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C H A P T E R 1
Overview
Using System Software
1-17
The NewtApp framework consists of a special collection of protos that are designed
to be used together in a layered hierarchy to build a complete application. For more
information about the NewtApp protos, refer to Chapter 4, "NewtApp Applications."
Using System Software
1
Most of the routines and application components that comprise the Newton system
software reside in ROM, provided in special chips contained in every Newton
device. When your application calls a system routine, the operating system executes
the appropriate code contained in ROM.
This is different from traditional programming environments where system
software routines are accessed by linking a subroutine library with the application
code. That approach results in much larger applications and makes it harder to
provide new features and fix bugs in the system software.
The ROM-based model used in the Newton provides a simple way for the
operating system to substitute the code that is executed in response to a particular
system software routine, or to substitute an application component. Instead of
executing the ROM-based code for some routine, the operating system might
choose to load some substitute code into RAM; when your application calls the
routine, the operating system intercepts the call and executes the RAM-based code.
RAM-based code that substitutes for ROM-based code is called a system update.
Newton system updates are stored in the storage memory domain, which is
persistent storage.
Besides application components, the Newton ROM contains many other objects
such as fonts, sounds, pictures, and strings that might be useful to applications.
Applications can access these objects by using special references called magic
pointers.
Magic pointers provide a mechanism for code written in a development
system separate from the Newton to reference objects in the Newton ROM or in
other packages. Magic pointer references are resolved at run time by the operating
system, which substitutes the actual address of the ROM or package object for the
magic pointer reference.
Magic pointers are constants defined in Newton Toolkit. For example, the names of
all the application components, or protos, are actually magic pointer constants. You
can find a list of all the ROM magic pointer constants in the Newton 2.0 Defs file,
included with Newton Toolkit.
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