The following code is an example of how to implement a syscall without much effort using the CASIO SDK:
(f. i. to check out, if it is of some use, before you include it in your library and headerfiles)
After defining some function pointer types every syscall declaration needs two lines.

// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
// NEVER try undocumented syscall numbers randomly!
// mostly the calc will do nothing or hang, if the parameters are not chosen correctly.
// but someday you will call the sector erase syscall, which will kill your calc permanently!
// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

// the following definitions are only needed once
#define SCA 0xD201D002
#define SCB 0x422B0009
#define SCE 0x80010070
// 0x80010070 is the fx-9860-syscall-entry point
// 0x80020070 is the fx-CG-syscall-entry point (but remember: the syscall numbers are different!)

// now define some function pointer types
// (for every syscall's interface a different function pointer type is required)
// the following type is for syscalls, which return an int and require no input.
typedef int(*sc_iv)(void);
// the following type is for syscalls, which return an int and require an int-pointer as input (like GetKey).
typedef int(*sc_ipi)(int*);

// example 1
const unsigned int sc0998[] = { SCA, SCB, SCE, 0x0998 };
#define App_DYNA (*(sc_iv)sc0998)

// now you could use
// to call the built-in DYNA.

// or

// example 2
const unsigned int sc090F[] = { SCA, SCB, SCE, 0x090F };
#define GetKey (*(sc_ipi)sc090F)

// to call
  GetKey( &key );

for reference:
this are the assembler instructions, which represent the int arrays of the type
"const unsigned int scSyscallNo[] = { SCA, SCB, SCE, SyscallNo };"

	mov.l   #h'80010070, r2
	mov.l   #SyscallNo, r0
	jmp     @r2