diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -1,3 +1,85 @@
 # ARM debug/trace extension
 
-ARM debug/trace HLA extension for Saleae Logic2
+Simple ARM/Cortex debug/trace HLA extension for Saleae Logic2.
+
+Since the Saleae HLA extension world does not allow for nesting of HLA
+extensions on top of an existing extension (only on top of a base
+supported analyser) this extension provides a `Decode Style` choice to
+allow for some control over how and what parts of the TPIU ITM stream
+are decoded.
+
+This means the user can instantiate multiple copies of the extension
+each showing specific aspects of the stream as required. The following
+image is an example of two instances of the analyser being attached to
+a 2MHz SWO capture. The yellow instance is a raw decode of the basic
+TPIU packets. The green instance is decoding port 24 packets into
+RTOS/application specific instrument records:
+
+![instrumentation](docs/tpiu_port24_instrumentation.png "instrumentation")
+
+## Configuration
+
+### `All`
+
+When the `Decode Style` selected is `All` then the `Port` field is
+**ignored** and can be any value. For example the following will
+display raw decoding of all the TPIU packets:
+
+![config_raw](docs/config_tpiu_all.png "configure All raw")
+
+### `Port`
+
+When the `Decode Style` configured is `Port` then raw ITM packet
+decode is provided for packets that match the configured trace port
+number. All other packets are ignored.
+
+### `Console`
+
+When the `Decode Style` configured is `Console` then ITM packet decode
+is provided for packets that match the configured trace port
+number. All other packets are ignored. The contents of matching trace
+port packets are treated as `ASCII`.
+
+### `Instrumentation`
+
+The `Instrumentation` style does basic decoding of generic
+[eCosPro](https://www.ecoscentric.com/ecos/ecospro.shtml)
+instrumentation records. The analyser currently only displays the raw
+hexadecimal data, and does not yet decode the
+class/type/etc. instrumentation information since we would need to
+execute external tools to obtain the per-ELF-file (non-loaded)
+description structures that define the individual record encoding for
+the application being executed.
+
+![config_instrumentation](docs/config_tpiu_port24_instrumentation.png "configure instrumentation")
+
+Similarly we would need to execute external tools to decode DWT
+addresses to the original application source locations.
+
+#### eCosPro instrumentation
+
+The [eCosPro](https://www.ecoscentric.com/ecos/ecospro.shtml)
+instrumentation consists of:
+
+ITM packet size | Use    | Description
+:---------------|:-------|:-----------
+2-byte          | Header | Little-endian 0xNNSS where NN=number of fields : SS=sequence#
+4-byte * NN     | Body   | 0 or more instrumentation record (structure) fields
+1-byte          | Tail   | 0xSS where SS=sequence# should match the header sequence#
+
+The use of fixed ITM packet sizes of 2 for the header, 1 for the tail
+and ensuring instrumention records consist of a multiple (0..255)
+number of 4-byte fields allows for synchronisation when the underlying
+TPIU transport may "drop" packets. Processing tools can spot truncated
+or dropped instrumentation records by matching the embedded header and
+tail sequence numbers, and the header `NN` number of 4-byte fields
+value.
+
+The default transport for eCosPro instrumentation is traceport 24, but
+can be configured to any arbitary port#. So when configuring the
+analyser instance without access to the ELF descriptor sections the
+user will need to match the analyser setting against the application
+run-time.
+
+ASIDE: An encoded full-timing recorded 5-word instrumentation record
+takes ~150us to be transferred over an 8N1 2MHz UART (SWO) connection.
diff --git a/debug.py b/debug.py
index c8e2aca..c87d0b2 100644
--- a/debug.py
+++ b/debug.py
@@ -1,26 +1,5 @@
 # ARM Debug High Level Analyzer extension
 
-# Since the Saleae extension API does not allow nested extensions; we
-# abstract the lower-layers inside this source file so that we can
-# provide the higher level decodings:
-
-#                      +--- port0
-#                      |
-#          +--- ITM ---+--- portN
-#          |           |
-#          |           +--- portX --  Instrumentation -- O/S specific decoding
-#          |
-#  TPIU ---+
-#          |
-#          +--- ETM
-
-# The ITM port is just be a setting: [All|0|1|...|x]
-
-# So we provide a single extension with a setting that decides how the
-# debug data is decoded. We then allow the user to have multiple ins
-# instances of the extension if they want to show the different
-# embedded data fields.
-
 # ETMv3 - Cortex-M, etc.
 # PFTv1 - Cortex-A9, Cortex-A12 and Cortex-A15
 # ETMv4 - Cortex-R7, Cortex-A53 and Cortex-A57
@@ -49,15 +28,6 @@ class DecodeStyle(IntEnum):
     Console = 2 # decode specific port# as ASCII console
     Instrumentation = 3 # decode specific port# as eCosPro style multi-frame O/S instrumentation
 
-# NOTE: eCosPro instrumentation (default traceport 24, but can be arbitrary port#)
-# Consists of:
-#  2-byte header : 0xNNSS : NN=number of fields : SS=sequence#
-#    NN * 4-byte : instrumentation record (structure) fields
-#    1-byte tail : 0xSS : SS=sequence#
-#
-# An encoded 5 word instrumentation record takes ~150us to be transferred over
-# an 8N1 2MHz UART (SWO) connection.
-
 # ITM
 # Synchronisation:
 ITMDWTPP_SYNC = 0x00 # Terminated by single set bit after at least 47 bits.
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