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ST9 USER GUIDE

/* define a function that has a single argument of type pointer to character

void MyFunc ( char * Arg ) ;

{

/* body of the function */

}

void main ( void ) ;

{

/* some code */

/* invoke the function with the address of the character element of the

structure */

MyFunc ( &MyStruct.C1 ) ;/* &MyStruct.C1 = 4(rr2) if rr2 contains the

address of MyStruct */

/* more code */

}

The lddd, ldpp, lddp, ldpd instructions are used for block copies such as assignments of struc-

tures, etc.

Powerful addressing modes such as indirect, indirect with increment or decrement and in-

dexed shorten the code needed to access data even in structures or arrays. They also facili-

tate access to local variables created on the stack on entering functions. Working registers

that benefit from the most powerful instructions and addressing modes are heavily used by the

compiler. In fact, the GNU9 compiler does not always translate the source code as suggested

above. There are optimization schemes that save execution time and/or memory by judi-

ciously allocating the working registers, so that in many cases arguments are not pushed to

the stack, but merely to an available working register.

3.4 INTERRUPTS

The interrupt system of the ST9 is very powerful, and, in consequence, requires some thor-

ough study to get the most out of it. However, it is worth learning since it allows you to build

very efficient programs with excellent interrupt response times.

The ST9 interrupt system works the same as that of any microcontroller, except for two points

that call for special attention: the vector mechanism and the priority mechanism(4).

(4) Device Datasheet; Interrupts § 4.

ST9 データシート(PDF) 41 Page - STMicroelectronics