This document explains how modules work in Microvium.
Note that modules do not exist at "runtime" on the firmware device. By the time the snapshot is taken, all modules have been loaded and evaluated, and there are no module features of the runtime VM.
Modules are "linked" by calling VirtualMachine.evaluateModule, giving it the source code to evaluate and a import hook to fetch dependencies.
evaluateModule compiles the source text to a Unit, and then transitively loads (and evaluates) the imported dependencies of the module.
A source code file is compiled to IL using the compileScript function, the output of which is an IL.Unit. This compilation is completely independent of other modules.
Compiled Units have a entry IL function referenced by Unit.entryFunctionID. This is the function that will be run to evaluate the module (the module's root-level code).
Modules are not "linked" at compile time like in a C compiler, but rather loaded into a running VM using VirtualMachine.loadUnit.
During loading, a new global slot in the VM is allocated for each module-level variable, and similarly a globally-unique function name is found for each function in the module (the function namespace and variable namespace are orthogonal). The IL for each function is then "relocated":
- Function names are remapped to their new globally-unique names
- References to module level variables are similarly remapped
- And the same for references to imported modules