diff --git a/include/gui/BitTube.h b/include/gui/BitTube.h
index 3022d05..d32df84 100644
--- a/include/gui/BitTube.h
+++ b/include/gui/BitTube.h
@@ -33,30 +33,49 @@
 {
 public:
 
-            BitTube();
-            BitTube(const Parcel& data);
+    // creates a BitTube with a default (4KB) send buffer
+    BitTube();
+
+    // creates a BitTube with a a specified send and receive buffer size
+    explicit BitTube(size_t bufsize);
+
+    explicit BitTube(const Parcel& data);
     virtual ~BitTube();
 
+    // check state after construction
     status_t initCheck() const;
+
+    // get receive file-descriptor
     int getFd() const;
-    ssize_t write(void const* vaddr, size_t size);
-    ssize_t read(void* vaddr, size_t size);
 
-    status_t writeToParcel(Parcel* reply) const;
-
+    // send objects (sized blobs). All objects are guaranteed to be written or the call fails.
     template <typename T>
     static ssize_t sendObjects(const sp<BitTube>& tube,
             T const* events, size_t count) {
         return sendObjects(tube, events, count, sizeof(T));
     }
 
+    // receive objects (sized blobs). If the receiving buffer isn't large enough,
+    // excess messages are silently discarded.
     template <typename T>
     static ssize_t recvObjects(const sp<BitTube>& tube,
             T* events, size_t count) {
         return recvObjects(tube, events, count, sizeof(T));
     }
 
+    // parcels this BitTube
+    status_t writeToParcel(Parcel* reply) const;
+
 private:
+    void init(size_t rcvbuf, size_t sndbuf);
+
+    // send a message. The write is guaranteed to send the whole message or fail.
+    ssize_t write(void const* vaddr, size_t size);
+
+    // receive a message. the passed buffer must be at least as large as the
+    // write call used to send the message, excess data is silently discarded.
+    ssize_t read(void* vaddr, size_t size);
+
     int mSendFd;
     mutable int mReceiveFd;