+
+        # Symbiflow-specific fixes
+        for instance in fragment.specials:
+            if isinstance(instance, Instance):
+                self._fix_instance(instance)
+
+        # Generate timing constraints
+        self._build_clock_constraints(platform)
+
+        # Generate verilog
+        v_output = platform.get_verilog(fragment, name=build_name, **kwargs)
+        named_sc, named_pc = platform.resolve_signals(v_output.ns)
+        v_file = build_name + ".v"
+        v_output.write(v_file)
+        platform.add_source(v_file)
+
+        self._generate_makefile(
+            platform   = platform,
+            build_name = build_name
+        )
+
+        # Generate design constraints
+        tools.write_to_file(build_name + ".xdc", _build_xdc(named_sc))
+        tools.write_to_file(build_name + ".pcf", _build_pcf(named_sc))
+        tools.write_to_file(build_name + ".sdc", _build_sdc(named_pc))
+
+        if run:
+            _run_make()
+
+        os.chdir(cwd)
+
+        return v_output.ns
+
+    def add_period_constraint(self, platform, clk, period, phase=0):
+        clk.attr.add("keep")
+        phase  = math.floor(phase % 360.0 * 1e3)/1e3
+        period = math.floor(period*1e3)/1e3 # round to lowest picosecond
+        if clk in self.clocks:
+            if period != self.clocks[clk][0]:
+                raise ValueError("Clock already constrained to {:.2f}ns, new constraint to {:.2f}ns"
+                    .format(self.clocks[clk][0], period))
+            if phase != self.clocks[clk][1]:
+                raise ValueError("Clock already constrained with phase {:.2f}deg, new phase {:.2f}deg"
+                    .format(self.clocks[clk][1], phase))
+        self.clocks[clk] = (period, phase)
+
+    def add_false_path_constraint(self, platform, from_, to):
+        if (from_, to) in self.false_paths or (to, from_) in self.false_paths:
+            return
+        from_.attr.add("keep")
+        to.attr.add("keep")
+        self.false_paths.add((from_, to))
+
+
+def symbiflow_build_args(parser):
+    pass
+
+
+def symbiflow_build_argdict(args):
+    return dict()