National Semiconductor 48-bit and 56-bit ECC polynomials

[Eric Smith]

Has anyone determined what 48-bit and 56-bit ECC polynomials are used by
the National Semiconductor hard disk controllers?  The DP8496/97 allows
choice of hard-wired 16-bit CRC, or 32-bit, 48-bit, or 56-bit ECC.  The
32-bit ECC is a common polynomial known as the Glover polynomial, and it's
the same one used by WD and others.  However, National was apparently
extremely proud of the 48-bit and 56-bit polynomials they chose, and the
data sheets say that they require a license agreement with National.

The more common DP8466 supports 32-bit 48-bit, but allows the user to
configure the polynomial. The data sheet states that National's 48-bit
polynomial is available under license.

WD wasn't as proud of their 56-bit polynomial; it's given in the WD42C22
data sheet. It doesn't seem to match National Semicondutor's 56-bit
polynomial.