Building the hwinfo section

To build an item:

1. Call hwi_alloc_item() to build a top-level item (an item in which the owner field will be set to HWI_NULL_OFF).
2. Use hwi_alloc_tag() to add whatever other tag structures you want in the item.
3. Call hwi_alloc_item() again to start a new item. This item can be either another top-level item or a child of the first item you created.

You can build the items in any order you wish, provided that the parent is built before the child.

When building a child item, if you remembered its owner only in a variable, or you know only its item name, you can find the correct value of the owner argument by calling the hwi_find_item() function.

Default items and tags

Before main() is invoked in the startup program, the library adds some initial entries to serve as a basis for later items.

HWI_TAG_INFO() is a macro defined in the startup.h header and expands out to the three name, size, align parameters for hwi_alloc_tag() and hwi_alloc_item() based on some clever macro names.

void hwi_default() {
    hwi_tag     *tag;
    hwi_tag     *tag;

    hwi_alloc_item(HWI_TAG_INFO(group), HWI_ITEM_ROOT_AS, HWI_NULL_OFF);
    tag = hwi_alloc_item(HWI_TAG_INFO(group), HWI_ITEM_ROOT_HW, 
                         HWI_NULL_OFF);

    hwi_alloc_item(HWI_TAG_INFO(bus), HWI_ITEM_BUS_UNKNOWN,
                   hwi_tag2off(tag));

    loc = hwi_find_item(HWI_NULL_OFF, HWI_ITEM_ROOT_AS, NULL);

    tag = hwi_alloc_item(HWI_TAG_INFO(addrspace),
                         HWI_ITEM_AS_MEMORY, loc);
    tag->addrspace.base = 0;
    tag->addrspace.len  = (uint64_t)1 << 32;
    #ifndef __X86__
       loc = hwi_tag2off(tag);
    #endif
    tag = hwi_alloc_item(HWI_TAG_INFO(addrspace), HWI_ITEM_AS_IO, loc);
    tag->addrspace.base = 0;
    #ifdef __X86__
        tag->addrspace.len  = (uint64_t)1 << 16;
    #else
        tag->addrspace.len  = (uint64_t)1 << 32;
    #endif
}

Other useful hwi_*() functions