| 1 Jun 2025 |
 emily | also, this is the only chip you can find in twisted pair transceivers that actually runs relatively cool, so I'm sorta locked in to buying a transceiver that has it specifically | 12:52:34 |
| emily | from skimming the data sheet, I guess the BCM84891L has an integrated MAC that it can use, but it can also talk directly to a MAC on the host end if you use it in one of these modes? | 12:53:24 |
 K900 | Yes that's usually how those work | 12:53:35 |
| emily | something that worries me a little is that, even if the SFP+ vendor did absolutely everything I wanted, how is the Broadcom chip going to know it's meant to talk 2500BASE-X when the R4 can only talk 2500BASE-X if it skips any in-band negotiation? | 12:54:47 |
| K900 | It would read the EEPROM | 12:55:49 |
| K900 | Or the fake-EEPROM | 12:55:52 |
| K900 | But hopefully the real EEPROM | 12:56:00 |
 magic_rb | In reply to @emilazy:matrix.org
also, this is the only chip you can find in twisted pair transceivers that actually runs relatively cool, so I'm sorta locked in to buying a transceiver that has it specifically honestly, bpir4 <-fiber-> switch <-copper-> whatever | 12:56:10 |
| K900 | The autonegotiation stuff doesn't mean nothing is negotiated | 12:56:16 |
| K900 | Or rather | 12:56:18 |
| K900 | It means there is no negotiation happening | 12:56:24 |
| K900 | But there is capability information passed around | 12:56:33 |
| emily | this is about WAN | 12:56:46 |
| magic_rb | oh | 12:56:51 |
| emily | my uplink to the WAN is (going to be) 2.5GBASE-T | 12:56:52 |
| K900 | SFP modules always have an EEPROM | 12:56:55 |
| magic_rb | you get wan over copper? | 12:56:56 |
| magic_rb | damn | 12:56:57 |
| emily | it's fibre | 12:57:02 |
| emily | but the ONT turns it into 2.5GBASE-T | 12:57:05 |
| K900 | The EEPROM specifies what modes the module understands | 12:57:27 |
| emily | yes I could mess about with a PON module, but as K900 has shown those are also very cursed :P | 12:57:29 |
| emily | and it would be illegal, also | 12:57:32 |
| emily | since everything up to and including the ONT is property of the network operator (even though it's in my house) | 12:57:43 |
| emily | so 2.5GBASE-T for WAN is non-negotiable | 12:57:55 |
| emily | I could use a separate media converter but that would just have the same problems of "not controlling the MAC" | 12:58:07 |
| K900 | So presumably the module would report itself | 12:58:14 |
| emily | e.g., I need mini jumbo frames and so on | 12:58:16 |
| emily | I see, makes sense | 12:58:23 |
| K900 | * So presumably the module would report itself as whatever it's configured to do | 12:58:24 |
