add readme file

README.MD

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+# Overview
+
+This is a template file for bare metal applications for the STM32F407xx controller.
+
+Currently, the template is for the STM32F407VEx controllers which have 512k of Flash and 128k of RAM + 64k of core-coupled memory (in sum 192k of RAM), but can easily be changed for other F407 controllers by adapting the Flash and RAM sizes in the linkerscript.
+
+
+# Structure
+
+
+-  the whole project is built by a sinbgel ``Makefile``. On one hand, this is rather comfortable, but can become quite a pain for larger projects.
+- The ``obj`` folder contains all build derived files.
+- The ``startup`` folder contains my own startup code written in C. Most projects for STM32 controllers use Assembly for their startup codes, which is unnecessary. A downside of the C startup code, is that it has a slighly bigger memory footprint.
+- The ``stm32f407ve.ld`` is the linkerscript.
+- The ``setup`` folder contains ST's generated clock setup file. It contains the ``SystemInit()`` function which configures the system clocks and flash waitcycles. It is currently set up for a system frequency of 168 MHz. The Code is automatically called by the startup code right before jumping into the ``main()`` function
+- The ``mathlib`` folder contains CMSIS's math and DSP library in form of a precompiled static library and the corresponding header file. I never use it. No clue, if it works. A quick function check showed that the functions work, but no guarantee here. (Btw. there is no guarantee anywhere in this code, according to my GPLv2 license).
+
+# Compiler
+
+The Makefile expects a ``arm-none-eabi-gcc`` which has to be available in the PATH. For most linux users this should work fine.
+