[j-nsp] MPC7 / QSFP28 I2C issue

[Jared Mauch]

> On Dec 7, 2018, at 10:19 AM, Theo Voss <mail at theo-voss.de> wrote:
> 
> Hi all,
> 
> we’re experiencing a strange issue on MPC7, configured for 2x40G 4x100G. On two different routers, two different QSFP28 (not same PIC/Port) ports on MPC7 do not recognize the inserted 100G LR4 transceiver while showing I2C errors. We’ve already exchanged the transceiver and verified that the transceivers are OK. Next step is a PIC and FPC reboot, then JTAC case. Just wanted to check if someone has seen an identical issue?
> 

I don’t know the electrical design of the MPC7 but ideally you want either to be doing a bitbang i2c or be going via an i2c mux.  I’ve seen issues with cheaper optics and not handling the higher i2c rates, eg: over 100.  You start to see errors when asking them to respond.

I ask my vendors to make sure they’re implementing reading of all the SFF reading relevant for the optic families that we use.  Make sure you ask and specify a revision number, eg:  version 12.2 of the document, or sff-8690 if your hardware needs that.

- Jared