Improve documentation of Stack Checking

doc/source/firmware/index.rst

@@ -11,6 +11,6 @@ mechanisms and the behavior. For a detailed code documentation see the doxygen o
 	:maxdepth: 2
 	
 	pt1000-processing
-	safety
+	safety/index
 	code/index
 

doc/source/firmware/safety/flags.rst

@@ -8,6 +8,10 @@ The safety flags are represented in software by the following enums
 .. doxygenenum:: safety_flag
 
 The safety flags can be temporarily or permanent. Some temporary flags are reset automatically, once the error condition disappears. Others have to be explicitly cleared. 
+The safety weights (if a flag stops the PID controller, or triggers the panic mode) are configured by default as described below. However, it will be possible to override these weights by
+setting config entries in the safety memory.
+
+.. todo:: Change docu of config entires in memory
 
 ----------------------------------------------------------------------------------------------------------------------------------
 
@@ -91,3 +95,20 @@ persistent self-clearing Stops PID     Panic Mode
 ========== ============= ============= ===========
 yes        no            yes           no
 ========== ============= ============= ===========
+
+
+.. _safety_flags_stack:
+
+ERR_FLAG_STACK
+---------------------------
+
+``ERR_FLAG_STACK`` ialization of the controller, in case a corrupted safety memory is encountered.
+This error is not recoverable and will trigger the panic mode.
+
+.. seealso:: :ref:`safety_stack_checking`
+
+========== ============= ============= ===========
+persistent self-clearing Stops PID     Panic Mode
+========== ============= ============= ===========
+yes        no            yes           yes
+========== ============= ============= ===========

doc/source/firmware/safety/index.rst

@@ -21,3 +21,4 @@ which are used to retain boot information across resets, for example to communic
 	flags
 	backup-ram
 	error-handling
+	stack-checking

doc/source/firmware/safety/stack-checking.rst

@@ -0,0 +1,39 @@
+.. _safety_stack_checking:
+
+Safety Stack Checking
+=====================
+
+To ensure correct operation of the controller, the stack is continuously monitored. For this, the :ref:`firmware_safety` checks the stack in each run.
+These checks include:
+
+1. Checking of used stack space and limit to end of stack
+2. Checking a protection area between heap and stack for memory corruption
+
+Any detected error will set the :ref:`safety_flags_stack` error flag.
+
+Stack Pointer Checking
+----------------------
+
+The stack pointer is checked using :c:func:`stack_check_get_free`. The returned value for the remaining stack space is checked against
+
+.. doxygendefine:: SAFETY_MIN_STACK_FREE
+
+.. doxygenfunction:: stack_check_get_free 
+
+
+Stack and Heap Corruption Checking
+----------------------------------
+
+A section of memory is located between the stack and the heap. It is defined inside the linker script. It's size is configured by the linker script parameter ``__stack_corruption_area_size``, which is set to ``128`` by default.
+This section is filled at the initializazion of the safety controller by a call to
+
+.. doxygenfunction:: stack_check_init_corruption_detect_area
+
+On each run of the safety controller's handling function (:c:func:`safety_controller_handle`) the following function is called:
+
+.. doxygenfunction:: stack_check_corruption_detect_area
+
+
+This function constantly checks the memory area for write modifications, and therefore detects, if the stack or heap have grown outside their boundaries.
+
+

stm-firmware/include/reflow-controller/safety/safety-config.h

@@ -72,6 +72,9 @@ enum analog_value_monitor {
 
 #define WATCHDOG_PRESCALER 8
 
+/**
+ * @brief Minimum number of bytes that have to be free on the stack. If this is not the case, an error is detected
+ */
 #define SAFETY_MIN_STACK_FREE 0x100
 
 #define PID_CONTROLLER_ERR_CAREMASK (ERR_FLAG_STACK | ERR_FLAG_AMON_UC_TEMP | ERR_FLAG_AMON_VREF | \

stm-firmware/include/reflow-controller/safety/stack-check.h

@@ -25,8 +25,16 @@
 
 #define STACK_CHECK_MIN_HEAP_GAP 16UL
 
+/**
+ * @brief Get usage of the stack
+ * @return Usage of the stack in bytes
+ */
 int32_t stack_check_get_usage();
 
+/**
+ * @brief Get free stack space
+ * @return free stack space in bytes. If negative, a stack overflow occured
+ */
 int32_t stack_check_get_free();
 
 static inline int stack_check_collision()
@@ -50,8 +58,32 @@ static inline uint32_t read_stack_pointer()
 	return stack_pointer;
 }
 
+/**
+ * @brief Init the stack corruption detection area.
+ *
+ * This function initializes the memory area between heap and stack with random values generated by the
+ * STM's random number generator. A 32 bit CRC generated by the CRC unit of the STM is appended for verification of the
+ * area.
+ *
+ *
+ * @return 0 if successful, else an error has occured in generating a random number. This should never happen
+ * @note This function turns on the CRC unit but does not disable it afterwards. Therefore, the CRC unit does not have
+ * to be explicitly initialized before calling @ref stack_check_corruption_detect_area.
+ */
 int stack_check_init_corruption_detect_area(void);
 
+/**
+ * @brief Check the CRC of the stack corruption detection area
+ *
+ * This function checks the stack corruption detection area, which must be initialized by
+ * @ref stack_check_init_corruption_detect_area beforehand.
+ *
+ * The CRC unit must be enabled for this function to work properly.
+ * After calling @stack_check_init_corruption_detect_area, this is the case.
+ *
+ * @return 0 if no error is detected, all other values are an error.
+ * @note Make sure CRC unit is enabled.
+ */
 int stack_check_corruption_detect_area(void);
 
 #endif /* __STACK_CHECK_H__ */