See merge request teichman/ebpfcat!14

this improves ethercat compatibility by actually setting the correct PDO size and other minor details.

See merge request teichman/ebpfcat!12

we still have to artificially tell that this is a float
value, although that's actually in the SDO.

we used to initialize the sync manager to what was
in the eeprom, which is big enough normally, but not always.

Now we read out the pdo assignment first, and set the sync
manager size accordingly.

See merge request teichman/ebpfcat!13

for most operations, pre-operational is good enough a state.
By thinko we went to safe operational, which is not needed.

See merge request teichman/ebpfcat!11

the Leybold TurboVac does not like to be put into operational unless
it is already getting PDO data. This actually seems like a good idea.

See merge request teichman/ebpfcat!10

f is already used for float, so use x, not great but the first
free letter.

This is the basics to starting to support Leybold turbo pumps, which have some peculiar quirks.

Also general improvements.

See merge request teichman/ebpfcat!9

all kinds of stuff updated:

- EEPROMs can now be written, especially the serial number
- tests should work again
- ebpf devices can now act cyclic like slow devices

See merge request teichman/ebpfcat!7

the anybus client does not like our index datagram with zero
length data. While we are already at it, we also do proper padding
according to the ethercat standard. Hopefully this way we are
compatible with many more devices.

we were already able to use huge values in assignments, now
we can also use them in operations.

somehow the anybus thing wants to return a EoE frame when
asked for a CoE frame. We can just ignore it, then it works
fine.

this can easier be done earlier

some terminals do not support reading 8 bytes of the eeprom at
a time, we have to limit to 4 bytes at a time

this involves restructuring quite a bit, probably with compatibility
problems.

as Python makes a difference here, follow its logic and call
floor division as such.

this is not actually ethercat specific

the format characters already include the information whether they
are signed or long, no need to add this information again.

this means we know what values were set in ebpf. It is a bit
magic how often this will get called.