<whitequark[cis]>
<wklaebe> "hmm... I wonder how hard it will..." <- pretty hard
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<whitequark[cis]>
same problem
<whitequark[cis]>
the voltage there is 1.1 V
<whitequark[cis]>
the level shifters don't go that low
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<WilfriedKlaebe[m>
<whitequark[cis]> "pretty hard" <- Uh. Would it be easier to just sniff the conversation on the CC line?
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<theorbtwo[m]>
Oh! Somehow, I thought they would go arbitrarily low.
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<stary[m]>
looks like even at the edge of the minimum spec it's just about a miss - 1.65v min vcc, then V_ih is 0.65*vcc for 1.0725v
<stary[m]>
but that's only sniffing, not actually carrying out your own pd transactions
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<whitequark[cis]>
what you could do is ac-couple it
<whitequark[cis]>
like, bias the input to always be at Vcc/2, then couple the PD input (which is DC-balanced for inscrutable historical reasons) into it
<whitequark[cis]>
you'll be able to get captures quite easily
<whitequark[cis]>
note that that 1.1V actually depends on whether the device is a source or a sink (again for inscrutable USB reasons)
<whitequark[cis]>
so you really do want AC coupling
<theorbtwo[m]>
Most inscrutable usb reasons are "we don't want to add more pins", I think.
<theorbtwo[m]>
You probably know better than me, sorry.
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<galibert[m]>
Isn't USB-PD a RF protocol without the RF?
<galibert[m]>
(which is as insane as it reads, yes)
<whitequark[cis]>
but it still is 4b5b encoded
<whitequark[cis]>
presumably because they wanted to reuse existing ASICs by just cutting in before the modulator/demodulator
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<WilfriedKlaebe[m>
"or 24MHz BFSK on the Vbus line" sounds RF to me 😅
<galibert[m]>
yeah but wit the central frequency at 0Hz
<galibert[m]>
s/wit/with/
<whitequark[cis]>
I think it had like 21.4 MHz?
<galibert[m]>
That would be before they un-RFed it, right?
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<whitequark[cis]>
am i insane or is openocd awful at documenting their behavior?
<whitequark[cis]>
(if you incorrectly assume that the two low bits are the states of the signals, like everything else in the remote_bitbang protocol does)