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33 lines
1.0 KiB
Markdown
33 lines
1.0 KiB
Markdown
# Data card
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The data card deals with binary data, thus there must be a simple format.
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## Hamming ECC
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Each nibble (4-bit sequence) uses a Hamming (7, 4) code encoded in 1 byte, with the ability to detect 2 bit errors (but not correct them)
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Given N bytes to encode, the final encoded output will take 2N bytes.
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This also means when decoding, the length must be even.
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A byte is split into 2 nibbles, with the one comprised of the lowest bits first.
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Each nibble is ECC encoded separately.
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In a nibble there are 4 bits d0, d1, d2 and d3, from lowest to highest.
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In the output, there are p0, p1, p2, p3 bits, where p1 and above represent hamming code parity data, and p0 is a parity check on the whole block.
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### Nibble arrangement
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```
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| d0 | d1 | d2 | d3 |
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```
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### Hamming code arrangement
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```
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| p0 | p1 | p2 | d0 |
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| p3 | d1 | d2 | d3 |
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```
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The bits are arranged such that p0 is the lowest bit and d3 is the highest.
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This creates a fairly generic hamming code structure. Do note that p0 is the bit for checking the whole block's parity.
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