[Libre-soc-bugs] [Bug 763] Work on I/O Core Pad JTAG Tests

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Sun Jan 30 17:48:56 GMT 2022


--- Comment #2 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---

io_bd - and in fact io_sr itself directly - is set to directly be
sent out via TDOs, one bit at a time (line 673)

io_sr is only shifted "in" from tdi in "shift" mode (line 620)

io_sr only takes data *from* pads and core in *capture* mode (line 592)

so you cannot just set a few signals and "hope for the best", you have
to actually make sure that the correct "Modes" (shift, update, capture)
are set.

the JTAG example in soc that i referred you to does this correctly.
it took me something mad like 2 days to understand it.

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