IBM BSC CRC?

[Mattis Lind]

Den mån 27 jan. 2020 kl 02:07 skrev Chuck Guzis via cctalk <
cctalk at classiccmp.org>:

> On 1/26/20 3:12 PM, Bob Smith via cctalk wrote:
> > I ma rusty on this, been almost 50 years since I worked on the DP8EP
> > aka the KG83. then the KG11, and the Autodin 2 CRC32 designs in
> > hardware.
> > I don't recall whether bisync, aka bsc used LRC8, 12, 16, or crc16 as
> > the error detection algorithm.
> > I don't think it used VRC. I did find a refresher that might help, but
> > I don't think the polynomial you have for crc 16 has enough terms.
> > BUT I could be misremembering.
>
> If you've got the message and the checksum, however computed, there are
> free tools to grind through the usual suspects.  I've used it on alien
> disk formats very successfully.
>
>
Yes, there are the crc reveng for example. But I cannot get it to generate
the CRC digits that matches. Neither does it give me anything when I ask it
to search for algorithm used.
Of course it is probably just me that don't understand it well enough.

It is slightly worrying though that I cannot recreate known examples that I
find online using crc reveng:

 https://stackoverflow.com/questions/23638939/crc-16-ibm-reverse-lookup-in-c

The first answer by Mark Adler involves a pretty simple CRC algorithm that
given the data buffer and initiial crc value in the Maxim example generates
the mentioned output. But I cannot gat the same output using crc reveng. So
I just have to do something wrong when using it. But cannot figure out what.

/Mattis


> --Chuck
>
>