asinfo

The asinfo (Address Space Information) section consists of an array of the asinfo structure:

start

The first physical address of the range being described.

end

The last physical address of the range being described. Note that this is the actual last byte, not one beyond the end.

owner

An offset from the start of the section giving the owner of this entry (its “parent” in the tree). It's set to AS_NULL_OFF if the entry doesn't have an owner (it's at the “root” of the address space tree).

name

An offset from the start of the strings section of the system page giving the string name of this entry.

attr

A bitfield describing attributes of the address range (see “attr” below).

priority

Indicates the speed of the memory in the address range. A smaller numbers mean slower memory. The macro AS_PRIORITY_DEFAULT is defined to use a default value for this field (currently defined as 100).

alloc_checker

Not currently used.

Each entry in the array describes the attributes of one section of address space on the machine. The memory map has a tree format; that is, an address range can have a parent. The information in the asinfo structures can be hard-coded from the system memory map, or read in from the memory controller.

When procnto is managing virtual memory for process address spaces, it uses the information in asinfo to know from where in RAM it can allocate memory.

attr

The attr field can have the following bits:

AS_ATTR_READABLE 0x0001

Address range is readable.

AS_ATTR_WRITABLE 0x0002

Address range is writable.

AS_ATTR_CACHABLE 0x0004

Address range can be cached (this bit should be off if you're using device memory).

AS_ATTR_VISIBLE 0x0008u

Other entries can know this entry exists, but not read its contents.

AS_ATTR_KIDS 0x0010

Other entries use this entry as their owner.

Note that the library turns on this bit automatically; you shouldn't specify it when creating the section.

AS_ATTR_CONTINUED 0x0020

There are multiple entries being used to describe one “logical” address range. This bit will be on in all but the last entry.

Note that the library turns on this bit and uses it internally; you shouldn't specify it when creating the section.

Address space trees

The asinfo section contains trees describing address spaces (where RAM, ROM, flash, etc. are located).

The general hierarchy for address spaces is:

/memory/memclass/....

or:

/io/memclass/....

or:

/memory/io/memclass/....

The memory or io indicates if this entry describes something in the memory or in the I/O address space. The third form (/memory/io/memclass/....) is used on a machine without separate in/out instructions, and where everything is memory-mapped.

The memclass is something like ram, rom, flash, etc. Below memclass are further classifications, allowing the process manager to provide typed memory support.