[Libre-soc-bugs] [Bug 746] I2C needs an Open Drain IO Pad

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=746

--- Comment #5 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Cesar Strauss from comment #1)
> It seems that Open Drain can be implemented by a constant zero output, and
> switching the tri-state/direction/oe control signal (1=tri-state,
> 0=push-pull to ground).

# Open Drain Mode, made with a standard FlexLib IOlib cell
with m.If(sda.oe):
  with m.If(sda.o == 1):
    comb += pad.oe.eq(1)
    comb += pad.o.eq(1)
  with m.Else():
    comb += pad.oe.eq(0)
    comb += pad.o.eq(0)
with m.Else():
    comb += pad.oe.eq(0)
    comb += sda.i.eq(pad.i)

this will do the job, Staf: no need to change IOLib

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