[sdcc-devel] [ sdcc-Bugs-1350366 ] Option "--xram-loc" ignored

[SourceForge.net <no...@so...>]

Bugs item #1350366, was opened at 2005-11-07 15:59
Message generated for change (Comment added) made by maartenbrock
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=1350366&group_id=599

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: msc51(8051) target
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: grasbon (grasbon)
Assigned to: Nobody/Anonymous (nobody)
Summary: Option "--xram-loc" ignored

Initial Comment:

Version:
SDCC :
mcs51/gbz80/z80/avr/ds390/pic16/pic14/TININative/xa51/ds400/hc08
2.5.4 #1148 (Nov  6 2005) (MINGW32)

OS: Win

The compiler ignores the option "--xram-loc", when
xdata-variables are initialized outside the code like this:

"Main.c":

xdata unsigned char v = 'x';	// Will be placed at 0x0000!

void main(void)
{    
	v = 'u';			// Ok, Places at 0x0100!
}


Compiler-call: "sdcc --xram-loc  0x0100  Main.c"

The option for the compiler let start the xdata-area
at 0x0100. The value 'x' of the variable 'v' will be placed
at wrong destination (0x0000). The second assignment,
inside main() places the value at the correct address,
at 0x0100. So, maybe there's a problem within the startup-
code.


Nice Greetings
Reimar Grasbon.

Questions? Here I am: "ma...@gr..."



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

>Comment By: Maarten Brock (maartenbrock)
Date: 2005-11-14 13:38

Message:
Logged In: YES 
user_id=888171

Reimar,

You don't have to download all sources to view crtxinit.asm. 
Click CVS on the SourceForge site and browse to 
sdcc/device/lib/mcs51/crtxinit.asm

As you can see movx @r0,a is preceeded by
mov	__XPAGE,#(s_XISEG >> 8)
and __XPAGE is incremented outside the inner loop.

"--xram-loc 0x100" sets s_XISEG to 0x100. __XPAGE in asm 
equals _XPAGE in C and defaults to P2 if not explicitly 
defined. This should be sufficient on an 8031.

Maarten

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

Comment By: Nobody/Anonymous (nobody)
Date: 2005-11-14 10:04

Message:
Logged In: NO 

"movx @Rn instructions are used ..."

Exactly that's the problem. Initialization of upper external
memory (above 0x100)  with "movx @Rn" instructions isn't
possible.
Obviously the problem is inside "crtxinit.asm" but I can not
prove it because I didn't download the sources so far. So,
have a look at the assembly from "main.ihx" starting at
address 0x0022:
[...]
0022     93     movc  A, @A+DPTR  ; Load  'x'
0023     A3     movx  @R0, A          ; Place 'x' in @R0 (= 0)
[...]

Hence, the 'x' will be placed at xdata-address 0 (= pdata
address 0) by what the "--xram-loc"-option will be ignored. 

Later in the code we will find the the 'u'-assignment:
[...]
0064    90 01 00    movc  DPTR, #0100   ; address: 0x100
0067    74 75         mov  A, #75              ; Load 'u'
0069    F0             movx   @DPTR, A     ; Place 'u' in 0x100
[...]
The value 'u' will be written to 0x0100. That's correct.
Did I overlook something in the documentation?

Regards,
Reimar


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

Comment By: Maarten Brock (maartenbrock)
Date: 2005-11-13 14:57

Message:
Logged In: YES 
user_id=888171

movx @Rn instructions are used during xdata initialization in 
crtxinit.asm.

If you use a standard 8031 I see no reason why this would 
fail. I cannot reproduce the bug.

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

Comment By: grasbon (grasbon)
Date: 2005-11-13 13:38

Message:
Logged In: YES 
user_id=1374486

Hi Maarten,

it's no special derivate. I use a standard 8031 without
internal xram. Also I do not use pdata (movx @Rn). So,
there's no sfr or something else to initialize before using
xdata.

Greetings,
Reimar


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

Comment By: Maarten Brock (maartenbrock)
Date: 2005-11-12 16:40

Message:
Logged In: YES 
user_id=888171

Reimar,

Which derivative are you using? One with internal xram? If 
so, chances are that you must tell SDCC which sfr is used 
for page addressing in xram. You must define sfr _XPAGE for 
that. Another possibility is that you must enable the internal 
xram before you can use it. That should happen in 
_sdcc_external_startup(). The last option is that you cannot 
use movx @Rn instructions to access outside the first 256 
bytes of xram on the derivative at all. This would require a 
changed version of crtxinit.asm, maybe using dual data 
pointers.

Maarten

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

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=1350366&group_id=599