#47 CRC output from linker

[Maarten Brock]

Hello,

I would like to see the option added to the linker to be
able to have it compute a CRC on the produced code
and insert that into the output code as well. This way a
program can sanity check itself before startup. This way
one could also decide (based on an educated guess) not
to download code to a target, because it wasn't
changed, which saves development time.

To implement this, I think the following are required:
1) Generate a symbol for the CRC
2) Select an area to compute the CRC over
3) Fill unused bytes in the area with a default value (FF)
4) Compute the CRC (8/16/32)
5) Store the CRC outside this area.

Keep up the good work, hope this helps improving SDCC
further and further.

Maarten

[Frieder Ferlemann]

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Hi Maarten,

just to make things complicated: I'm using the following
command line to fill the unused
bytes with 0x12 (0x12 is good for a 8051) and to insert
several additive checksums:

srec_cat myfile.ihx -Intel -fill 0x12 0x0000 0x006FFE
-Big_Endian_Checksum_Negative 0x006FFE 0x02 0x02 -fill 0x12
0x007000 0x007FFE -Big_Endian_Checksum_Negative 0x007FFE
0x02 0x02 -fill 0x12 0x008000 0x00EFFE
-Big_Endian_Checksum_Negative 0x00EFFE 0x02 0x02 -Output
myfile.hex -Intel

The link to srecord is in the manual (srecord supports CRC16
and CRC32 in little and big-endian)

[Maarten Brock]

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Hi Frieder,

I know there is something like srecord. But a quick glance
learned me it doesn't support omf files, that's why I popped
the question. Otherwise using srecord would be perfectly ok,
allthough integrating into sdcc is nicer. But maybe I should
just request this feature for srecord and not for sdcc.

Greets,
Maarten

[Maarten Brock]

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Follow up,

So I asked at SRecord and they implemented! Sometimes, life
is just great. I'll try to create a piece of library code that can
be integrated into SDCC and used in conjuction with SRecord.

Greetings,
Maarten

[Maarten Brock]

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SRecord supports omf files, but only the memory contents
and it throws away all debug info. Still no good solution then :-
(

But wait. With SRecord 1.22 you can generate C source files
with the data in a "const unsigned char crc[]" array. And
SDCC 2.5.2 can place const data in a specified segment
with an absolute address. So this is what I do now:
1) Compile and link all project files with SDCC.
2) Let srecord fill unused spaces in the hex-file.
3) Let srecord compute the length of the hex-file and store it
inside the hex-file.
4) Let srecord compute the crc over the hex-file and store it
inside the hex-file.
5) Let srecord extract the length and crc into a C source file.
6) Compile this with SDCC --constseg CRC.
7) Link the project again with the new file added and option -
Wl-bCRC=0x4000 to store the crc and length data at a
predetermined memory place.

The result is that the CRC is included in the omf file as well
and still fully debuggable.

This works for me and closes this request.