R: Re: Question about md output

U-Boot ffileppo at libero.it 3 participants 3 messages May 12, 2012 – May 30, 2012

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ffileppo at libero.it

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2012-05-12 16:12 UTC #0 lore raw

Quoted 4 lines

Ditto.

Quoted 8 lines

Have a look at itest; if you still make no progress then please describe what you actually want to do, so we can show you how to do it efficiently - without need to modify code.
Best regards,
Wolfgang Denk

Dear Wolfgang,

thanks for your support.
Let me understand if I get this right.

for example, I have a block of 8 words, starting at 0x0:

00000000: a b c d
00000010: e f g h

where a is the crc32 computed on b,c,d,e,f,g,h

Within uboot, I would like to compute the crc32 of b,c,d,e,f,g,h and compare it with a.

-- Compute CRC and store at address 20
crc 1 7 20
-- Compare CRCs
if itest *0 == *20; then echo CRC ok; else echo CRC bad; fi

Is that correct?

Thanks and best regards,

Wolfgang Denk

2012-05-29 20:37 UTC #1 lore raw

Dear "ffileppo at libero.it",

Quoted 11 lines · In message <809266.7065381336839126651.JavaMail.defaultUser@defaultHost> you…

for example, I have a block of 8 words, starting at 0x0:
00000000: a b c d
00000010: e f g h
where a is the crc32 computed on b,c,d,e,f,g,h
Within uboot, I would like to compute the crc32 of b,c,d,e,f,g,h and compare it with a.

Quoted 7 lines

-- Compute CRC and store at address 20
crc 1 7 20
-- Compare CRCs
if itest *0 == *20; then echo CRC ok; else echo CRC bad; fi
Is that correct?

Basicly yes, except that the crc32 command does not operate on 32 bit "words", but on an area of memory (i. e. a number of octets). Depending on your expectations on endianess etc. this may or may bot be the same. The "32" in the crc32 command name is just an indication for the size of the computed checksum.

Best regards,

Wolfgang Denk

Signature · 5 lines

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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                                                   -- Dennis Ritchie

Anthony Foiani

2012-05-30 05:40 UTC #2 lore raw

Quoted 5 lines · Wolfgang Denk

Basicly yes, except that the crc32 command does not operate on 32 bit "words", but on an area of memory (i. e. a number of octets). Depending on your expectations on endianess etc. this may or may bot be the same. The "32" in the crc32 command name is just an indication for the size of the computed checksum.

I don't know if the usage is the same in German, but in (USA) English Computer Science, "crc32" most often refers specifically to the algorithm implemented for Ethernet checksumming (which, with slight variants is the same used in zlib, u-boot, and many others.)

CRC32 is not the only 32-bit CRC, but it is one of the most popular, and was chosen for certain desirable properties.

(Wolfgang, I am sure you know all this, I am mostly clarifying for the original poster.)

Lots of good info here:

http://en.wikipedia.org/wiki/Crc32#Commonly_used_and_standardized_CRCs

Happy hacking!

Best regards,
Anthony Foiani