Palm OS Network Programming

Using the Net Library

This is all very well and good, but what does the application do in this wonderful world of the Net Library? Let’s take a look.

Before we dive into the functions themselves, let’s talk briefly about system libraries. When your compiler comes to normal function calls, it embeds the symbolic function name into your code. Then the linker comes along and resolves this symbolic name to the actual address of the function’s implementation. If the linker can’t find the implementation of the function, then it generates a linker error.

Palm OS System Libraries work differently. They operate according to something known as the 68K Trap Dispatch mechanism. 68K refers to the series of processors from Motorola that run the Palm, the MAC, and a bunch of other devices. What we care about, though, is the Trap Dispatch Mechanism. When your compiler comes across a call to a function in a system library, instead of inserting a symbolic name, it puts in assembly instructions that generate an exception that is caught by the Palm OS’s system trap dispatcher. The system trap dispatcher uses the first parameter to select the correct system library to invoke a function from. As a result, every call to the NetLib API takes a reference number as its first parameter (well, actually there are a few byte-ordering functions that don’t, but they turn out to be macros).

Finding the Net Library

The very first thing you must do is to find the Net Library. This is a three-step process. First, ...