Fix up the incomplete Webserver project so that it integrates with the uIP stack...

[pub/USBasp.git] / LUFA / Drivers / USB / Class / Device / CDC.h

diff --git a/LUFA/Drivers/USB/Class/Device/CDC.h b/LUFA/Drivers/USB/Class/Device/CDC.h
index 30d3526..d248868 100644 (file)
--- a/LUFA/Drivers/USB/Class/Device/CDC.h
+++ b/LUFA/Drivers/USB/Class/Device/CDC.h
@@ -38,6 +38,23 @@
  *  \section Module Description\r
  *  Device Mode USB Class driver framework interface, for the CDC USB Class driver.\r
  *\r
+ *  \note There are several major drawbacks to the CDC-ACM standard USB class, however\r
+ *        it is very standardized and thus usually available as a built-in driver on\r
+ *        most platforms, and so is a better choice than a proprietary serial class.\r
+ *        \r
+ *        One major issue with CDC-ACM is that it requires two Interface descriptors,\r
+ *        which will upset most hosts when part of a multi-function "Composite" USB\r
+ *        device, as each interface will be loaded into a separate driver instance. To\r
+ *        conbat this, you should use the "Interface Association Descriptor" addendum to\r
+ *        the USB standard which is available on most OSes when creating Composite devices.\r
+ *\r
+ *        Another major oversight is that there is no mechanism for the host to notify the\r
+ *        device that there is a data sink on the host side ready to accept data. This\r
+ *        means that the device may try to send data while the host isn't listening, causing\r
+ *        lengthy blocking timeouts in the transmission routines. To combat this, it is\r
+ *        recommended that the virtual serial line DTR (Data Terminal Ready) be used where\r
+ *        possible to determine if a host application is ready for data.\r
+ *\r
  *  @{\r
  */\r
  \r
@@ -155,7 +172,9 @@
                        void EVENT_CDC_Device_ControLineStateChanged(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo) ATTR_NON_NULL_PTR_ARG(1);\r
 \r
                        /** Sends a given string to the attached USB host, if connected. If a host is not connected when the function is called, the\r
-                        *  string is discarded.\r
+                        *  string is discarded. Bytes will be queued for transmission to the host until either the endpoint bank becomes full, or the\r
+                        *  \ref CDC_Device_Flush() function is called to flush the pending data to the host. This allows for multiple bytes to be \r
+                        *  packed into a single endpoint packet, increasing data throughput.\r
                         *\r
                         *  \note This function must only be called when the Device state machine is in the DEVICE_STATE_Configured state or\r
                         *        the call will fail.\r
@@ -170,7 +189,9 @@
                                                      ATTR_NON_NULL_PTR_ARG(1) ATTR_NON_NULL_PTR_ARG(2);\r
                        \r
                        /** Sends a given byte to the attached USB host, if connected. If a host is not connected when the function is called, the\r
-                        *  byte is discarded.\r
+                        *  byte is discarded. Bytes will be queued for transmission to the host until either the endpoint bank becomes full, or the\r
+                        *  \ref CDC_Device_Flush() function is called to flush the pending data to the host. This allows for multiple bytes to be \r
+                        *  packed into a single endpoint packet, increasing data throughput.\r
                         *\r
                         *  \note This function must only be called when the Device state machine is in the DEVICE_STATE_Configured state or\r
                         *        the call will fail.\r