This is only a preliminary version. There is certainly some room for
improvement, but the basic functionality is already in place. That
should be sufficient for daily use, and possibles issues can always be
fixed when discovered.
The Nemo Wide 2 uses the same communication protocol as the Icon HD,
except for two differences:
The Nemo Wide 2 requires a different baudrate and parity setting.
Unfortunately it doesn't seem possible to autodetect the correct
protocol variant at runtime. Attempting to proceed with incorrect
settings will render the device unresponsive and requires a battery
reset to recover.Therefore the model code needs to be provided as an
extra parameter, when opening the connection.
The Nemo Wide 2 also appears to have trouble downloading the entire
memory with a single request. Therefore the single large request is
split into many smaller ones. The offical Mares application uses 256
byte packets, and so do we. The Icon HD keeps using the large packets
because they are significant faster.
The extra model parameter breaks backwards compatibility!
The version function requires device specific knowledge to use it (at
least the required buffer size), it is already called internally when
necessary, and only a few backends support it. Thus there is no good
reason to keep it in the high-level public api.
I forgot to update the device and parser initialization functions to
store the context pointer into the objects. As a result, the internal
context pointers were always NULL.
The public api is changed to require a context object for all
operations. Because other library objects store the context pointer
internally, only the constructor functions need an explicit context
object as a parameter.
The devinfo and clock event data is now cached internally at the device layer.
This allows the new dc_parser_new() convenience function to retrieve the event
data directly from the device handle, and applications don't have to deal with
the events anymore to create a parser.
With the introduction of the device descriptors, the new dc_device_open()
convenience function can take care of the mapping from a particular model to
the corresponding backend internally, without needing any device specific
knowledge in the application. An application can simply query the list of
supported devices, and the library will automatically do the right thing.
Adding the "dc_" namespace prefix (which is of course an abbreviation
for libdivecomputer) should avoid conflicts with other libraries. For
the time being, only the high-level device and parser layers are
changed.
To be able to cancel an operation, an application should register a
callback function that returns a non-zero value whenever the active
operaton should be cancelled. A backend can invoke this callback function
to query the application for a pending cancellation request.
A helper function is added to simplify implementing the devic_dump()
function on top of the device_read() function, and enable progress
events automatically.
Using a resizable memory buffer allows to allocate the right amount of
memory inside the backend, avoiding having to know the required buffer
size in advance.
When necessary, an output parameter is added to provide the size
information. Status codes are strictly reserved for providing status
information only.
For this new api, each device will be implemented as a separate backend
for a common interface. This will make it easier to support multiple
devices in a single application.
