FPGA flake

flake.nix

@@ -27,5 +27,10 @@
       description = "Minimal python flake";
       welcomeText = "hisss 🐍🐍🐍";
     };
+    templates.verilog= {
+      path = ./fpga;
+      description = "FPGA flake, running verilog on ice40";
+      welcomeText = "mjau 🧊";
+    };
   };
 }

fpga/.envrc

@@ -0,0 +1 @@
+use flake

fpga/.gitignore

@@ -0,0 +1,3 @@
+abc.history
+.direnv
+result

fpga/flake.lock

@@ -0,0 +1,59 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1694529238,
+        "narHash": "sha256-zsNZZGTGnMOf9YpHKJqMSsa0dXbfmxeoJ7xHlrt+xmY=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "ff7b65b44d01cf9ba6a71320833626af21126384",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1697009197,
+        "narHash": "sha256-viVRhBTFT8fPJTb1N3brQIpFZnttmwo3JVKNuWRVc3s=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "01441e14af5e29c9d27ace398e6dd0b293e25a54",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

fpga/flake.nix

@@ -0,0 +1,80 @@
+{
+  description = "FPGA flake, running verilog on ice40";
+
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (sys:
+      let pkgs = nixpkgs.legacyPackages.${sys};
+
+          verilator = import ./verilator.nix pkgs ;
+          yosys = pkgs.yosys;
+
+          vflags = ''-DSIMULATE -Wno-fatal -Wpedantic -Wwarn-lint -Wwarn-style -Wno-PINCONNECTEMPTY -Wno-BLKSEQ -CFLAGS "-Wpedantic -std=c++20"'';
+
+          verilate-src = cmd: ''
+            cp -r ${./src} ./src
+            cp -r ${./simulation} ./simulation
+            find ./src/ -name '*.v' -exec ${verilator}/bin/verilator ${vflags} ${cmd} {} +
+          '';
+
+          lint = pkgs.runCommand "lint" {} ''
+             ${verilate-src "--lint-only"}
+             echo "compiler didn't get angry :3"
+             : 3 > $out
+          '';
+
+          test-trace = pkgs.runCommandCC "test-trace" {} ''
+            set -e
+            ${verilate-src "--cc --build --exe --trace -CFLAGS -DTRACE=1 ./simulation/test_led.cpp -top top"}
+            mv obj_dir "$out" && mkdir "$out/bin"
+            cp "$out/Vtop" "$out/bin/sim"
+            $out/bin/sim $out/trace.vcd
+            echo "${pkgs.gtkwave}/bin/gtkwave $out/trace.vcd" > $out/bin/test-trace
+            chmod u+x $out/bin/test-trace
+          '';
+
+          synth = pkgs.runCommandCC "synth" {} ''
+            mkdir -p "$out"
+            find ${./src} -name '*.v' -exec ${yosys}/bin/yosys -f ' -sv' -q -p "synth_ice40 -top top -json $out/synth.json" {} +
+          '';
+
+          pnr-interactive = pkgs.writeScriptBin "pnr-interactive" ''
+            ${pkgs.nextpnrWithGui}/bin/nextpnr-ice40 --up5k --package sg48 --pcf ${./pins.pcf} --json ${synth}/synth.json --gui
+          '';
+
+          pnr = pkgs.runCommandCC "pnr" {} ''
+            mkdir -p "$out"
+            ${pkgs.nextpnrWithGui}/bin/nextpnr-ice40 --up5k --package sg48 --pcf ${./pins.pcf} --json ${synth}/synth.json --asc "$out/pnr.asc" \
+              --freq 50
+          '';
+
+          flash = pkgs.writeScriptBin "flash" ''
+            set -e
+            bin="$(mktemp)"
+            ${pkgs.icestorm}/bin/icepack ${pnr}/pnr.asc "$bin"
+            ${pkgs.icestorm}/bin/iceprog "$bin"
+          '';
+
+          deps = [
+            yosys pkgs.nextpnrWithGui pkgs.icestorm verilator pkgs.gtkwave
+            pkgs.picocom
+          ];
+      in rec {
+        packages.verilator = verilator;
+
+        packages.lint = lint;
+
+        packages.test-trace = test-trace;
+
+        packages.synth = synth;
+        packages.pnr-interactive = pnr-interactive;
+        packages.pnr = pnr;
+        packages.flash = flash;
+
+        devShells.default = pkgs.mkShell { packages = deps; };
+      }
+    );
+}

fpga/pins.pcf

@@ -0,0 +1,2 @@
+set_io clk_12m 35
+set_io led_red 26

fpga/simulation/test_led.cpp

@@ -0,0 +1,56 @@
+#include "Vtop.h"
+#include "verilated.h"
+
+#include <stdint.h>
+#include <iostream>
+#include <random>
+
+#include "verilated_vcd_c.h"
+
+struct state {
+    VerilatedContext *ctx;
+    Vtop *vtop;
+    VerilatedVcdC *trace;
+};
+
+void posedge(state &state) {
+    state.ctx->timeInc(1);
+    state.vtop->clk_12m = 1;
+    state.vtop->eval();
+    state.trace->dump(state.ctx->time());
+
+    state.ctx->timeInc(1);
+    state.vtop->clk_12m = 0;
+    state.vtop->eval();
+    state.trace->dump(state.ctx->time());
+}
+
+int main(int argc, char **argv) {
+    VerilatedContext *vctx = new VerilatedContext;
+    Verilated::traceEverOn(true);
+    Vtop *vtop = new Vtop(vctx);
+
+    if (argc != 2) {
+        std::cout << "Run with argument for destination!" << std::endl;
+        return 1;
+    }
+
+    VerilatedVcdC *trace = new VerilatedVcdC;
+    vtop->trace(trace, 99);
+    trace->open(argv[1]);
+    std::cout << "(writing trace to " << argv[1] << ")" << std::endl;
+
+    state state = {
+        .ctx = vctx,
+        .vtop = vtop,
+        .trace = trace,
+    };
+
+
+    for (int i = 0; i < 2<<24; i++) {
+        posedge(state);
+    }
+
+    state.trace->close();
+}
+

fpga/src/top.v

@@ -0,0 +1,43 @@
+module top(
+  input clk_12m,
+
+  output led_red
+);
+
+// want clock to blink at a rate of 1Hz
+// intermediate clock at 2^24 Hz = 16.77MHz
+// 12MHz * 7/5 = 16.8MHz, within 0.2%
+
+wire clk_16_8m;
+wire clk_stable;
+// set ethernet clock to 50 MHz
+`ifndef SIMULATE
+SB_PLL40_PAD #(
+    .FEEDBACK_PATH("SIMPLE"),
+    .DIVR(4'd4), // divide by 4+1=5
+    .DIVF(7'd6), // multiply by 6+1=7
+    .DIVQ(3'd0), // divide by 2^0
+    .FILTER_RANGE(3'b001)
+) SB_PLL40_PAD_inst (
+    .PACKAGEPIN(clk_12m),
+    .PLLOUTGLOBAL(clk_16_8m),
+    .RESETB(1'b1),
+    .BYPASS(1'b0),
+    .LOCK(clk_stable)
+);
+`else
+// in simulation, tie clocks together
+assign clk_16_8m = clk_12m;
+assign clk_stable = 1;
+`endif
+
+// divide 16.8MHz clock by 2^24
+reg [24:0] clk_ctr;
+
+always @(posedge clk_16_8m) begin
+  clk_ctr <= clk_ctr + 1;
+end
+
+assign led_red = clk_stable & clk_ctr[24];
+
+endmodule

fpga/verilator.nix

@@ -0,0 +1,47 @@
+pkgs: with pkgs;
+
+# From https://github.com/NixOS/nixpkgs/blob/nixos-23.11/pkgs/applications/science/electronics/verilator/default.nix
+# Patches out SystemC-support, as the SystemC does not build on Darwin
+stdenv.mkDerivation rec {
+  pname = "verilator";
+  version = "5.018";
+
+  src = fetchFromGitHub {
+    owner = pname;
+    repo = pname;
+    rev = "v${version}";
+    hash = "sha256-f06UzNw2MQ5me03EPrVFhkwxKum/GLDzQbDNTBsJMJs=";
+  };
+
+  enableParallelBuilding = true;
+  buildInputs = [ perl python3 ];  # ccache
+  nativeBuildInputs = [ makeWrapper flex bison autoconf help2man git ];
+  nativeCheckInputs = [ which numactl ];  # cmake
+
+  doCheck = stdenv.isLinux; # darwin tests are broken for now...
+  checkTarget = "test";
+
+  preConfigure = "autoconf";
+
+  postPatch = ''
+    patchShebangs bin/* src/* nodist/* docs/bin/* examples/xml_py/* \
+    test_regress/{driver.pl,t/*.{pl,pf}} \
+    ci/* ci/docker/run/* ci/docker/run/hooks/* ci/docker/buildenv/build.sh
+  '';
+  # grep '^#!/' -R . | grep -v /nix/store | less
+  # (in nix-shell after patchPhase)
+
+  postInstall = lib.optionalString stdenv.isLinux ''
+    for x in $(ls $out/bin/verilator*); do
+      wrapProgram "$x" --set LOCALE_ARCHIVE "${glibcLocales}/lib/locale/locale-archive"
+    done
+  '';
+
+  meta = with lib; {
+    description = "Fast and robust (System)Verilog simulator/compiler and linter";
+    homepage    = "https://www.veripool.org/verilator";
+    license     = with licenses; [ lgpl3Only artistic2 ];
+    platforms   = platforms.unix;
+    maintainers = with maintainers; [ thoughtpolice amiloradovsky ];
+  };
+}