XC16 Put a data table in PSV memory (PIC)

Question

I want to put a table in Flash and read it directly from my C program. According to Microchip this is done by __attribute__((space(psv))) However, as the most things around microchip, their own examples doesn't work that well (usually obsolete and not updated): https://microchipdeveloper.com/16bit:psv

So this is what I'm trying to do:

uint16_t __attribute__((space(psv))) ConfDiskImage[] = {
    /*AOUT*/ 0x01E0,0x0004,0x3333,0x4053,
    /*   1*/ 0x01E1,0x0012,0x0005,0x0000,0x0000,0x0000,0x4120,0x0000,0x0000,0x0000,0x4120,
    /*   2*/ 0x01E2,0x0012,0x0006,0x0000,0x0000,0x0000,0x4120,0x0000,0x0000,0x0000,0x4120,
    /*   3*/ 0x01E3,0x0012,0x0007,0x0000,0x0000,0x0000,0x4120,0x0000,0x0000,0x0000,0x4120,
    /*EOD */ 0x0000,0x0000
};

When I compile I get: "warning: ignoring space attribute applied to automatic ConfDiskImage"

I'm using MPLAB X IDE 5.45 with XC16-gcc v1.50. Microcontroller: dsPIC33EP256MC506

Any ideas of how to get it to stay in Flash (not being copied to RAM) and read it directly from flash with a pointer?

Answer 1

I suspect what you really need is perhaps more involved but the simple answer to the question you asked is to use the const storage class.

For example:

/*
 * File:   main.c
 * Author: dan1138
 * Target: dsPIC33EP256MC506
 * Compiler: XC16 v1.61
 * IDE: MPLABX v5.45
 *
 * Created on February 19, 2021, 11:56 PM
 */

#pragma config ICS = PGD2, JTAGEN = OFF, ALTI2C1 = OFF, ALTI2C2 = OFF, WDTWIN = WIN25
#pragma config WDTPOST = PS32768, WDTPRE = PR128, PLLKEN = ON, WINDIS = OFF
#pragma config FWDTEN = OFF, POSCMD = NONE, OSCIOFNC = ON, IOL1WAY = OFF, FCKSM = CSECMD
#pragma config FNOSC = FRCDIVN, PWMLOCK = OFF, IESO = ON, GWRP = OFF, GCP = OFF

#include "xc.h"

const uint16_t ConfDiskImage[] = {
    /*AOUT*/ 0x01E0,0x0004,0x3333,0x4053,
    /*   1*/ 0x01E1,0x0012,0x0005,0x0000,0x0000,0x0000,0x4120,0x0000,0x0000,0x0000,0x4120,
    /*   2*/ 0x01E2,0x0012,0x0006,0x0000,0x0000,0x0000,0x4120,0x0000,0x0000,0x0000,0x4120,
    /*   3*/ 0x01E3,0x0012,0x0007,0x0000,0x0000,0x0000,0x4120,0x0000,0x0000,0x0000,0x4120,
    /*EOD */ 0x0000,0x0000
};

int main(void) 
{
    const uint16_t *pData;
    
    pData = ConfDiskImage; /* point to the start of the image */
    /*
     * Walk the image
     */
    for(;;)
    {
        if((!*pData) && (!*pData+1))
        {
            /* At end of image point to the start */
            pData = ConfDiskImage;
        }
        pData++; /* skip record type */
        pData += 1+*pData/2;
    }
    return 0;
}