diff --git a/docs/code-overview.md b/docs/code-overview.md
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@@ -0,0 +1,40 @@
+# Overview of firmware
+
+This is a high level overview of the code.  We aim to make the code self documenting
+and easy to understand, especially when paired with a high level overview.
+
+## FIDO2 codebase
+
+* main.c - calls high level functions and implements event loop.
+
+* ctaphid.c - implements [USBHID protocol](https://fidoalliance.org/specs/fido-v2.0-id-20180227/fido-client-to-authenticator-protocol-v2.0-id-20180227.html#usb) for FIDO.
+
+* u2f.c - implements [U2F protocol](https://fidoalliance.org/specs/fido-u2f-v1.2-ps-20170411/fido-u2f-raw-message-formats-v1.2-ps-20170411.html).
+
+* ctap.c - implements [CTAP2 protocol](https://fidoalliance.org/specs/fido-v2.0-id-20180227/fido-client-to-authenticator-protocol-v2.0-id-20180227.html).
+
+* ctap_parse.c - implements parsing for CTAP protocol.
+    * this could use some work minimizing.
+
+* log.c - embedded friendly debug logging.
+
+* crypto.c - software implementation of the crypto needs of the application.   Generally this will be copied and edited for different platforms.  API defined in crypto.h should be the same.
+
+* device.h - definitions of functions that are platform specific and should be implemented separately.  See device.c in any of the implementations to see examples.
+
+## Data flow
+
+The main loop will poll the USB peripheral to see if any messages arrived,
+and then pass each one to the USBHID layer.
+
+Once a USBHID message is fully buffered, it will be acted on, unless there was a previous error.
+This will get passed up to U2F or CTAP2 layer.  The response is buffered and then written out to USB.
+
+Depending on platform, there should be a minimum number of interrupts configured.  USB will need interrupts,
+and possibly timer interrupts for keeping track of time.  ST implementation users a 16-bit timer to track time,
+and interrupts to count overflows.
+
+If the application is waiting on user input in CTAP2, then USBHID messages need to be continued to be polled,
+to catch any [cancel command](https://fidoalliance.org/specs/fido-v2.0-id-20180227/fido-client-to-authenticator-protocol-v2.0-id-20180227.html#usb-hid-cancel).
+Also, every 100ms or so, an update needs to be sent via USBHID if the CTAP2 application is still processing a getAssertion request,
+a makeCredential request, or is waiting on user input.  ST leverages same 16-bit timer interrupt for this.
diff --git a/mkdocs.yml b/mkdocs.yml
index 92ed99c..508e6ec 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -11,6 +11,7 @@ nav:
     - FIDO2 Implementation: fido2-impl.md
     - Signed update process: signed-updates.md
     - Building: building.md
+    - Code documentation: code-overview.md
     - Contributing Code: contributing.md
     - Contributing Docs: documenting.md
     - What the udev?!: udev.md