Improve documentation and beatify pieces of code

doc/source/firmware/hw-version-detect.rst

@@ -0,0 +1,31 @@
+.. _hw_version_detect:
+
+Automatic Hardware Version detection
+====================================
+
+Functional Description
+----------------------
+
+In order to automatically select the available hardware features, the firmware checks the PCB's version
+using vertain pins on the microcontroller.
+
+The hardware revision is represented by the enum type :c:enum:`hw_revision`. A call to :c:func:`get_pcb_hardware_version` retrieves the revision.
+When the function is called for the first time, it activates pull-up resistors on pin numbers :c:macro:`HW_REV_DETECT_PIN_LOW` to :c:macro:`HW_REV_DETECT_PIN_HIGH`
+on port :c:macro:`HW_REV_DETECT_GPIO` and reads in the binary number. 
+
+The revision is set by externally connecting the pins to ground. The bit pattern read from the port is inverted and then checked internally to derive the hardware version.
+After the version is read for the first time, it is stored internally and subsequent calls to :c:func:`get_pcb_hardware_version` only retrieve the internally stored value to reduce the overhead of the function.
+
+Hardware Version Dependent Features
+-----------------------------------
+
+- The settings module searches for an external EEPROM on the SPI interface to store some settings, like the calibration. This is enabled for all versions higher or equal to ``v1.3``.
+- The safety controller enables the acknowledging of the external watchdog for all versions higher or equal to ``v1.3``.
+- The oven driver has a separate safety enable for the solid state relay which it enables on all versions higher or equal to ``v1.3``.
+
+
+API Documentation
+-----------------
+
+.. doxygengroup:: hw-version-detect
+   :project: Reflow Controller Firmware

doc/source/firmware/index.rst

@@ -14,4 +14,5 @@ mechanisms and the behavior. For a detailed code documentation see the doxygen o
 	pid-controller
 	safety/index
 	code/index
+	hw-version-detect
 

doc/source/firmware/safety/index.rst

@@ -21,4 +21,5 @@ which are used to retain boot information across resets, for example to communic
 	flags
 	backup-ram
 	error-handling
+	startup-tests
 	stack-checking

doc/source/firmware/safety/startup-tests.rst

@@ -0,0 +1,23 @@
+.. _safety_startup_tests:
+
+Startup Tests
+=============
+
+The following tests will be performed after each reset / power cycle of the controller.
+
+Internal Memory Test
+--------------------
+Directly after startup and after setting up the system clocks, the controller performs memory checks on the internal SRAM and the core coupled memory.
+
+RAM checking is performed by testing the following sequences:
+
+- Alternating 0x55AA55AA / 0xAA55AA55 pattern
+- Alternating 0xAA55AA55 / 0x55AA55AA pattern
+- 0xFFFFFFFF constant value
+- 0x00000000 constant value
+
+The following functions implement the RAM checking:
+
+.. doxygenfunction:: startup_test_perform_ccm_ram_check
+
+.. doxygenfunction:: startup_test_perform_system_ram_check