.. there is an instance of it that looks like a "true positive", but it only
affects sdhc transfers that are not a multiple of 4 bytes, which I don't think
happens. (sd card blocks are always 512 bytes) I can fix this in our
asf4 repo but that would mean this should be deferred until after #3384 is
merged, since that also touches asf4 very invasively by adding a whole new
chip family.
If any diagnostics occur, we will want to either add `/* FALLTHROUGH */`
or `break;` as appropriate. I only tested a few builds (trinket m0
and metro m4 express)
While checking whether we can enable -Wimplicit-fallthrough, I encountered
a diagnostic in mp_binary_set_val_array_from_int which led to discovering
the following bug:
```
>>> struct.pack("xb", 3)
b'\x03\x03'
```
That is, the next value (3) was used as the value of a padding byte, while
standard Python always fills "x" bytes with zeros. I initially thought
this had to do with the unintentional fallthrough, but it doesn't.
Instead, this code would relate to an array.array with a typecode of
padding ('x'), which is ALSO not desktop Python compliant:
```
>>> array.array('x', (1, 2, 3))
array('x', [1, 0, 0])
```
Possibly this is dead code that used to be shared between struct-setting
and array-setting, but it no longer is.
I also discovered that the argument list length for struct.pack
and struct.pack_into were not checked, and that the length of binary data
passed to array.array was not checked to be a multiple of the element
size.
I have corrected all of these to conform more closely to standard Python
and revised some tests where necessary. Some tests for micropython-specific
behavior that does not conform to standard Python and is not present
in CircuitPython was deleted outright.
Limor confirmed that the all shipping revisions starting with Rev D had QSPI flash chips installed.
Note that when neither EXTERNAL_FLASH_QSPI_SINGLE nor EXTERNAL_FLASH_QSPI_DUAL is specified quad mode is assumed, so this is addressed by removing the setting altogether.
Two problems: The lead byte for 3-byte sequences was wrong, and one
mid-byte was not even filled in due to a missing "++"!
Apparently this was broken ever since the first "Compress as unicode,
not bytes" commit, but I believed I'd "tested" it by running on the
Pinyin translation.
This rendered at least the Korean and Japanese translations completely
illegible, affecting 5.0 and all later releases.
