Description of Header Files (TWL-SDK)

TWL-SDK System Header

Include these header files in modules that use TWL-SDK.

Module Initialization Function

Enables the use of the C language static initializer NitroStaticInit().

Place this header file in an include statement only in the module that defines NitroStaticInit(). The static initializer of the overlay module starts when the overlay is linked. With this mechanism, you can prepare an entry for a pointer to a function so that the corresponding function gets registered in NitroStaticInit() when the overlay module is linked.

Switching Between ARM & THUMB Instruction Sets

The ARM9 and ARM7 CPUs of the TWL can use two kinds of instruction sets: ARM and THUMB instructions. You can switch between these two instruction sets using jump instructions. In C, switching between jump instructions is performed with function calls. Therefore, the instruction set is normally selected by a function.

Use code32.h or code16.h by combining with codereset.h. With code32.h and codereset.h, enclose the function for the instruction set you want to fix with the ARM. With code16.h and codereset.h, enclose the function you want to fix with the THUMB. When you are using assembly, always enclose the function with code32.h or code16.h, depending on the instruction set.

#include <twl/code32.h>     // This outputs the following arm_inst() using the ARM instruction set
int arm_inst(int n)
{
    // 32-bit code area
    return n * n;
}
#include <twl/codereset.h>  // The instruction set is restored (as per the compiler options)

Using TCM (TCM section specification)

The TWL ARM9 processor has a scratchpad region in CPU (a high-speed buffer region that is fixed in the memory map) called TCM. The region can be accessed as fast as cache in the CPU; so by making better use of this region you can limit the slow-down in processing speed that might otherwise occur because of a cache miss.

When defining the functions you want to place in the TCM region, enclose them with twl/itcm_begin.h and twl/itcm_end.h as shown below. Function regions that are enclosed this way are transferred to the instruction TCM (ITCM) region at startup.

#include <twl/itcm_begin.h>  //  Place the following tcm_inst() in ITCM
int tcm_inst(int n)
{
    // 32-bit code area
    return n * n;
}
#include <twl/item_end.h>    // Return the placement destination to normal

When you want to place a data block in the data TCM (DTCM) region, enclose it with twl/dtcm_begin.h and twl/dtcm_end.h, as shown below.

#include <twl/dtcm_begin.h>  // Place the following tcm_data() in DTCM
u32  tcm_data[] =
{
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9
}
#include <twl/dtcm_end.h>    // Return the placement destination to normal

Specifying Special Sections

There are also other special sections besides the TCM sections.

The *.parent section is essential for clone boot--one form of DS Download Play.

The .ltdmain section is used with HYBRID applications. This section is only loaded when an application runs on TWL, not when an application is run on a Nintendo DS.

The *.version section and the *.wram section are used in the TWL-SDK implementation internally, so there is no need to be aware of them when using the SDK.

TWL-SDK Version Information

This defines the TWL-SDK version information.

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