ruby krishna

RAM PAGING MC9S12 FAMILY ISSUE CRITICAL

Discussion created by ruby krishna on Jun 5, 2012
Latest reply on Jun 6, 2012 by kef

Dear friends,

 

              Hi friends..in our company, we are using MC9S12XEQ512 microcontroller for our automotive microcontroller.

specification of the microcontroller is,

 flash memory is 512kb

ram memory is 32kb.

 

1. My doubt is, if i use another microcontroller say MC9S12XEQ384(MC9S12 family) where the ram memory is 20kb. Where will be the allocation ram size would be done in different variants of the microcontroller belonging to the same family ?...

In sense, ram size in mc9s12xeq384  is 20kb and in MC9S12XEQ512 it is 32kb.

 

Where will be difference in ram size will be framed is it in start_up code? datapage.c?hidef.h?

 

What makes the system to understand that this microcontroller can acces only 20kb ram or 32 kb ram?

 

 

2. Is there way of allocating of memory without actually defining in the prm?

 

//RAM_F8=F8000 TO F81FFF

//RAM_F9=F9000 TO F91FFF

RAM_FC =FC000 TO FC1FFF

 

 if a particular rampage is commented in the prm, is there any way  of using that ram. This may look funny, but in our project they have actually commented 8kb ram pages, but it's claimed it is being used somehow?.... can we preallocate

memory from the compiler end? like CSTV ? cp? commands like that?

 

 

3. XGATE ram allocation

 

Consider a case where we use mc9s12x microncontroller ( where XGATE is in RAM) and in the linker file we have allocated 4kb  ram for x-gate. What will happen when the code size exceed 4kb ???.... how start_up code willl push the  large amount x gate code in flash to RAM ( CONSIDER CASE WHERE THE CODE SIZE IS MORE THAN 4K BUT THE RAM ALLOCATION IS 4K).

 

 

 

Please clear my doubts.... thanks

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