From 2aaeee4e55571fdb49322ac7d2035b2b8fdfecab Mon Sep 17 00:00:00 2001
From: Paul Goeser <paul@rakka.de>
Date: Tue, 12 Jul 2011 15:01:53 +0200
Subject: [PATCH] added ringbuf_small

---
 firmware/slavechip/ringbuf_small.c | 67 ++++++++++++++++++++++++++++++
 firmware/slavechip/ringbuf_small.h | 12 ++++++
 2 files changed, 79 insertions(+)
 create mode 100644 firmware/slavechip/ringbuf_small.c
 create mode 100644 firmware/slavechip/ringbuf_small.h

diff --git a/firmware/slavechip/ringbuf_small.c b/firmware/slavechip/ringbuf_small.c
new file mode 100644
index 0000000..a180fdc
--- /dev/null
+++ b/firmware/slavechip/ringbuf_small.c
@@ -0,0 +1,67 @@
+#include "ringbuf_small.h"
+
+#include <util/atomic.h>
+
+
+/* Very generic implementation of an interrupt-safe ringbuffer
+ *
+ * Contention handling:
+ * - writing of pointers only with interrupt lock
+ * - reading of pointers allowed at any time
+ * - volatile not really necessary, unless you really need the functions to
+ *   react to freespace/newdata while they're running
+ * 
+ * PUT AND GET ARE NOT REENTRANT!
+ */
+
+void ringbuf_init(ringbuf_t *rb, char* buf, int size){
+    rb->startptr = buf;
+    rb->size = size;
+    rb->readpos = 0;
+    rb->writepos = 0;
+}
+
+/* pushes a value onto the ringbuffer
+ * returns 0 on success, 1 on buffer full
+ */
+uint8_t ringbuf_put(ringbuf_t *rb, uint8_t value){
+    // calculate next ptr pos
+    uint8_t next = rb->writepos + 1;
+    char* readpos;
+    if(next >= rb->size){
+        next = 0;
+    }
+    // check for space
+    if(next == rb->readpos){
+        return(1); // give up
+    }
+    *(rb->startptr + rb->writepos) = value;
+    // do we need a barrier here?
+    rb->writepos = next;
+    return(0);
+}
+
+/* gets a value from the ringbuffer
+ * returns value on success, -1 on buffer empty
+ */
+int16_t ringbuf_get(ringbuf_t *rb){
+    uint8_t value;
+    uint8_t next;
+    // calculate next ptr pos
+    next = rb->readpos + 1;
+    if(next >= rb->size){
+        next = 0;
+    }
+    //check for empty
+    if(rb->readpos == rb->writepos){
+        return(-1);
+    }
+    value = *(rb->startptr + rb->readpos);
+    rb->readpos = next;
+    return(value);
+}
+
+
+
+
+
diff --git a/firmware/slavechip/ringbuf_small.h b/firmware/slavechip/ringbuf_small.h
new file mode 100644
index 0000000..14c7091
--- /dev/null
+++ b/firmware/slavechip/ringbuf_small.h
@@ -0,0 +1,12 @@
+#include <stdint.h>
+
+typedef struct {
+    char* startptr;
+    uint8_t size;
+    uint8_t readpos;
+    uint8_t writepos;
+} ringbuf_t;
+
+
+void ringbuf_init(ringbuf_t* rb, char* buf, int size);
+