Add a passthrough example

This commit adds a simple proc that forwards the received
information from an input channel to an output channel.

Signed-off-by: Robert Winkler <rwinkler@antmicro.com>

xls/examples/BUILD

@@ -899,3 +899,29 @@ filegroup(
     srcs = glob(["*.x"]),
     visibility = ["//xls:xls_internal"],
 )
+
+xls_dslx_library(
+    name = "passthrough_dslx",
+    srcs = [
+        "passthrough.x",
+    ],
+)
+
+xls_dslx_test(
+    name = "passthrough_dslx_test",
+    srcs = ["passthrough.x"],
+    deps = [":passthrough_dslx"],
+)
+
+xls_dslx_verilog(
+    name = "passthrough_verilog",
+    codegen_args = {
+        "module_name": "passthrough",
+        "delay_model": "unit",
+        "pipeline_stages": "1",
+        "reset": "rst",
+    },
+    dslx_top = "Passthrough",
+    library = "passthrough_dslx",
+    verilog_file = "passthrough.sv",
+)

xls/examples/passthrough.x

@@ -0,0 +1,58 @@
+// Copyright 2024 The XLS Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// A simple proc that forwards the received information from
+// an input channel to an output channel.
+
+import std;
+
+proc Passthrough {
+    data_r: chan<u32> in;
+    data_s: chan<u32> out;
+
+    config(data_r: chan<u32> in, data_s: chan<u32> out) { (data_r, data_s) }
+
+    init { () }
+
+    next(tok: token, state: ()) {
+        let (tok, data) = recv(tok, data_r);
+        let tok = send(tok, data_s, data);
+    }
+}
+
+#[test_proc]
+proc PassthroughTest {
+    terminator: chan<bool> out;
+    data_s: chan<u32> out;
+    data_r: chan<u32> in;
+
+    config(terminator: chan<bool> out) {
+        let (data_s, data_r) = chan<u32>("data");
+        spawn Passthrough(data_r, data_s);
+        (terminator, data_s, data_r)
+    }
+
+    init { u32:10 }
+
+    next(tok: token, count: u32) {
+        let data_to_send = count * count;
+        let tok = send(tok, data_s, data_to_send);
+        let (tok, received_data) = recv(tok, data_r);
+
+        assert_eq(data_to_send, received_data);
+        send_if(tok, terminator, count == u32:0, true);
+
+        count - u32:1
+    }
+}