ARM VERSION 1.2 Guide de l'utilisateur télécharger pdf (Page 58)

From C/C++, declare the SWI as an __SWI function, and call it. For example:

__swi(0) void my_swi(int);

my_swi(65);

This allows a SWI to compiled inline, without additional calling overhead, provided that:

• any arguments are passed in r0-r3 only

• any results are returned in r0-r3 only.

The parameters are passed to the SWI as if the SWI were a real function call. However, if there are between two and

four return values, you must tell the compiler that the return values are being returned in a structure, and use the

__value_in_regs directive. This is because a struct-valued function is usually treated as if it were a void function

whose first argument is the address where the result structure should be placed.

Example 5-9 and Example 5-10 show a SWI handler that provides SWI numbers 0x0, 0x1, 0x2 and 0x3. SWIs 0x0

and 0x1 each take two integer parameters and return a single result. SWI 0x2 takes four parameters and returns a

single result. SWI 0x3 takes four parameters and returns four results. This example is in Examples\SWI\main.c.

and Examples\SWI\swi.h.

Example 5-9 main.c

#include <stdio.h>

#include "swi.h"

unsigned *swi_vec = (unsigned *)0x08;

extern void SWI_Handler(void);

int main( void )

{

int result1, result2;

struct four_results res_3;

Install_Handler( (unsigned) SWI_Handler, swi_vec );

printf("result1 = multiply_two(2,4) = %d\n", result1 = multiply_two(2,4));

printf("result2 = multiply_two(3,6) = %d\n", result2 = multiply_two(3,6));

printf("add_two( result1, result2 ) = %d\n", add_two( result1, result2 ));

printf("add_multiply_two(2,4,3,6) = %d\n", add_multiply_two(2,4,3,6));

res_3 = many_operations( 12, 4, 3, 1 );

printf("res_3.a = %d\n", res_3.a );

printf("res_3.b = %d\n", res_3.b );

printf("res_3.c = %d\n", res_3.c );

printf("res_3.d = %d\n", res_3.d );

return 0;

}

Example 5-10 swi.h

__swi(0) int multiply_two(int, int);

__swi(1) int add_two(int, int);

__swi(2) int add_multiply_two(int, int, int, int);

struct four_results

{

int a;

int b;

int c;

int d;

};

__swi(3) __value_in_regs struct four_results

many_operations(int, int, int, int);

5.4.5 Calling SWIs dynamically from an application

In some circumstances it can be necessary to call a SWI whose number is not known until runtime. This situation can

Handling Processor Exceptions

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ARM VERSION 1.2 Guide de l'utilisateur Page 58

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