Accessing memory segments in _system_pre_init()

Mark Rush1

Hello,

I am trying to initialize a specific memory segment using _system_pre_init(). I've defined .lowram as:

.lowram : {} > RAM

in the linker script, but now am having a problem accessing that segment in _system_pre_init().

I've tried looking at every pre_init.c example I can find. What I cannot find is how to reference a self-defined memory segment. Is this possible only for the pre-defined segment names like __BSS__ ?

EDIT:
Using CCS v5.5

over 11 years ago

0 Archaeologist over 11 years ago

TI__Guru* 84225 points

There's no way to refer to the address by section name from within source code, but you can refer to symbols. You'll need to add a START directive to your .lowram declaration, like so:

.lowram : {} > RAM, START(__lowram_start)

Some standard sections like .bss get this treatment automatically.

0 Mark Rush1 over 11 years ago in reply to Archaeologist

Intellectual 600 points

Thank you. This works. I did:

.lowram : {} > RAM, START(__lowram_start), END(__lowram_end)

and it compiles without problems. However, what is the proper way to access these symbols from 'C'? Are they pointers?

Also, could you point me to some documentation wrt these directives?

Thank you very much for your help.

0 Archaeologist over 11 years ago in reply to Mark Rush1

TI__Guru* 84225 points

It's not a pointer, it is a linker constant. Use _symval(&__lowram_start); see the MSP430 Optimizing C/C++ Compiler v 4.3 User's Guide (SLAU132I), section 6.5.3.2 "Accessing Assembly Language Constants"

0 Archaeologist over 11 years ago in reply to Archaeologist

TI__Guru* 84225 points

For the linker command file directives, see MSP430 Assembly Language Tools v4.3 User's Guide (SLAU131I), section 8.5.9.7 "Address and Dimension Operators"

http://processors.wiki.ti.com/index.php/TI_Compiler_Information#Compiler_Manuals

0 Mark Rush1 over 11 years ago in reply to Archaeologist

Intellectual 600 points

Thank you for your time.

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Accessing memory segments in _system_pre_init()