Messages in this thread | | | Date | Wed, 26 Feb 2020 12:30:48 +0100 | From | Michael Walle <> | Subject | Re: [RFC PATCH 0/2] AT8031 PHY timestamping support |
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Am 2020-02-26 03:54, schrieb Richard Cochran: > On Wed, Feb 26, 2020 at 01:07:26AM +0100, Michael Walle wrote: >> Am 26. Februar 2020 00:50:40 MEZ schrieb Andrew Lunn <andrew@lunn.ch>: >> >That sounds fundamentally broken. > > Right. It can't work unless the PHY latches the time stamp.
To make things worse, it only has one slot for RX and one slot for TX timestamps.
>> This might be the case, but the datasheet (some older revision can >> be found on the internet, maybe you find something) doesn't mention >> it. Nor does the PTP "guide" (I don't know the exact name, I'd have >> to check at work) of this PHY. Besides the timestamp there's also >> the sequence number and the source port id which would need to be >> read atomically together with the timestamp. > > Maybe the part is not intended to be used at all in this way? > > AFAICT, PHYs like this are meant to feed a "PTP frame detected" pulse > into the time stamping unit on the attached MAC. The interrupt serves > to allow the SW to gather the matching fields from the frame.
But then there would need to be such a hardware pin, correct? Unless you'd misuse the INT# for it. Also, why should the PHY then have a PHC which can be adjusted.
>> That sounds fundamentally broken. Which would be odd. Sometimes there >> is a way to take a snapshot of the value. Reading the first word could >> trigger this snapshot. Or the last word, or some status register. One >> would hope the datasheet would talk about this. > > This might be the case, but the datasheet (some older revision can > be found on the internet, maybe you find something) doesn't mention > it. Nor does the PTP "guide" (I don't know the exact name, I'd have > to check at work).
BTW, the name of the document is "AR8031 1588v2 Precision Time Protocol, Application Note, 80-Y0618-15 Rev. A", which describes a use case where the RTC (ie PHC) is in the AR8031. I don't argue that the PHY is not broken, only that Atheros at least intended to have that use case.
-michael
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