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>Starting up a USB Device</TITLE
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>Starting up a USB Device</TITLE
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TITLE="eCos USB Slave Support"
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TITLE="USB Enumeration Data"
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><H1
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><H1
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><A
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><A
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NAME="USBS-START">Starting up a USB Device</H1
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NAME="USBS-START">Starting up a USB Device</H1
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><DIV
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><DIV
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CLASS="REFNAMEDIV"
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CLASS="REFNAMEDIV"
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><A
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><A
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NAME="AEN16210"
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NAME="AEN16210"
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></A
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></A
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><H2
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><H2
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>Name</H2
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>Name</H2
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><TT
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><TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
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>usbs_start</TT
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>usbs_start</TT
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> -- Starting up a USB Device</DIV
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> -- Starting up a USB Device</DIV
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><DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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CLASS="REFSYNOPSISDIV"
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><A
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><A
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NAME="AEN16214"><H2
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NAME="AEN16214"><H2
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>Synopsis</H2
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>Synopsis</H2
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><DIV
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><DIV
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CLASS="FUNCSYNOPSIS"
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CLASS="FUNCSYNOPSIS"
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><A
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><A
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NAME="AEN16215"><P
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></P
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><TD
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><TD
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><PRE
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><PRE
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CLASS="FUNCSYNOPSISINFO"
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CLASS="FUNCSYNOPSISINFO"
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>#include <cyg/io/usb/usbs.h></PRE
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>#include <cyg/io/usb/usbs.h></PRE
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></TD
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></TD
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><P
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><P
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><CODE
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><CODE
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><CODE
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><CODE
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CLASS="FUNCDEF"
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CLASS="FUNCDEF"
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>void usbs_start</CODE
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>void usbs_start</CODE
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>(usbs_control_endpoint* ep0);</CODE
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>(usbs_control_endpoint* ep0);</CODE
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></P
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></P
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><P
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><P
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></P
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></P
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><DIV
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CLASS="REFSECT1"
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><A
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><A
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NAME="AEN16222"
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NAME="AEN16222"
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></A
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></A
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><H2
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><H2
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>Description</H2
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>Description</H2
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><P
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><P
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>Initializing a USB device requires some support from higher-level
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>Initializing a USB device requires some support from higher-level
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code, typically the application, in the form of enumeration data.
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code, typically the application, in the form of enumeration data.
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Hence it is not possible for the low-level USB driver to activate a
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Hence it is not possible for the low-level USB driver to activate a
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USB device itself. Instead the higher-level code has to take care of
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USB device itself. Instead the higher-level code has to take care of
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this by invoking <TT
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this by invoking <TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
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>usbs_start</TT
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>usbs_start</TT
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>. This function takes
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>. This function takes
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a pointer to a USB control endpoint data structure. USB device drivers
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a pointer to a USB control endpoint data structure. USB device drivers
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should provide exactly one such data structure for every USB device,
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should provide exactly one such data structure for every USB device,
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so the pointer uniquely identifies the device.</P
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so the pointer uniquely identifies the device.</P
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><TD
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><TD
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><PRE
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><PRE
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CLASS="PROGRAMLISTING"
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CLASS="PROGRAMLISTING"
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>const usbs_enumeration_data usb_enum_data = {
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>const usbs_enumeration_data usb_enum_data = {
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…
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…
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};
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};
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int
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int
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main(int argc, char** argv)
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main(int argc, char** argv)
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{
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{
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usbs_sa11x0_ep0.enumeration_data = &usb_enum_data;
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usbs_sa11x0_ep0.enumeration_data = &usb_enum_data;
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…
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…
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usbs_start(&usbs_sa11x0_ep0);
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usbs_start(&usbs_sa11x0_ep0);
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…
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…
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}</PRE
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}</PRE
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></TD
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></TD
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></TR
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></TABLE
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></TABLE
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><P
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><P
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>The exact behaviour of <TT
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>The exact behaviour of <TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
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>usbs_start</TT
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>usbs_start</TT
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> depends on the
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> depends on the
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USB hardware and the device driver. A typical implementation would
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USB hardware and the device driver. A typical implementation would
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change the USB data pins from tristated to active. If the peripheral
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change the USB data pins from tristated to active. If the peripheral
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is already plugged into a host then the latter should detect this
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is already plugged into a host then the latter should detect this
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change and start interacting with the peripheral, including requesting
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change and start interacting with the peripheral, including requesting
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the enumeration data. Some of this may happen before
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the enumeration data. Some of this may happen before
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<TT
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<TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
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>usbs_start</TT
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>usbs_start</TT
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> returns, but given that multiple
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> returns, but given that multiple
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interactions between USB host and peripheral are required it is likely
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interactions between USB host and peripheral are required it is likely
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that the function will return before the peripheral is fully
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that the function will return before the peripheral is fully
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configured. Control endpoints provide a <A
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configured. Control endpoints provide a <A
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HREF="usbs-control.html#AEN16552"
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HREF="usbs-control.html#AEN16552"
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>mechanism</A
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>mechanism</A
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> for informing
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> for informing
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higher-level code of USB state changes.
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higher-level code of USB state changes.
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<TT
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<TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
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>usbs_start</TT
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>usbs_start</TT
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> will return even if the peripheral is
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> will return even if the peripheral is
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not currently connected to a host: it will not block until the
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not currently connected to a host: it will not block until the
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connection is established.</P
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connection is established.</P
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><P
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><P
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><TT
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><TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
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>usbs_start</TT
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>usbs_start</TT
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> should only be called once for a given
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> should only be called once for a given
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USB device. There are no defined error conditions. Note that the
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USB device. There are no defined error conditions. Note that the
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function affects the entire USB device and not just the control
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function affects the entire USB device and not just the control
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endpoint: there is no need to start any data endpoints as well.</P
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endpoint: there is no need to start any data endpoints as well.</P
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>USB Enumeration Data</TD
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