====== The MESS Driver Lifecycle ======
----
**When does my code get called?**
<note important>This page is outdated and needs to be updated for the current MAME and MESS version.</note>

Imagine we want to create, update, or understand a MESS driver. We have all these wonderful ADDRESS_MAP, MACHINE_RESET, VIDEO_START, DEVICE_INIT, etc. structures and functions we can use. The key to implementing the things properly is understanding the MESS driver lifecycle; knowing when what is created and/or available when a driver is started or reset (soft or hard reset).

This information can be found in the MAME and MESS source code. Most of which is available in the mame.c file. Additional information can be found on the mamedev wiki.

The section where information is used or code is called that we have defined in our own driver or cpu core code have been marked in **bold**.

    - create_machine() to create the machine structure
    - reset_machine() to initialize the machine strucutre
    - mame_validitycheck() to perform validity checks on all compiled drivers
    - game start/hard reset
        - reset_machine() to initialize the machine strucutre
        - init_resource_tracking()
        - begin_resource_tracking()
        - init_machine()
            - cpuintrf_init() to determine which CPUs are available
            - sndintrf_init() to determine which sound chips are available
            - fileio_init() to initialize file I/O info
            - config_init() to initialize the configuration system
            - output_init() to initialize the output system
            - state_init() to initialize the save state system
            - state_save_allow_registration() to allow save state registrations
            - drawgfx_init() to initialize rendering globals
            - palette_init() to initialize palette system
            - render_init() to initialize the rendering system
            - ui_init() to initialize the user interface
            - generic_machine_init() to initialize generic machine structures
            - generic_video_init() to initialize generic video structures
            - timer_init() and register soft_reset_timer handler to reset the timer system
            - osd_init() to do platform specific initialization
            - code_init() to initialize the input system
            - input_port_init() to set up the input ports from the driver's **INPUT_PORTs**
            - rom_init() to load the system's ROMs
            - memory_init() to process the system's memory maps from the driver's **ADDRESS_MAPs**
            - cpuexec_init() to initialize the CPUs
            - cpuint_init() to initialize the CPU interrupts
            - devices_init (MESS specific)
                - inputx_init() to initialize natural keyboard support
                - devices_allocate() to create the device information structures
                - ram_init() to initialize the RAM settings
                - image_init() to initialize all devices
                    - for each device type
                        - **DEVICE_INIT(image)**
                - for each device type in the driver's [[reference:SYSTEM_CONFIG]]
                    - for each device of type
                        - image_from_device_and_index() to identify the image
                        - image_load() to load the image
                            - image verify
                            - **DEVICE_CREATE(image,format,args)** or **DEVICE_LOAD(image)**
            - mame_debug_init() to set up the debugger
            - **DRIVER_INIT()**
            - video_init() to start the video system
            - sound_init() to start the audio system
            - **MACHINE_START()**
            - **SOUND_START()**
            - **VIDEO_START()**
            - free disposable memory regions
            - saveload_init() to set up for save/load
            - cheat_init() to initialize the cheat system
        - config_load_settings() to load the configuration file
        - nvram_load() to load the system's NVRAM by calling **NVRAM_HANDLER()** if available
        - ui_display_startup_screens() to display the startup screens
        - begin_resource_tracking()
        - soft_reset() (can also be initiated while the machine is running)
            - end_resource_tracking()
            - begin_resource_tracking()
            - state_save_allow_registrations() to allow save state registrations
            - cpuint_reset
            - **MACHINE_RESET()**
            - **SOUND_RESET()**
            - **VIDEO_RESET()**
            - call everything on the reset callback lit
            - state_save_allow_registrations() to disallow save state registrations
        - while running
            - execute cpu slices and video_frame_update
        - end_resource_tracking() to free all auto_mallocs and timers
        - nvram_save() to save the system's NVRAM by calling **NVRAM_HANDLER()** if available
        - config_save_settings() to save the system's configuration
        - call exit routines
        - exit_resource_tracking()
        - empty exit, reset, and pause callback lists
    - destroy_machine