Structure of the system page

As mentioned at the beginning of this chapter (Customizing Image Startup Programs), one of the main jobs of the startup program is to initialize the system page.

The system page structure struct syspage_entry is defined in the include file <sys/syspage.h>. The structure contains a number of constants, references to other structures, and a union shared between the various processor platforms supported by the QNX Neutrino RTOS.

It's important to realize that there are two ways of accessing the data within the system page, depending on whether you're adding data to the system page at startup time or reading data from the system page later (as would be done by an application program running after the system has been booted). Regardless of which access method you use, the fields are the same.

Here's the system page structure definition, taken from <sys/syspage.h>:

 * contains at least the following:
struct syspage_entry {
    uint16_t            size;
    uint16_t            total_size;
    uint16_t            type;
    uint16_t            num_cpu;
    syspage_entry_info  system_private;
    syspage_entry_info  asinfo;
    syspage_entry_info  hwinfo;
    syspage_entry_info  cpuinfo;
    syspage_entry_info  cacheattr;
    syspage_entry_info  qtime;
    syspage_entry_info  callout;
    syspage_entry_info  callin;
    syspage_entry_info  typed_strings;
    syspage_entry_info  strings;
    syspage_entry_info  intrinfo;
    syspage_entry_info  smp;
    syspage_entry_info  pminfo;
    union {
        struct x86_syspage_entry    x86;
        struct arm_syspage_entry    arm;
    } un;

Note that some of the fields presented here may be initialized by the code provided in the startup library, while some may need to be initialized by code provided by you. The amount of initialization required really depends on the amount of customization that you need to perform.

Let's look at the various fields.