SCC or SMC for console ?

SCC or SMC for console ?

[Laurent Pinchart]

Hi everybody,

I'm developping a board based on a MPC860T.

I need 4 serial ports at runtime, and was wondering if I should rather
use 2SMC + 2SCC or 4 SCC (or 1SMC + 3SCC).

I need a console, but no hardware flow control (which would force the
use of SCC).

Thanks for your help.

Laurent Pinchart


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Re: SCC or SMC for console ?

[Dan Malek]

Laurent Pinchart wrote:

> I need 4 serial ports at runtime, and was wondering if I should rather
> use 2SMC + 2SCC or 4 SCC (or 1SMC + 3SCC).

Always use SCCs for real work and the SMC for console and other low
speed things (like connected to low bit rate TDM).

The SMCs require a large amount of CPM software overhead, so not only
are they relatively slow devices, they also steal cycles from other
peripherals.

Is one of your serial ports in the example above the console?  If you
need four ports not including the console that can be a little more
challenging.  Carefully investigate the I/O pin multiplexing to ensure
you can get the SMC2 I/O, as that is one of the first ones stolen for
other uses.

Have fun!


	-- Dan


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Re: SCC or SMC for console ?

[Laurent Pinchart]

>
>
>> I need 4 serial ports at runtime, and was wondering if I should rather
>> use 2SMC + 2SCC or 4 SCC (or 1SMC + 3SCC).
>
> Always use SCCs for real work and the SMC for console and other low
> speed things (like connected to low bit rate TDM).

4 SCC then, and 1 SMC for console. Both SMC1 and SMC2 I/Os are available
on the design (I only need serial ports + FEC ethernet).

I'd like to use 2 serial ports for RS232 (should be really
straightforward), and the other 2 for RS485 (with of course no flow
control). Is there something I should know ?

Laurent Pinchart


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Re: SCC or SMC for console ?

[Wolfgang Denk]

Dear Laurent,

in message <3C6BF3B1.2040906@capflow.com> you wrote:
>
> I need 4 serial ports at runtime, and was wondering if I should rather
> use 2SMC + 2SCC or 4 SCC (or 1SMC + 3SCC).

Assuming that you need Ethernet: if you can use the FEC for Ethernet,
that it does not matter much; otherwise I'd recommend to use  2SMC  +
2SCC  or  1SMC  +  3SCC  so  that  you  have at east one SCC left for
Ethernet.

> I need a console, but no hardware flow control (which would force the
> use of SCC).

Should be no problem. The kernel on our FTP server was tested with  6
serial  ports  on  a  MPC860, with HW flow controll on all SCC's. The
only problem in such a configuration is that you have only 4 BRG's so
two ports have to share the baudrate with another port.

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
See us @ Embedded Systems Nuremberg, Feb 19-21, Hall 12 K01 (with TQ)

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Re: SCC or SMC for console ?

[Laurent Pinchart]

>
>
>Should be no problem. The kernel on our FTP server was tested with  6
>serial  ports  on  a  MPC860, with HW flow controll on all SCC's.
>
Reading arch/ppc/8xx_io/uart.c, I found out that all the flow control
related code was surrounded by false #if #endif. It seems that there is
no flow control at all on either the SMC or SCC serial ports in UART
mode. Is there a patch somewhere to implement flow control, or is it
still missing ? I was wondering what to do with CD/DTR/DSR (as Linux
only support RTS/CTS flow control for now), and had hoped to find an
answer in the source code...

Laurent Pinchart


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Re: SCC or SMC for console ?

[Wolfgang Denk]

In message <3C6D1A26.1040209@capflow.com> you wrote:
>
> >Should be no problem. The kernel on our FTP server was tested with  6
> >serial  ports  on  a  MPC860, with HW flow controll on all SCC's.
> >
> Reading arch/ppc/8xx_io/uart.c, I found out that all the flow control
> related code was surrounded by false #if #endif. It seems that there is

You're reading the wrong code, it seems.

Get the sources from ftp://ftp.denx.de/pub/LinuxPPC/usr/src/
You will find a lot of CONFIG_UART_CTS_CONTROL_SCCx,
CONFIG_UART_RTS_CONTROL_SCCx, CONFIG_UART_CD_CONTROL_SCCx, and
CONFIG_UART_DTR_CONTROL_SCCx stuff there.

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
See us @ Embedded Systems Nuremberg, Feb 19-21, Hall 12 K01 (with TQ)

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