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<meta name="description" content="Learn about the USBX Device Class considerations.">
<title>Chapter 5 - USBX Device Class Considerations</title>
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</head>
<body class="article">
<div id="header">
<h1>Chapter 5 - USBX Device Class Considerations</h1>
</div>
<div id="content">
<div class="sect1">
<h2 id="_device_class_registration">Device Class registration</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Each device class follows the same principle for registration. A structure containing specific class parameters is passed to the class initialize function.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-c" data-lang="c">/* Set the parameters for callback when insertion/extraction of a HID device. */
hid_parameter.ux_slave_class_hid_instance_activate = tx_demo_hid_instance_activate;
hid_parameter.ux_slave_class_hid_instance_deactivate = tx_demo_hid_instance_deactivate;
/* Initialize the hid class parameters for the device. */
hid_parameter.ux_device_class_hid_parameter_report_address = hid_device_report;
hid_parameter.ux_device_class_hid_parameter_report_length = HID_DEVICE_REPORT_LENGTH;
hid_parameter.ux_device_class_hid_parameter_report_id = UX_TRUE;
hid_parameter.ux_device_class_hid_parameter_callback = demo_thread_hid_callback;
/* Initialize the device hid class. The class is connected with interface 0 */
status = ux_device_stack_class_register(_ux_system_slave_class_hid_name,
ux_device_class_hid_entry,1,0, (VOID *)&hid_parameter);</code></pre>
</div>
</div>
<div class="paragraph">
<p>Each class can register, optionally, a callback function when a instance of the class gets activated. The callback is then called by the device stack to inform the application that an instance was created.</p>
</div>
<div class="paragraph">
<p>The application would have in its body the 2 functions for activation and deactivation, as shown in the following example.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-c" data-lang="c">VOID tx_demo_hid_instance_activate(VOID *hid_instance)
{
/* Save the HID instance. */
hid_slave = (UX_SLAVE_CLASS_HID *) hid_instance;
}
VOID tx_demo_hid_instance_deactivate(VOID *hid_instance)
{
/* Reset the HID instance. */
hid_slave = UX_NULL;
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>It is not recommended to do anything within these functions but to memorize the instance of the class and synchronize with the rest of the application.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_general_considerations_for_bulk_transfer">General Considerations for Bulk Transfer</h2>
<div class="sectionbody">
<div class="paragraph">
<p>As per the USB 2.0 specification, an endpoint must always transmit data payloads with a data field less than or equal to the endpoint’s
reported wMaxPacketSize value. The size of a data packet is limited to bMaxPacketSize. Transfer can be completed with the following cases</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>The endpoint has transferred exactly the amount of data expected</p>
</li>
<li>
<p>When a device or host endpoint receives a packet with size less than max packet size(wMaxPacketSize). This short packet indicates that there is no more data packet left and transfer is complete or when the data packets to be transmitted are all equal to wMaxPacketSize, then the end of transfer cannot be determined. In order for transfer completion a Zero Length Packet(ZLP) must be sent
Short packets and Zero Length Packets signify the end of a bulk data transfer.
The above considerations apply to raw bulk data transfer APIs, e.g., ux_device_class_cdc_acm_read().</p>
</li>
</ol>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_usb_device_storage_class">USB Device Storage Class</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The USB device storage class allows for a storage device embedded in the system to be made visible to a USB host.</p>
</div>
<div class="paragraph">
<p>The USB device storage class does not by itself provide a storage solution. It merely accepts and interprets SCSI requests coming from the host. When one of these requests is a read or a write command, it will invoke a pre-defined call back to a real storage device handler, such as an ATA device driver or a Flash device driver.</p>
</div>
<div class="paragraph">
<p>When initializing the device storage class, a pointer structure is given to the class that contains all the information necessary. An example is given below.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-c" data-lang="c">/* Initialize the storage class parameters to customize vendor strings. */
storage_parameter.ux_slave_class_storage_parameter_vendor_id
= demo_ux_system_slave_class_storage_vendor_id;
storage_parameter.ux_slave_class_storage_parameter_product_id
= demo_ux_system_slave_class_storage_product_id;
storage_parameter.ux_slave_class_storage_parameter_product_rev
= demo_ux_system_slave_class_storage_product_rev;
storage_parameter.ux_slave_class_storage_parameter_product_serial
= demo_ux_system_slave_class_storage_product_serial;
/* Store the number of LUN in this device storage instance: single LUN. */
storage_parameter.ux_slave_class_storage_parameter_number_lun = 1;
/* Initialize the storage class parameters for reading/writing to the Flash Disk. */
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_last_lba = 0x1e6bfe;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_block_length = 512;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_type = 0;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_removable_flag = 0x80;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_read_only_flag
= UX_FALSE;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_read
= tx_demo_thread_flash_media_read;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_write
= tx_demo_thread_flash_media_write;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_status
= tx_demo_thread_flash_media_status;
/* A simple write caching support.
If this callback is assigned, host gets notification from caching page
that write caching is supported, and can send SYNCHRONIZE_CACHE to
flush cache. But caching options are not allowed to be changed. */
storage_parameter.ux_slave_class_storage_parameter_lun[0].
ux_slave_class_storage_media_flush =
tx_demo_thread_flash_media_flush;
/* Initialize the device storage class. The class is connected with interface 0 */
status = ux_device_stack_class_register(_ux_system_slave_class_storage_name,
ux_device_class_storage_entry, ux_device_class_storage_thread, 0, (VOID *)&storage_parameter);</code></pre>
</div>
</div>
<div class="paragraph">
<p>In this example, the driver storage strings are customized by assigning string pointers to corresponding parameter. If any one of the string pointer is left to UX_NULL, the default ThreadX string is used.</p>
</div>
<div class="paragraph">
<p>In this example, the drive’s last block address or LBA is given as well as the logical sector size. The LBA is the number of sectors available in the media --1. The block length is set to 512 in regular storage media. It can be set to 2048 for optical drives.</p>
</div>
<div class="paragraph">
<p>The application needs to pass three callback function pointers to allow the storage class to read, write and obtain status for the media.</p>
</div>
<div class="paragraph">
<p>The prototypes for the read and write functions are shown in the example below.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-c" data-lang="c">UINT media_read(
VOID *storage,
ULONG lun,
UCHAR *data_pointer,
ULONG number_blocks,
ULONG lba,
ULONG *media_status);
UINT media_write(
VOID *storage,
ULONG lun,
UCHAR *data_pointer,
ULONG number_blocks,
ULONG lba,
ULONG *media_status);</code></pre>
</div>
</div>
<div class="paragraph">
<p>Where:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><em>storage</em> is the instance of the storage class.</p>
</li>
<li>
<p><em>lun</em> is the LUN the command is directed to.</p>
</li>
<li>
<p><em>data_pointer</em> is the address of the buffer to be used for reading or writing.</p>
</li>
<li>
<p><em>number_blocks</em> is the number of sectors to read/write.</p>
</li>
<li>
<p><em>lba</em> is the sector address to read.</p>
</li>
<li>
<p><em>media_status</em> should be filled out exactly like the media status callback return value.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The return value can have either the value UX_SUCCESS or UX_ERROR indicating a successful or unsuccessful operation. These operations do not need to return any other error codes. If there is an error in any operation, the storage class will invoke the status call back function.</p>
</div>
<div class="paragraph">
<p>This function has the following prototype.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-c" data-lang="c">ULONG media_status(
VOID *storage,
ULONG lun,
ULONG media_id,
ULONG *media_status);</code></pre>
</div>
</div>
<div class="paragraph">
<p>The calling parameter media_id is not currently used and should always be 0. In the future it may be used to distinguish multiple storage devices or storage devices with multiple SCSI LUNs. This version of the storage class does not support multiple instances of the storage class or storage devices with multiple SCSI LUNs.</p>
</div>
<div class="paragraph">
<p>The return value is a SCSI error code that can have the following format.</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>Bits 0-7</strong> Sense_key</p>
</li>
<li>
<p><strong>Bits 8-15</strong> Additional Sense Code</p>
</li>
<li>
<p><strong>Bits 16-23</strong> Additional Sense Code Qualifier</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The following table provides the possible Sense/ASC/ASCQ combinations.</p>
</div>
<table class="tableblock frame-all grid-all stretch">
<colgroup>
<col style="width: 25%;">
<col style="width: 25%;">
<col style="width: 25%;">
<col style="width: 25%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Sense Key</th>
<th class="tableblock halign-left valign-top">ASC</th>
<th class="tableblock halign-left valign-top">ASCQ</th>
<th class="tableblock halign-left valign-top">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">NO SENSE</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">17</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">RECOVERED DATA WITH RETRIES</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">18</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">RECOVERED DATA WITH ECC</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">04</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL DRIVE NOT READY - BECOMING READY</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">04</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL DRIVE NOT READY - INITIALIZATION REQUIRED</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">04</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">04</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL UNIT NOT READY - FORMAT IN PROGRESS</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">04</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">FF</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL DRIVE NOT READY - DEVICE IS BUSY</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">06</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">NO REFERENCE POSITION FOUND</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">08</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL UNIT COMMUNICATION FAILURE</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">08</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL UNIT COMMUNICATION TIME-OUT</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">08</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">80</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL UNIT COMMUNICATION OVERRUN</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">3A</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">MEDIUM NOT PRESENT</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">54</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">USB TO HOST SYSTEM INTERFACE FAILURE</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">80</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">INSUFFICIENT RESOURCES</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">FF</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">FF</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">UNKNOWN ERROR</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">NO SEEK COMPLETE</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">WRITE FAULT</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">10</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">ID CRC ERROR</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">11</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">UNRECOVERED READ ERROR</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">12</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">ADDRESS MARK NOT FOUND FOR ID FIELD</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">13</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">ADDRESS MARK NOT FOUND FOR DATA FIELD</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">14</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">RECORDED ENTITY NOT FOUND</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">30</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">CANNOT READ MEDIUM - UNKNOWN FORMAT</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">03</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">31</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">FORMAT COMMAND FAILED</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">04</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">40</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">NN</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">DIAGNOSTIC FAILURE ON COMPONENT NN (80H-FFH)</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">1A</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">PARAMETER LIST LENGTH ERROR</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">20</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">INVALID COMMAND OPERATION CODE</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">21</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL BLOCK ADDRESS OUT OF RANGE</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">24</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">INVALID FIELD IN COMMAND PACKET</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">25</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOGICAL UNIT NOT SUPPORTED</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">26</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">INVALID FIELD IN PARAMETER LIST</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">26</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">01</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">PARAMETER NOT SUPPORTED</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">26</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">02</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">PARAMETER VALUE INVALID</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">05</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">39</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">SAVING PARAMETERS NOT SUPPORT</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">06</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">28</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">NOT READY TO READY TRANSITION — MEDIA CHANGED</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">06</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">29</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">POWER ON RESET OR BUS DEVICE RESET OCCURRED</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">06</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">2F</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">COMMANDS CLEARED BY ANOTHER INITIATOR</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">07</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">27</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">WRITE PROTECTED MEDIA</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">0B</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">4E</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">00</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">OVERLAPPED COMMAND ATTEMPTED</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>There are two additional, optional callbacks the application may implement; one is for responding to a <strong>GET_STATUS_NOTIFICATION</strong> command and the other is for responding to the <strong>SYNCHRONIZE_CACHE</strong> command.</p>
</div>
<div class="paragraph">
<p>If the application would like to handle the <strong>GET_STATUS_NOTIFICATION</strong> command from the host, it should implement a callback with the following prototype.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-c" data-lang="c">UINT ux_slave_class_storage_media_notification(
VOID *storage,
ULONG lun,
ULONG media_id,
ULONG notification_class,
UCHAR **media_notification,
ULONG *media_notification_length);</code></pre>
</div>
</div>
<div class="paragraph">
<p>Where:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><em>storage</em> is the instance of the storage class.</p>
</li>
<li>
<p><em>media_id</em> is not currently used. notification_class specifies the class of notification.</p>
</li>
<li>
<p><em>media_notification</em> should be set by the application to the buffer containing the response for the notification.</p>
</li>
<li>
<p><em>media_notification_length</em> should be set by the application to contain the length of the response buffer.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The return value indicates whether or not the command succeeded — should be either <strong>UX_SUCCESS</strong> or <strong>UX_ERROR</strong>.</p>
</div>
<div class="paragraph">
<p>If the application does not implement this callback, then upon receiving the <strong>GET_STATUS_NOTIFICATION</strong> command, USBX will notify the host that the command is not implemented.</p>
</div>
<div class="paragraph">
<p>The <strong>SYNCHRONIZE_CACHE</strong> command should be handled if the application is utilizing a cache for writes from the host. A host may send this command if it knows the storage device is about to be disconnected, for example, in Windows, if you right click a flash drive icon in the toolbar and select "Eject [storage device name]", Windows will issue the <strong>SYNCHRONIZE_CACHE</strong> command to that device.</p>
</div>
<div class="paragraph">
<p>If the application would like to handle the <strong>SYNCHRONIZE_CACHE</strong> command from the host, it should implement a callback with the following prototype.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-c" data-lang="c">UINT ux_slave_class_storage_media_flush(
VOID *storage,
ULONG lun,
ULONG number_blocks,
ULONG lba,
ULONG *media_status);</code></pre>
</div>
</div>
<div class="paragraph">
<p>Where:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><em>storage</em> is the instance of the storage class.</p>
</li>
<li>
<p><em>lun</em> parameter specifies which LUN the command is directed to.</p>
</li>
<li>
<p><em>number_blocks</em> specifies the number of blocks to synchronize.</p>
</li>