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+
+$Id$
+Mike Isely <isely@pobox.com>
+
+                            pvrusb2 driver
+
+Background:
+
+  This driver is intended for the "Hauppauge WinTV PVR USB 2.0", which
+  is a USB 2.0 hosted TV Tuner.  This driver is a work in progress.
+  Its history started with the reverse-engineering effort by Björn
+  Danielsson <pvrusb2@dax.nu> whose web page can be found here:
+
+    http://pvrusb2.dax.nu/
+
+  From there Aurelien Alleaume <slts@free.fr> began an effort to
+  create a video4linux compatible driver.  I began with Aurelien's
+  last known snapshot and evolved the driver to the state it is in
+  here.
+
+  More information on this driver can be found at:
+
+    http://www.isely.net/pvrusb2.html
+
+
+  This driver has a strong separation of layers.  They are very
+  roughly:
+
+  1a. Low level wire-protocol implementation with the device.
+
+  1b. I2C adaptor implementation and corresponding I2C client drivers
+      implemented elsewhere in V4L.
+
+  1c. High level hardware driver implementation which coordinates all
+      activities that ensure correct operation of the device.
+
+  2.  A "context" layer which manages instancing of driver, setup,
+      tear-down, arbitration, and interaction with high level
+      interfaces appropriately as devices are hotplugged in the
+      system.
+
+  3.  High level interfaces which glue the driver to various published
+      Linux APIs (V4L, sysfs, maybe DVB in the future).
+
+  The most important shearing layer is between the top 2 layers.  A
+  lot of work went into the driver to ensure that any kind of
+  conceivable API can be laid on top of the core driver.  (Yes, the
+  driver internally leverages V4L to do its work but that really has
+  nothing to do with the API published by the driver to the outside
+  world.)  The architecture allows for different APIs to
+  simultaneously access the driver.  I have a strong sense of fairness
+  about APIs and also feel that it is a good design principle to keep
+  implementation and interface isolated from each other.  Thus while
+  right now the V4L high level interface is the most complete, the
+  sysfs high level interface will work equally well for similar
+  functions, and there's no reason I see right now why it shouldn't be
+  possible to produce a DVB high level interface that can sit right
+  alongside V4L.
+
+  NOTE: Complete documentation on the pvrusb2 driver is contained in
+  the html files within the doc directory; these are exactly the same
+  as what is on the web site at the time.  Browse those files
+  (especially the FAQ) before asking questions.
+
+
+Building
+
+  To build these modules essentially amounts to just running "Make",
+  but you need the kernel source tree nearby and you will likely also
+  want to set a few controlling environment variables first in order
+  to link things up with that source tree.  Please see the Makefile
+  here for comments that explain how to do that.
+
+
+Source file list / functional overview:
+
+  (Note: The term "module" used below generally refers to loosely
+  defined functional units within the pvrusb2 driver and bears no
+  relation to the Linux kernel's concept of a loadable module.)
+
+  pvrusb2-audio.[ch] - This is glue logic that resides between this
+    driver and the msp3400.ko I2C client driver (which is found
+    elsewhere in V4L).
+
+  pvrusb2-context.[ch] - This module implements the context for an
+    instance of the driver.  Everything else eventually ties back to
+    or is otherwise instanced within the data structures implemented
+    here.  Hotplugging is ultimately coordinated here.  All high level
+    interfaces tie into the driver through this module.  This module
+    helps arbitrate each interface's access to the actual driver core,
+    and is designed to allow concurrent access through multiple
+    instances of multiple interfaces (thus you can for example change
+    the tuner's frequency through sysfs while simultaneously streaming
+    video through V4L out to an instance of mplayer).
+
+  pvrusb2-debug.h - This header defines a printk() wrapper and a mask
+    of debugging bit definitions for the various kinds of debug
+    messages that can be enabled within the driver.
+
+  pvrusb2-debugifc.[ch] - This module implements a crude command line
+    oriented debug interface into the driver.  Aside from being part
+    of the process for implementing manual firmware extraction (see
+    the pvrusb2 web site mentioned earlier), probably I'm the only one
+    who has ever used this.  It is mainly a debugging aid.
+
+  pvrusb2-eeprom.[ch] - This is glue logic that resides between this
+    driver the tveeprom.ko module, which is itself implemented
+    elsewhere in V4L.
+
+  pvrusb2-encoder.[ch] - This module implements all protocol needed to
+    interact with the Conexant mpeg2 encoder chip within the pvrusb2
+    device.  It is a crude echo of corresponding logic in ivtv,
+    however the design goals (strict isolation) and physical layer
+    (proxy through USB instead of PCI) are enough different that this
+    implementation had to be completely different.
+
+  pvrusb2-hdw-internal.h - This header defines the core data structure
+    in the driver used to track ALL internal state related to control
+    of the hardware.  Nobody outside of the core hardware-handling
+    modules should have any business using this header.  All external
+    access to the driver should be through one of the high level
+    interfaces (e.g. V4L, sysfs, etc), and in fact even those high
+    level interfaces are restricted to the API defined in
+    pvrusb2-hdw.h and NOT this header.
+
+  pvrusb2-hdw.h - This header defines the full internal API for
+    controlling the hardware.  High level interfaces (e.g. V4L, sysfs)
+    will work through here.
+
+  pvrusb2-hdw.c - This module implements all the various bits of logic
+    that handle overall control of a specific pvrusb2 device.
+    (Policy, instantiation, and arbitration of pvrusb2 devices fall
+    within the jurisdiction of pvrusb-context not here).
+
+  pvrusb2-i2c-chips-*.c - These modules implement the glue logic to
+    tie together and configure various I2C modules as they attach to
+    the I2C bus.  There are two versions of this file.  The "v4l2"
+    version is intended to be used in-tree alongside V4L, where we
+    implement just the logic that makes sense for a pure V4L
+    environment.  The "all" version is intended for use outside of
+    V4L, where we might encounter other possibly "challenging" modules
+    from ivtv or older kernel snapshots (or even the support modules
+    in the standalone snapshot).
+
+  pvrusb2-i2c-cmd-v4l1.[ch] - This module implements generic V4L1
+    compatible commands to the I2C modules.  It is here where state
+    changes inside the pvrusb2 driver are translated into V4L1
+    commands that are in turn send to the various I2C modules.
+
+  pvrusb2-i2c-cmd-v4l2.[ch] - This module implements generic V4L2
+    compatible commands to the I2C modules.  It is here where state
+    changes inside the pvrusb2 driver are translated into V4L2
+    commands that are in turn send to the various I2C modules.
+
+  pvrusb2-i2c-core.[ch] - This module provides an implementation of a
+    kernel-friendly I2C adaptor driver, through which other external
+    I2C client drivers (e.g. msp3400, tuner, lirc) may connect and
+    operate corresponding chips within the the pvrusb2 device.  It is
+    through here that other V4L modules can reach into this driver to
+    operate specific pieces (and those modules are in turn driven by
+    glue logic which is coordinated by pvrusb2-hdw, doled out by
+    pvrusb2-context, and then ultimately made available to users
+    through one of the high level interfaces).
+
+  pvrusb2-io.[ch] - This module implements a very low level ring of
+    transfer buffers, required in order to stream data from the
+    device.  This module is *very* low level.  It only operates the
+    buffers and makes no attempt to define any policy or mechanism for
+    how such buffers might be used.
+
+  pvrusb2-ioread.[ch] - This module layers on top of pvrusb2-io.[ch]
+    to provide a streaming API usable by a read() system call style of
+    I/O.  Right now this is the only layer on top of pvrusb2-io.[ch],
+    however the underlying architecture here was intended to allow for
+    other styles of I/O to be implemented with additonal modules, like
+    mmap()'ed buffers or something even more exotic.
+
+  pvrusb2-main.c - This is the top level of the driver.  Module level
+    and USB core entry points are here.  This is our "main".
+
+  pvrusb2-sysfs.[ch] - This is the high level interface which ties the
+    pvrusb2 driver into sysfs.  Through this interface you can do
+    everything with the driver except actually stream data.
+
+  pvrusb2-tuner.[ch] - This is glue logic that resides between this
+    driver and the tuner.ko I2C client driver (which is found
+    elsewhere in V4L).
+
+  pvrusb2-util.h - This header defines some common macros used
+    throughout the driver.  These macros are not really specific to
+    the driver, but they had to go somewhere.
+
+  pvrusb2-v4l2.[ch] - This is the high level interface which ties the
+    pvrusb2 driver into video4linux.  It is through here that V4L
+    applications can open and operate the driver in the usual V4L
+    ways.  Note that **ALL** V4L functionality is published only
+    through here and nowhere else.
+
+  pvrusb2-video-*.[ch] - This is glue logic that resides between this
+    driver and the saa711x.ko I2C client driver (which is found
+    elsewhere in V4L).  Note that saa711x.ko used to be known as
+    saa7115.ko in ivtv.  There are two versions of this; one is
+    selected depending on the particular saa711[5x].ko that is found.
+
+  pvrusb2.h - This header contains compile time tunable parameters
+    (and at the moment the driver has very little that needs to be
+    tuned).
+
+
+  -Mike Isely
+  isely@pobox.com
+