> First, when using the UDATA directive, am i supposed to specify the
starting
> address for the section ? Looks like i am because if i don't, the linker
> chooses 0x120, wich is not a  very clever decision....

I use UDATA with explicitly named sections, one section for each RAM bank.
Here is the appropriate snippet from my default linker control file for the
16F876:


//   Linker control file for the PIC 16F876 processor.
//
CODEPAGE NAME=config START=0x2007  END=0x2007 //special processor config word

CODEPAGE NAME=code0      START=0  END=0x7FF //code page 0
CODEPAGE NAME=code1  START=0x800  END=0xFFF //code page 1
CODEPAGE NAME=code2 START=0x1000 END=0x17FF //code page 2
CODEPAGE NAME=code3 START=0x1800 END=0x1FFF //code page 3

DATABANK NAME=bank0  START=0x20  END=0x6F //register bank 0
DATABANK NAME=bank1  START=0xA0  END=0xEF //register bank 1
DATABANK NAME=bank2 START=0x110 END=0x16F //register bank 2
DATABANK NAME=bank3 START=0x190 END=0x1EF //register bank 3

SHAREBANK NAME=globalram  START=0x70  END=0x7F PROTECTED //global regs, bank 0
SHAREBANK NAME=globalram  START=0xF0  END=0xFF PROTECTED //global regs, bank 1
SHAREBANK NAME=globalram START=0x170 END=0x17F PROTECTED //global regs, bank 2
SHAREBANK NAME=globalram START=0x1F0 END=0x1FF PROTECTED //global regs, bank 3

SECTION NAME=.udata_shr RAM=globalram //global memory mapped to all register banks
SECTION NAME=.BANK0 RAM=bank0 //for registers explicitly in bank 0
SECTION NAME=.BANK1 RAM=bank1 //for registers explicitly in bank 1
SECTION NAME=.BANK2 RAM=bank2 //for registers explicitly in bank 2
SECTION NAME=.BANK3 RAM=bank3 //for registers explicitly in bank 3


To get variables in bank 0 for example, I do:

.bank0   udata

This can be done in as many modules as you like, and the variables will be
allocated sequentially.  Most of the time you don't care where a variable is
within a bank, but knowing the bank at assembly time allows for a number of
optimizations.  In the rare event when a variable needs to be at a
particular address, you can put a starting address after UDATA.  If you want
to see all this in action, take a look at my standard project templates and
the HAL project at http://www.embedinc.com/pic.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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