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--- doc:crazyflie:dev:arch:communication [2015-03-03 16:23]
macke created
+++ doc:crazyflie:dev:arch:communication [2021-06-24 16:36]
kimberly
@@ Line 1: / Line 1: @@
+<WRAP center round important 60%>
+This page has deprecated and will be archived. Please go to [[https://www.bitcraze.io/]].
+</WRAP>
+{{ :doc:crazyflie:dev:arch:crazyflie-comm-stack.png?direct&400|}}
+====== Communication stack ======
+The Crazyflie communication stack is divided into three layers:
+  * **Module**: End receiving service of data
+  * **CRTP**: Protocol for communication
+  * **Link**: Physical communication link
+Each layer communicates on a logical level with the same layer on the other side.
+===== Module =====
+Each module is assigned a port, which works much like the ports in UDP. Sending data on a specific port will make sure it's routed to the registered module for this port. The data that is sent to/from a specific port also contains a channel id of 3 bits. This channel id can be used to more easily route the data once inside the module.
+===== CRTP =====
+The protocol used for sending data to/from the Crazyflie is named CRTP (Crazyflie RealTime Protocol). In it's current state the protocol isn't real-time, but there's bits over in the header to implement this functionality.
+Each CRTP packet is 32 bytes, of which 1 byte is taken by the header. This gives a total payload of 31 bytes per packet. The header holds the port (8 bits), channel (2 bits) and reserved (2 bits).
+===== Link =====
+The link is responsible for transferring the packet to/from the Crazyflie. Currently there's two types of physical links implemented: A radio link using the Crazyradio and a wired link using USB directly to the Crazyflie (only implemented for 2.0).
+Since no CRC/checksum is added to the CRTP packet it's the link layers responsibility to check the integrity of the packets.
+====== Architecture ======
+===== Modules =====
+In the firmware most modules (that are connected to ports) are implemented as tasks. Each task is blocking on a message delivery queue where incoming CRTP packets are delivered. At start up each of these tasks (and other modules) register a callback with the communication layer for their pre-defined ports.
+For every module that is used to send/receive CRTP packets there's a Python API object that is used to interact with it. For instance for logging there's a module named //log.c// in the Crazyflie firmware and a class named //Log// in the Python API. This part of the API is then used to directly interact with the logging functionality in the Crazyflie.

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