After lot 713, Microsoft fingerprint readers changed. The new version
comes with a new USB product ID and a challenge-response authentication
scheme where the device challenges the authenticity of the driver.
An independent third party produced documentation on the computations
needed to convert a challenge into the correct response, and I then used
this documentation to produce a clean-room reimplementation of the
authentication scheme.
I want to offer the ability for an application to view a binarized
version of a scanned print. This lead onto a few changes:
1. Store minutiae and binarized data inside fp_img
2. Move resize code to the capture path, it previously happened much
later.
3. Add fp_img_binarize() to return a new image in binarized form.
4. Add a BINARIZED_FORM flag to prevent an image being binarized again.
In future, it would be nice to be able to binarize without detecting
minutiae, but this involves some work on the NBIS interaction.
My UareU4000 device isn't working properly -- only seeing an all-white
image and no finger-on detection, however I think this code should work
for working devices.
When we include the await_finger_off procedure (i.e. set mode 12), the
current power-up code is unreliable - no 56aa interrupt arrives sometimes.
Comparing the F0 data and hwstat at this point between a working and a
non-working run yields no differences.
Work around this issue by retrying power-on 3 times.
While testing the new code on my MS keyboard, I found some strange
conditions where occasionally, the device will stop providing images
headers until it is replugged.
Detect and work around this when it happens.
This should improve driver stability somewhat. Powerup problems seem to
happen when we receive 3 unrelated interrupts while waiting for the
power-on interrupt, so let's assume that the device can only buffer 3
interrupts, and when the buffer is full, it discards new ones.
When we detect a possible buffer overflow, ask the caller to retry the
operation.
Also, saw the interrupt of death a few times, so add in a warning when
this happens. Haven't seen it since handling interrupt overflows though.
Drivers now have an ID number. These will be assigned by me and documented
on the wiki. 0 cannot be used.
Drivers now define a devtype for each device they initialise. This is to
cope with the situation where a driver can support varying devices where
their print data is incompatible (i.e. image scaling is totally changed).
This doesn't apply to any existing supported devices.
Print data no longer includes driver name, and includes driver ID instead.
Paths to saved print data now include driver ID and devtype, and no longer
include driver name.
APIs exposed for converting a print_data into a blob which can then
be loaded back again later. Useful for systems who don't want to use
my simple storage system (which is only aimed at a single user).
File format is now defined and will be documented on the wiki. The header
is larger as we can no longer rely on directory paths in all scenarios.
Print data compat check now checks devtype and driver ID.
