[Solved] Issue with checksums when using custom message and rosserial

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In my experience, using any variable-size arrays for arduino messages can lead to problems. It seems that when generated, these headers contain realloc() calls and do not check them for failure. For example, std_msgs::Float32MultiArray has

this->data = (float*)realloc(this->data, data_lengthT * sizeof(float));

which could, theoretically, return a null pointer if there is not enough memory left to realloc successfully. 85% of arduino memory is usually cutting it close to when some dynamic allocation calls can break the limit. When I changed std_msgs::Float32MultiArray to a custom message with fixed-size variables, weird problems went away.

Also, it is probably possible for a bunch of such allocations from different callbacks to eventually fragment the available memory into unusable small chunks, so the memory failures can appear after some time or when a lot of messages were passed via the topic.