add an architecture section and a couple diagrams...

Mark this as a Markdeep document..  If you hard link or copy README.md
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README.md

@@ -23,6 +23,41 @@ IDE's like ST's STM32CubeIDE which is only available in binary form
 was not a choice, as that would preclude building on an operating
 system other than Windows/MaxOS/Linux.
 
+Architecture
+------------
+
+There are a number of components to make this system work.  The overall
+flow is:
+************************************************************************************************
+*                                                                                              *
+* +---------+              +-------------+            +-------------+         +--------------+ *
+* | lora.py |  multicast   | loraserv.py |  USB VCP   | lora.gw.elf |  LoRa   | lora.irr.elf | *
+* |         +--------------+             +------------+   main.c    +---------+  irr_main.c  | *
+* +---------+              +-------------+            +-------------+         +--------------+ *
+*                                                                                              *
+************************************************************************************************
+
+The `lora.py` component is the front end/UI that is used to send commands
+to controller.  This program establishes a secure communications channel
+to the controller.  It's firmware is in `lora.irr.elf`, and the main
+source file is `irr_main.c`.
+
+The middle to components, `loraserv.py` and `lora.gw.elf` are used to
+pass messages between the former two.  The `loraserv.py` program takes
+multicast datagrams that are received on 239.192.76.111:21089, which
+are with out any framing, prepends `pkt:`, hex encodes the data and
+terminated w/ the new line character, and sends them via the USB VCP
+provided by `lora.gw.elf`.  The gateway firmware then decodes the
+packet and transmits it via the LoRa radio to the irrigation
+controller.  The received packet is returned similarly, but this time
+with `data:` prepended, for `loraserv.py` to multicast back to
+`lora.py`.
+
+The reason no particular framing is required for addressing or
+destination is that the protocol is secure, and only the party that
+is able to encrypt or decrypt the proper packets will be accepted,
+and any invalid packets will be ignored.
+
 Building
 --------
 
@@ -84,6 +119,25 @@ should be grounded.
 Deploying
 ---------
 
+Here is a diagram of the connections:
+
+*******************************************************************************************
+*                                                                                         *
+*                                   GND                                                   *
+*                     +--------------------------------------------------+                *
+*                     |                                                  |                *
+* +--------+  ~/~   +-+-----------+  GND           +---------+  GPIO   +-+--------------+ *
+* | 24V AC +--------+             +----------------+ Node151 +---------+     Relay      | *
+* +--------+        |             |                +-+-------+         +-+--------------+ *
+*                   |             |  +5V -> VUSB     |                   |                *
+*                   | AC-DC PS 5V +------------------+                   | +5V -> JD-VCC  *
+*                   |             |                                      |                *
+*                   |             |                                      |                *
+*                   |             +--------------------------------------+                *
+*                   +-------------+                                                       *
+*                                                                                         *
+*******************************************************************************************
+
 The noral supply used for irrigation values is 24V AC.  This means
 an additional power supply is needed to convert to the 5V supply that
 is used by the Node151.  Make sure this is well filtered as both the
@@ -105,3 +159,5 @@ NOT for the VCC->INx pins, despite them being next to each other.  The
 GND and JD-VCC should be connected to the 5V power supply, while VCC
 is connected to VDD on the Node151, and INx pins to the respective
 GPIO pins.
+
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