<h1><big><fontcolor="#3c34ec"><i>NuttX USB Device Trace</i></font></big></h1>
<p>Last Updated: March 20, 2011</p>
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<p><b>USB Device Tracing Controls</b>.
The NuttX USB device subsystem supports a fairly sophisticated tracing facility.
The basic trace cabability is controlled by these NuttX configuration settings:
</p>
<ul>
<li><code>CONFIG_USBDEV_TRACE</code>: Enables USB tracing</li>
<li><code>CONFIG_USBDEV_TRACE_NRECORDS</code>: Number of trace entries to remember</li>
</ul>
<p><b>Trace IDs</b>.
The trace facility works like this:
When enabled, USB events that occur in either the USB device driver or in the USB class driver are logged.
These events are described in <code>include/nuttx/usb/usbdev_trace.h</code>.
The logged events are identified by a set of event IDs:
</p>
<ul><table>
<tr>
<td><code>TRACE_INIT_ID</code></td>
<td>Initialization events</td>
</tr>
<tr>
<td><code>TRACE_EP_ID</code></td>
<td>Endpoint API calls</td>
</tr>
<tr>
<td><code>TRACE_DEV_ID</code></td>
<td>USB device API calls</td>
</tr>
<tr>
<td><code>TRACE_CLASS_ID</code></td>
<td>USB class driver API calls</td>
</tr>
<tr>
<td><code>TRACE_CLASSAPI_ID</code></td>
<td>Other class driver system API calls</td>
</tr>
<tr>
<td><code>TRACE_CLASSSTATE_ID</code></td>
<td>Track class driver state changes</td>
</tr>
<tr>
<td><code>TRACE_INTENTRY_ID</code></td>
<td>Interrupt handler entry</td>
</tr>
<tr>
<td><code>TRACE_INTDECODE_ID</code></td>
<td>Decoded interrupt event</td>
</tr>
<tr>
<td><code>TRACE_INTEXIT_ID</code></td>
<td>Interrupt handler exit</td>
</tr>
<tr>
<td><code>TRACE_OUTREQQUEUED_ID</code></td>
<td>Request queued for OUT endpoint</td>
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<tr>
<td><code>TRACE_INREQQUEUED_ID</code></td>
<td>Request queued for IN endpoint</td>
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<tr>
<td><code>TRACE_READ_ID</code></td>
<td>Read (OUT) action</td>
</tr>
<tr>
<td><code>TRACE_WRITE_ID</code></td>
<td>Write (IN) action</td>
</tr>
<tr>
<td><code>TRACE_COMPLETE_ID</code></td>
<td>Request completed</td>
</tr>
<tr>
<td><code>TRACE_DEVERROR_ID</code></td>
<td>USB controller driver error event</td>
</tr>
<tr>
<td><code>TRACE_CLSERROR_ID</code></td>
<td>USB class driver error event</td>
</tr>
</table></ul>
<p><b>Logged Events</b>.
Each logged event is 32-bits in size and includes
</p>
<ol>
<li>8-bits of the trace ID (values associated with the above)</li>
<li>8-bits of additional trace ID data, and</li>
<li>16-bits of additonal data.</li>
</ol>
<p><b>8-bit Trace Data</b>
The 8-bit trace data depends on the specific event ID. As examples,
</p>
<ul>
<li>
For the USB serial and mass storage class, the 8-bit event data is provided in <code>include/nuttx/usb/usbdev_trace.h</code>.
</li>
<li>
For the USB device driver, that 8-bit event data is provided within the USB device driver itself.
So, for example, the 8-bit event data for the LPC1768 USB device driver is found in <code>arch/arm/src/lpc17xx/lpc17_usbdev.c</code>.
</li>
</ul>
<p><b>16-bit Trace Data</b>.
The 16-bit trace data provided additional context data relevant to the specific logged event.
</p>
<p><b>Trace Control Interfaces</b>.
Logging of each of these kinds events can be enabled or disabled using the interfaces described in <code>include/nuttx/usb/usbdev_trace.h</code>.
</p>
<p><b>Enabling USB Device Tracing</b>.
USB device tracing will be configured if <code>CONFIG_USBDEV</code> and either of the following are set in the NuttX configuration file:
</p>
<ul>
<li><code>CONFIG_USBDEV_TRACE</code>, or</li>
<li><code>CONFIG_DEBUG and CONFIG_DEBUG_USB</code></li>
</ul>
<p><b>Log Data Sink</b>.
The logged data itself may go to either (1) an internal circular buffer, or (2) may be provided on the console.
If <code>CONFIG_USBDEV_TRACE</code> is defined, then the trace data will go to the circular buffer.
The size of the circular buffer is determined by <code>CONFIG_USBDEV_TRACE_NRECORDS</code>.
Otherwise, the trace data goes to console.
<p>
<p><b>Example</b>.
Here is an example of USB trace output using <code>apps/examples/usbserial</code> for an LPC1768 platform with the following NuttX configuration settings:
