Internal Communications Introduction
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Overview
RISC OS is no different to other Operating Systems, in the sense that it must pass information from one part of the system to another. RISC OS achieves this critical process of internal communication by using specific SWI Calls.
The SWI calls used can be divided into four discrete categories:
Vectors
The OS_CallAVector SWI is used to call the routine(s) on a software vector. More information can be found in the Software Vectors section.
Service calls
The OS_ServiceCall SWI is used to pass a service around modules. It is the responsibility of a module if it wishes to provide the service or pass the call on to other modules. More information can be found in the Modules? section.
Window Manager
The Window Manager is used to communicate with applications that run within the window environment. The full list of Wimp SWI calls are provided here.
CallBacks
CallBacks are routines that are to be called at a later date via a function pointer (address). There are two types:
- Transient: These routines are called only once and may be called when RISC OS is threaded, but idle. The OS_AddCallBack SWI is used to set up transient callbacks
- Non-Transient: The OS_SetCallBack SWI is used to set up non-transient callbacks. They are handled by the CallBack handler, and the default on can be replaced by OS_ChangeEnvironment
UpCalls
Used by the OS to notify applications of particular situations. The OS_UpCall SWI performs many different operations (different reason codes). Routines that handle UpCalls must only call the error-returning SWI calls. That is SWI calls that have their X bit set. i.e. either add the value &20000 to the SWI number, or add the letter ‘X’ in front of the SWI name