GIET_VM / Boot-Loader

The GIET-VM boot-loader is defined in the 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()