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<concept id="GUID-6430A8D0-CC8B-56DF-8218-05FC00FD02DE" xml:lang="en"><title>Other

Device Driver Issues</title><shortdesc>This topic describes some other issues that you need to be aware

of when writing device drivers. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<ul>

<li id="GUID-16BFF003-C452-59E7-A2ED-9BE13709E209"><p>The logical channel's <codeph>Request()</codeph> function

is called in the context of the calling thread, and when called, the <xref href="GUID-38D1534C-AA01-33AF-9937-CDD818A85F97.dita#GUID-38D1534C-AA01-33AF-9937-CDD818A85F97/GUID-9014BB87-14EB-3ECA-A030-9797E3631C46"><apiname>DThread::iTempObj</apiname></xref> member

for the current thread, i.e. the calling thread, is in use. It contains a

pointer to the logical channel object being used (i.e. the instance of the <xref href="GUID-E7550422-5121-3393-A85E-BB797969CD2A.dita"><apiname>DLogicalChannelBase</apiname></xref> derived

class). This pointer is reference counted to avoid problems if user code closes

the channel from another thread while the current thread is using it. </p> <p>If

a device driver needs to use a temporary object, it should use the <xref href="GUID-38D1534C-AA01-33AF-9937-CDD818A85F97.dita#GUID-38D1534C-AA01-33AF-9937-CDD818A85F97/GUID-18C0E9E9-825D-3904-9502-545E9E26E2DE"><apiname>DThread::iExtTempObj</apiname></xref> member. </p> </li>

<li id="GUID-EB5AFAD3-1E86-5C42-943C-B1662F12C1AC"><p>All messages are processed

as DFCs on DFC queues. A DFC can use its own thread, or one of the kernel

threads. DFC queue thread 0 is the standard thread; it pre-empts the file

server. DFC queue thread 1 is used by the timer and anything else that needs

a fast response. You can create your own thread if you need a priority other

than one of the defaults, but note that if your thread has a higher priority

than that of DFC queue thread 1, then the accuracy of the nanokernel timers

may be <i>adversely affected</i> if the nanokernel timer DFC is delayed by

more than 16 nanokernel timer ticks. </p> </li>

<li id="GUID-40863867-6F6D-5DC5-AA31-DFD1439A8755"><p>EKA2 has no limit on

the number of asynchronous requests, but you need to do the house keeping

yourself, such as storing request status objects and pointers because the

device driver framework does not provide this. </p> </li>

</ul>