example_saverestore_psvpag.c

Mplab C30编译器

 /* Example illustrating how to Save and Restore the PSVPAG register   */
 
 /***********************************************************************
 *  In this example, the constant status_string is located in the       *
 *  compiler-managed PSV section, while the constant gamma_factor is    *
 *  located in a separate PSV section. You are required to place a      *
 *  constant in a separate PSV section if the compiler-managed PSV      *
 *  section is full or if you want to locate the constant at a specific *
 *  address. A PSV section has a capacity of 32 Kbytes.                 *
 *                                                                      *
 *  The compiler will initialize the PSV bit in the CORCON register and *
 *  the PSVPAG register only for the compiler-managed PSV section       *
 *  (auto_psv) on startup (in crt0.s). To properly access gamma_factor, *
 *  you must manually manage the PSVPAG register. Namely, save the      *
 *  PSVPAG register before accessing gamma_factor, set the PSVPAG to    *
 *  access gamma_factor and restore the original PSVPAG after accessing *
 *  gamma_factor. To determine the PSVPAG of a constant stored in       *
 *  program memory, one can use the __builtin_psvpage() helper function.*
 *                                                                      *
 *  When the PSVPAG is modified to access gamma_factor, be careful not  *
 *  to access constants stored in the compiler-managed PSV section,     *
 *  such as string constants used with printf(). Any attempts to access *
 *  constants stored in the compiler-managed PSV section with an        *
 *  incorrect PSVPAG will fail.                                         *
 *                                                                      *
 *  On devices with less than 16K instruction words, there is only one  *
 *  PSVPAG and manual mangement of the PSVPAG register is not required. *
 *                                                                      *
 *  You can view the results of the printf statements by enabling the   *
 *  MPLAB SIM tool then enabling the UART1 I/O with Output set to       *
 *  Window. The printf results are then displayed in the output window. *
 *                                                                      *
 *  A defined heap size is required since we are using a standard I/O   *
 *  function.                                                           *
 *                                                                      *
 *                                                                      *
 *  For additional information about dsPIC architecture and language    *
 *  tools, refer to the following documents:                            *
 *                                                                      *
 *  MPLAB C30 Compiler User's Guide                        : DS51284    *
 *  dsPIC 30F MPLAB ASM30, MPLAB LINK30 and Utilities                   *
 *                                           User's Guide  : DS51317    *
 *  Getting Started with dsPIC DSC Language Tools          : DS51316    *
 *  dsPIC 30F Language Tools Quick Reference Card          : DS51322    *
 *  dsPIC 30F 16-bit MCU Family Reference Manual           : DS70046    *
 *  dsPIC 30F Programmer's Reference Manual                : DS70030    *
 *                                                                      *
 *  Example file has been compiled with MPLAB C30 v1.30.00              *
 *                                                                      *
 ************************************************************************
 *                                                                      * 
 *    Author:                                                           *
 *    Company:                                                          * 
 *    Filename:       Ex_SaveRestore_PSVPAG.c                           *
 *    Date:           02/01/2005                                        *
 *    File Version:   1.00                                              *
 *    Other Files Required: p30f6014.gld                                *
 *    Tools Used: MPLAB IDE -> 7.01.00                                  *
 *                Compiler  -> 1.30.00                                  *
 *                Assembler -> 1.30.00                                  *
 *                Linker    -> 1.30.00                                  *
 *                                                                      *
 ***********************************************************************/

/* Include the appropriate header (.h) file, depending on device used */
/* Example (for dsPIC30F5013): #include <p30f5013.h>                  */
/* Alternatively include the generic header file, p30fxxxx.h, as shown 
   below.                                                             */

	#include <p30fxxxx.h>
	#include "stdio.h"


const char __attribute__ ((space(auto_psv))) status_string[2][10] =
{"System OK", "Key Made"};

const int __attribute__ ((space(psv))) gamma_factor[3] = {13, 23, 7};


int main( void )
{
	unsigned psv_shadow;
	unsigned key, seed = 17231;

	/* print the first status string */
	printf ("%s\n", status_string[0]);
	
	/* save the PSVPAG */
	psv_shadow = PSVPAG;

	/* set the PSVPAG for accessing gamma_factor[] */
	PSVPAG = __builtin_psvpage (gamma_factor);

	/* build the key from gamma_factor */
	key = (seed + gamma_factor[0] + gamma_factor[1]) / gamma_factor[2];

	/* restore the PSVPAG for the compiler-managed PSVPAG */
	PSVPAG = psv_shadow;

	/* print the second status message */
	printf ("%s \n", status_string[1]);

	while ( 1 );
}