topic Re: what is GPAGE_SEG? in S12 / MagniV Microcontrollers

what is GPAGE_SEG?

100asong — Mon, 24 Oct 2011 13:43:38 GMT

My MCU type:MC9S12X.

I don't know what GPAGE_SEG?

If I write

#pragma CONST_SEG _GPAGE_SEG myseg

const int16 myVar[2] = {0x01,0x02}

in Code,

I will find GPAGE_SEG in map file:myVar D881 6 6 4 _GPAGE_SEG

GPAGE_SEG is compiler known symbol, But I don't find the defination and what is the exact meaning.

Re: what is GPAGE_SEG?

kef — Mon, 24 Oct 2011 14:57:45 GMT

It tells compiler that global addressing (GPAGE register + gstaa/gldd etc CPU instructions) are should be used to access data, wich is allocated in memory segment you specify (myseg in your case).

Similarly __RPAGE_SEG is used to access paged RAM switching RPAGE register. __EPAGE_SEG for EPAGE paged EEPROM etc.

It shouldn't affect your map file. PRM file defines addresses of memory segments. Since compiler doesn't know at compile time where will be specific segments allocated, compiler need more information, and you help compiler specifying segment attributes like __GPAGE_SEG. This means that if some variables are accessed from different files, all source units should see not only extern variable declarations, but all those shared externs should be also declared in H-files between the same DATA_SEG pragmas

#pragma DATA_SEG xxxxx

put you vars here

#pragma DATA_SEG DEFAULT

Re: what is GPAGE_SEG?

100asong — Mon, 24 Oct 2011 20:08:40 GMT

Hi,Dear kef.

Thanks for your help.

I implement these work:

In prm file:

MySeg INTO PAGE_FE;

MyCode INTO PAGE_FC;

In my.c file:

#pragma CONST_SEG __GPAGE_SEG MySeg

const int sa[4] = {0x11, 0x12, 0x13, 0x14};

#pragma CONST_SEG DEFAULT

And then I want to access sa in PAGE_FE flash area.

int * __far g_psa;

int x = 0;

#pragma CODE_SEG MyCode

void ReadSa()

{

g_psa = (int* __far)sa ;

x = *(int * __far)g_psa++;//x = 0,not 0x11

x = *(int * __far)g_psa++;//x = 0, not 0x12

x = *(int * __far)g_psa++;//x = 0, not 0x13

x = *(int * __far)g_psa;

}

#pragma CODE_SEG DEFAULT

How to get the right data:0x11,0x12,0x13?

How to access access 0xFE from page 0xFC?

Thanks.

Re: what is GPAGE_SEG?

kef — Mon, 24 Oct 2011 21:17:39 GMT

But last write to x is working, right? If so, then compiler has optimized away unused stores to x. Try making x volatile.

I wonder what is purpose of storing your function in specific page of flash?

Re: what is GPAGE_SEG?

100asong — Tue, 25 Oct 2011 07:58:25 GMT

Try volatile is okay.

I want to store some constant data in one page of flash, and then I can access it.

Re: what is GPAGE_SEG?

kef — Tue, 25 Oct 2011 16:20:26 GMT

Unless there are special requirements, like the need to allocate ISR functions in nonbanked flash, it is more convenient to allocate code in default memory.

Project wizard (in case you don't use Processor Expert) creates single placement record for all paged flash and calls it DEFAULT_ROM. Unless you have big >16k arrays of data, it makes sense to use this DEFAULT_ROM to allocate your constants. This may free you from the task of allocating data in specific flash pages.

Re: what is GPAGE_SEG?

100asong — Thu, 27 Oct 2011 12:49:26 GMT

So good.