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+>Halted Endpoints</TITLE
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+TITLE="eCos USB Slave Support"
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+TITLE="Sending Data to the Host"
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+><HR
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+><H1
+><A
+NAME="USBS-HALT">Halted Endpoints</H1
+><DIV
+CLASS="REFNAMEDIV"
+><A
+NAME="AEN16457"
+></A
+><H2
+>Name</H2
+>Halted Endpoints -- Support for Halting and Halted Endpoints</DIV
+><DIV
+CLASS="REFSYNOPSISDIV"
+><A
+NAME="AEN16460"><H2
+>Synopsis</H2
+><DIV
+CLASS="FUNCSYNOPSIS"
+><A
+NAME="AEN16461"><P
+></P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="FUNCSYNOPSISINFO"
+>#include <cyg/io/usb/usbs.h></PRE
+></TD
+></TR
+></TABLE
+><P
+><CODE
+><CODE
+CLASS="FUNCDEF"
+>cyg_bool usbs_rx_endpoint_halted</CODE
+>(usbs_rx_endpoint* ep);</CODE
+></P
+><P
+><CODE
+><CODE
+CLASS="FUNCDEF"
+>void usbs_set_rx_endpoint_halted</CODE
+>(usbs_rx_endpoint* ep, cyg_bool new_state);</CODE
+></P
+><P
+><CODE
+><CODE
+CLASS="FUNCDEF"
+>void usbs_start_rx_endpoint_wait</CODE
+>(usbs_rx_endpoint* ep, void (*)(void*, int) complete_fn, void * complete_data);</CODE
+></P
+><P
+><CODE
+><CODE
+CLASS="FUNCDEF"
+>cyg_bool
+usbs_tx_endpoint_halted</CODE
+>(usbs_tx_endpoint* ep);</CODE
+></P
+><P
+><CODE
+><CODE
+CLASS="FUNCDEF"
+>void usbs_set_tx_endpoint_halted</CODE
+>(usbs_tx_endpoint* ep, cyg_bool new_state);</CODE
+></P
+><P
+><CODE
+><CODE
+CLASS="FUNCDEF"
+>void usbs_start_tx_endpoint_wait</CODE
+>(usbs_tx_endpoint* ep, void (*)(void*, int) complete_fn, void * complete_data);</CODE
+></P
+><P
+></P
+></DIV
+></DIV
+><DIV
+CLASS="REFSECT1"
+><A
+NAME="AEN16505"
+></A
+><H2
+><TT
+CLASS="FUNCTION"
+>Description</TT
+></H2
+><P
+>Normal USB traffic involves straightforward handshakes, with either an
+<TT
+CLASS="LITERAL"
+>ACK</TT
+> to indicate that a packet was transferred
+without errors, or a <TT
+CLASS="LITERAL"
+>NAK</TT
+> if an error occurred, or
+if a peripheral is currently unable to process another packet from the
+host, or has no packet to send to the host. There is a third form of
+handshake, a <TT
+CLASS="LITERAL"
+>STALL</TT
+>, which indicates that the
+endpoint is currently <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>halted</I
+></SPAN
+>.</P
+><P
+>When an endpoint is halted it means that the host-side code needs to
+take some sort of recovery action before communication over that
+endpoint can resume. The exact circumstances under which this can
+happen are not defined by the USB specification, but one example would
+be a protocol violation if say the peripheral attempted to transmit
+more data to the host than was permitted by the protocol in use. The
+host can use the standard control messages get-status, set-feature and
+clear-feature to examine and manipulate the halted status of a given
+endpoint. There are USB-specific functions which can be used inside
+the peripheral to achieve the same effect. Once an endpoint has been
+halted the host can then interact with the peripheral using class or
+vendor control messages to perform appropriate recovery, and then the
+halted condition can be cleared.</P
+><P
+>Halting an endpoint does not constitute a device state change, and
+there is no mechanism by which higher-level code can be informed
+immediately. However, any ongoing receive or transmit operations will
+be aborted with an <TT
+CLASS="LITERAL"
+>-EAGAIN</TT
+> error, and any new
+receives or transmits will fail immediately with the same error.</P
+><P
+>There are six functions to support halted endpoints, one set for
+receive endpoints and another for transmit endpoints, with both sets
+behaving in essentially the same way. The first,
+<TT
+CLASS="FUNCTION"
+>usbs_rx_endpoint_halted</TT
+>, can be used to determine
+whether or not an endpoint is currently halted: it takes a single
+argument that identifies the endpoint of interest. The second
+function, <TT
+CLASS="FUNCTION"
+>usbs_set_rx_endpoint_halted</TT
+>, can be
+used to change the halted condition of an endpoint: it takes two
+arguments; one to identify the endpoint and another to specify the new
+state. The last function
+<TT
+CLASS="FUNCTION"
+>usbs_start_rx_endpoint_wait</TT
+> operates in much the
+same way as <TT
+CLASS="FUNCTION"
+>usbs_start_rx_buffer</TT
+>: when the
+endpoint is no longer halted the device driver will invoke the
+supplied completion function with a status of 0. The completion
+function has the same signature as that for a transfer operation.
+Often it will be possible to use a single completion function and have
+the foreground code invoke either
+<TT
+CLASS="FUNCTION"
+>usbs_start_rx_buffer</TT
+> or
+<TT
+CLASS="FUNCTION"
+>usbs_start_rx_endpoint_wait</TT
+> depending on the
+current state of the endpoint.</P
+></DIV
+><DIV
+CLASS="NAVFOOTER"
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+SUMMARY="Footer navigation table"
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+WIDTH="33%"
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+HREF="usbs-start-tx.html"
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+>Prev</A
+></TD
+><TD
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+ALIGN="center"
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+>Home</A
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+>Next</A
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+><TR
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+WIDTH="33%"
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+VALIGN="top"
+>Sending Data to the Host</TD
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+ACCESSKEY="U"
+>Up</A
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+WIDTH="33%"
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+>
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