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enjoy-digital / litesdcard

Small footprint and configurable SDCard core
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core: fix long response register off-by-8bit shift #19

Closed gsomlo closed 4 years ago

gsomlo commented 4 years ago

Ensure each bit of the long (16 byte) response register is shifted into its appropriate position (off by 8 bits before this patch).

E.g., on my 32GB sdcard, with spi-sdcard the CSD register comes back (correctly) as:

400e0032_5b590000_edc87f80_0a4040c3

However, before this patch, with litesdcard, the CSD register of the very same SDcard is shown as:

3f400e00_325b5900_00edc87f_800a4040

After the patch, the CSD register is the same as in SPI mode, which means the (long) response register should now be returned correctly, hopefully in all cases, not just when returning the CSD register :)

@enjoy-digital: I tried just shifting things into place in software (in the linux driver), and that resulted in the same behavior as this patch, so anything further that's broken is probably broken in software, and this patch should be applied anyway as-is, since it's most likely doing the right thing :)

EDIT: well, the least-significant byte is 0a404000 (instead of 0a4040c3 -- i.e., the CRC isn't computed, but that's already a known FIXME item in litesdcard, so I'm not worried about it for now)

gsomlo commented 4 years ago

updated with a better comment and commit log explanation: the long-response register is still 136bits internally, it's just that right now, the most convenient way to expose the right 128-bit portion is to add an extra 8-bit shift to the FSM. There's probably a more elegant way to assign the proper 128 bits to the software-visible response register, but this seems to work for now...

enjoy-digital commented 4 years ago

Thanks @gsomlo, this makes sense and we can merge it with the comment.