Initializing static variables (GNU gcc tools for H8S/2633)

"Paul Carpenter" <paul$@pcserv.demon.co.uk> wrote in message
news:20040415.2307.298224snz@pcserv.demon.co.uk...
> I have never seen "Hitachi" compilers, just IAR from Hitachi/Renesas, with
> more recognition of GCC.

IIRC, it was around the time that HEW came out ('99?) that the sales reps
were offering us three toolchains (gcc, IAR, Hitachi), and the Hitachi one
was being heavily promoted (as you'd expect). I do distinctly remember my
rep telling me that the IAR compilers were being "de-emphasised" in favour
of Hitachi versions, but I also remember wondering later if it was purely a
badging exercise.

More recently I've been working on the H8 again, with up-to-date tools
provided by my customer's R&D dept. And the compilers again are overtly IAR.
I think I missed the middle of the story (roughly '01 through late '03).

Steve
http://www.sfdesign.co.uk
http://www.fivetrees.com

On 14 Apr 2004 23:11:47 -0700, robert.bielik@gyros.com (Robert Bielik)
wrote:

>Hi all,
>
>I have "inherited" a project with a H8S/2633F MPU (using the GNU gcc
>toolchain). I need static variables. Problem is that there is no init
>code for static variables in the bootloader code. I.e. the initial
>static data is correctly placed in the FLASH ROM, but the data is
>never transferred at startup to the RAM. I have searched everywhere
>for a simple example showing how to do it but have come up empty so
>far.
>
>Does anyone have a (asm) code snippet for this ?? I guess any MPU in
>the 26xx series would do...
>
>If you do, please send a copy to my email address also.
>
>TIA
>/Rob

Hi Rob,
	As you've already surmised you need to create a startup code
section which takes the ROM-based .data section and copies it into the
.bss section. The linker, LD, configuartion file is so organised to
refer to an image of the .data section but offset into the .bss or RAM
area. The GNU manual on LD provides you with information on how to
setup the linker file. From that you can write the companion startup
code. The startup code is initiated from the Power-on-reset. The start
and end boundaries of the .data section can be defined in the linker
configuration file -- this is required to mark out the start & range
of the ROM code to copy.

	Of course there is the simple solution and that is to
eliminate all use of initialised variables.

Ken.

+====================================+
I hate junk email. Please direct any 
genuine email to: kenlee at hotpop.com

Ken Lee wrote:
> 	As you've already surmised you need to create a startup code
> section which takes the ROM-based .data section and copies it into the
> .bss section. 

A small nit here. The initialized data is copied to RAM, but
not the bss. The bss is for global/static variables that are
initialized by default to zero.

> The linker, LD, configuartion file is so organised to
> refer to an image of the .data section but offset into the .bss or RAM
> area. The GNU manual on LD provides you with information on how to
> setup the linker file. From that you can write the companion startup
> code. The startup code is initiated from the Power-on-reset. The start
> and end boundaries of the .data section can be defined in the linker
> configuration file -- this is required to mark out the start & range
> of the ROM code to copy.
> 
> 	Of course there is the simple solution and that is to
> eliminate all use of initialised variables.

While this eliminates the need to copy initialized data
into RAM, it does not do the other important setup of
the C runtime, which is to zero the bss section. I assume
that if your startup code is missing the data initialization
it may also be missing the bss initialization.

-- 
Michael N. Moran           (h) 770 516 7918
5009 Old Field Ct.         (c) 678 521 5460
Kennesaw, GA, USA 30144    http://mnmoran.org

"... abstractions save us time working, but they don't
  save us time learning."
Joel Spolsky, The Law of Leaky Abstractions

The Beatles were wrong: 1 & 1 & 1 is 1

On 2004-04-16, Ken Lee <postmaster@noname.com> wrote:

> As you've already surmised you need to create a startup code
> section which takes the ROM-based .data section and copies it
> into the .bss section.

Nooo!

The .bss section should be initialized to all zeros.  

The .data section should have two addresses:

  VMA (virtial memory address): the run-time address where the
      compiled code expects the variables to be.  This will be
      in RAM.

  LMA (load memory address): the addresses to which the
      initialization data are stored by the linker.  This will
      be in ROM.

Startup code should copy from .data's LMA to .data's VMA.
      
> The linker, LD, configuartion file is so organised to refer to
> an image of the .data section but offset into the .bss or RAM
> area.

It sounds like you're doing a round-about, home-made
implimenation of the VMA/LMA capabilities built into the
linker?

>[...]

> Of course there is the simple solution and that is to
> eliminate all use of initialised variables.

That's rarely simple.

It takes 4-5 lines of code to copy all of the initializer
values from .data LMA to the .data VMA.  It takes at least one
line of code per vairable to itialize them piecemeal in
application code.  Your "simpler" solution can take thousands
of times more code.

-- 
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