mem is a utility tool that provides detailed information about the current status of memory maps and paging. In general, a memory map is a structure of data that indicates how memory is arranged. In different contexts, the term “memory map” can have different meanings, for more detailed information, refer to the Memory management section.


mem [options]
  -p:  prints pages map
  -m:  prints entries map for specified process
  -h:  prints help

Summary of the memory map#

Calling the mem command with no arguments prints a summary of the memory map as in the following example:


This is described by the following formula:

(used_memory+boot_memory)/total_memoryKB used_entries/total_entries


  • used_memory - memory used by the system (excluding boot_memory) in kilobytes,

  • boot_memory - memory used by internal boot firmware in kilobytes,

  • total_memory - total amount of memory in kilobytes,

  • used_entries - number of used entries,

  • total_entries - total amount of entries.

Read more about memory map entries in the Memory mapper subsection.

Map of memory pages#

Calling mem -p prints the page view:


The following markings are used:

  • A - some application owns the indicated pages,

  • B - pages reserved by internal boot firmware,

  • C - pages for CPU purposes,

  • H - pages reserved by kernel heap,

  • K - page reserved by kernel code and data,

  • P - pages storing structures used for paging,

  • S - pages reserved by kernel stack,

  • U - pages allocated for the user space process,

  • Y - pages holding the system page structure,

  • x - gaps, there are no pages available,

  • . - free pages.

Referring to the screenshot above:

The first page is allocated by kernel, next two pages are used for CPU purposes and syspage_t structure, two pages for paging, one reserved by kernel stack, 128 reserved by kernel heap, and so on.

A page view is not available on targets without MMU (memory management unit).

Memory map of a specified process#

Calling mem -m [pid] or mem -m kernel prints information about entries of a process’ memory map:


By default, (when calling without arguments) memory map of current process is printed out. There is also a possibility to pass the ID of a process (pid) or pass the kernel argument, which displays information about the kernel process.

The column titles in the table displayed are as follows:

  • SEGMENT - address space of the specified memory segment (i.e. entry) presented in hexadecimal format,

  • PROT - read, write and execute permissions of the specified entry

  • FLAGS - additional information about entry presented using flags (temporarily unavailable)

  • OFFSET - mapped memory offset within object

  • OBJECT - entry description, it can be (anonymous), mem or object_port.object_id, there can be printed information about anonsize in kilobytes too.

See also#

  1. Phoenix-RTOS shell

  2. Phoenix-RTOS Utilities

  3. Table of Contents