The NewtonOS Communications System
I guess a bit of clarification regarding the whole comms system on the Newton might be useful at this point. The big picture is still unclear at some points and might even be incorrect here and there, but this is how it is supposed to work…
A communications mechanism is encapsulated in a comm tool. There are several tools on the Newton, including the serial and IrDA tool. They are derived from the class TCommTool. For the IrDA tool, the full inheritance chain is: TUTaskWorld, TCommTool, TSerTool, TAsyncSerTool and finally TIrDATool. Comm tool classes make use of virtual functions to overload needed functionality (good for hacking too). A comm tool is running in its own task.
Comm tools are instantiated via an associated service. For the IrDA tool, this is the TIrDAService class. A service is an implementation of the TCMService protocol. When declaring a service class, the capabilities macro has to be used to state which service this class provides. This is also the parameter used when instantiating an endpoint.
Services are managed by the Communications Manager. The CM is not implemented in a single class but instead via several global functions and classes. The CMGetEndpoint function is the starting point for all endpoint communication. It triggers starting the necessary comm tool task by looking up the requested service and calling the Start method.
Endpoints and comm tools are bound together via an event handler (TEndpointEventHandler). It is important to know that an endpoint can be used by the NewtonScript task and the comm tool task, requiring synchronisation to prevent crashes.
On the lowest level, a comm tool uses hardware specific drivers to perform the actual I/O operations. The drivers can be layered, in the IrDA cases it is the TIrGlue class talking to a serial chip that controls the Ir LED. The TSerialChip protocol is an example for such a driver.
So far, I have been able to implement, replace or modify some of the more interesting classes in this picture: TSerialChip, TSerialEndpoint, TEndpointEventHandler and finally, TIrDATool. This would eventually pave the way for stuff like Bluetooth, SSL or SSH.