pw_interrupt: Add backend for xtensa processors

Change-Id: Ie883afce68738469fe88257468edd9ae43c18189
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/160031
Reviewed-by: Jonathon Reinhart <jrreinhart@google.com>
Commit-Queue: Austin Foxley <afoxley@google.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ted Pudlik <tpudlik@google.com>

4 files changed, 108 insertions, 0 deletions

diff --git a/pw_interrupt_xtensa/BUILD.bazel b/pw_interrupt_xtensa/BUILD.bazel
new file mode 100644
index 000000000..c3ab8e2aa
--- /dev/null
+++ b/pw_interrupt_xtensa/BUILD.bazel
@@ -0,0 +1,36 @@
+# Copyright 2023 The Pigweed 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
+#
+#     https://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.
+
+load(
+    "//pw_build:pigweed.bzl",
+    "pw_cc_library",
+)
+
+package(default_visibility = ["//visibility:public"])
+
+licenses(["notice"])
+
+constraint_value(
+    name = "backend",
+    constraint_setting = "//pw_interrupt:backend_constraint_setting",
+)
+
+pw_cc_library(
+    name = "context",
+    srcs = ["context.cc"],
+    target_compatible_with = [":backend"],
+    deps = [
+        "//pw_interrupt:context_facade",
+    ],
+)
diff --git a/pw_interrupt_xtensa/BUILD.gn b/pw_interrupt_xtensa/BUILD.gn
new file mode 100644
index 000000000..c822cb3cb
--- /dev/null
+++ b/pw_interrupt_xtensa/BUILD.gn
@@ -0,0 +1,31 @@
+# Copyright 2023 The Pigweed 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
+#
+#     https://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.
+
+import("//build_overrides/pigweed.gni")
+
+import("$dir_pw_build/target_types.gni")
+import("$dir_pw_docgen/docs.gni")
+import("$dir_pw_unit_test/test.gni")
+
+pw_source_set("context") {
+  public_deps = [ "$dir_pw_interrupt:context.facade" ]
+  sources = [ "context.cc" ]
+}
+
+pw_doc_group("docs") {
+  sources = [ "docs.rst" ]
+}
+
+pw_test_group("tests") {
+}
diff --git a/pw_interrupt_xtensa/context.cc b/pw_interrupt_xtensa/context.cc
new file mode 100644
index 000000000..9c16fcaf5
--- /dev/null
+++ b/pw_interrupt_xtensa/context.cc
@@ -0,0 +1,34 @@
+// Copyright 2023 The Pigweed 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
+//
+//     https://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.
+
+#include "pw_interrupt/context.h"
+
+#include <xtensa/config/core.h>
+#include <xtensa/hal.h>
+
+#include <cstdint>
+
+namespace pw::interrupt {
+
+bool InInterruptContext() {
+  // xthal_intlevel_get returns the current interrupt level of the processor
+  // (value of PS.INTLEVEL register). C based handlers are always dispatched
+  // from an interrupt level below XCHAL_EXCM_LEVEL - handlers running above
+  // this level must be written in assembly. The interrupt level is set to zero
+  // when interrupts are enabled but the core isn't currently procesing one.
+  const uint32_t int_level = xthal_intlevel_get();
+  return (int_level < XCHAL_EXCM_LEVEL) && (int_level > 0);
+}
+
+}  // namespace pw::interrupt
diff --git a/pw_interrupt_xtensa/docs.rst b/pw_interrupt_xtensa/docs.rst
new file mode 100644
index 000000000..182bdbd35
--- /dev/null
+++ b/pw_interrupt_xtensa/docs.rst
@@ -0,0 +1,7 @@
+.. _module-pw_interrupt_xtensa:
+
+-------------------
+pw_interrupt_xtensa
+-------------------
+Pigweed's interrupt Xtensa module provides an architecture specific
+backend for ``pw_interrupt``.