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Initialization

Initial startup

The first code executed in the NetBSD kernel is low-level startup code provided as part of the board-specific software. This code is specified by the SYSTEM_FIRST_OBJ and SYSTEM_FIRST_SFILE defines in the Makefile fragment mk.vx115_vep (discussed in the section on configuration); the source file is vx115_vep_start.S in this project.

This assembly file is responsible for setting up the system so initial kernel execution can take place. It performs the following operations.

Copy the kernel to RAM
Set up initial MMU page tables, using all section (1 MB) maps to start. In particular:

Map all physical addresses to same virtual addresses (VA == PA), for any peripherals that may need this
Map the physical peripheral space to the corresponding virtual address range

Do this so can use bus mapping functions during setup in the init_arm( ) function

Map the RAM with VA == PA, but set to be cacheable
Map kernel virtual addresses to RAM physical addresses

Enable the MMU

The initial MMU mapping is really just to allow the kernel to start executing from its relocated location in RAM, before it sets up its real page tables in the init_arm( ) routine, and to allow it to access peripherals during configuration.

Machine startup

The file vx115_vep_machdep.c provides platform-specific initialization. This file defines several functions and data structures: an initarm( ) function that performs basic system initialization, a cpu_reboot( ) function that restarts the system on reboot, and a pmap_devmap structure that defines the peripheral virtual-to-physical memory mapping. Fortunately, the vast majority of these functions are common across platforms, so existing code can be used with minor modifications. The vx115_vep_machdep.c file was based on the smdk2800_machdep.c source, and used the cpu_reboot function verbatim and the initarm function with minor changes.

struct pmap_devmap vx115_vep_devmap[ ]

array of specifications of virtual-physical memory mappings for peripherals

initarm( )

The initarm( ) function provides basic machine setup. It's called during initialization from arch/arm/arm32/locore.S, before the kernel main( ) function is called in kern/init_main.c. The initialization performed in this function is as follows.

call set_cpufuncs to set up basic cpu functions
call pmap_devmap_register(vx115_vep_devmap) so can use bus_space_map; the appropriate ranges must have been mapped in vx115_vep_start.S
call vx115_intr_bootstrap(PIC1_BASE_PHYS, PIC1_SIZE) to do early setup of interrupts needed for spl functionality
call consinit for early console output
set up bootconfig struct
set values of memory parameters

physical_start, physical_end, physical_freestart, physical_freeend, physmem

allocate pages for L1 page directory and L2 page tables
allocate pages for vectors, stacks, msgbuf
set up page tables

call pmap_link_l2pt to link L2 page tables into L1 page table
call pmap_chunk to map a chunk of memory into L1/L2 page tables, pmap_entry to map a single page, pmap_section to map a single section

call pmap_devmap_bootstrap to map static devices
call cpu_domains to set cpu domains
call setttb to set page table base
call cpu_tlb_flushID to flush TLB for I and D
call arm32_vector_init
call set_stackptr to set stack pointers
set data abort, prefetch abort, undefined instruction handlers
call uvm_setpagesize to set up page size
call uvm_page_physload to load physical pages into VM system, and add free pages to free page pool
call pmap_bootstrap to initialize the BSD page map structure from the ARM-specific page tables built above
return stack pointer

consinit( )

The consinit( ) function is used to initialize the serial console just sufficiently to allow console messages to be printed. Further initialization of the serial interface is deferred to the autoconfig process.


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