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tojape
Joined: 14 Jan 2007
Posts: 20
Location: Hungary
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| Built-in assembler missing pseudo operator high & low |
 Posted: Mon May 14, 2007 3:27 am |
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Hi, guys,
The following asm code results to an error compiling my project:
...
#asm
...
MOVLW flash_wr_block //get the number of writable bytes constant
MOVWF flash_wr_counter // store it in a data memory location
MOVLW high datbuf // page address of the start of data buffer (HI byte)
MOVWF FSR0H
MOVLW low datbuf // address of start of the buffer within the page (LO byte)
MOVWF FSR0L
...
#endasm
...
The CCS C compiler seems not to understand high & low operators.
The code compiled with MPASM works fine.
CCS C write_flash doesn't work correctly with PIC18F45J10, that's why I have to implement it in asembly.
How can I refer to the higher and lower parts of a data memory location using the built-in assembler? Can anyone help?
bye
tojape
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The computer helps solving the problems which would have never arised without computers |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Mon May 14, 2007 3:50 am |
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| Code: | movff datbuf, FSR0L // Low byte of pointer
movff &datbuf+1, FSR0H // High byte of pointer |
This works in v3.249. I haven't tested in v4.xxx but because of a changed pointer arithmetic it might be you have to cast the pointer to a char pointer. |
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tojape
Joined: 14 Jan 2007
Posts: 20
Location: Hungary
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| Posted: Mon May 14, 2007 4:55 am |
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| ckielstra wrote: | | Code: | movff datbuf, FSR0L // Low byte of pointer
movff &datbuf+1, FSR0H // High byte of pointer |
This works in v3.249. I haven't tested in v4.xxx but because of a changed pointer arithmetic it might be you have to cast the pointer to a char pointer. |
Thanks, but the compiler reports an error that it needs an identifier instead of "&datbuf+1" .
I use v4.22.
I am afraid, you misunderstood me, since datbuf is a name of a variable (array of bytes) and "movff datbuf,FSR0L" would copy the content of the first byte of datbuf to the register FSR0L while I want to load the address of datbuf to FSR0L and H.
However, thank you for taking care of my problem.
Hi,
tojape
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The computer helps solving the problems which would have never arised without computers |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Mon May 14, 2007 6:38 am |
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You didn't give the definition for datbuf, it must be a pointer.
The syntax is kind of confusing and undocumented, see also http://www.ccsinfo.com/forum/viewtopic.php?t=27114
This should work (tested in v4.032): | Code: | int8 DatBuf[25];
int8* p_data;
p_data = DatBuf;
#ASM
movff p_data, FSR0L // copy low byte of pointer
movff &p_data+1, FSR0H // copy high byte of pointer
#ENDASM |
I've tried several pointer cast variations but could only get it to work when using a _real_ pointer variable. |
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tojape
Joined: 14 Jan 2007
Posts: 20
Location: Hungary
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| Posted: Mon May 14, 2007 8:13 am |
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Dear ckielstra,
thanks a lot, the solution you suggested works fine.
Heve a nice day,
tojape
_________________
The computer helps solving the problems which would have never arised without computers |
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Ttelmah
Guest
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| Posted: Mon May 14, 2007 9:12 am |
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This was discussed some time ago, in the early days of the V4 compilers. Completely 'non intuitively', you can use a 'cast', but only by casting the _value_, not the pointer!.
| Code: |
int16 fred;
#ASM
movff fred, FSR0L // copy low byte of value
movff &(int8)fred+1, FSR0H // copy high byte of 16bit value!...
#ENDASM
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Totally silly syntax, but it appears that the internal 'address reference' function inside the assembler, only works with 8bit values. However it happily moves to the next byte of a 16bit value, if you tell it that the value is 8bit!...
This generates:
| Code: |
.................... #ASM
.................... movff fred, FSR0L // copy low byte of pointer
001E: MOVFF 28,FE9
.................... movff &(int8)fred+1, FSR0H // copy high byte of pointer
0022: MOVFF 29,FEA
.................... #ENDASM
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Correctly accessing the second byte.
The syntax of the internal assembler, is really silly at times.
Best Wishes |
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