Lpc2000

On 29 Jan 2005 at 17:50, Rick Collins wrote:

> 
> 
> --- In lpc2000@yahoogroups.com, "Anton Erasmus" <antone@s...> wrote: >
> If you really need ethernet on a chip without external bus-interface,
> then > using the Wiznet W3100A, makes much more sense. It alread has
> an > I2C interface and runs the TCP/IP stack in hardware for upto 4
> simultaneous > connections. If you want to connect it using the
> parallel bus, it has a mode > where it needs only 2 address lines, 8
> data lines, Read, Write, interrrupt and > Chip Select. A total of 14
> pins. If you want more than 4 simultanoues connections, > then you
> have to have a complete TCP/IP stack as with other ethernet
> controllers.
> 
> 
> That may be one solution, but I don't see how you can say it makes
> "much more sense".  I2C is very slow compared to even 10 Mbps.  The
> SSC port on the AT91SAM7S parts will operate at speeds above 10 Mbps
> and will add much less latency and boost throughput than an I2C
> connection.  The FPGA will be on the board anyway, so it seems natural
> to use it to make the connection to the Ethernet chip.  
> 

In your previous posts you said you are considering ADDING a FPGA to enable
you to easier / faster access a ethernet controller using a MCU without external
bus. If you already have an FPGA, and it has enough spare capacity, then it
makes sense to use it. Even if you can use SPI interface which is in the order
of 5MHz, it will also be a lot slower than the ethernet's 10MB/s. The overhead of
accesing a normal ethernet chip together with all the data you have to handle
as part of the TCP/IP stack means that you will not get that high a speed overall.
With the Wiznet chip, even though the I2C is fairly low speed, you ONLY need to
transfer data you actually are going to use in your app. The TCP/IP stack overhead
is handled within the Wiznet chip. Hence the ethernet interface has got no overhead
asociated with it, until there is data for the specific socket you have opened. 
In a previous message someone pointed to an Olimex LPC board, together with
one of these Wiznet chips, where they could serve web pages using the I2C
interface at 350kb/s if I recall correctly.  using 14 port pins to emulate a parallel 
interface, should be even faster.

Regards
   Anton Erasmus
-- 
A J Erasmus