Merge pull request #2030 from mlnx/memap_docs

Adding memap documentation

docs/memap.md

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+# memap - Static Memory Map Analysis
+
+## Introduction
+
+*memap* is a simple utility useful to display static memory information required by [mbed](https://github.com/mbedmicro/mbed) applications. This information is produced by analysing the memory map file previously generated by your toolchain.
+
+Note: this tool is showing static RAM usage and the total size of allocated heap and stack space defined at compile time, not the actual heap and stack usage (which may be different depending on your application).
+
+## Table of Contents
+
+1. [Using memap](#using-memap)
+1. [Information on memory sections](#info-mem-sections)
+1. [Current support](#current-support)
+1. [Known problems](#known-problems)
+
+## Using memap
+
+*memap* is automatically invoked after an mbed build finishes succesfully. But it's also possible to manually run the program with different command line options, for example:
+
+```
+$> python memap.py
+usage: memap.py [-h] -t TOOLCHAIN [-o OUTPUT] [-e EXPORT] [-v] file
+
+Memory Map File Analyser for ARM mbed version 0.3.11
+
+positional arguments:
+  file                  memory map file
+
+optional arguments:
+  -h, --help            show this help message and exit
+  -t TOOLCHAIN, --toolchain TOOLCHAIN
+                        select a toolchain used to build the memory map file
+                        (ARM, GCC_ARM, IAR)
+  -o OUTPUT, --output OUTPUT
+                        output file name
+  -e EXPORT, --export EXPORT
+                        export format (examples: 'json', 'csv-ci', 'table':
+                        default)
+  -v, --version         show program's version number and exit
+```
+
+Example:
+
+```
+$> python memap.py GCC_ARM\myprog3.map -t GCC_ARM
+
++----------------------------+-------+-------+------+
+| Module                     | .text | .data | .bss |
++----------------------------+-------+-------+------+
+| Fill                       |   170 |     0 | 2294 |
+| Misc                       | 36282 |  2220 | 2152 |
+| core/hal                   | 15396 |    16 |  568 |
+| core/rtos                  |  6751 |    24 | 2662 |
+| features/FEATURE_IPV4      |    96 |     0 |   48 |
+| frameworks/greentea-client |   912 |    28 |   44 |
+| frameworks/utest           |  3079 |     0 |  732 |
+| Subtotals                  | 62686 |  2288 | 8500 |
++----------------------------+-------+-------+------+
+Allocated Heap: 65540 bytes
+Allocated Stack: 32768 bytes
+Total Static RAM memory (data + bss): 10788 bytes
+Total RAM memory (data + bss + heap + stack): 109096 bytes
+Total Flash memory (text + data + misc): 66014 bytes
+
+```
+
+## Information on memory sections
+
+Find here extended description on the multiple memory sections shown in the previous table.
+
+- text: is where the code application and constants are located in Flash
+- data: non-zero initialized variables; allocated in both RAM and Flash memory (variables are initialized in RAM at run time from Flash)
+- bss: uninitialized data allocated in RAM, or variables initialized to zero
+- heap: dynamic allocated memory defined at build time, usually used by malloc, etc, in RAM
+- stack: used to store local data, temporary data when branching to a subroutine and context switch info; it's considered dynamic allocated memory region in RAM defined at build time
+
+On the other hand, there are other entries which do not correspond to modules directly and require a bit of clarification:
+
+- Fill: this entry represents the bytes in multiple sections (RAM and Flash) that the toolchain has filled with zeros because requires subsequent data or code to be aligment appropriately in memory
+- Misc: it mainly represents helper libraries introduced by the toolchain (e.g. libc) but there might be other modules not part of mbed
+
+## Current support
+
+*memap* has been tested on Windows 7, Linux and Mac.
+
+Supported map files generated by the following toolchains: GCC_ARM, ARM (ARM Compiler 5) and IAR.
+
+## Known problems & New features
+
+This utility is considered 'Alpha' quality at the moment.
+Please note, the information generated by this utility may not be fully accurate and may vary from one toolchain to another.
+
+If you are seeing problems or would like new features to be added then please raise a ticket on [GitHub](https://github.com/mbedmicro/mbed/issues) and use ```[memap] ``` in the title.