November
2004, Issue 172
TCP/IP
Stack Solution
A
Detailed Look at the CMX-MicroNet
LAN
BUGGY
My
new LAN buggy is composed of a 2 × 16 LCD, a Packet
Whacker, a programmer/debugger interface (for the hockey
puck), a regulated 5-VDC supply, and a microEngineering
Labs PICProto 80 development board carrying a PIC18F8621
running at 20 MHz. My new form of LAN locomotion is
posing in Photo 3. The PIC18F8621 is an 84-pin part.
As you can see in Photo 3, I didn’t use all 84 pins.
So, only the active connections are shown in Figure
3.
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(Click
here to enlarge)
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Photo
3—No rocket science here. The Packet Whacker is
wired into the PIC18F8621 according to the I/O layout
specified in the CMX-MicroNet rtlregs.h file. I
modified the hockey puck interface cable to accommodate
the microEngineering Labs PICProto 80 ICSP connector
and added some code to drive the LCD. |
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(Click
here to enlarge)
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Figure
3—It’s extremely uncharacteristic of me not to wire
in a serial port. However, I won’t be exercising
the CMX-MicroNet PPP or SLIP functionality, so it
would be a waste to include a serial port here.
Here’s yet another microcontroller that is supported
by the ubiquitous Packet Whacker. |
I’ve
already test driven CMX-MicroNet TCP and UDP functionality
with the Easy Ethernet W/PIC18. The reason I built up
this new LAN ride is to provide extra space for the
other CMX-MicroNet components to run.
In
addition to added headroom, the LAN buggy sports more
horsepower. Although the LAN buggy is cruising along
at 20 MHz, the PIC18F8621 has an engine that can run
at 40 MHz. So, I put the pedal to the floor and turned
on DHCP, TCP, and UDP. The statistics for ROM and RAM
usage for the Packet Whacker/PIC18F8621 LAN buggy are
shown in Figure 2c.
Although
the LAN buggy has plenty of legroom and lots of horsepower,
I had to do a bit of engine tuning to get DHCP to cooperate.
The Netgear router never granted the LAN buggy an IP
address although it saw the LAN buggy’s MAC address.
Again, I turned to the CMX-MicroNet support team. Paul’s
initial site-unseen diagnosis was that my receive buffer
was probably too small. Hmm. I slapped the sniffer into
action. The DHCP offers from the router were 590 bytes
in length. My LAN buggy’s receive buffer size was set
for 122 bytes. As you can see in the Photo 4 sniffer
shot, the LAN buggy was asking for an IP address but
was unable to swallow the 590-byte offer. After I modified
mnconfig.h and increased the receive buffer size, my
little LAN buggy was granted a lease for 192.168.0.3.
It
isn’t likely that you would ever try to cram all of
the CMX-MicroNet functionality into an application.
However, I had to know if it could be done. So, I turned
on everything with the exception of PPP and SLIP. The
usage statistics for the big PIC are shown in Figure
2d.
Now
that everything is loaded, let’s take a look at some
of the other functionality the CMX-MicroNet offers beginning
with SMTP. I’ve already put most of the pieces of SMTP
into place. Listing 2 is a summary
of what I have defined and where I defined it. The only
additional thing I had to do to get SMTP online was
set up the mail addresses and put some words into the
mail body. After instructing the LAN Buggy to run the
CMX-MicroNet SMTP example code, I ended up with what
you see in Photo 5.
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here to enlarge)
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Photo
5—This was easy to accomplish. After I had all of
my IP ducks pointed in the right direction, it was
just a simple matter of filling in the blanks and
kicking off the program. |
I
got really tired of not knowing which portion of the
CMX-MicroNet example code I was running. So, I decided
to insert some choice code of my own to drive the LCD
and tell me which piece of example code I had selected.
The PICC-18 C compiler comes with an LCD code module
that can drive LCDs in 4- or 8-bit mode. All of the
necessary LCD commands are also included in the source
code module. After studying the source code for the
LCD driver, I figured that all I had to do was modify
the lcd.h file and map the LCD driver’s I/O scheme to
the LAN buggy’s I/O scheme. To preserve the original
I/O definitions, I copied the original LCD include file,
modified it to suit the LAN buggy, and renamed it freds_lcd.h.
The PICC-18 C compiler also contains a nice delay function
that I included and used with the modified LCD driver
code.
Putting
the PICC-18 C compiler code together to realize my custom
LCD utility function was a piece of cake. The modifications
and additions I made to get the LCD module up are shown
in Listing 3.
