Hi,
I am making tests and calculating inhex32 ascii and lst files to get
idea how much rom and ram I am using So mainly testing at the moment. I
think you are right about PIC16 and static memory allocation and I
should be using that kind of approach. But just want to test what
happens if using dynamic memory allocation. I am big SDCC newbie so need
to test and study a lot pretty long time here :)
Thanks for comments !
-Mika
> Mika,
>
> Using a heap in a small embedded device is usually
> regarded as unwise and not appreciating the limitations
> of small embedded devices. A microcontroller is no PC.
>
> SDCC supports some targets which can have 64k of ram or
> even more, but I've never heard of any PIC14 or PIC16
> that can. I admit I know very little about the PICs so I
> might be wrong.
>
> But are you sure you want to use the heap in such a
> small device? Wouldn't you better use static allocation
> and save the code and memory costs of malloc and
> friends?
>
> Greetings,
> Maarten
>
> > Hi,
> >
> > Thank you very much. This really helped a lot :)
> >
> > -Mika
> >
> > > Hi Mika,
> > >
> > >> Managed to compile a sample code below with sdcc, but the xdata
> > >> definition can not be found from header files (except from testfwk.h).
> > >
> > > The PIC architectures do not offer anything like external data memory;
> > > so either just
> > > #define xdata __data
> > > or replace it (as you did).
> > >
> > >> What would be the correct way to introduce the heap ?
> > >> data char heap[256];
> > >
> > > That looks pretty good, __data instead of data is safer, though.
> > >
> > >> // data char heap[512]; This gives linker error, do not know why
> > >
> > > The reason for the linker error is that the PIC organizes its memory in
> > > banks of 256 bytes each. You cannot declare structures/arrays larger
> > > than that unless you know what you are doing and modify the .lkr script
> > > (combine two adjacent banks (END address of first = START address of
> > > second - 1), i.e., turn
> > >
> > > DATABANK NAME=gpr1 START=0x100 END=0x1FF
> > > DATABANK NAME=gpr2 START=0x200 END=0x2FF
> > >
> > > into
> > >
> > > DATABANK NAME=gpr1 START=0x100 END=0x2FF
> > >
> > > Save the modified 18f4550.lkr in your project directory and add
> > > -Wl,-s,18f4550.lkr to sdcc's command line (or -s 18f4550.lkr to gplink's
> > > command line, depending on your build system/style) to use it.
> > >
> > > Make sure, though, that you *always* statically allocate the heap of at
> > > least 256 bytes if you do this, otherwise a random multi-byte entity (an
> > > int, a struct, ...) might be placed across the bank boundaries, which
> > > breaks compiler assumptions about BANKSEL placement and might cause
> > > accesses to the entity to fail (read/write in the wrong bank, good luck
> > > hunting such bugs!).
> > >
> > > Also, make sure to add
> > > #pragma stack 0x300 0x100
> > > to your main() file to move the stack from its standard location
> > > (0x200-0x2FF) to 0x300-0x3FF. You might also reduce the stack size
> > > (0x100 => 256 bytes, 0x80 => 128 bytes *might* suffice, you could try).
> > >
> > > Note that using a 512 byte heap and a 256 byte stack leaves 'just' 160
> > > byte of the 4550 available for other stuff.
> > >
> > > Hope that helped,
> > > Raphael
>
>
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