[Libre-soc-bugs] [Bug 855] add libre-soc to kestrel

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=855

--- Comment #12 from tpearson at raptorengineering.com ---
I'm holding off on posting the patches until I'm a little bit further along --
basically I'm still validating the overall approach to integration here to make
sure I'm not going down a dead end.

There are still a couple of issues, mostly centered around the timebase /
decrementer but also some general problems and functional differences from
Microwatt that I need to investigate.

As a bit of background, Zephyr (the RTOS underlying the full network-enabled
version of Kestrel) uses both the timebase and the decrementer, along with the
decrementer interrupt, for thread scheduling and delays / timeouts.  For some
reason I haven't been able to track down yet, Zephyr operates as if it is under
continual overload -- timeouts are running way too fast, it's literally
saturated a test network with continuous DHCP requests instead of waiting the
normal second or two for a response.

Potentially related to the abocve: I have noticed that LibreSoC is
significantly slower than Microwatt in at least the bootloader memory test
loop, and that would be explained by a decrementer interrupt firing more often
than under Microwatt.

Finally, I've noticed problems with the GPIO setup / set using the LiteX CSR
access routines.  I need to determine if this is a difference in how LibreSoC
is executing an instruction specific to the CSR bytewise access, or a general
problem in the new integration "glue logic".

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