<?xml version="1.0" encoding="UTF-8" ?>
<?xml-stylesheet type="text/xsl" href="https://community.arm.com/utility/feedstylesheets/rss.xsl" media="screen"?><rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:slash="http://purl.org/rss/1.0/modules/slash/" xmlns:wfw="http://wellformedweb.org/CommentAPI/"><channel><title>USB nack</title><link>https://community.arm.com/developer/tools-software/tools/f/keil-forum/24340/usb-nack</link><description> 
Hello, 

 
can you tell me which function in the Keil USB library sends a
nack back to the host? I have a CDC bulk endpoint. I cannot find any
reference to this in the code itself (it was mentioned in the forum
but nobody says HOW...) 

 
thanks 
 </description><dc:language>en-US</dc:language><generator>Telligent Community 10</generator><item><title>RE: USB nack</title><link>https://community.arm.com/thread/56384?ContentTypeID=1</link><pubDate>Mon, 13 Jul 2009 03:36:39 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:0a67feca-de86-4a9b-b6c9-1cdcda3b70b3</guid><dc:creator>Chinzei Tsuneo</dc:creator><description>&lt;p&gt;&lt;p&gt;
As long as I know, all of USB devices return NAK (not nack - NACK
is the term for I2C) &lt;b&gt;automatically&lt;/b&gt;, responding to IN or OUT
transactions from host. The required timing for NAK response is too
short to handle it with a firmware. Then, NAK is handled by
hardware.&lt;/p&gt;

&lt;p&gt;
Endpoint returns NAK when it is configured (enabled) on the USB
register of the chip.&lt;br /&gt;
- IN endpoint returns NAK, when an IN transaction comes from host,
AND when the endpoint is empty.&lt;br /&gt;
- OUT endpoint returns NAK when an OUT-DATAx transaction comes from
host, AND when the endpoint is still occupied by the last data.&lt;/p&gt;

&lt;p&gt;
Tsuneo&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item></channel></rss>