= GIET_VM / Boot-Loader =

The GIET-VM boot-loader is defined in the [source:soft/giet_vm/giet_boot/boot.c boot.c] file.

The ''boot_init()'' function makes the initialisation in two steps:
 
== __Sequencial step__ ==

The first step executed by proc[0][0][0], while other processors are in wait state.

=== void '''boot_pmem_init()''' ===
This function makes the physical memory allocators initialisation. The GIET VM uses two types of pages: 
 * BPP : Big Physical Page (2 Mbytes).
 * SPP : Small Physical Page (4 Kbytes).
There is one SPP and one BPP allocator per cluster containing a physical memory bank.
All the physical memory allocation is done by the boot-loader in the boot phase, and these memory allocators
should not be used by the kernel in the execution phase.

=== void '''boot_ptabs_init()''' ===
This function makes the page table initialisation. There is one page table per user application (vspace) defined in the mapping.
All these pages tables are packed in one segment (seg_ptab) occupying one single big page (2 Mbytes), but this PTAB segment is replicated in all clusters.
As the kernel read-only segments (seg_kcode and seg_kinit) are replicated in all clusters to avoid contention, the content of the page tables depends
on the cluster-coordinates: for the kernel code, a given virtual address is mapped to different physical addresses, depending on the cluster coordinates.

 


=== '''boot_schedulers init()''' ===
This function makes the schedulers initialisation, as specified in the mapping, with the following principles.
 * There is one scheduler per processor. 
 * Any task defined in any application can be allocated to any processor.
 * The allocation of task to processors is fully static (no task migration).
 * One single processor cannot schedule more than 14 tasks.
 s One scheduler occupies 8 Kbytes. The user
 * Peripherals initialisation : ''boot_peripherals_init()''
 * Kernel & application code loading : ''boot_elf_load()''
 * Start all other processors

== __Parallel step__ ==

This second step is executed in parallel by all processors:
 * CP0_SCHED register initialisation
 * MMU Activation 
 * Status Register Initialisation (to use the GIET_VM exception handler).
 * Jump to ''kernel_init()''