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<font color="#FFFFFF" size="5" face="Arial, Helvetica, sans-serif"><strong>Embedded SDIO Driver Kit Help </strong></font></td>
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<p class="BODYTEXT"> <strong>PDK Topics:</strong>
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<td><a href="#pdkfaq1">Is it ok to issue a synchronous CMD53 in the pProbe context?</a></td>
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<td><a href="#pdkfaq2">I am hitting this assert : SDIO Bus Driver: IssueRequestToHCD - request already in use...what is going?</a></td></tr>
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<td><a href="#pdkfaq3">Can I use SDCONFIG_FUNC_MASK_IRQ and SDCONFIG_FUNC_UNMASK_IRQ to synchronize with interrupts?
</a> </td>
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<td><a href="#pdkfaq4">Can we have more than one outstanding CMD53/CMD52 requests to the driver.
We are issuing a mixture of synchronous and asynchronous calls to the driver
without waiting for the previous commands to complete. Is that ok to do?</a></td>
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<td><a href="#pdkfaq5">The linux kernel disables interrupts before it calls into my driver. What can I do if I cannot use
synchronous calls?</a></td>
</tr>
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<td><a href="#pdkfaq6">What can I do Linux Kernel Timer Callback?</a></td>
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<td><a href="#pdkfaq7">ques7</a></td>
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<p class="HEADING3"><strong><a name="pdkfaq1"></a>Is it ok to issue a synchronous CMD53 in the pProbe context?</strong></p>
<p class="BODYTEXT">You can allocate and submit CMD53 requests safely (synch or asynch) from your pProbe callback. <blockquote>
<a href="#BackToTop">Back
to top.</a></p>
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<p class="HEADING3"><strong><a name="pdkfaq2"></a>I am hitting this assert : SDIO Bus Driver: IssueRequestToHCD - request already in use...what is going?</strong></p>
<p class="BODYTEXT">
The assert indicates the reuse of a <font face="Courier New, Courier, mono">SDREQUEST</font> packet
before it was finished. For example, if you allocate a request and submit it
asynchronously and then at a later time re-use
the request before
the completion routine was called.
The request should not be used until the completion routine has been called.
<blockquote>
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<p class="HEADING3"><strong><a name="pdkfaq3"></a>Can I use SDCONFIG_FUNC_MASK_IRQ and SDCONFIG_FUNC_UNMASK_IRQ to synchronize with interrupts?</strong></p>
<p class="BODYTEXT">These two config requests should not be used to synchronize
with the IRQ handlers (see : <a href="periph_using_irqs.htm#EnableDisableIrq"> Enabling
Disabling IRQ</a>).
Typically the I/O function should implement its own interrupt mask register
in it's function
I/O space
and not
rely too
heavily
on masking/unmasking
the interrupt register that is present in the common I/O space. The SDCONFIG_FUNC_(UN)MASK_IRQ
request should only used for enabling IRQ detection at initialization and
masking them off when removing and instance.
As an example, the Bluetooth class has a separate function register for enabling/disabling
interrupts. This obviates the need to call a bus driver API that has to make
the atomic operation to clear/set the IRQ enable register bits.
</p>
<blockquote>
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<p class="HEADING3"><strong><a name="pdkfaq4"></a>Can we have more than one outstanding CMD53/CMD52 requests to the driver.
We are issuing a mixture of synchronous and asynchronous calls to the driver
without waiting for the previous commands to complete. Is that ok to do?</strong></p>
<p class="BODYTEXT">Yes, you can have as many requests outstanding in the driver.
They have to be unique bus request structures of course. The HCD will only
process one at a time. The bus driver serializes all requests through an internal
queue.
A synchronous call will simply block until its request (which could be stuck
in the queue) is pulled out of the queue, started and completed. As for asynch
requests, the request will not start until it reaches the front of the queue.
So mixing synch and asynch before either operation completes is safe to do.
Developers have to make sure that the request
structures that you allocate are NOT
shared between these operations.
</p>
<blockquote>
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to top.</a></p>
</blockquote>
<p class="HEADING3"><strong><a name="pdkfaq5"></a>The linux kernel disables interrupts before it calls into my driver. What can I do if I cannot use
synchronous calls?</strong></p>
<p class="BODYTEXT">Some driver models in the linux kernel disable interrupts before a driver callback is invoked. If your driver model uses such a technique you
should pre-allocate a list of bus requests because allocation of a bus request may invoke a kernel allocation which is not allowed if
interrupts are disabled. You can only submit bus requests asynchronously under these conditions. Avoid calling any bus configuration requests as some may be synchronous
or require a pre-emptible context.
</p>
<blockquote>
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to top.</a></p>
</blockquote>
<p class="HEADING3"><strong><a name="pdkfaq6"></a>What can I do Linux Kernel Timer Callback?</strong></p>
<p class="BODYTEXT">Firstly, avoid doing any SDIO requests in a linux timer callback,
you should queue a work item to get the actual work done. For synchronization
you should disable local bottom halves as spin-locks will not guard against a
timer callback. If you must issue a request from a kernel timer callback, preallocate
your bus request structure ahead of time and only use asynchronous requests.
If you choose to use a work item you may allocate a bus request and then submit
the request asynchronously.
While executing in the context of a work item , you can synchronize using normal
spin locks and semaphores with other parts of
your driver.
</p>
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