[sdcc-devel] [ sdcc-Bugs-1378648 ] Insufficient bank selection during global initialization

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Bugs item #1378648, was opened at 2005-12-12 23:59
Message generated for change (Comment added) made by smcauliffe
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Category: pic14 target
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Simon (smcauliffe)
Assigned to: Nobody/Anonymous (nobody)
Summary: Insufficient bank selection during global initialization

Initial Comment:
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.


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>Comment By: Simon (smcauliffe)
Date: 2005-12-18 08:30

Message:
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.

----------------------------------------------------------------------

Comment By: Slade Rich (slade_rich)
Date: 2005-12-13 12:50

Message:
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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.


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Comment By: Simon (smcauliffe)
Date: 2005-12-13 00:06

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

----------------------------------------------------------------------

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