This is a forwarded message
From: Ryan Niemi <ryan@fireserve.net>
To: lpc2000@yahoogroups.com
Date: Sunday, January 8, 2006, 2:17:21 PM
Date: 8 ÿíâàðÿ 2006 ã., 14:17:21
Subject: [lpc2000] Re: LPC's w/ ENC28J60 for ethernet via SPI

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> Have you looked at the Atmel AT91SAM7X?

I took a brief look, but availability concerns me.  Actually, while
getting into an alternate CPU discussion, I came up with an
interesting silicon cost comparison for some of my options.  These
prices below are based on single unit quantities priced via Digikey:

LPC2292                  $13.46
CS8900A                   $8.36
256Kx16 SRAM              $4.41     Total:  $26.23

EP9302                   $16.14
64Mb (4Mx16) SDRAM        $5.67
Micrel 10/100 PHY         $3.78
4Mb (512KB) SPI flash     $2.15     Total:  $27.74

Hmm, $26.23 for an ARM7TDMI @ 60MHz, 256KB flash, 512KB SRAM, 10mbps
ethernet, vs. $27.74 for an ARM920T @ 200MHz, 512KB flash, 8MB SDRAM,
10/100 ethernet.  A whole $1.51 additional silicon cost.

Granted however that the EP9302 solution takes up more board space,
requires somewhat more complicated code to bring up the chip w/ cache
and MMU config, and there's a lot more core power decoupling
requirements (possibly necesitating going to 4 layers vs. 2 w/ the
LPC).  I've been down the EP9301/2 route before, and I'll admit that
designing and bringing up an ARM920T microprocessor design *is* quite
a bit more complex than the LPC microcontrollers..  On the otherhand,
it can run eCos or Linux (if some more flash is added) with the Cirrus
board support package nearly out-of-the-box..

That bugs me that a full ARM920T ethernet solution comes that close to
cost to the ARM7TDMI LPC's.  Its things like that which make our lives
difficult in selecting chips!  Now if the ethernet LPC's w/ onboard
PHY's were on the scene in some reasonable timeframe, it would be a
no-brainer..

For anyone confused on my SPI flash choice above in the comparison,
the reason is that the Cirrus ARM920T's (and Atmel ARM920T if I recall
correctly) will happily boot off a SPI flash.  Minimal pin and netlist
count for the flash interfacing (board routing mayhem, especially when
you have SDRAM on the bus too!), then I whip up a simple bootloader
that loads the firmware from serial flash to SDRAM.  I usually
compress the serial flash image with an LZO variant and decompress in
the small bootloader program while loading to SDRAM.

-Ryan
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