Checkpointing
As constructing the object graph can be quite complex, it is useful to
do this once using the command line interface. The object graph can
then be serialised to a JSON file. This is done using the
checkpoint-save and checkpoint-restore commands (these have
aliases save and restore).
A checkpoint normally consist of the JSON file containing the object graph and property values, and separate binary blobs containing ROM and RAM contents.
The JSON checkpoints are human readable, so, simple editing can be done on them by hand using a text editor.
JSON Caveats
64-Bit Values
JSON does not allow for larger than 53 bit integers to be stored (as
JavaScript uses doubles for storing integer values). In case a JSON
file is edited, pay attention that when data of type uint64_t is
serialised, it is split into two separate 32 bit values, thus the
arrays storing the values will contain twice the elements that are
actually in the object’s property.
ROM and RAM Contents
Another issue is that JSON is not practical for storing RAM and ROM dumps which are needed if saving and restoring a checkpoint not at time 0. Thus ROM and RAM is stored in a binary dump (which is host endian dependent) and the JSON file with the saved system configuration contain references to these RAM and ROM dump files.