Inter 'Board' Communication

On Apr 12, 11:33=A0pm, "azraiyl" <azraiyl@n_o_s_p_a_m.gmail.com> wrote:
> I've a 'Main' Board that needs to communicate with 4 other processors on
> other boards with at least 1 MiByte/s. A prefer to use the Adress/Data-Bu=
s
> on the 'Main' Board. The 'other' processors support SPI, I2C, UART and ha=
ve
> an A/D-Bus aswell.
> My first idea was to take a quad UART an put it on the 'Main' board.
> Problem is that they are all expensive. Any other idea?

Perhaps a CPLD ?
Depends on the total data rates and usage % and duplex/simplex, but a
cpld can do a BUS <-> SPI quite well.
It allows SPI on the slaves, in master or slave mode.

-jg

On Mon, 12 Apr 2010 06:33:10 -0500, "azraiyl"
<azraiyl@n_o_s_p_a_m.gmail.com> wrote:

>I've a 'Main' Board that needs to communicate with 4 other processors on
>other boards with at least 1 MiByte/s. A prefer to use the Adress/Data-Bus
>on the 'Main' Board. The 'other' processors support SPI, I2C, UART and have
>an A/D-Bus aswell.
>My first idea was to take a quad UART an put it on the 'Main' board.
>Problem is that they are all expensive. Any other idea?

How about a Motorola/Freescale processor with various QUICC
co-processors, such as (MC68360,) MPC860, MPC8260 etc. that have at
least 4 SCC channels. The main processor overhead is quite low due to
the DMA system.

Are the other 4 processors capable of handling 10 Mbit/s speeds
through the UART interface ?
   

While I'm quite sure that the 'main' processor is an OMAP-L138 I'm not sure
what the slave processors are. The problem is that I've to think about a
possible future, while not making the 'main' board too expensive. But some
Cortex-M3 processors with with 80 MHz are a good starting point (somehting
between 5$ and 15$).

One idea also had, was using a dual port RAM on every slave board. This
allows me to use the A/D-Bus from the 'main' board without investing
anything.

I've to add, that I currently investigate the USB idea. The OMAP-L138 has
an additional USB 1.1 host controller (The is a possbility that we use the
OTG port for something else) and most Luminary Cortex-M3 support Full-Speed
(which is enough) and have some additional USB functions included in their
ROM. The 'main' board then only needs an USB hub, which seems to be cheaper
then a quad UART.

But anyway, thanks everyone for the input.	   
					
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azraiyl wrote:
> While I'm quite sure that the 'main' processor is an OMAP-L138 I'm not sure
> what the slave processors are. The problem is that I've to think about a
> possible future, while not making the 'main' board too expensive. But some
> Cortex-M3 processors with with 80 MHz are a good starting point (somehting
> between 5$ and 15$).
> 
> One idea also had, was using a dual port RAM on every slave board. This
> allows me to use the A/D-Bus from the 'main' board without investing
> anything.

Dual-port RAM tends to be expensive -- even if you just opt for
a pair of back to back FIFOs.  And, it adds explicit synchronization
issues that are implicitly handled with a message oriented interface
(e.g., USB).  Consider it only if you *really* need the
bandwidth it will provide.

You also have to be conciously (to some extent) aware of the
fact that now you're embracing NUMA and it can have subtle
consequences for you (depending on how you use it and
the characteristics of your application).  Not a "big deal"
but not something you can just choose to ignore, either
(especially depending on how the DPRAM is implemented)

> I've to add, that I currently investigate the USB idea. The OMAP-L138 has
> an additional USB 1.1 host controller (The is a possbility that we use the
> OTG port for something else) and most Luminary Cortex-M3 support Full-Speed
> (which is enough) and have some additional USB functions included in their
> ROM. The 'main' board then only needs an USB hub, which seems to be cheaper
> then a quad UART.

Remember, you need a "host" *somewhere* in the architecture!

> But anyway, thanks everyone for the input.	   

Host (and PHY) is included in the OMAP-L138. OS is Linux. I've already
tested it somewhat and the first impressions is ok.	   
					
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