[chbot] AVR linker issue (?)

[Mark Atherton]

Yup, or the newer __flash

I need to get a tiny trivial fragment compiled and linked before attempting anything clever

-mark




> On 18 July 2021 at 11:46 "hamster at snap.net.nz" <hamster at snap.net.nz> wrote:
> 
>     Is the PROGMEM attribute still a thing to put constant data into program flash? 
> 
>     Mike
> 
> 
> 
> 
>     -------- Original message --------
>     From: Mark Atherton <markaren1 at xtra.co.nz>
>     Date: Sun, 18 Jul 2021, 11:32 AM
>     To: Christchurch Robotics <chchrobotics at lists.ourshack.com>, Andrew Dachs <dachsa492 at gmail.com>
>     Subject: Re: [chbot] AVR linker issue (?)
> 
>         > > Thanks Andy, Richard.
> > 
> >         Was hoping that I had just something daft.
> > 
> >         Started looking at disassembly of the OBJ modules.
> > 
> >         I don't plan to waste too much time on the problem. Failing all else, the parent module can subsume the table and the problem goes away; this will detract from modularity. Ho-hum.
> > 
> >         Hope to see you all tomorrow eve at Robotics :)
> > 
> >         -mark
> > 
> > 
> > 
> > 
> >         > On 18 July 2021 at 10:14 Andrew Dachs <dachsa492 at gmail.com> wrote:
> >         >
> >         >
> >         > A dependency issue maybe. Did it definitely recompile font.c?
> >         > Andy
> >         >
> >         > Sent from my iPhone
> >         >
> >         > > On 18/07/2021, at 9:02 AM, Mark Atherton <markaren1 at xtra.co.nz> wrote:
> >         > >
> >         > > I need another pair of eyes to look at this issue as am obviously doing something daft. This is part of a larger problem; minimal code to show issue is below.
> >         > >
> >         > > All I am trying to do is move a table into a separate module, but the linker is giving me a hard time.
> >         > >
> >         > > Remove 'const' in the external module and everything works fine.
> >         > >
> >         > > Thoughts please !
> >         > >
> >         > > -Mark
> >         > >
> >         > >
> >         > > -------------
> >         > >
> >         > > mkdir -p .build
> >         > > avr-g++ -c -g -Os -Wall -w -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L font.c -o .build/font.o
> >         > > avr-g++ -c -g -Os -Wall -w -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L main.c -o .build/main.o
> >         > > avr-gcc .build/font.o .build/main.o -o .build/hw.elf -Os -Wl,--gc-sections -mmcu=atmega328p -lm
> >         > >
> >         > > .build/main.o: In function `main':
> >         > > C:\Temp\linker_test/main.c:18: undefined reference to `ext_font'
> >         > > collect2.exe: error: ld returned 1 exit status
> >         > > make: *** [.build/hw.elf] Error 1
> >         > >
> >         > > ------------- font.c
> >         > >
> >         > > #include <avr\pgmspace.h>
> >         > >
> >         > > const unsigned char ext_font[] =        // links OK with const removed
> >         > > {
> >         > >  0x00, 0x00, 0x00, 0x00, 0x00
> >         > > };
> >         > >
> >         > > ------------- font.h
> >         > >
> >         > > #ifndef    _FONT_H_
> >         > > #define _FONT_H_
> >         > >
> >         > > extern const unsigned char ext_font[5]; // links OK with const removed
> >         > >
> >         > > #endif
> >         > >
> >         > > ------------- main.c
> >         > >
> >         > > #include <avr\io.h>
> >         > > #include <avr\pgmspace.h>
> >         > > #include <ctype.h>
> >         > > #include "font.h"
> >         > >
> >         > > const unsigned char local_font[] = // const has no effect on linker !!
> >         > > {
> >         > >  0x00, 0x00, 0x00, 0x00, 0x00
> >         > > };
> >         > >
> >         > > int main(void)
> >         > > {
> >         > >  volatile unsigned char val;
> >         > >  val = local_font[3];        // links OK
> >         > >  val = ext_font[3];        // link Fails
> >         > >
> >         > > }
> >         > >
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