#1038 Insufficient bank selection during global initialization

closed-fixed
nobody
5
2013-05-25
2005-12-12
Simon McAuliffe
No

When initializing globals, it looks like the register
bank is selected only for the first variable, however
they may not all be in the same bank when they are
allocated (particularly as you start to use more data).

sdcc version:
2.5.4 #1183 (Dec 10 2005)

command used:
sdcc/bin/sdcc -c -mpic14 -p16f627 bug5.c && gplink -m
-c -o bug.hex bug5.o

Sample code (bug5.c):
------------------------
#define __16f627
#include <pic/pic16f627.h>

char x1 = 1;
char stuff1[49];
char x9 = 9;
char stuff1a[29];
char x2 = 2;
char stuff2[62];
char x3 = 3;
char stuff3[46];
char x4 = 4;
char stuff4[6];
char x5 = 5;

void main()
{
}
------------------------

Looking at the map file produced by the linker, the
data is spanning a few banks:

_x1 0x0000ee data
extern bug5.asm
_stuff1 0x0000a0 data
extern bug5.asm
_x9 0x00014e data
extern bug5.asm
_stuff1a 0x0000d1 data
extern bug5.asm
_x2 0x000064 data
extern bug5.asm
_stuff2 0x000020 data
extern bug5.asm
_x3 0x000065 data
extern bug5.asm
_stuff3 0x000120 data
extern bug5.asm
_x4 0x000066 data
extern bug5.asm
_stuff4 0x00005e data
extern bug5.asm
_x5 0x000067 data
extern bug5.asm

The initialisation code only sets the bank at the
start, however it can't do that because some of them
will be allocated to different banks at link time.
MOVLW 0x01
BANKSEL _x1
MOVWF _x1
MOVLW 0x09
MOVWF _x9
MOVLW 0x02
MOVWF _x2
MOVLW 0x03
MOVWF _x3
MOVLW 0x04
MOVWF _x4
MOVLW 0x05
MOVWF _x5

This may be a more general problem than just global
initialization, but I haven't checked.

Discussion

  • Logged In: YES
    user_id=1304410

    Oh, also, here is the include file referred to by the code.

     
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  • Slade Rich
    Slade Rich
    2005-12-12

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    user_id=849691

    > This may be a more general problem than just global
    > initialization, but I haven't checked.
    Correct it is.

    The SDCC PIC 14 port does not support the ability to
    allocate data into named data sections. Where the linker
    places the data is not known to the compiler, it only
    assumes that it will be in the same bank for that C file.
    In this example the data is too big to fit into a single
    bank and the linker then decides to place it across
    multiple banks, of course the compiler has not provided any
    BANKSEL statements so the code will not run correctly.
    Although I am puzzled as I had believed that all the data
    from a separate 'C' file went into an individual data bank,
    which sould mean the linker ought to give an error and not
    separate the data.

    It is possible however to use multiple ram banks with SDCC
    PIC 14 port. It require carefully placing the data into
    different C files and declaring them static. When a global
    (non static) function is called the complier will generate
    a BANKSEL when it first accesses it's local variable (as in
    this example where function main as generated a BANKSEL).

    Supporting named data section within the PIC 14 port will
    require some effort to achieve - volunteers needed. (The
    linker should then keep all named data sections in one
    bank, generating an error if it does not fit.) This will
    allow code in a single C file to refer to data that are in
    different RAM banks and generate correct the BANKSEL code.

     
  • Logged In: YES
    user_id=1304410

    Oh, sorry, I knew that from previous occasions (and the
    documentation), but had a brain outage and forgot. I had to
    remove my statics and carefully allocated variables because
    I was having some other new problems with sdcc and statics.
    I'll see if I can find that problem instead. Thanks.

     
  • Raphael Neider
    Raphael Neider
    2006-10-16

    • milestone: --> fixed
    • status: open --> closed-fixed
     
  • Raphael Neider
    Raphael Neider
    2006-10-16

    Logged In: YES
    user_id=1115835

    Fixed in r4411.