[Elecraft] KDSP2 development: How 'open source' is the code?

[Andrew Moore]

I recently acquired a KDSP2 from a fellow list member, and would like to do
some KDSP2 development - ideas include

- implementing a continuously-variable bandwidth DSP filter (like on K3) by
interfacing to an external rotary encoder
- implementing APF
- simplifying the user interface (fewer pushbuttons/menus)
- using external rotary encoder to vary noise reduction paramters
- ditch RTTY/SSB support, preserve RTC support

I don't want to get into a debate about which features you'd like to see
(everyone's different) - this is probably just a one-off project for now,
for myself.

What I'm wondering is given the appropriate development tools, how much of
the KDSP2 code can be rewritten?  Do we have access to only the the shapes
of the filters, for example, or is it possible to take over the KDSP2 and do
external I/O, write functions, etc. as if it's an embedded system? So as not
to reinvent the wheel, do we have access to code that's already been written
for AuxBus communication, startup/init, routines to read pushbuttons, etc.?

If I do custom coding like this, how does it "hook" into the K2 for button
presses and display stuff -- is this where the AuxBus comes in? Is there
counterpart code inside the K2 that needs to be written, or is there some
sort of API that I'd go through for button reads / display updates / etc?

Help from anyone who has been this route would be appreciated --
recommendations for tools, description of K2/KDSP2 architecture, etc...  I
understand Lyle KK7P has loads of knowledge about this, and I've
communicated with him some, but I've trying to give him some elbow room
until he's got more availability in a few weeks.

Thanks,
--Andrew, NV1B
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