How to declare constant in flash on fixed address

[arco]

How do I declare a constant at a fixed address? I now tried:

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Const BOOT_VERSION As Word[1] = (0x0400) Org 0x1FFE

It seems this is stripped by the compiler because it's never used.
But I need this constant in a bootloader application, so main application can see what version the bootloader is...
Constants declared on fixed locations should never be stripped... (they are placed there for a reason)

[marcus]

Place it in program flash (eg, 0x9D000800). If it still doesn't compile make a reference to it in code

[arco]

Yes,

I know it works if it is referenced, but that's a bit of a kludge...
I hate to embed useless code in my program just to let the compiler behave correctly...
Constants with a fixed address should always be left alone by the compiler. (It's placed there for a reason.)
Could for instance be a serialnumber that normally is never accessed or with indirect addressing.

BTW: ORG is always in program flash...

[marcus]

Sorry, was looking at the PIC32 compiler.

All compilers exclude unused code and constants, otherwise the hex will be far larger. Personally, I'm ok with the way the compiler works in this regard. Adding a dummy reference is not a big deal for me, it's rare to have an unused fixed const in the program.

[arco]

Fixed address constants should *never* be omitted. The're placed there on purpose.
I disabled the compilers optimization, with no luck, still strips them out...

[filip]

Hi,

When I compile your line of code, I get the following ASM listing :

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//** Constants locations ** 
//ADDRESS    SIZE    CONSTANT
//----------------------------------------------
0x1FFE       [2]    _BOOT_VERSION

It seems that the compiler did not exclude this constant even though it is not used anywhere in the code.

Can you see your ASM listing ?

Regards,
Filip.

[arco]

The compiler says that there is a _BOOT_VERSION constant, but there isn't
You won't find any other reference to it in that listing file. (it's never initialized with the requested value)
If you want to set value to 0x0400 and you reference the constant in code by assigning it to a variable you get code in picture in your list file.
If you do not reference the constant, that code is omitted. (listing says there is a _BOOT_VERSION constant, but there isn't)

You can also see it in the hex file: location 0x1FFE (is 0x3FFC in bytes) is never set to 0x0400... (see 2nd picture with correct value if referenced)