/** \file
*
- * Ultra lightweight ring buffer, for fast insertion/deletion.
+ * Ultra lightweight ring buffer, for fast insertion/deletion. This uses inlined functions
+ * for maximum speed. All buffers created with this library must be of the same size, however
+ * multiple independant buffers can be created.
+ *
+ * Note that for each buffer, insertion and removal operations may occur at the same time (via
+ * a multithreaded ISR based system) however the same kind of operation (two or more insertions
+ * or deletions) must not overlap. If there is possibility of two or more of the same kind of
+ * operating occuring at the same point in time, atomic (mutex) locking should be used.
*/
#ifndef _ULW_RING_BUFF_H_
#define _ULW_RING_BUFF_H_
/* Includes: */
+ #include <util/atomic.h>
+
#include <stdint.h>
#include <stdbool.h>
/* Defines: */
- /** Size of each ring buffer, in bytes */
- #define BUFFER_SIZE 128
+ /** Size of each ring buffer, in data elements - must be between 1 and 255. */
+ #define BUFFER_SIZE 255
- /** Type of data to store into the buffer */
- #define RingBuff_Data_t uint8_t
+ /** Type of data to store into the buffer. */
+ #define RingBuff_Data_t uint8_t
+
+ /** Datatype which may be used to store the count of data stored in a buffer, retrieved
+ * via a call to \ref RingBuffer_GetCount().
+ */
+ #if (BUFFER_SIZE <= 0xFF)
+ #define RingBuff_Count_t uint8_t
+ #else
+ #define RingBuff_Count_t uint16_t
+ #endif
/* Type Defines: */
+ /** Type define for a new ring buffer object. Buffers should be initialized via a call to
+ * \ref RingBuffer_InitBuffer() before use.
+ */
typedef struct
{
- RingBuff_Data_t Buffer[BUFFER_SIZE];
- RingBuff_Data_t* In;
- RingBuff_Data_t* Out;
- uint8_t Count;
+ RingBuff_Data_t Buffer[BUFFER_SIZE]; /**< Internal ring buffer data, referenced by the buffer pointers. */
+ RingBuff_Data_t* In; /**< Current storage location in the circular buffer */
+ RingBuff_Data_t* Out; /**< Current retrieval location in the circular buffer */
+ RingBuff_Count_t Count;
} RingBuff_t;
/* Inline Functions: */
+ /** Initializes a ring buffer ready for use. Buffers must be initialized via this function
+ * before any operations are called upon them. Already initialized buffers may be reset
+ * by re-initializing them using this function.
+ *
+ * \param[out] Buffer Pointer to a ring buffer structure to initialize
+ */
static inline void RingBuffer_InitBuffer(RingBuff_t* const Buffer)
{
- Buffer->In = Buffer->Buffer;
- Buffer->Out = Buffer->Buffer;
- Buffer->Count = 0;
+ ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+ {
+ Buffer->In = Buffer->Buffer;
+ Buffer->Out = Buffer->Buffer;
+ }
}
- static inline void RingBuffer_Insert(RingBuff_t* const Buffer, RingBuff_Data_t Data)
+ /** Retrieves the minimum number of bytes stored in a particular buffer. This value is computed
+ * by entering an atomic lock on the buffer while the IN and OUT locations are fetched, so that
+ * the buffer cannot be modified while the computation takes place. This value should be cached
+ * when reading out the contents of the buffer, so that as small a time as possible is spent
+ * in an atomic lock.
+ *
+ * \note The value returned by this function is guaranteed to only be the minimum number of bytes
+ * stored in the given buffer; this value may change as other threads write new data and so
+ * the returned number should be used only to determine how many successive reads may safely
+ * be performed on the buffer.
+ *
+ * \param[in] Buffer Pointer to a ring buffer structure whose count is to be computed
+ */
+ static inline RingBuff_Count_t RingBuffer_GetCount(RingBuff_t* const Buffer)
{
- *Buffer->In = Data;
+ RingBuff_Count_t Count;
+
+ ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+ {
+ Count = Buffer->Count;
+ }
+
+ return Count;
+ }
+ /** Atomically determines if the specified ring buffer contains any free space. This should
+ * be tested before storing data to the buffer, to ensure that no data is lost due to a
+ * buffer overrun.
+ *
+ * \param[in,out] Buffer Pointer to a ring buffer structure to insert into
+ *
+ * \return Boolean true if the buffer contains no free space, false otherwise
+ */
+ static inline bool RingBuffer_IsFull(RingBuff_t* const Buffer)
+ {
+ return (RingBuffer_GetCount(Buffer) == BUFFER_SIZE);
+ }
+
+ /** Atomically determines if the specified ring buffer contains any data. This should
+ * be tested before removing data from the buffer, to ensure that the buffer does not
+ * underflow.
+ *
+ * If the data is to be removed in a loop, store the total number of bytes stored in the
+ * buffer (via a call to the \ref RingBuffer_GetCount() function) in a temporary variable
+ * to reduce the time spent in atomicity locks.
+ *
+ * \param[in,out] Buffer Pointer to a ring buffer structure to insert into
+ *
+ * \return Boolean true if the buffer contains no free space, false otherwise
+ */
+ static inline bool RingBuffer_IsEmpty(RingBuff_t* const Buffer)
+ {
+ return (RingBuffer_GetCount(Buffer) == 0);
+ }
+
+ /** Inserts an element into the ring buffer.
+ *
+ * \note Only one execution thread (main program thread or an ISR) may insert into a single buffer
+ * otherwise data corruption may occur. Insertion and removal may occur from different execution
+ * threads.
+ *
+ * \param[in,out] Buffer Pointer to a ring buffer structure to insert into
+ * \param[in] Data Data element to insert into the buffer
+ */
+ static inline void RingBuffer_Insert(RingBuff_t* const Buffer,
+ const RingBuff_Data_t Data)
+ {
+ *Buffer->In = Data;
+
if (++Buffer->In == &Buffer->Buffer[BUFFER_SIZE])
Buffer->In = Buffer->Buffer;
-
- Buffer->Count++;
+
+ ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+ {
+ Buffer->Count++;
+ }
}
+ /** Removes an element from the ring buffer.
+ *
+ * \note Only one execution thread (main program thread or an ISR) may remove from a single buffer
+ * otherwise data corruption may occur. Insertion and removal may occur from different execution
+ * threads.
+ *
+ * \param[in,out] Buffer Pointer to a ring buffer structure to retrieve from
+ *
+ * \return Next data element stored in the buffer
+ */
static inline RingBuff_Data_t RingBuffer_Remove(RingBuff_t* const Buffer)
{
RingBuff_Data_t Data = *Buffer->Out;
-
+
if (++Buffer->Out == &Buffer->Buffer[BUFFER_SIZE])
Buffer->Out = Buffer->Buffer;
-
- Buffer->Count--;
+ ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+ {
+ Buffer->Count--;
+ }
+
return Data;
}
#endif
-
\ No newline at end of file
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