On further thought, you'd be better clone-and-owning the standard
linker scripts (msp430.x at least, maybe a couple of the other ones,
but you shouldn't need to touch the mcu-specific ones). Insert a
section specifically for your variables into the correct region
(presumably REGION_DATA). The main script assumes that it has full
knowledge of everything that goes into each region, and sets markers
to denote the start and end addresses for things like initializing BSS
and copying initialized data from ROM into RAM. I think there would
be subtle problems that would arise if you tried to append something:
either the variables you declare would overlay other ones placed by
the linker, or the address markers would be wrong.
Not knowing your application I can't suggest removing the requirement
that variables be placed at specific locations, though it's an avenue
I would seriously explore if it were my problem. The primary case I
can think of that justifies what you describe involves overlaying
structures on data placed in peripheral memory (such as the USB
buffers), in which case this can be done without modifying linker
scripts (re-use existing symbols, or define new ones).
Peter
On Tue, Dec 13, 2011 at 9:17 AM, Timothy Logan <timothy.lo...@gmail.com> wrote:
> Thanks for everyone's input.
>
> I agree that having a linker script would be a cleaner way of implementing
> this and think I am just going to buckle down and use a linker script so I
> do not end up shooting myself in the foot.
>
> I want to make it however so that the "sections" that I define like
> CrazyCasta said are merely appended to the end of the default linker script.
> Reading into the msp430-ld man page, it has the following to say:
>
> "If the linker cannot recognize the format of an object file, it will assume
> that it is a linker script. A script specified in this way augments the
> main linker script used for the link ..... Specifying a script in this way
> merely augments the main linker script, with the extra commands placed after
> the main script; use the -T option to replace the default linker script
> entirely, but note the effect of the "INSERT" command."
>
> So, making a linker script like this (called linker.x):
>
> 1 SECTIONS
> 2 {
> 3 .mySection 0x0100:
> 4 {
> 5 variable1 = 0x2280;
> 6 variable2 = 0x0820;
> 7 variable3 = 0x22C8;
> 8 variable4 = 0x2288;
> 9 variable5 = 0x2278;
> 10 variable6 = 0x2270;
> 11
> 12 }
> 13 }
>
> And passing it in to the linking step of my Makefile like:
>
> $(CC) -Wall $(LDFLAGS) linker.x $(ALLOBJS) -o $(BUILDDIR)/EXAMPLE.ELF
>
> should do the trick, right? I do get the following warning:
>
> /usr/lib/gcc/msp430/4.5.3/../../../../msp430/bin/ld: warning: linker.x
> contains output sections; did you forget -T?
>
> .. but maybe this is normal?
>
> Sorry if this is going too deep into generic-linker questions.
>
> Cheers,
> Tim
>
>
> On Tue, Dec 13, 2011 at 6:48 AM, Peter Bigot <big...@acm.org> wrote:
>>
>> On Tue, Dec 13, 2011 at 6:03 AM, JMGross <msp...@grossibaer.de> wrote:
>> > ----- Ursprüngliche Nachricht -----
>> > Von: Peter Bigot
>> > Gesendet am: 12 Dez 2011 21:39:15
>> >
>> > On Mon, Dec 12, 2011 at 2:31 PM, Timothy Logan <timothy.lo...@gmail.com>
>> > wrote:
>> >>> I am porting some code from IAR which involves me having to place a
>> >>> few
>> >>> different structures in very specific addresses in the MSP430 memory.
>> >
>> >> You can use asm statements, as are done with the peripheral register
>> >> declarations. Something like:
>> >> volatile unsigned int specialdata __asm__("0x1320");
>> >> will force the definition of specialdata to be placed at address
>> >> 0x1320.
>> >
>> > That's the obvious way.
>> > However, it must be used with care.
>> > The variable locations are put as direct addresses into the
>> > compiler-generated assembly output.
>> > The linker won't see them or know of them.
>>
>> Which is why the real peripheral register declarations use:
>>
>> volatile unsigned int P1OUT __asm__("__P1OUT");
>>
>> where __P1OUT is a symbolic constant defined at final link time from
>> the MCU-specific periph.x file. The same thing can be done in this
>> case so ensure all modules get the same address. The original request
>> was for a simple way that didn't muck with linker scripts, but if the
>> potential for inconsistency is a concern the symbol value can also be
>> provided on the linker command line; see the msp430-ld man page.
>>
>> Peter
>>
>> > So if two independent compilaiton units (C files)
>> > Use their own "superstatic variable" and it happens
>> > to be placed on the same location, you won't get
>> > an error or even a warning. And the two code parts
>> > will mess with each others storage then.
>> >
>> > Especially dangerous when using libraries, where
>> > the particular code is not checked/adjusted for every project.
>> > (so it could be noticed)
>> >
>> > JMGross
>> >
>> >
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