Application Processor Boot. More...

Functions
void	relocateSetupCode ()
	Relocate the real mode setup code.

void	boot ()
	Boot all application processors.

Variables
constexpr GDT::SegmentDescriptor	ap_gdt []
	Temporary Global Descriptor Table.

const uintptr_t	RELOCATED_SETUP = 0x40000
	Address (below 1 MiB) to which the setup code gets relocated.

Detailed Description

Application Processor Boot.

Interface to boot the APs

Function Documentation

◆ boot()

void ApplicationProcessor::boot ( )

Boot all application processors.

Performs relocation by calling relocateSetupCode()

See also: ISDMv3, 8.4.4.2 Typical AP Initialization Sequence

◆ relocateSetupCode()

void ApplicationProcessor::relocateSetupCode ( )

Relocate the real mode setup code.

The application processors (APs) start in real mode, which means that your setup code must be placed within the first megabyte – your operating system resides currently at a much higher address (16 MiB), so the code has to be copied down there first.

Luckily, the code in setup_ap() can be relocated by copying – because it does not use any absolute addressing (except when jumping to the protected mode function startup_ap()). The function must be copied to the address of RELOCATED_SETUP (0x40000), so that the APs can start there.

The memory section contains a reserved area for the GDT and its descriptor, which has to be assigned first with the contents of ap_gdt.

Note: You could also tell the linker script to put the code directly at the appropriate place, but unfortunately the Qemu multiboot implementation (via -kernel parameter) can't handle it properly.

Variable Documentation

◆ ap_gdt

constexpr GDT::SegmentDescriptor ApplicationProcessor::ap_gdt[]

constexpr

Initial value:

= {
    
    {},
 
    
    {    0x0,
         0xFFFFFFFF,
         true,
         0,
         GDT::SIZE_32BIT  },
 
    
    {    0x0,
         0xFFFFFFFF,
         false,
         0,
         GDT::SIZE_32BIT  },
}

Temporary Global Descriptor Table.

Blue print, to be copied into real mode code