Add ringbuf.c. This works like a FreeRTOS queue, but allows for variable-length items which in some cases is more memory efficient than a queue.

components/freertos/include/freertos/ringbuf.h

@@ -0,0 +1,206 @@
+#ifndef FREERTOS_RINGBUF_H
+#define FREERTOS_RINGBUF_H
+
+/*
+Header definitions for a FreeRTOS ringbuffer object
+
+A ringbuffer instantiated by these functions essentially acts like a FreeRTOS queue, with the
+difference that it's strictly FIFO and with the main advantage that you can put in randomly-sized
+items. The capacity, accordingly, isn't measured in the amount of items, but the amount of memory
+that is used for storing the items. Dependent on the size of the items, more or less of them will 
+fit in the ring buffer.
+
+This ringbuffer tries to be efficient with memory: when inserting an item, the item data will
+be copied to the ringbuffer memory. When retrieving an item, however, a reference to ringbuffer
+memory will be returned. The returned memory is guaranteed to be 32-bit aligned and contiguous.
+The application can use this memory, but as long as it does, ringbuffer writes that would write
+to this bit of memory will block.
+
+The requirement for items to be contiguous is slightly problematic when the only way to place
+the next item would involve a wraparound from the end to the beginning of the ringbuffer. This can
+be solved in two ways:
+- allow_split_items = pdTRUE: The insertion code will split the item in two items; one which fits
+in the space left at the end of the ringbuffer, one that contains the remaining data which is placed
+in the beginning. Two xRingbufferReceive calls will be needed to retrieve the data.
+- allow_split_items = pdFALSE: The insertion code will leave the room at the end of the ringbuffer
+unused and instead will put the entire item at the start of the ringbuffer, as soon as there is 
+enough free space.
+
+The maximum size of an item will be affected by this decision. When split items are allowed, it's
+acceptable to push items of (buffer_size)-16 bytes into the buffer. When it's not allowed, the
+maximum size is (buffer_size/2)-8 bytes.
+*/
+
+//An opaque handle for a ringbuff object.
+typedef void * RingbufHandle_t;
+
+
+/**
+ * @brief  Create a ring buffer
+ *
+ * @param  buf_length : Length of circular buffer, in bytes. Each entry will take up its own length, plus a header
+ *                      that at the moment is equal to sizeof(size_t).
+ * @param allow_split_items : pdTRUE if it is acceptable that item data is inserted as two
+ *                            items instead of one.
+ *
+ * @return A RingbufHandle_t handle to the created ringbuffer, or NULL in case of error.
+ */
+RingbufHandle_t xRingbufferCreate(size_t buf_length, BaseType_t allow_split_items);
+
+
+/**
+ * @brief  Delete a ring buffer
+ *
+ * @param  ringbuf - Ring buffer to delete
+ *
+ * @return void
+ */
+void vRingbufferDelete(RingbufHandle_t ringbuf);
+
+
+/**
+ * @brief  Get maximum size of an item that can be placed in the ring buffer
+ *
+ * @param  ringbuf - Ring buffer to query
+ *
+ * @return Maximum size, in bytes, of an item that can be placed in a ring buffer.
+ */
+size_t xRingbufferGetMaxItemSize(RingbufHandle_t ringbuf);
+
+
+/**
+ * @brief  Insert an item into the ring buffer
+ *
+ * @param  ringbuf - Ring buffer to insert the item into
+ * @param  data - Pointer to data to insert. NULL is allowed if data_size is 0.
+ * @param  data_size - Size of data to insert. A value of 0 is allowed.
+ * @param  xTicksToWait - Ticks to wait for room in the ringbuffer.
+ *
+ * @return pdTRUE if succeeded, pdFALSE on time-out or when the buffer is larger 
+ *         than indicated by xRingbufferGetMaxItemSize(ringbuf).
+ */
+BaseType_t xRingbufferSend(RingbufHandle_t ringbuf, void *data, size_t data_size, TickType_t ticks_to_wait);
+
+
+/**
+ * @brief  Insert an item into the ring buffer from an ISR
+ *
+ * @param  ringbuf - Ring buffer to insert the item into
+ * @param  data - Pointer to data to insert. NULL is allowed if data_size is 0.
+ * @param  data_size - Size of data to insert. A value of 0 is allowed.
+ * @param  higher_prio_task_awoken - Value pointed to will be set to pdTRUE if the push woke up a higher
+ *                                     priority task.
+ *
+ * @return pdTRUE if succeeded, pdFALSE when the ring buffer does not have space.
+ */
+BaseType_t xRingbufferSendFromISR(RingbufHandle_t ringbuf, void *data, size_t data_size, BaseType_t *higher_prio_task_awoken);
+
+/**
+ * @brief  Retrieve an item from the ring buffer
+ *
+ * @param  ringbuf - Ring buffer to retrieve the item from
+ * @param  item_size - Pointer to a variable to which the size of the retrieved item will be written.
+ * @param  xTicksToWait - Ticks to wait for items in the ringbuffer.
+ *
+ * @return Pointer to the retrieved item on success; *item_size filled with the length of the 
+ *         item. NULL on timeout, *item_size is untouched in that case.
+ */
+void *xRingbufferReceive(RingbufHandle_t ringbuf, size_t *item_size, TickType_t ticks_to_wait);
+
+
+/**
+ * @brief  Retrieve an item from the ring buffer from an ISR
+ *
+ * @param  ringbuf - Ring buffer to retrieve the item from
+ * @param  item_size - Pointer to a variable to which the size of the retrieved item will be written.
+ *
+ * @return Pointer to the retrieved item on success; *item_size filled with the length of the 
+ *         item. NULL when the ringbuffer is empty, *item_size is untouched in that case.
+ */
+void *xRingbufferReceiveFromISR(RingbufHandle_t ringbuf, size_t *item_size);
+
+
+/**
+ * @brief  Return a previously-retrieved item to the ringbuffer
+ *
+ * @param  ringbuf - Ring buffer the item was retrieved from
+ * @param  item - Item that was received earlier
+ *
+ * @return void
+ */
+void vRingbufferReturnItem(RingbufHandle_t ringbuf, void *item);
+
+
+
+/**
+ * @brief  Return a previously-retrieved item to the ringbuffer from an ISR
+ *
+ * @param  ringbuf - Ring buffer the item was retrieved from
+ * @param  item - Item that was received earlier
+ * @param  higher_prio_task_awoken - Value pointed to will be set to pdTRUE if the push woke up a higher
+ *                                     priority task.
+ *
+ * @return void
+ */
+void vRingbufferReturnItemFromISR(RingbufHandle_t ringbuf, void *item, BaseType_t *higher_prio_task_awoken);
+
+
+/**
+ * @brief  Add the ringbuffer to a queue set. This specifically adds the semaphore that indicates
+ *         more space has become available in the ringbuffer.
+ *
+ * @param  ringbuf - Ring buffer to add to the queue set
+ * @param  xQueueSet - Queue set to add the ringbuffer to
+ *
+ * @return pdTRUE on success, pdFALSE otherwise
+ */
+BaseType_t xRingbufferAddToQueueSetRead(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet);
+
+
+/**
+ * @brief  Add the ringbuffer to a queue set. This specifically adds the semaphore that indicates
+ *         something has been written into the ringbuffer.
+ *
+ * @param  ringbuf - Ring buffer to add to the queue set
+ * @param  xQueueSet - Queue set to add the ringbuffer to
+ *
+ * @return pdTRUE on success, pdFALSE otherwise
+ */
+BaseType_t xRingbufferAddToQueueSetWrite(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet);
+
+
+/**
+ * @brief  Remove the ringbuffer from a queue set. This specifically removes the semaphore that indicates
+ *         more space has become available in the ringbuffer.
+ *
+ * @param  ringbuf - Ring buffer to remove from the queue set
+ * @param  xQueueSet - Queue set to remove the ringbuffer from
+ *
+ * @return pdTRUE on success, pdFALSE otherwise
+ */
+BaseType_t xRingbufferRemoveFromQueueSetRead(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet);
+
+
+/**
+ * @brief  Remove the ringbuffer from a queue set. This specifically removes the semaphore that indicates
+ *         something has been written to the ringbuffer.
+ *
+ * @param  ringbuf - Ring buffer to remove from the queue set
+ * @param  xQueueSet - Queue set to remove the ringbuffer from
+ *
+ * @return pdTRUE on success, pdFALSE otherwise
+ */
+BaseType_t xRingbufferRemoveFromQueueSetWrite(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet);
+
+
+/**
+ * @brief  Debugging function to print the internal pointers in the ring buffer
+ *
+ * @param  ringbuf - Ring buffer to show
+ *
+ * @return void
+ */
+void xRingbufferPrintInfo(RingbufHandle_t ringbuf);
+
+
+#endif

components/freertos/ringbuf.c

@@ -0,0 +1,474 @@
+// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
+//
+// 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 "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "freertos/semphr.h"
+#include "freertos/queue.h"
+#include "freertos/xtensa_api.h"
+#include "freertos/ringbuf.h"
+#include <stdint.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+typedef enum {
+    flag_allowsplit = 1,
+} rbflag_t;
+
+typedef enum {
+    iflag_free = 1,             //Buffer is not read and given back by application, free to overwrite
+    iflag_dummydata = 2,        //Data from here to end of ringbuffer is dummy. Restart reading at start of ringbuffer.
+} itemflag_t;
+
+
+//The ringbuffer structure
+typedef struct {
+    SemaphoreHandle_t free_space_sem;           //Binary semaphore, wakes up writing threads when there's more free space
+    SemaphoreHandle_t items_buffered_sem;       //Binary semaphore, indicates there are new packets in the circular buffer. See remark.
+    size_t size;                                //Size of the data storage
+    uint8_t *write_ptr;                         //Pointer where the next item is written
+    uint8_t *read_ptr;                          //Pointer from where the next item is read
+    uint8_t *free_ptr;                          //Pointer to the last block that hasn't been given back to the ringbuffer yet
+    uint8_t *data;                              //Data storage
+    portMUX_TYPE mux;                           //Spinlock for actual data/ptr/struct modification
+    rbflag_t flags;
+} ringbuf_t;
+
+
+
+/*
+Remark: A counting semaphore for items_buffered_sem would be more logical, but counting semaphores in
+FreeRTOS need a maximum count, and allocate more memory the larger the maximum count is. Here, we
+would need to set the maximum to the maximum amount of times a null-byte unit firs in the buffer,
+which is quite high and so would waste a fair amount of memory.
+*/
+
+
+//The header prepended to each ringbuffer entry. Size is assumed to be a multiple of 32bits.
+typedef struct {
+    size_t len;
+    itemflag_t flags;
+} buf_entry_hdr_t;
+
+
+//Calculate space free in the buffer
+static int ringbufferFreeMem(ringbuf_t *rb) 
+{
+    int free_size = rb->free_ptr-rb->write_ptr;
+    if (free_size <= 0) free_size += rb->size;
+    //Reserve one byte. If we do not do this and the entire buffer is filled, we get a situation 
+    //where read_ptr == free_ptr, messing up the next calculation.
+    return free_size-1;
+}
+
+//Copies a single item to the ring buffer. Assumes there is space in the ringbuffer and
+//the ringbuffer is locked. Increases write_ptr to the next item. Returns pdTRUE on
+//success, pdFALSE if it can't make the item fit and the calling routine needs to retry
+//later or fail.
+//This function by itself is not threadsafe, always call from within a muxed section.
+static BaseType_t copyItemToRingbuf(ringbuf_t *rb, uint8_t *buffer, size_t buffer_size) 
+{
+    size_t rbuffer_size=(buffer_size+3)&~3; //Payload length, rounded to next 32-bit value
+    configASSERT(((int)rb->write_ptr&3)==0); //write_ptr needs to be 32-bit aligned
+    configASSERT(rb->write_ptr-(rb->data+rb->size) >= sizeof(buf_entry_hdr_t)); //need to have at least the size 
+                                            //of a header to the end of the ringbuff
+    size_t rem_len=(rb->data + rb->size) - rb->write_ptr; //length remaining until end of ringbuffer
+    
+    //See if we have enough contiguous space to write the buffer.
+    if (rem_len < rbuffer_size + sizeof(buf_entry_hdr_t)) {
+        //The buffer can't be contiguously written to the ringbuffer, but needs special handling. Do
+        //that depending on how the ringbuffer is configured.
+        //The code here is also expected to check if the buffer, mangled in whatever way is implemented,
+        //will still fit, and return pdFALSE if that is not the case.
+        if (rb->flags & flag_allowsplit) {
+            //Buffer plus header is not going to fit in the room from wr_pos to the end of the 
+            //ringbuffer... we need to split the write in two.
+            //First, see if this will fit at all.
+            if (ringbufferFreeMem(rb) < (sizeof(buf_entry_hdr_t)*2)+rbuffer_size) {
+                //Will not fit.
+                return pdFALSE;
+            }
+            //Because the code at the end of the function makes sure we always have 
+            //room for a header, this should never assert.
+            configASSERT(rem_len>=sizeof(buf_entry_hdr_t));
+            //Okay, it should fit. Write everything.
+            //First, place bit of buffer that does fit. Write header first...
+            buf_entry_hdr_t *hdr=(buf_entry_hdr_t *)rb->write_ptr;
+            hdr->flags=0;
+            hdr->len=rem_len-sizeof(buf_entry_hdr_t);
+            rb->write_ptr+=sizeof(buf_entry_hdr_t);
+            rem_len-=sizeof(buf_entry_hdr_t);
+            if (rem_len!=0) {
+                //..then write the data bit that fits.
+                memcpy(rb->write_ptr, buffer, rem_len);
+                //Update vars so the code later on will write the rest of the data.
+                buffer+=rem_len;
+                rbuffer_size-=rem_len;
+                buffer_size-=rem_len;
+            } else {
+                //Huh, only the header fit. Mark as dummy so the receive function doesn't receive
+                //an useless zero-byte packet.
+                hdr->flags|=iflag_dummydata;
+            }
+            rb->write_ptr=rb->data;
+        } else {
+            //Buffer plus header is not going to fit in the room from wr_pos to the end of the 
+            //ringbuffer... but we're not allowed to split the buffer. We need to fill the 
+            //rest of the ringbuffer with a dummy item so we can place the data at the _start_ of
+            //the ringbuffer..
+            //First, find out if we actually have enough space at the start of the ringbuffer to
+            //make this work (Again, we need 4 bytes extra because otherwise read_ptr==free_ptr)
+            if (rb->free_ptr-rb->data < rbuffer_size+sizeof(buf_entry_hdr_t)+4) {
+                //Will not fit.
+                return pdFALSE;
+            }
+            //If the read buffer hasn't wrapped around yet, there's no way this will work either.
+            if (rb->free_ptr > rb->write_ptr) {
+                //No luck.
+                return pdFALSE;
+            }
+
+            //Okay, it will fit. Mark the rest of the ringbuffer space with a dummy packet.
+            buf_entry_hdr_t *hdr=(buf_entry_hdr_t *)rb->write_ptr;
+            hdr->flags=iflag_dummydata;
+            //Reset the write pointer to the start of the ringbuffer so the code later on can
+            //happily write the data.
+            rb->write_ptr=rb->data;
+        }
+    } else {
+        //No special handling needed. Checking if it's gonna fit probably still is a good idea.
+        if (ringbufferFreeMem(rb) < sizeof(buf_entry_hdr_t)+rbuffer_size) {
+            //Buffer is not going to fit, period.
+            return pdFALSE;
+        }
+    }
+
+    //If we are here, the buffer is guaranteed to fit in the space starting at the write pointer.
+    buf_entry_hdr_t *hdr=(buf_entry_hdr_t *)rb->write_ptr;
+    hdr->len=buffer_size;
+    hdr->flags=0;
+    rb->write_ptr+=sizeof(buf_entry_hdr_t);
+    memcpy(rb->write_ptr, buffer, buffer_size);
+    rb->write_ptr+=rbuffer_size;
+
+    //The buffer will wrap around if we don't have room for a header anymore.
+    if ((rb->data+rb->size)-rb->write_ptr < sizeof(buf_entry_hdr_t)) {
+        //'Forward' the write buffer until we are at the start of the ringbuffer.
+        //The read pointer will always be at the start of a full header, which cannot 
+        //exist at the point of the current write pointer, so there's no chance of overtaking
+        //that.
+        rb->write_ptr=rb->data;
+    }
+    return pdTRUE;
+}
+
+//Retrieves a pointer to the data of the next item, or NULL if this is not possible.
+//This function by itself is not threadsafe, always call from within a muxed section.
+static uint8_t *getItemFromRingbuf(ringbuf_t *rb, size_t *length)
+{
+    uint8_t *ret;
+    configASSERT(((int)rb->read_ptr&3)==0);
+    if (rb->read_ptr == rb->write_ptr) {
+        //No data available.
+        return NULL;
+    }
+    //The item written at the point of the read pointer may be a dummy item.
+    //We need to skip past it first, if that's the case.
+    buf_entry_hdr_t *hdr=(buf_entry_hdr_t *)rb->read_ptr;
+    configASSERT((hdr->len < rb->size) || (hdr->flags & iflag_dummydata));
+    if (hdr->flags & iflag_dummydata) {
+        //Hdr is dummy data. Reset to start of ringbuffer.
+        rb->read_ptr=rb->data;
+        //Get real header
+        hdr=(buf_entry_hdr_t *)rb->read_ptr;
+        configASSERT(hdr->len < rb->size);
+        //No need to re-check if the ringbuffer is empty: the write routine will
+        //always write a dummy item plus the real data item in one go, so now we must
+        //be at the real data item by definition.
+    }
+    //Okay, pass the data back.
+    ret=rb->read_ptr+sizeof(buf_entry_hdr_t);
+    *length=hdr->len;
+    //...and move the read pointer past the data.
+    rb->read_ptr+=sizeof(buf_entry_hdr_t)+((hdr->len+3)&~3);
+    //The buffer will wrap around if we don't have room for a header anymore.
+    if ((rb->data + rb->size) - rb->read_ptr < sizeof(buf_entry_hdr_t)) {
+        rb->read_ptr=rb->data;
+    }
+    return ret;
+}
+
+//Returns an item to the ringbuffer. Will mark the item as free, and will see if the free pointer
+//can be increase.
+//This function by itself is not threadsafe, always call from within a muxed section.
+static void returnItemToRingbuf(ringbuf_t *rb, void *item) {
+    uint8_t *data=(uint8_t*)item;
+    configASSERT(((int)rb->free_ptr&3)==0);
+    configASSERT(data >= rb->data);
+    configASSERT(data < rb->data+rb->size);
+    //Grab the buffer entry that preceeds the buffer
+    buf_entry_hdr_t *hdr=(buf_entry_hdr_t*)(data-sizeof(buf_entry_hdr_t));
+    configASSERT(hdr->len < rb->size);
+    configASSERT((hdr->flags & iflag_dummydata)==0);
+    configASSERT((hdr->flags & iflag_free)==0);
+    //Mark the buffer as free.
+    hdr->flags|=iflag_free;
+
+    //Do a cleanup pass.
+    hdr=(buf_entry_hdr_t *)rb->free_ptr;
+    //basically forward free_ptr until we run into either a block that is still in use or the write pointer.
+    while (((hdr->flags & iflag_free) || (hdr->flags & iflag_dummydata)) && rb->free_ptr != rb->write_ptr) {
+        if (hdr->flags & iflag_dummydata) {
+            //Rest is dummy data. Reset to start of ringbuffer.
+            rb->free_ptr=rb->data;
+        } else {
+            //Skip past item
+            size_t len=(hdr->len+3)&~3;
+            rb->free_ptr+=len+sizeof(buf_entry_hdr_t);
+            configASSERT(rb->free_ptr<=rb->data+rb->size);
+        }
+        //The buffer will wrap around if we don't have room for a header anymore.
+        if ((rb->data+rb->size)-rb->free_ptr < sizeof(buf_entry_hdr_t)) {
+            rb->free_ptr=rb->data;
+        }
+        //Next header
+        hdr=(buf_entry_hdr_t *)rb->free_ptr;
+    }
+}
+
+
+void xRingbufferPrintInfo(RingbufHandle_t ringbuf)
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    configASSERT(rb);
+    ets_printf("Rb size %d free %d rptr %d freeptr %d wptr %d\n",
+            rb->size, ringbufferFreeMem(rb), rb->read_ptr-rb->data, rb->free_ptr-rb->data, rb->write_ptr-rb->data);
+}
+
+
+
+RingbufHandle_t xRingbufferCreate(size_t buf_length, BaseType_t allow_split_items)
+{
+    ringbuf_t *rb = malloc(sizeof(ringbuf_t));
+    if (rb==NULL) goto err;
+    memset(rb, 0, sizeof(ringbuf_t));
+    rb->data = malloc(buf_length);
+    if (rb->data == NULL) goto err;
+    rb->size = buf_length;
+    rb->free_ptr = rb->data;
+    rb->read_ptr = rb->data;
+    rb->write_ptr = rb->data;
+    rb->free_space_sem = xSemaphoreCreateBinary();
+    rb->items_buffered_sem = xSemaphoreCreateBinary();
+    rb->flags=0;
+    if (allow_split_items) rb->flags|=flag_allowsplit;
+    if (rb->free_space_sem == NULL || rb->items_buffered_sem == NULL) goto err;
+    vPortCPUInitializeMutex(&rb->mux);
+    return (RingbufHandle_t)rb;
+
+err:
+    //Some error has happened. Free/destroy all allocated things and return NULL.
+    if (rb) {
+        free(rb->data);
+        if (rb->free_space_sem) vSemaphoreDelete(rb->free_space_sem);
+        if (rb->items_buffered_sem) vSemaphoreDelete(rb->items_buffered_sem);
+    }
+    free(rb);
+    return NULL;
+}
+
+void vRingbufferDelete(RingbufHandle_t ringbuf) {
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    if (rb) {
+        free(rb->data);
+        if (rb->free_space_sem) vSemaphoreDelete(rb->free_space_sem);
+        if (rb->items_buffered_sem) vSemaphoreDelete(rb->items_buffered_sem);
+    }
+    free(rb);
+}
+
+size_t xRingbufferGetMaxItemSize(RingbufHandle_t ringbuf)
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    configASSERT(rb);
+    //In both cases, we return 4 bytes less than what we actually can have. If the ringbuffer is
+    //indeed entirely filled, read_ptr==free_ptr, which throws off the free space calculation.
+    if (rb->flags & flag_allowsplit) {
+        //Worst case, we need to split an item into two, which means two headers of overhead.
+        return rb->size-(sizeof(buf_entry_hdr_t)*2)-4;
+    } else {
+        //Worst case, we have the write ptr in such a position that we are lacking four bytes of free
+        //memory to put an item into the rest of the memory. If this happens, we have to dummy-fill
+        //(item_data-4) bytes of buffer, then we only have (size-(item_data-4) bytes left to fill
+        //with the real item. (item size being header+data)
+        return (rb->size/2)-sizeof(buf_entry_hdr_t)-4;
+    }
+}
+
+BaseType_t xRingbufferSend(RingbufHandle_t ringbuf, void *data, size_t dataSize, TickType_t ticks_to_wait)
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    size_t needed_size=dataSize+sizeof(buf_entry_hdr_t);
+    BaseType_t done=pdFALSE;
+    portTickType ticks_end=xTaskGetTickCount() + ticks_to_wait;
+
+    configASSERT(rb);
+
+    if (dataSize > xRingbufferGetMaxItemSize(ringbuf)) {
+        //Data will never ever fit in the queue.
+        return pdFALSE;
+    }
+
+    while (!done) {
+        //Check if there is enough room in the buffer. If not, wait until there is.
+        do {
+            if (ringbufferFreeMem(rb) < needed_size) {
+                //Data does not fit yet. Wait until the free_space_sem is given, then re-evaluate.
+
+                BaseType_t r = xSemaphoreTake(rb->free_space_sem, ticks_to_wait);
+                if (r == pdFALSE) {
+                    //Timeout.
+                    return pdFALSE;
+                }
+                //Adjust ticks_to_wait; we may have waited less than that and in the case the free memory still is not enough,
+                //we will need to wait some more.
+                ticks_to_wait = ticks_end - xTaskGetTickCount();
+            }
+        } while (ringbufferFreeMem(rb) < needed_size && ticks_to_wait>=0);
+        
+        //Lock the mux in order to make sure no one else is messing with the ringbuffer and do the copy.
+        portENTER_CRITICAL(&rb->mux);
+        //Another thread may have been able to sneak its write first. Check again now we locked the ringbuff, and retry
+        //everything if this is the case. Otherwise, we can write and are done.
+        done=copyItemToRingbuf(rb, data, dataSize);
+        portEXIT_CRITICAL(&rb->mux);
+    }
+    xSemaphoreGive(rb->items_buffered_sem);
+    return pdTRUE;
+}
+
+
+BaseType_t xRingbufferSendFromISR(RingbufHandle_t ringbuf, void *data, size_t dataSize, BaseType_t *higher_prio_task_awoken) 
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    BaseType_t write_succeeded;
+    configASSERT(rb);
+    size_t needed_size=dataSize+sizeof(buf_entry_hdr_t);
+    portENTER_CRITICAL_ISR(&rb->mux);
+    if (needed_size>ringbufferFreeMem(rb)) {
+        //Does not fit in the remaining space in the ringbuffer.
+        write_succeeded=pdFALSE;
+    } else {
+        copyItemToRingbuf(rb, data, dataSize);
+        write_succeeded=pdTRUE;
+    }
+    portEXIT_CRITICAL_ISR(&rb->mux);
+    if (write_succeeded) {
+        xSemaphoreGiveFromISR(rb->items_buffered_sem, higher_prio_task_awoken);
+    }
+    return write_succeeded;
+}
+
+
+void *xRingbufferReceive(RingbufHandle_t ringbuf, size_t *item_size, TickType_t ticks_to_wait) 
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    uint8_t *itemData;
+    BaseType_t done=pdFALSE;
+    configASSERT(rb);
+    while(!done) {
+        //See if there's any data available. If not, wait until there is.
+        while (rb->read_ptr == rb->write_ptr) {
+            BaseType_t r=xSemaphoreTake(rb->items_buffered_sem, ticks_to_wait);
+            if (r == pdFALSE) {
+                //Timeout.
+                return NULL;
+            }
+        }
+        //Okay, we seem to have data in the buffer. Grab the mux and copy it out if it's still there.
+        portENTER_CRITICAL(&rb->mux);
+        itemData=getItemFromRingbuf(rb, item_size);
+        portEXIT_CRITICAL(&rb->mux);
+        if (itemData) {
+            //We managed to get an item.
+            done=pdTRUE;
+        }
+    }
+    return (void*)itemData;
+}
+
+
+void *xRingbufferReceiveFromISR(RingbufHandle_t ringbuf, size_t *item_size) 
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    uint8_t *itemData;
+    configASSERT(rb);
+    portENTER_CRITICAL_ISR(&rb->mux);
+    itemData=getItemFromRingbuf(rb, item_size);
+    portEXIT_CRITICAL_ISR(&rb->mux);
+    return (void*)itemData;
+}
+
+
+void vRingbufferReturnItem(RingbufHandle_t ringbuf, void *item) 
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    portENTER_CRITICAL_ISR(&rb->mux);
+    returnItemToRingbuf(rb, item);
+    portEXIT_CRITICAL_ISR(&rb->mux);
+    xSemaphoreGive(rb->free_space_sem);
+}
+
+
+void vRingbufferReturnItemFromISR(RingbufHandle_t ringbuf, void *item, BaseType_t *higher_prio_task_awoken) 
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    portENTER_CRITICAL_ISR(&rb->mux);
+    returnItemToRingbuf(rb, item);
+    portEXIT_CRITICAL_ISR(&rb->mux);
+    xSemaphoreGiveFromISR(rb->free_space_sem, higher_prio_task_awoken);
+}
+
+
+BaseType_t xRingbufferAddToQueueSetRead(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet)
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    configASSERT(rb);
+    return xQueueAddToSet(rb->items_buffered_sem, xQueueSet);
+}
+
+
+BaseType_t xRingbufferAddToQueueSetWrite(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet)
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    configASSERT(rb);
+    return xQueueAddToSet(rb->free_space_sem, xQueueSet);
+}
+
+
+BaseType_t xRingbufferRemoveFromQueueSetRead(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet)
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    configASSERT(rb);
+    return xQueueRemoveFromSet(rb->items_buffered_sem, xQueueSet);
+}
+
+BaseType_t xRingbufferRemoveFromQueueSetWrite(RingbufHandle_t ringbuf, QueueSetHandle_t xQueueSet)
+{
+    ringbuf_t *rb=(ringbuf_t *)ringbuf;
+    configASSERT(rb);
+    return xQueueRemoveFromSet(rb->free_space_sem, xQueueSet);
+}
+