added ringbuffer from thermocouple-project

TODO

@@ -3,8 +3,13 @@
 
 - programmieren
     - sdcard
+        - timing von soft-spi
+        - streaming funktion
     - pwm
+        - 11bit-pwm-emu
     - drumherum
+        - data-streaming von sdcard
+        - ringbuf (ryx)
 
 - testen
     - sdcard
@@ -19,5 +24,4 @@
 
 
 == ryx ==
-- belastbarkeit von kleinen Tastern nachschlagen
 

ringbuf_small.c

@@ -0,0 +1,66 @@
+#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;
+    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);
+}
+
+
+
+
+

ringbuf_small.h

@@ -0,0 +1,18 @@
+#ifndef __RINGBSML_H
+#define __RINGBSML_H
+
+#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);
+uint8_t ringbuf_put(ringbuf_t *rb, uint8_t value);
+int16_t ringbuf_get(ringbuf_t *rb);
+
+#endif