Issue
153 April 2003
E-Chips
MAC
ATTACK
Let’s
take a look at five—count ’em, five—new chips with built-in
Ethernet. Indeed, the pace of announcements may indicate
Ethernet—like UARTs, I2C, and SPI ports before it—is
well on its way to becoming standard equipment.
What’s
impressive is the range of performance and I/O capabilities
represented, which are summed up in Table
1. That means choosing an integrated Ethernet solution
need not be an exercise in compromise. Covering a range
from 8 to 32 bits and everything in-between, one of
these parts is likely a close fit with your application
requirements. If not, just wait awhile, and no doubt
there will be even more E-Chips to choose from.
Give
NetSilicon credit for being one of the first companies
to kick things off with their NET+ARM product line,
which was introduced five years ago. As the name implies,
NET+ARM combines an ARM chip, Ethernet, and the required
stacks of RTOS, network protocols, and development tools.
What’s
striking about the latest incarnation, the NS7520, is
what’s missing, notably the most significant digit of
the price tag. The sticker for this little puppy is
a mere $7.95 (10,000 quantity), and that’s today, not
some future price projection. As I’ve said all along,
the penetration of networking into embedded apps is
only limited by the cost, and chips like the NS7520
will further the cause.
The
NS7520 extends its cost-cutting aspirations from the
chip price itself to the entire system’s cost. Budget-burning
extremes typically associated with 32-bit chips (factors
such as clock rate, power consumption, packaging, and
glue logic) are avoided.
Consider
that the entry-level, no-cache ARM7TDMI core runs at
a leisurely 55 MHz off a plain 18.432-MHz crystal. Furthermore,
that core includes the denser Thumb 16-bit code option,
reducing the software footprint. There’s a full-fledged,
no-glue-logic bus interface for direct connection to
all the popular memory chips: SRAM, flash memory, and
DRAM/SDRAM (the latter via built-in address multiplexing
and refresh). Dynamic bus sizing and programmable wait
states support a mixture of 8-, 16-, and 32-bit add-ons.
In
many respects, the NS7520 is more like a controller
than a processor. There’s a decent set of peripherals
including timers (two general-purpose 16-bit, watchdog,
and bus error), 16 general-purpose I/O lines (four programmable
as interrupt inputs), and two high-performance UART-,
SDLC-, and SPI-capable serial ports.
The
built-in 802.3u-compliant Ethernet media access controller
(MAC) supports both traditional 10BaseT half duplex
(i.e., multidrop) and increasingly popular 100BaseTX
(point-to-point) links via 512-byte transmit and 2-KB
receive FIFOs. A 13-channel DMA controller does the
heavy lifting, servicing the network and all the other
on-chip and off-chip peripherals.
That’s
a lot of functionality compressed into a 177-pin BGA
package less than 0.5” on a side. However, despite
external appearances, this is a 32-bit chip after all,
and power consumption is a nontrivial 500-mW peak (55
MHz) regardless of the low 1.5-V core and 3.3-V I/O
(5-V tolerant) voltages. Of course, you can cut power
by running at a slower clock rate and using application-level
power management.
The
chip may be a bargain, but just don’t forget to budget
for the development tools. NetSilicon uses proven industrial-strength
software from Express Logic (ThreadX RTOS) and Green
Hills (IDE and C++ compiler) as well as the former Pacific
Softworks (TCP/IP stack), a company NetSilicon purchased
a couple of years ago. There is also a GNU-based tool
suite, but even that will set you back a cool $1500.
For
a more budget friendly option, consider the $299 NS7520-based
universal network controller (UNC20) development kit
from Embedded Solutions (see Photo 1). Two versions
of the kit are available. One runs uClinux on the board
and uses Linux-based GNU tools. The other version sticks
with the ThreadX RTOS (i.e., the same as NetSilicon’s
NET+OS package), but uses GNU tools and Cygwin running
on a PC host.
|
|
Photo
1—The UNC20 imodule (here mounted on the evaluation
kit's base board) is an easy and low-cost way to
get under the hood or quickly to production with
a NetSilicon NS7520-based solution. |
