[Libre-soc-bugs] [Bug 1004] FPGA bring up for platform definitions

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1004

--- Comment #13 from Cesar Strauss <cestrauss at gmail.com> ---
I got Blinky to work on the Nexys Video!

It seems the leds didn't light up before because the 2,5V I/O buffers were only
recently implemented in nextpnr-xilinx, and our version was too old. Updating
it to current git master worked.

However this brings a massive regression when building ls2 for Arty... Routing
no longer converges on that design, it goes on forever.

Some options are:

1) Don't do anything, and forget about the leds on the Nexys Video (also,
Ethernet and HDMI).
2) Update nextpnr-xilinx to the commit that fixed the leds
3) Update nextpnr-xilinx to the last commit that still worked for ls2
4) Backport just the led fix, to the commit we currently use.

As for #3, I did find a fork of nextpnr-xilinx called openXC7
(https://github.com/openXC7/nextpnr-xilinx), which seems actively developed,
and whose latest release does work with both leds and ls2. In fact, for ls2 on
the Arty, it increases the maximum clock speed from 19 MHz to 25 MHz...

Also, someone would need to run the bitsream on a real Arty, to see if the
update really works.

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