Does CCS compiler always keep reset vector clear?

[Ron]

Hello,

Does the compiler always keep the four addresses 0000 - 0003 clear, so I can use my bootload code with any program I make? (PIC18f452)

I have a bootloader which has some code at the reset vector. Normally, the compiler seems to place a goto instruction to the main loop at addresses 0000 - 0003.

But is this always the only code at these four addresses 0000 - 0003? In that case I can safely use my bootload code with any program I make. For the 'goto main' instruction can be easily copied to another location and be run from there. (reset-vector re-location)

Any comments would be appreciated,
Regards,
Ron
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This message was ported from CCS's old forum
Original Post ID: 8652

[Ivar Johnsrud]

The bootloader is moving the two-four first instructions
to another location, so the bootloaders goto wont get
overwritten. If it relocates 2,3 or 4 instructions depends
on how the hex file looks like. The bootloader I have
written is searching for a goto instruction in the reset
vector, and relocates everything before and including the
goto instruction.

-Ivar

:=Hello,
:=
:=Does the compiler always keep the four addresses 0000 - 0003 clear, so I can use my bootload code with any program I make? (PIC18f452)
:=
:=I have a bootloader which has some code at the reset vector. Normally, the compiler seems to place a goto instruction to the main loop at addresses 0000 - 0003.
:=
:=But is this always the only code at these four addresses 0000 - 0003? In that case I can safely use my bootload code with any program I make. For the 'goto main' instruction can be easily copied to another location and be run from there. (reset-vector re-location)
:=
:=Any comments would be appreciated,
:=Regards,
:=Ron
___________________________
This message was ported from CCS's old forum
Original Post ID: 8662

[Ron]

:=The bootloader I have
:=written is searching for a goto instruction in the reset
:=vector, and relocates everything before and including the
:=goto instruction.

Yeah, alright, mine too. But what if the reset vector has other instructions than a goto in it? If this is the case, those instructions cannot be re-located, because other parts of the program expect these instructions around the reset vector. (e.g. address 0002, or 0006).

So my question still stands: Is there a possibility for the compiler to generate other code at the reset vector than a goto main instruction?

Any comments would be appreciated.

Best regards,
Ron
___________________________
This message was ported from CCS's old forum
Original Post ID: 8686

[Tomi]

The Interrupt Handler starts at 0x0004 word address. So you have max. 4 instructions to do something PLUS step over the IT handler(s). A correct "long jump" is 3 instructions (load upper address word into W reg, store W reg into PCLATH and the GOTO itself) for 16F87X...
So you could be sure about GOTO main.


:=So my question still stands: Is there a possibility for the compiler to generate other code at the reset vector than a goto main instruction?
:=
:=Any comments would be appreciated.
:=
:=Best regards,
:=Ron
:=
:=
:=
___________________________
This message was ported from CCS's old forum
Original Post ID: 8695

[Ron]

Thanks Tomi,

You are right there's not much space for other code. Although for the 18f452 things are a bit different:

A GOTO is only 2 instructions long. So in theory there is room for 2 GOTO's. (or 1 GOTO and 2 other instructions, if no interrupts are used. I don't know if the compiler would use interrupt vector location for other purposes, if no interrupts are used)

Therefore I'm not 100\% sure of the reset vector area to be clean of other instructions. That's why I asked.

Best regards,
Ron

:=The Interrupt Handler starts at 0x0004 word address. So you have max. 4 instructions to do something PLUS step over the IT handler(s). A correct "long jump" is 3 instructions (load upper address word into W reg, store W reg into PCLATH and the GOTO itself) for 16F87X...
:=So you could be sure about GOTO main.
:=
:=
:=:=So my question still stands: Is there a possibility for the compiler to generate other code at the reset vector than a goto main instruction?
:=:=
:=:=Any comments would be appreciated.
:=:=
:=:=Best regards,
:=:=Ron
:=:=
:=:=
:=:=
___________________________
This message was ported from CCS's old forum
Original Post ID: 8745

[Ron]

I learned from CSS that it is possible to change the reset vector:

Use:

#Build(reset=0x200) [for example]

Best regards,
Ron

:=Hello,
:=
:=Does the compiler always keep the four addresses 0000 - 0003 clear, so I can use my bootload code with any program I make? (PIC18f452)
:=
:=I have a bootloader which has some code at the reset vector. Normally, the compiler seems to place a goto instruction to the main loop at addresses 0000 - 0003.
:=
:=But is this always the only code at these four addresses 0000 - 0003? In that case I can safely use my bootload code with any program I make. For the 'goto main' instruction can be easily copied to another location and be run from there. (reset-vector re-location)
:=
:=Any comments would be appreciated,
:=Regards,
:=Ron
___________________________
This message was ported from CCS's old forum
Original Post ID: 8778