The role of the startup program

The second step performed by the software is to configure the processor and hardware, detect system resources, and start the OS. This is done by the startup program. (For details, see the chapter on Customizing Image Startup Programs.)

While the IPL did the bare minimum configuration necessary to get the system to a state where the startup program can run, the startup program's job is to "finish up" the configuration. If the IPL detected various resources, it would communicate this information to the startup program (so it wouldn't have to redetect the same resources.)

To keep QNX Neutrino as configurable as possible, we've given the startup program the ability to program such things as the base timers, interrupt controllers, cache controllers, and so on. It can also provide kernel callouts, which are code fragments that the kernel can call to perform hardware-specific functions. For example, when a hardware interrupt is triggered, some piece of code must determine the source of the interrupt, while another piece of code must be able to clear the source of the interrupt.

Note that the startup program does not configure such things as the baud rate of serial ports. Nor does it initialize standard peripheral devices like an Ethernet controller or EIDE hard disk controller — these are left for the drivers to do themselves when they start up later.

Once the startup code has initialized the system and has placed the information about the system in the system page area (a dedicated piece of memory that the kernel will look at later), the startup code is responsible for transferring control to the QNX Neutrino kernel and process manager (procnto), which perform the final loading step.