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| <div class="section" id="flash-circular-buffer-fcb"> |
| <h1>Flash Circular Buffer (FCB)<a class="headerlink" href="#flash-circular-buffer-fcb" title="Permalink to this headline">ΒΆ</a></h1> |
| <p>Flash circular buffer provides an abstration through which you can treat |
| flash like a FIFO. You append entries to the end, and read data from the |
| beginning.</p> |
| <div class="section" id="description"> |
| <h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">ΒΆ</a></h2> |
| <p>Elements in the flash contain the length of the element, the data within |
| the element, and checksum over the element contents.</p> |
| <p>Storage of elements in flash is done in a FIFO fashion. When user |
| requests space for the next element, space is located at the end of the |
| used area. When user starts reading, the first element served is the |
| oldest element in flash.</p> |
| <p>Elements can be appended to the end of the area until storage space is |
| exhausted. User has control over what happens next; either erase oldest |
| block of data, thereby freeing up some space, or stop writing new data |
| until existing data has been collected. FCB treats underlying storage as |
| an array of flash sectors; when it erases old data, it does this a |
| sector at a time.</p> |
| <p>Elements in the flash are checksummed. That is how FCB detects whether |
| writing element to flash completed ok. It will skip over entries which |
| donβt have a valid checksum.</p> |
| </div> |
| <div class="section" id="usage"> |
| <h2>Usage<a class="headerlink" href="#usage" title="Permalink to this headline">ΒΆ</a></h2> |
| <p>To add an element to circular buffer:</p> |
| <ul class="simple"> |
| <li><p>Call fcb_append() to get the location where data can be written. If |
| this fails due to lack of space, you can call fcb_rotate() to make |
| some. And then call fcb_append() again.</p></li> |
| <li><p>Use flash_area_write() to write element contents.</p></li> |
| <li><p>Call fcb_append_finish() when done. This completes the entry by |
| calculating the checksum.</p></li> |
| </ul> |
| <p>To read contents of the circular buffer: * Call fcb_walk() with a |
| pointer to your callback function. * Within callback function copy in |
| data from the element using flash_area_read(). You can tell when all |
| data from within a sector has been read by monitoring returned elementβs |
| area pointer. Then you can call fcb_rotate(), if youβre done with that |
| data.</p> |
| <p>Alternatively: * Call fcb_getnext() with 0 in element offset to get |
| the pointer to oldest element. * Use flash_area_read() to read |
| element contents. * Call fcb_getnext() with pointer to current element |
| to get the next one. And so on.</p> |
| </div> |
| <div class="section" id="data-structures"> |
| <h2>Data structures<a class="headerlink" href="#data-structures" title="Permalink to this headline">ΒΆ</a></h2> |
| <p>This data structure describes the element location in the flash. You |
| would use it figure out what parameters to pass to flash_area_read() |
| to read element contents. Or to flash_area_write() when adding a new |
| element.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">fcb_entry</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">flash_area</span><span class="w"> </span><span class="o">*</span><span class="n">fe_area</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">fe_elem_off</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">fe_data_off</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">fe_data_len</span><span class="p">;</span> |
| <span class="p">};</span> |
| </pre></div> |
| </div> |
| <table class="docutils align-default"> |
| <colgroup> |
| <col style="width: 43%" /> |
| <col style="width: 57%" /> |
| </colgroup> |
| <thead> |
| <tr class="row-odd"><th class="head"><p>Element</p></th> |
| <th class="head"><p>Description</p></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="row-even"><td><p>fe_area</p></td> |
| <td><p>Pointer to |
| info about the |
| flash sector. |
| Pass this to |
| flash_area_x |
| x() |
| routines.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>fe_elem_ |
| off</p></td> |
| <td><p>Byte offset |
| from the start |
| of the sector |
| to beginning |
| of element.</p></td> |
| </tr> |
| <tr class="row-even"><td><p>fe_data_ |
| off</p></td> |
| <td><p>Byte offset |
| from start of |
| the sector to |
| beginning of |
| element data. |
| Pass this to |
| to |
| flash_area_x |
| x() |
| routines.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>fe_data_ |
| len</p></td> |
| <td><p>Number of |
| bytes in the |
| element.</p></td> |
| </tr> |
| </tbody> |
| </table> |
| <p>The following data structure describes the FCB itself. First part should |
| be filled in by the user before calling fcb_init(). The second part is |
| used by FCB for its internal bookkeeping.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">fcb</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Caller of fcb_init fills this in */</span> |
| <span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">f_magic</span><span class="p">;</span><span class="w"> </span><span class="cm">/* As placed on the disk */</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">f_version</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Current version number of the data */</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">f_sector_cnt</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Number of elements in sector array */</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">f_scratch_cnt</span><span class="p">;</span><span class="w"> </span><span class="cm">/* How many sectors should be kept empty */</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">flash_area</span><span class="w"> </span><span class="o">*</span><span class="n">f_sectors</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Array of sectors, must be contiguous */</span> |
| |
| <span class="w"> </span><span class="cm">/* Flash circular buffer internal state */</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">os_mutex</span><span class="w"> </span><span class="n">f_mtx</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Locking for accessing the FCB data */</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">flash_area</span><span class="w"> </span><span class="o">*</span><span class="n">f_oldest</span><span class="p">;</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">fcb_entry</span><span class="w"> </span><span class="n">f_active</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">f_active_id</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">f_align</span><span class="p">;</span><span class="w"> </span><span class="cm">/* writes to flash have to aligned to this */</span> |
| <span class="p">};</span> |
| </pre></div> |
| </div> |
| <table class="docutils align-default"> |
| <colgroup> |
| <col style="width: 43%" /> |
| <col style="width: 57%" /> |
| </colgroup> |
| <thead> |
| <tr class="row-odd"><th class="head"><p>Element</p></th> |
| <th class="head"><p>Description</p></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="row-even"><td><p>f_magic</p></td> |
| <td><p>Magic number |
| in the |
| beginning of |
| FCB flash |
| sector. FCB |
| uses this when |
| determining |
| whether sector |
| contains valid |
| data or not.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>f_version</p></td> |
| <td><p>Current |
| version number |
| of the data. |
| Also stored in |
| flash sector |
| header.</p></td> |
| </tr> |
| <tr class="row-even"><td><p>f_sector_cnt</p></td> |
| <td><p>Number of |
| elements in |
| the f_sectors |
| array.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>f_scratch |
| _cnt</p></td> |
| <td><p>Number of |
| sectors to |
| keep empty. |
| This can be |
| used if you |
| need to have |
| scratch space |
| for garbage |
| collecting |
| when FCB fills |
| up.</p></td> |
| </tr> |
| <tr class="row-even"><td><p>f_sectors</p></td> |
| <td><p>Array of |
| entries |
| describing |
| flash sectors |
| to use.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>f_mtx</p></td> |
| <td><p>Lock |
| protecting |
| access to FCBs |
| internal data.</p></td> |
| </tr> |
| <tr class="row-even"><td><p>f_oldest</p></td> |
| <td><p>Pointer to |
| flash sector |
| containing the |
| oldest data. |
| This is where |
| data is served |
| when read is |
| started.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>f_active</p></td> |
| <td><p>Flash location |
| where the |
| newest data |
| is. This is |
| used by |
| fcb_append() |
| to figure out |
| where the data |
| should go to.</p></td> |
| </tr> |
| <tr class="row-even"><td><p>f_active_id</p></td> |
| <td><p>Flash sectors |
| are assigned |
| ever-increasin |
| g |
| serial |
| numbers. This |
| is how FCB |
| figures out |
| where oldest |
| data is on |
| system |
| restart.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>f_align</p></td> |
| <td><p>Some flashes |
| have |
| restrictions |
| on alignment |
| for writes. |
| FCB keeps a |
| copy of this |
| number for the |
| flash here.</p></td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <div class="section" id="list-of-functions"> |
| <h2>List of Functions<a class="headerlink" href="#list-of-functions" title="Permalink to this headline">ΒΆ</a></h2> |
| <p>The functions available in this OS feature are:</p> |
| </div> |
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