Extra port?

Hi,

I am using an Atmel AT91RM9200 (ARM9) processor which has a single MAC
built-in. I also have software drivers which support Ethernet through
this MAC. I have a reference design which uses the RMII interface to a
PHY chip (Davicom DM9161). So far so good.

However, I want to be able to change the reference design so that I can
simultaneously attach two 10/100Base-T devices to this single MAC
without having to change the software driver (just as if the reference
design board has had its cable connected to an external hub).

I have seen some chips which have repeater functionality as well as
RMII interfaces. Is it as simple as just using one of these chips (ie
the RMII talks to one of the PHYs on the chip and then that PHY
connects in a hub-like way to the other PHYs on the chip), and then
bring out two of the other PHY connections to RJ45 connectors?

Thanks in advance for any help.

paul.cabble@kingsmith.com wrote:
> Hi,
> 
> I am using an Atmel AT91RM9200 (ARM9) processor which has a single MAC
> built-in. I also have software drivers which support Ethernet through
> this MAC. I have a reference design which uses the RMII interface to a
> PHY chip (Davicom DM9161). So far so good.
> 
> However, I want to be able to change the reference design so that I can
> simultaneously attach two 10/100Base-T devices to this single MAC
> without having to change the software driver (just as if the reference
> design board has had its cable connected to an external hub).
> 
> I have seen some chips which have repeater functionality as well as
> RMII interfaces. Is it as simple as just using one of these chips (ie
> the RMII talks to one of the PHYs on the chip and then that PHY
> connects in a hub-like way to the other PHYs on the chip), and then
> bring out two of the other PHY connections to RJ45 connectors?

Cirrus KS8993 (3 port) or KS8995 (5 port). You'll need SPI (bitbanged is 
fine) to set them up.

Paul Burke

Hi Paul,

Thanks for your rapid response. I found the Micrel KS8993 (is this the
one you meant?), but I was hoping for something with the RMII interface
as I don't have access to the full MII interface.

Anyway, I think you are telling me that it really is as simple as just
using such a chip to do what I want, right?

Regards,
Paul.

pingSmith wrote:
>
>  I found the Micrel KS8993 (is this the
> one you meant?), but I was hoping for something with the RMII interface
> as I don't have access to the full MII interface.
> 
> Anyway, I think you are telling me that it really is as simple as just
> using such a chip to do what I want, right?

Has some other greedy bugger used up all the pins then? The !!MICREL not 
cirrus!! KS8993/5 use the full MII. But the AMD Am79C875 seems to have RMII.

Yes, just drop the appropriate device in. Then spend 6 weeks making it 
work, because the data sheet gets very vague at times, at least Micrel's 
did. It was actually very easy once I knew how, and it's amazing what it 
will let you get away with (*). I was expecting layout etc. to be 
totally critical, but it seemed to forgive my sins in a most indulgent 
manner. Also, having automatic crossover detect, I didn't have to be too 
worried about whether transmit means receive, as long as I got the true 
and inverse right.

Paul Burke

* like forgetting to put termination networks on the (discrete) 
transformers.

Hi Paul,

Thanks for your further information. I can well believe the 6 weeks you
mentioned. I had a nightmare getting a quad UART working on the
platform (linux driver/interrupt problems). It's nice to know that the
layout isn't all that critical.

I must admit, though - I am the greedy bugger who used the other port
lines of the MII <blush>.

Thanks again for your help.

Regards,
Paul.

These chips basically have one RMII interface per channel, but the
AT91RM9200 has only one and only one MAC so this won't work. You need a
MAC and PHYSICAL chip that sits on the processor bus. A 10/100 version
of the cirrus CS8900.

Hi sjo,

Thanks for your input on this.

Regards,
Paul.