Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: [EFM] Half-duplex deferral for MAC-PHY rate matching a

christophe.del-toso@xxxxxx wrote:
>      Vladimir, Steven, Arthur and all,

 stuff deleted for brevity

> In the other hand, I am wondering myself if, by anticipating long-term
> requirements, the group should also investigate the possibility to extend
> capabilities of MII interfaces by adding few signals.
> On this point I remember a presentation from Michael Beck (Alcatel) (in the
> Austin meeting) presenting the concept of VMII.
> I think that the first objective could be MAC-PHY rate adapation through CRS and
> that second objective could be something of the kind of VMII or something less
> but something that lets maximum freedom.
> Your comments are welcome !
> Regards
> Christophe Del-Toso, ST Micro

   I disagree with adding extra signals for full duplex MII
flow control.

   Firstly it is unnecessary to add extra signals, if you 
accept that the MII interface is going to be redefined you 
could define "col", the collision indication signal, to pause 
full duplex transmissions in mid-frame, and pause reception
by asserting rx_er as rx_dv goes low. Or you could just
stretch rx_clk and tx_clk.

   Personally I don't think the MII interface needs to
be redefined. Keeping the MAC and MII definitions the
same means less work for the task force and means the EFM
PHY should work with existing silicon. Note clock stretching
causes problems with SMII and RMII and so will not work
with MAC's that have these interfaces.

   Also 100Mbits full-duplex throughput may be possible using
half-duplex deferral with existing MAC's. It all depends
on whether existing MAC's allow reception while transmitting
in half-duplex. The 802.3 spec allows MAC's to do this but
there is some debate over whether existing MAC's actually 
do do this.