System calls implementation

Functions
uint32_t	os_dispatch_system_call (uint32_t LR)
	ARM-specific entrypoint for system call handlers.
void	SVC_Handler (void)
void	os_core_sleep (void)
	Park current core This function is free to park current core in whatever way that will still allow the core to be woken up by external interrupts.
static unsigned	os_exception_frame_size (bool fp_used)
ExceptionFrame *	push_exception_frame (ExceptionFrame *frame, unsigned args, bool fp_active)
	Duplicate exception frame on thread's stack.
ExceptionFrame *	shim_exception_frame (ExceptionFrame *frame, unsigned args, bool fp_active)
	Creates space for additional arguments under exception frame.
ExceptionFrame *	pop_exception_frame (ExceptionFrame *frame, unsigned args, bool fp_active)
	Remove exception frame from thread's stack.

Variables
static SYSCALL_DEFINITION struct Syscall_Entry_t	nvic_syscalls []

Detailed Description

Function Documentation

os_core_sleep()

void os_core_sleep

(

void

)

Park current core This function is free to park current core in whatever way that will still allow the core to be woken up by external interrupts.

os_dispatch_system_call()

uint32_t os_dispatch_system_call

(

uint32_t

LR

)

ARM-specific entrypoint for system call handlers.

This routine is common entrypoint for all syscall routines. It decodes the syscall ID requested by userspace application and calls generic method to service the system call. It is callable by executing the SVC instruction. Code of SVC_Handler will retrieve the requested SVC ID and let generic machinery to execute specified system call.

os_exception_frame_size()

static unsigned os_exception_frame_size ( bool  fp_used )

static

pop_exception_frame()

ExceptionFrame * pop_exception_frame	(	ExceptionFrame *	frame,
		unsigned	args,
		bool	fp_active
	)

Remove exception frame from thread's stack.

This function will revert effects of calling push_exception_frame. It will handle frame padding automatically.

Parameters

frame	exception frame base address
args	number of function arguments passed onto stack (function args - 4)
fp_active	if true then floating point unit is actively used in the thread exception is for

Returns

new address of stack top after frame has been removed from it

push_exception_frame()

ExceptionFrame * push_exception_frame	(	ExceptionFrame *	frame,
		unsigned	args,
		bool	fp_active
	)

Duplicate exception frame on thread's stack.

Parameters

frame	pointer of frame currently residing on top of process' stack
args	amount of arguments pushed onto stack (first four come into R0-R3, fifth and following are pushed onto stack)
fp_active	if true then floating point unit is actively used in the thread exception is for

Returns

address of duplicated exception frame

shim_exception_frame()

ExceptionFrame * shim_exception_frame	(	ExceptionFrame *	frame,
		unsigned	args,
		bool	fp_active
	)

Creates space for additional arguments under exception frame.

This function will move exception frame content args * 4 bytes lower. If resulting address won't be 8-byt aligned, then additional alignment is applied to it. Content of exception frame is copied automatically.

Parameters

frame	address of exception frame in memory
args	amount of additional arguments for which space should be created under exception frame
fp_active	if true then floating point unit is actively used in the thread exception is for

Returns

address of shimmed exception frame.

SVC_Handler()

void SVC_Handler

(

void

)

Variable Documentation

nvic_syscalls

SYSCALL_DEFINITION struct Syscall_Entry_t nvic_syscalls[]

static

Initial value:

= {
    { SYSCALL_ENABLE_IRQ, (Syscall_Handler_t) &os_nvic_enable },
    { SYSCALL_DISABLE_IRQ, (Syscall_Handler_t) &os_nvic_disable },
}