Import of the watch repository from Pebble

src/fw/util/hdlc.c

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * 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.
+ */
+
+#include "hdlc.h"
+
+#include "system/passert.h"
+
+
+void hdlc_streaming_decode_reset(HdlcStreamingContext *ctx) {
+  ctx->escape = false;
+}
+
+bool hdlc_streaming_decode(HdlcStreamingContext *ctx, uint8_t *data, bool *should_store,
+                           bool *hdlc_error) {
+  PBL_ASSERTN(data != NULL && should_store != NULL && hdlc_error != NULL);
+  bool is_complete = false;
+  *hdlc_error = false;
+  *should_store = false;
+  if (*data == HDLC_FLAG) {
+    if (ctx->escape) {
+      // extra escape character before flag
+      ctx->escape = false;
+      *hdlc_error = true;
+    }
+    // we've reached the end of the frame
+    is_complete = true;
+  } else if (*data == HDLC_ESCAPE) {
+    if (ctx->escape) {
+      // invalid sequence
+      ctx->escape = false;
+      *hdlc_error = true;
+    } else {
+      // ignore this character and escape the next one
+      ctx->escape = true;
+    }
+  } else {
+    if (ctx->escape) {
+      *data ^= HDLC_ESCAPE_MASK;
+      ctx->escape = false;
+    }
+    *should_store = true;
+  }
+
+  return is_complete;
+}
+
+bool hdlc_encode(uint8_t *data) {
+  if (*data == HDLC_FLAG || *data == HDLC_ESCAPE) {
+    *data ^= HDLC_ESCAPE_MASK;
+    return true;
+  }
+  return false;
+}