[J-core] Numato board oscilloscope?

[Rob Landley]

On 09/10/2016 02:51 AM, D. Jeff Dionne wrote:
> What is the objective of this?   To monitor the SDcard activity?

In theory we could monitor an arbitrary bus in the design. If we
implemented it in VHDL, we can route those pins out to something that
can read them, just by tweaking the bitstream.

This wouldn't just helps us debug "this brand of sdcard is acting
weird", but could help people understand "and this is i2c works". We
could build tutorials on it for software people who've made it down to
the kernel but now want to drill down further into hardware-land.

> If so, having the option of integrating a small logic analyser
> core is both useful and something I've been meaning to to.
> 
> It doesn't even have to be very complex.  Because the SRAM can
> be directly mapped into the j-core address space, it can be even
> simpler than this http://hamsterworks.co.nz/mediawiki/index.php/CheapScope

Indeed.

> The C code shows just how small the UI can be.

Unfortunately I didn't understand what information the UI on that page
was trying to convey. :(

> SEI engineers use these, btw: https://www.saleae.com

Which is cool, but the downside of that is if you route an FPGA signal
out to a pin, you then have to hook up a probe to the right pin and have
a second machine set up to record it.

In theory, if your logic analyzer can be built-in logging to an sram
buffer, you tweak the vhdl to sample the right lines, install a fresh
bitstream, and then more or less run your test program under a debugger,
with the corresponding hardware signals accessible on the same machine
that's running the software to provoke them.

(I remember one time you explained how that the compiler really didn't
want to export signals into a "global" context', and that you had to do
some work to get some signals out where you needed them for debugging
purposes? I'm trying to learn enough VHDL that I have a context to plug
that random piece of information into, but am not there yet. In the case
in question I think you were trying to pull something out to drive an
LED when the line was active.)

Rob