Changes between Initial Version and Version 1 of KernelStartUp

Timestamp:

Dec 18, 2012, 6:04:17 PM (11 years ago)

Author:

becoulet

Comment:

--

KernelStartUp

@@ +1 @@
+= MutekH startup and initializations =
+
+This page describes how the various parts of the kernel are initialized when the operating system starts.
+
+== Modular startup process ==
+
+The MutekH statup process consists in calling many intialization functions for all components of the system.
+Depending on the current build configuration, different modules and features are enabled at compile time. This make the
+set of relevant initialization functions change with the current configuration.
+
+The initialization order of the various parts of the kernel is important because some components do
+depend on other components which need to be initialized first. The proper order may also be different
+depending on some configuration parameters like the target architecture.
+
+Rather than defining the initialization order directly, the MutekH build system generates a list of intialization
+function calls sorted in the right order based on some expressed ordering constraints. This allows the developper of a software
+component to insert its intialization function calls at the right time relative to intialization of other components.
+
+The kernel initialization stages are arranged in a hierarchical manner. Internal nodes of this intialization tree define
+the main steps of startup process whereas leaf nodes actually define the function calls which must take place.
+Ordering constraints are expressed along with the hierarchy using [BuildSystemDev#Initializationtokensdeclaration intialization tokens]
+in the build system configuration files.
+
+== Initialization functions ==
+
+The whole startup process is split in two main groups of intialization tokens:
+ * Intializations which take place on the bootstrap processor while other processors are waiting.
+ * Intializations which take place at the same time on all processors.
+
+The bootstrap processor usally starts execution in assembly code in the `cpu_boot` function.
+It then jumps to the `mutekh_startup` function which contains function calls generated
+by the build system for the `INIT_MUTEKH_STARTUP` initialization token.
+
+On multiprocessors platforms other processors enter the `mutekh_startup_smp`
+function when instructed to do so by the bootstrap processor. This function contains function
+calls corresponding to the `INIT_SMP` token which is actually the same as the second half of `INIT_MUTEKH_STARTUP`.
+
+Initialization tokens which are part of `INIT_SMP` group can call the `mutekh_startup_smp_barrier` function
+to ensure that all processors have reached this same point in code. If an intialization must be performed
+on a single processor in this intialization group, the result of the `cpu_isbootstrap` function must be tested.
+
+Startup related functions are declared in the [source:hg/mutek/include/mutek/startup.h mutek/startup.h] header file.
+
+== Main intialization steps ==
+
+The first part of the startup process executed on the boostrap processor only includes the following main steps (when relevant):
+ * initialization of memory sections `.bss` and `.data`.
+ * initialization of the early output console.
+ * initialization memory and page allocators.
+ * initialization and enumeration of devices present in the platform, including processors.
+ * initialization of the associated device drivers.
+
+The second part of the startup process which is executed by all processors includes:
+ * initialization of each processor registers
+ * initialization of the scheduler
+ * initialization of other libraries and software components
+ * initialization of the application
+ * enter the scheduler loop
+
+Below is an sample herarchical view of the main intialization tokens as output by the `make listinit` command
+with a multiprocessor build configuration (as described on the BuildSystem page).
+
+{{{
+  * INIT_MUTEKH_STARTUP
+     * INIT_BOOTSTRAP
+         * INIT_MEMORY                             
+             * INIT_MEMORY_SECTIONS                
+                 * ....
+             * INIT_MUTEK_EARLY_CONSOLE            
+                 * ....
+             * INIT_MUTEK_MEMALLOC                 
+                 * ....
+         * INIT_DEVICE                             
+             * INIT_DEVICE_TREE                    
+             * INIT_DEVICE_ENUM                    
+                 * ....
+             * INIT_DEVICE_DRIVERS                 
+         * INIT_SMP_STARTUP_BARRIER
+         * INIT_START_CPUS
+             * ....
+     * INIT_SMP                                    
+         * INIT_CPUS                               
+             * INIT_DEVICE_CPU_REGS                
+             * INIT_MUTEK_FAULT_HANDLER            
+         * INIT_MUTEK_SCHEDULER_INIT               
+         * INIT_MUTEK_CONSOLE                      
+         * INIT_LIBRARIES                          
+             * ....
+         * INIT_APPLICATION                        
+         * INIT_MUTEK_SCHEDULER_START              
+}}}
+
+
+The `INIT_APPLICATION` step calls the `app_start` function which must be defined in the application source code.
+
+Here is an example intialization function calls order retained by the build system:
+
+{{{
+   INIT_MUTEKH_STARTUP (init):
+       INIT_SOCLIB_BSS                  soclib_bss_section_init()
+       INIT_SOCLIB_DATA                 soclib_data_section_init()
+       INIT_SOCLIB_EARLY_CONSOLE        soclib_early_console_init()
+       INIT_SOCLIB_MEM_ALLOC            soclib_mem_init()
+       INIT_DEVICE_TREE                 device_tree_init()
+       INIT_SOCLIB_FDT                  soclib_fdt_init()
+       INIT_DEVICE_DRIVERS              libdevice_drivers_init()
+       INIT_SMP_STARTUP_BARRIER         mutek_startup_barrier_init()
+       INIT_SOCLIB_START_CPUS           soclib_start_cpus()
+       INIT_SOCLIB_SMP_WAIT_BOOTSTRAP   soclib_smp_wait_bootstrap()
+       INIT_DEVICE_CPU_REGS             libdevice_cpu_regs_initsmp()
+       INIT_MUTEK_FAULT_HANDLER         mutek_fault_initsmp()
+       INIT_MUTEK_SCHEDULER_INIT        mutek_scheduler_initsmp()
+       INIT_MUTEK_CONSOLE               mutek_console_initsmp()
+       INIT_APPLICATION                 mutek_app_initsmp()
+       INIT_MUTEK_SCHEDULER_START       mutek_scheduler_start()
+}}}