OS_InitContext

Syntax

#include <nitro/os.h>

void OS_InitContext( OSContext* context,
                     u32         newpc,
u32         newsp );

Arguments

`context`	Context
`newpc`	Start address
`newsp`	Stack

Return Values

None.

Description

Initializes context.

The context structure OSContext has the following members:

`u32 cpsr`	CPSR (Current Program Status Register)
`u32 r[13]`	Registers R0-R12
`u32 sp`	Stack pointer (R13 register)
`u32 lr`	Link register (R14 register)
`u32 pc_plus4`	Program counter + 4 (R15 register+4)
`u32 sp_svc`	Used to save to stack in Supervisor mode (see note 1)
`CPContext cp_context`	Context for the divider / square root calculator (see note 2)

Note 1: May not exist according to compile options. Note 2: Exists only in ARM9.

With the OS_InitContext function, the stack for SVC is allocated downward from newsp. (Depending on the compile option, this process may not occur.) cpsr is set appropriately by checking the processor mode (distinguishing ARM and THUMB) from the CPSR register. r[0] – r[12] (registers R0-R12) and lr (register R14) are zero-cleared. pc_plus4 takes a value 4 more than the specified value of newpc.

cp_context exists only in ARM9 as a member of the CPContext structure and is the context for the divider/square root calculator. CPContext structure contains the following members.

`u64 div_numer`	Parameter of the divider (divisor)
`u64 div_denom`	Parameter for the divider (dividend)
`u64 sqrt`	Parameter for the square root calculator
`u16 div_mode`	Divider mode
`u16 sqrt_mode`	Square root calculator mode

The OS_InitContext function does not change the content of cp_context.

Revision History

2004/06/30 Described cp_context.
2003/12/01 Initial version.