Lpc2000

--- In lpc2000@yahoogroups.com, "Anton Erasmus" <antone@s...> wrote:

> 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. 

Boy, leave it to engineers to nit pic.  But if you reread my message,
that is not what I said.  I said I would "use" an FPGA to do the
conversion.  

> 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. 

I didn't say I would use SPI.  The Atmel SAM7 chips have an SSC port
which is similar to the serial ports on DSP chips and will interface
directly to many codecs at very high speeds, >10 Mbps.  

> 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.

Certainly this is interesting.  But like I said, it is a far cry from
10 Mbps.  The overhead is not that great and regardless of how much
overhead you have, the time required to transfer the data across the
CPU/LAN chip interface will still add to that.  So having a 20x higher
interface speed is still a significant boost.