When trying to send a command, the first attempt always fails. We
receive the echo, but no data packet. A second attempt usually works,
but we always get back the same data packet. That's cleary wrong.
Now, when comparing the data packets with those of the Tusa application,
I noticed something very interesting. When we request the first packet
(page 0x0000), we get:
W: 520000
R: 520000
R: 00880124056202000250002890470824...19202720002000200020002000204145
The Tusa application also request this page, but the response is
completely different:
W: 520000
R: 520000
R: 22182224222322092203220522112210...0000000000f021fc0000000000000045
The response we get is identical to the response that the Tusa
application gets for page 0x0052:
W: 520052
R: 520052
R: 00880124056202000250002890470824...19202720002000200020002000204145
The only difference here is the echo of the command. But the echo should
be ignored, because it's generated by the pc interface, and not send by
the dive computer. This is easily verified by the fact that we always
receive an echo, even without a dive computer connected (e.g. only the
pc interface).
Notice how the command type (first byte) and page number (last byte) are
identical (0x52) for this request! I suspect that somehow the command
type ends up being interpreted as the page number. That would explain
why we're always getting the same response: as far as the device is
concerned we're always requesting page 0x52. This is probably also
related to the fact that the device doesn't respond after the first
request. It's not impossible that if the first command wasn't received
correctly and we resend the command, the device receives something that
contains parts of both attempts.
By sending the command and reading the echo byte by byte instead of all
at once, the above problem disappears.
Without the delay, the communication immediately fails. We receive the
command echo, but not the actual data packet. I suspect the device is
still be busy with the initialization and needs a bit more time before
it's ready to accept a request.
The fingerprint is used unconditionally, regardless of whether it's
explicitly set by the application or not. Therefore it needs to be
initialized properly.
Currently, each backend has it's own function to verify whether the
object vtable pointer is the expected one. All these functions can be
removed in favor of a single isintance function in the base class,
which takes the expected vtable pointer as a parameter.
Functions which are called through the vtable, don't need to verify the
vtable pointer, and those checks are removed.
The term "backend" can be confusing because it can refer to both the
virtual function table and the device/parser backends. The use of the
term "vtable" avoids this.
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.
These macros are used internally and don't need to be exposed. In some
cases, the actual values are not even constant, but dependant on the
model and/or the firmware version.
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.
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.
The public header files are moved to a new subdirectory, to separate
the definition of the public interface from the actual implementation.
Using an identical directory layout as the final installation has the
advantage that the example code can be build outside the project tree
without any modifications to the #include statements.
The internal memory appears to contain two separate areas. One for the
normal dives and one for the freedives. Currently, only the freedive
section is processed.
