From d24c7c38def470aa0615212a5afd007f091b750a Mon Sep 17 00:00:00 2001
From: Paul Selkirk <paul@psgd.org>
Date: Mon, 20 Jun 2016 21:22:54 -0400
Subject: Ring buffers for more reliable UART receives.

---
 ringbuf.h | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 ringbuf.h

diff --git a/ringbuf.h b/ringbuf.h
new file mode 100644
index 0000000..6251d6c
--- /dev/null
+++ b/ringbuf.h
@@ -0,0 +1,79 @@
+/*
+ * ringbuf.h
+ * ---------
+ * Ring buffers for more reliable UART receives.
+ *
+ * Copyright (c) 2016, NORDUnet A/S All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * - Redistributions of source code must retain the above copyright notice,
+ *   this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * - Neither the name of the NORDUnet nor the names of its contributors may
+ *   be used to endorse or promote products derived from this software
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef RINGBUF_SIZE
+#define RINGBUF_SIZE  256
+#endif
+
+typedef struct {
+    int ridx;
+    volatile int widx;
+    uint8_t buf[RINGBUF_SIZE];
+} ringbuf_t;
+
+inline void ringbuf_init(ringbuf_t *rb)
+{
+    memset(rb, 0, sizeof(*rb));
+}
+
+inline int ringbuf_read_char(ringbuf_t *rb, uint8_t *c)
+{
+    if (rb->ridx != rb->widx) {
+        *c = rb->buf[rb->ridx];
+        if (++rb->ridx >= sizeof(rb->buf))
+            rb->ridx = 0;
+        return 1;
+    }
+    return 0;
+}
+
+inline void ringbuf_write_char(ringbuf_t *rb, uint8_t c)
+{
+    rb->buf[rb->widx] = c;
+    if (++rb->widx >= sizeof(rb->buf))
+        rb->widx = 0;
+}
+
+inline int ringbuf_empty(ringbuf_t *rb)
+{
+    return (rb->ridx == rb->widx);
+}
+
+inline int ringbuf_count(ringbuf_t *rb)
+{
+    int len = rb->widx - rb->ridx;
+    if (len < 0)
+        len += sizeof(rb->buf);
+    return len;
+}
-- 
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