Remove D-FF from two upstream SFPs. Add mux to allow either direct or via D-FF on third

[DavidCussans]

The three upstream SFPs can each be connected to a different timing source. Hence return data can't be clocked from same clock.

However, would still like to preserve the ability to have clocking path go direct from clock gen , rather than via FPGA

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1. On two SFPs Remove D-FF (driven by the single board PLL) registering the data going from FPGA to SFP Tx
2. On third (primary) SFP, add a 1:2 fanout and 2:1 Mux with straight through in one arm and via D-FF in the other. Use, for example 854S01 as LVDS Mux

[oxfpete]

Sorry I think I might need a bit of help again here. I know I scribbled something down when we spoke but I can't find the paper. Devices U3/U8 need to be removed, leave U2 for SFP<2>/third SFP.

The newly placed IC3 (854S01) part is to replace "U2" for SFP<2>??

[DavidCussans]

Pete,

Yes, the “issue” doesn’t give much detail.

On two upstream channels remove the D-FF on SFP 0,1 and connect the FPGA directly to the SFP Tx pins:

U8 should be removed and UPSTREAMDATA{P,N}(0) connected directly to SFPTD{P,N}(0) via C106/C100

U3 should be removed and UPSTREAMDATA{P,N}(1) connected directly to SFPTD{P,N}(1) via C101/C98

On the third upstream channel it should be possible to switch between direct connect to the FPGA and connection via a D-FF:

SFPTD{P,N}(2) should be disconnected from U2 and instead connected to the output of multiplexer IC8 ( 854S01 )

One input of IC8 should be connected to the output of U2

For the other input of IC8 there are two choices:

1. Disconnect one pair of AUXIO signals from J4 and instead connect to U8 ( adding DC-blocking capacitors in series and adding 100-Ohm termination resistor near U8)
2. Disconnect UPSTREAMDATA{P,N}(2) from U2 and connect to the input of a 1:2 LVDS fanout ( Use a SY58608 like IC2 etc. ). One output of the newly added 1:2 fanout should go to the input of U2. The other output should go directly to the second input of U8

I don’t have a preference for which option is chosen ( 1. or 2. ). Go with the lowest staff cost one. Probably option 1. I guess.

Cheers! David

From: Peter Hastings @.> Sent: Friday, June 21, 2024 2:03 PM To: uob-hep-cad/uob-hep-pc072 @.> Cc: David Cussans @.>; Author @.> Subject: Re: [uob-hep-cad/uob-hep-pc072] Remove D-FF from two upstream SFPs. Add mux to allow either direct or via D-FF on third (Issue #18)

Sorry I think I might need a bit of help again here. I know I scribbled something down when we spoke but I can't find the paper. Devices U3/U8 need to be removed, leave U2 for SFP<2>/third SFP.

The newly placed IC3 (854S01) part is to replace "U2" for SFP<2>??

— Reply to this email directly, view it on GitHubhttps://github.com/uob-hep-cad/uob-hep-pc072/issues/18#issuecomment-2182714307, or unsubscribehttps://github.com/notifications/unsubscribe-auth/ABLNCKRRQEVNXQBDNPEQEXLZIQQA7AVCNFSM6AAAAABAS53F2WVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDCOBSG4YTIMZQG4. You are receiving this because you authored the thread.Message ID: @.**@.>>

[oxfpete]

Think it is almost done, need your eyes to look at schematic.

[DavidCussans]

Schematic change looks good. Need to double-check that it is OK to connect the "direct out" signal to B16_L14_P/N