A comprehensive analysis of the memory footprint of micro-ROS is available!
The full report can be found here.
micro-ROS targets microcontrollers, that is, systems with critically finite memory and processing resources. As such, a fundamental step towards fostering an ever broader adoption of this library is to assess how much of these valuable resources it consumes.
As a follow-up of a previous analysis addressing the memory usage of micro-ROS’ default middleware Micro XRCE-DDS, we now came up with an analysis of the memory consumption of the whole micro-ROS stack, taking into account all the rest of abstractions layers all the way up to the end user API.
We performed the measurements for micro-ROS apps running on FreeRTOS and on an ESP32 board connected by either UDP (via WiFi) or serial transport (UART) to a micro-ROS Agent running on a Linux machine.
We have explored both pub/sub and client/service applications. We went through several experimental setups by tuning key parameters such as topic size, entity number, history size and transport protocol. Also, we report both on the total memory and on how it is distributed between its static, stack and dynamic constituents as it is key to assess how much of each type of memory micro-ROS consumes, especially for what concerns real-timeness and determinism in its behaviour.
As an appetizer, find below the results obtained for the total memory consumption of pub/sub applications with variable entity number and topic size, with default paremeters (XRCE_history = RMW_history = 4, MTU = 512 B) and on UDP transport:
Summing up the most relevant results:
- A publisher app with default configuration parameters and with both transport protocols explored consumes ~ 400 B of total memory, which corresponds to the memory needed for creating the entity.
- A subscriber app with default configuration parameters and with both transport protocols explored consumes ~ 8700 B of total memory, which represents the sum of the memory needed for creating the entity and the static buffers allocated to store and handle the messages. Thanks to micro-ROS’ high configurability, this number can be heavily reduced to fit use cases with a lower memory profile.
- A single client/service app with default configuration parameters on UDP transport consumes ~ 8800 B of total memory. This reflects the fact that, in a request/response pattern, messages need to be stored and handled as in the subscription case.
Note: The handling of the RMW history for subscriptions and services, which are the most critical cases, can be revisited in order to reduce the growth of the static consumption. The current implementation reserves a memory of RMW_history * XRCE_history * MTU for each subscriber/client/service. Our most recent considerations are directed towards reducing this number by using a shared RMW history pool for every entity.
