We received an interesting case of a dive computer whose battery died
during a dive. Apparantly the device recorded some samples, but failed
to terminate the dive properly. In the linked list, the next pointer of
this dive points to itself, which is obviously an invalid value.
I suspect the device initializes the next pointer to point to itself at
the start of a new dive, and updates it again with the correct value
once the dive has finished. But due to the battery failure, that last
step never happened.
Anyway, since we are traversing the linked list backwards, we don't need
the next pointer, and we can simply skip the incomplete dive. The error
is not returned immediately anymore, but delayed until the end of the
download.
The D9tx, D6i and D4i have twice the amount of memory compared to the
previous versions (64K versus 32K). To support both variants, a new
layout descriptor is introduced.
When using the ringbuffer pointers to traverse the linked list, a full
ringbuffer appears as an empty one. This is probably a very rare
condition, but a very annoying one if you run into it it. Using byte
counts and the number of dives in the header avoids the problem.
In a ringbuffer implementation with only two begin/end pointers, it's
impossible to distinguish between an empty and a full ringbuffer. The
correct interpretation mode needs to be specified by the user.
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.
