fixed ROM addressing

[rmaier]

Hello,

I am trying to store several calibration values/tables into ROM at fixed addresses. I am using CodeWarrior on a 9S12P MCU. Right now, I am capable of defined addressing for individual constants as follows:

#pragma CONST_SEG PAGE_0C

volatile const UINT16 CalParameterA @ 0xC9000 = 1458;

#pragma CODE_SEG DEFAULT

This works just as I intend. However, with a bunch of constants, I want to add another definition where the location is sequentially located right behind the previous declaration. Some definition like:

#pragma CONST_SEG PAGE_0C

volatile const UINT16 CalParameterA @ 0xC9000 = 1458;

volatile const UINT16 CalParameterB = 6533;

volatile const UINT16 CalParameterC = 12;

#pragma CODE_SEG DEFAULT

Where the addressing would be:

CalParameterA      0xC9000

CalParameterB      0xC9002

CalParameterC      0xC9004

How can I best achieve this?

[ZhangJennie]

Hi Robert,

You tried to allocate three variables to 0xC9000-0xC9004 .

However with your code, I don’t think this can work.

There are two solutions:

Solution 1:

volatile const UINT16 CalParameterA @ 0xC9000 = 1458;

volatile const UINT16 CalParameterB @ 0xC9002 = 6533;

volatile const UINT16 CalParameterC @ 0xC9004 = 12;

You don’t need put above code under #pragma CONST_SEG PAGE_0C. Because you already use @ defining variables to specific address, there is no sense to put it under PAGE_0C segment.

Solution 2:

In prm, define  a section from 0xC9000

PAGE_0C_9000       = READ_ONLY   0x0C9000 TO 0x0C93FF;

...

USER_CONST_C9000       INTO  PAGE_ PAGE_0C_9000;

In C code,

#pragma CONST_SEG USER_CONST_C9000      

volatile const UINT16 CalParameterA  = 1458;

volatile const UINT16 CalParameterB = 6533;

volatile const UINT16 CalParameterC = 12;

#pragma CODE_SEG DEFAULT

Hope this helps.

Have a great day,
Jennie Zhang

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[rmaier]

Thank you. That was very helpful. As a follow up question: how do I keep space allocated in ROM if it is defined, but not used in an application? The order of each constant is critical. 

[ZhangJennie]

Hi Robert.

To allocate unused global variable to memory, we need add the object in ENTRIES section in prm file

Example:

thus "global_val" will not being optimized out.

Have a great day,
Jennie Zhang

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