Re: lack of address frame after reset
Ed,
Another suggestion would be to reset the address register to 02h.
Since nothing happens to the ID register on writes and errant write
doesn't affect anything. If a read happens after reset w/o an address
write then one just starts to read the IEEE ID. In fact if one does a
read inc and a second read right after reset then one will get the full
IEEE ID.
Howard Baumer
dpannell@xxxxxxxxxxx wrote:
>
> Allan brings up a valid issue with the new MDIO interface. If a read or write
> is done after a reset without the address register being set, undefined
> operation will result. But this is easy to fix. All we have to do is define
> that the address register is reset to zeros whenever a reset occurs. Now the
> operation is deterministic. We could further define the register at address
> zero to be a NOP. Writes don't effect anything and reads return all zeros.
> This prevents errant software from disrupting unintended register bits if it
> doesn't follow the correct protocol.
>
> --Don Pannell
>
> "Edward Turner" <Edward_Turner@xxxxxxxxxxxx> on 11/21/2000 02:39:14 AM
>
> To: stds-802-3-hssg@xxxxxxxx
> cc: (bcc: Donald Pannell/Marvell)
> Subject: RE: lack of address frame after reset
>
> Allan,
>
> I understand the concerns you are raising, but I don't think that any further
> sequence checking is required in the standard. I don't believe that guards
> against errant MDIO software have been included in previous parts of the
> standard. If the software is not working correctly its behaviour is undefined.
> It could issue address frames and start writing to random locations.
>
> Regards
> Ed
>
> "Allan Keung" <akeung@xxxxxxxxxxxxxxxxxx> on 20/11/2000 15:18:38
>
> Sent by: "Allan Keung" <akeung@xxxxxxxxxxxxxxxxxx>
>
> To: Edward Turner/GB/3Com@3Com, stds-802-3-hssg@xxxxxxxx
> cc:
> Subject: RE: lack of address frame after reset
>
> Ed,
>
> Draft D1.1 Clause 33 on P.92 said w.r.t. the address registers -
> "At power up or device reset, the contents of the address register
> are undefined."
>
> After power-up or reset, for the case of an ill-behaved software
> that does not specify at least one address frame first
> before proceeding to a write or read operation, what should be
> the response of a MMD?
>
> I suppose for a write operation, the write will be simply ignored.
> What about a read operation, should the MMD responds with a 0
> (as if addressed to an undefined register) or no response at all
> (as if the wrong port/device is addressed).
>
> Can the spec. be more definitive on this point?
>
> Regards,
>
> Allan
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