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Subject: RE: the last serial port question
Date: Mon, 26 Feb 2007 14:47:53 -0700
Message-ID: <BB375AF679D4A34E9CA8DFA650E2B04E029517F5@onstor-exch02.onstor.net>
In-Reply-To: <20070226100221.1fad0a16@ripper.onstor.net>
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Thread-Topic: the last serial port question
Thread-Index: AcdZ0ENigWhRK851Tom/iZeEuHY3IgAABW4w
References: <20070226100221.1fad0a16@ripper.onstor.net>
From: "Brian Stark" <brian.stark@onstor.com>
To: "Andy Sharp" <andy.sharp@onstor.com>

Andy,

Let me put it down on paper and see if that helps.

The RM9K has serial port support via 2 different chips.  The first is
the Marvell system controller that provides 2 ports, and one of these
ports is routed to the DB9 on the frontpanel.  The downside is that
memory must be working because the UARTs use descriptors and buffers.
Another downside is support for this UART has been lacking in OS
distributions, so the support had to be developed by us (at least this
is what Dan claimed).  There is limited support for a more traditional
register-based scheme, but there is no FIFO support to go along with
this so we can't use it in normal operation.  I believe that the PROM
and possibly BSD rely on this mode to some extent at the beginning of
boot-up, but they then switch over to the descriptor and buffer scheme.

The second UART supported on Bobcat is the very common Philips 16C2552.
This was added on Rev 2 Bobcats for gdb sessions and is memory-mapped at
0xbf200000.  The idea is that one of the UARTs is dedicated for the SSC
and the other for the FC core, although this is completely arbitrary and
can be changed by software.  At the moment, I don't believe we use this
for the SSC at all, but it is by the FC.  If you type 'debug' at the FC
prompt, one of the 552 ports is then targeted for gdb.

Since the Marvell UART has less OS support and requires memory, it may
be easier to use the Philips UART instead for development and then
eventually transition to the Marvell.  If you want to go down that path,
then the frontpanel DB9 can't be used for the SSC console.  You would
need to use the header marked J7201 or J7202, which most boxes have
brought out to the front via ribbon cables.  We may also have to provide
some different PROM support for you, but this shouldn't be that bad
since the PROM already sets up the Philips UART in case it's needed for
gdb.

As it stands right now, here's how all of the consoles are laid out:

Header	Description			Board Location
J1101		FP Core 0			Back right
J1102		FP Core 1			Back right
J2501		TXRX Core 0			Middle center
J2502		TXRX Core 1			Middle center
J5904		SSC				Back center, frontpanel
DB9
J5905		FC				Back center
J7201		Debug SSC			Front right
J7202		Debug FC			Front right


Call me if you have questions!


Brian
 =20

> -----Original Message-----
> From: Andy Sharp=20
> Sent: Monday, February 26, 2007 10:02 AM
> To: Brian Stark
> Subject: the last serial port question
>=20
> I've only asked this three times before, so that means that=20
> this time I will remember the answer, I swear.
>=20
> The serial port/console layout on bobcat.  Can you explain it=20
> to me again?  Feel free to call me, I've got pen and paper=20
> standing by to take notes.
>=20
> Cheers,
>=20
> a
>=20
