Lpc2000

On 30 Jan 2005 at 6:30, Rick Collins wrote:

> 
> 
> --- 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.  

:-)  Yes,  I have been involved in many HUGE arguments between engineers,
where someone made a statement, and because of some sort of slip misused 
a word without realising it. Everybody else picks up on this, and even though they
fully agree with what the other guy meant to say, they do not agree with what
he actually said.  Non-Technical people who listen to this, find this totally beyond 
comprehension.

Anyway, I accept your argument.

> > 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.  
> 

The higher speed serial interface would definitaly help. What is the cost of the ethernet 
controller you have in mind compared to the Wiznet W3100A chip ? If the pricing are 
similar, it might still be worthwhile using the Wiznet chip in parallel mode via the FPGA
and high speed serial combination. To get bootstrap code going to re-program or boot 
the board via ethernet needs very little code because of the hardware TCP/IP stack. If 
one then uses an RTOS or something else with a full TCP/IP stack, then one can use 
the W3100A chip as a normal type ethernet chip. Opening a TCP/IP socket using the
W3100A takes something like 20 lines of C code.

Regards
   Anton Erasmus
 

-- 
A J Erasmus