November
2004, Issue 172
TCP/IP
Stack Solution
A
Detailed Look at the CMX-MicroNet
CMX-MicroNet
& W/PIC18
The
Easy Ethernet W/PIC18 is shown in Photo 1a. The “W”
is short for Whacker because the Easy Ethernet W/PIC18’s
Ethernet hardware is based on the classic Packet Whacker
NIC shown in Photo 1b. The Packet Whacker consists of
an RTL8019AS Ethernet engine, a 20-MHz crystal, a Bothhand
LF1S022-34 integrated magnetics package, and a complement
of supporting power supply bypass capacitors. The Packet
Whacker is designed to interface to almost any microcontroller
that can supply it with a minimal set of address and
data I/O lines.
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(Click
here to enlarge)
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Photo
1a—The EDTP Electronics Easy Ethernet W/PIC18 is
actually a product of convenience. It’s basically
a Packet Whacker with all of the supporting circuitry
on a single PCB. b—The Packet Whacker is a minimal
implementation of the RTL8019AS Ethernet engine
IC. Despite its simplicity, the Packet Whacker is in service in every
free country of the world. |
The
Easy Ethernet W/PIC18 takes the basic design of the
Packet Whacker and adds a PIC18F452 microcontroller
running at 20 MHz, a regulated 5-V power supply, a programming/debugging
interface, a data latch (74HCT573 transparent octal
latch), and a regulation RS-232 port. The inclusion
of the programming/debugging interface allows the Easy
Ethernet W/PIC18 to be programmed using the new Microchip
PM3 programmer or debugged and programmed using the
hockey puck and the MPLAB IDE. The Easy Ethernet W/PIC18’s
hardware layout is depicted in Figure 1.
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(Click
here to enlarge)
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Figure
1—The Sipex SP233ACT-based RS-232 port is a luxury
option. Only the PIC and the RTL8019AS with their
associated support components are needed to put
the Easy Ethernet W/PIC18 on a LAN or the Internet.
However, the RS-232 port comes in handy when the
Easy Ethernet W/PIC18 is used as a serial-to-Ethernet
converter. |
Before
you can load any CMX-MicroNet firmware into the Easy
Ethernet W/PIC18’s microcontroller, you must first define
your desired TCP/IP operating environment and set up
the hardware. This is easily done by modifying the contents
of a couple of CMX-MicroNet network component files
and setting some microcontroller fuses within the MPLAB
IDE.
The
hardware setup is straightforward. Using the Configure
pull-down menu in the MPLAB IDE, I set up the microcontroller
clock for high-speed operation and turned off the watchdog
timer, brownout detect, low-voltage programming, and
anything that has to do with code or memory area protection.
At MPLAB IDE startup, the hockey puck sensed the PIC18F452
microcontroller and informed the MPLAB IDE that it had
found a valid PIC18F452 at the other end of its interface
cable. Because the CMX-MicroNet contains its own RTL8019AS
driver, I also needed to make sure that the Easy Ethernet
W/PIC18 I/O pin definitions matched the CMX-MicroNet
driver’s I/O pin definitions. The mapping of the RTL8019AS
drive to the hardware I/O structure is found in the
rtlregs.h file in the C:\MICRONET\netlib directory.
The code snippet that defines the I/O structure that
is used with the PICC-18 C compiler and the Easy Ethernet
W/PIC18 is shown in Listing 1.
The
CMX-MicroNet network file source code components are
found in the C:\MICRONET\netlib directory. The driver
for the Realtek RTL8019AS Ethernet engine IC also can
be found in the netlib directory. Each network source
code file is compiled and archived into the netlib.lib
library file depending on the protocols selected in
the mnconfig.h file, which is also located in the C:\MICRONET\netlib
directory.
Refer
to the Circuit Cellar ftp site for the code snippet
taken from mnconfig.h. I selected the TCP and UDP protocols,
which kick in TCP and UDP sockets, and requested to
use Ethernet with a checksummed UDP protocol. That pulls
tcp.c, udp.c, and mn_csum.c from the C:\MICRONET\netlib
directory into the netlib.lib compilation and archival
process. I elected to allow the Easy Ethernet W/PIC18
to be pinged. Notice that I also turned on the HTTP
server, SMTP, ARP, DHCP, and the CMX-MicroNet virtual
file system. That results in including arp.c, http.c,
smtp.c, and so forth.
There
are also other elements that are automatically included
that are common to all of the protocols, such as ip.c
and socket.c. The RTL8019AS driver is represented by
rtl8019.c. Judging from my list of protocols, it looked
like the PIC18F452 was going to be packed as tight as
a tube of deli bologna.
The
next step in the configuration process was to identify
and specify the IP addresses of the network players.
This is done to nail down hard-coded IP addresses if
DHCP is not being used. My network includes a Windows
2000-based PC loaded with packet-sniffing software,
a home-brewed Internet test panel, and a web browser.
The gateway device (192.168.0.1) is a Netgear wireless
router, which incorporates a four-port 10/100 wired
switch and DHCP server capabilities.
I
pinged my ISP’s mail server to get the mail server’s
IP address (65.32.5.130) and plugged that into the SMTP
IP address definition. All of my IP ducks were in a
row at that point. However, the CMX-MicroNet installation
set-up documentation suggests ensuring that the required
PICC-18 libraries, which are included in the path statement,
are built, and gives instructions on how to make that
happen. Otherwise, the initial build of the CMX-MicroNet
netlib.lib, which is a mandatory step in the CMX-MicroNet
stack generation process, will not happen.
The
library file netlib.lib must be built before any CMX-MicroNet
stack services can be called and used. Two batch files
are included with the CMX-MicroNet to facilitate the
construction of a netlib.lib file: one supports the
RTL8019AS, and one doesn’t include the RTL8019AS driver.
The netlib.lib compilation and archival process using
PICC-18 compiler and the CMX-MicroNet network library
files was performed without incident. Note that the
CMX-MicroNet installation process had already correctly
modified the path statements.
Everything
up to this point pointed to “go” for a test compile
and load of the example code included in the CMX-MicroNet
package. The PICC-18 C compiler installed without trouble.
It successfully registered and attached itself to the
MPLAB IDE.
I
decided to start with the CMX-MicroNet UDP example code
in Client mode because I could instantly test the operation
of the code and hardware using my trusty Internet test
panel, which enables a UDP echo port on the PC at 192.168.0.2
on the Florida room’s CMX-MicroNet LAN. Server mode
or Client mode for UDP and TCP sockets is available
by simply completing the #define SERVER_MODE statement
in the example code with a 0 for Client mode and a 1
for Server mode.
I
performed a final check on the PIC’s fuse settings and
kicked off the compile session. I could hear a TV game
show’s “loser” buzzer go off loudly as the error-filled
contents rolled through the MPLAB IDE output window.
(Refer to the Circuit Cellar ftp site for the code snippet.)
I fired off a quick note to the CMX-MicroNet support
folks describing my dilemma. The verdict: Stupid Fred
was out of PIC18F452 program and data memory. So, I
had to pull some of that bologna out of the tube.
I
turned off TCP, HTTP, DHCP, SMTP, and the virtual file
system by modifying mnconfig.h. I kept the maximum number
of sockets at two, and I didn’t touch the default receive
and transmit buffer sizes. I also kept Ethernet support
and ping capability enabled. The ping selection doesn’t
add any additional code to the final stack.
Turning
the knobs and throwing switches within the mnconfig.h
file requires a rebuild of the netlib.lib file. Rebuilding
the netlib.lib file is as simple as making the changes
in mnconfig.h, saving the changes, and executing the
CMX-MicroNet’s mkphpice.bat batch file. If Ethernet
support is not required, the mkphtpic.bat file can be
used to generate the new netlib.lib file. I compiled
the UDP example code again. This time I was rewarded
with a “BUILD SUCCEEDED” message and the statistics
you see in Figure 2a.
Photo
2 is a composite shot of the Internet test panel talking
UDP with the Easy Ethernet W/PIC18 and the Netgear router’s
view of its attached devices. Notice that because DHCP
is turned off, the Easy Ethernet W/PIC18’s IP address
is the IP address I hard-coded into the CALLBACK.c network
file in the snippet posted on the Circuit Cellar ftp
site.
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(Click
here to enlarge)
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Photo
2—The EDTP Electronics Internet test panel is a
Visual Basic application that implements a simple
UDP echo function on well-known port 7. The test
panel can also function as a UDP client that interacts
with an Easy Ethernet W/PIC18 acting as a UDP server.
You can test drive the Internet test panel by checking
out the EDTP web cam. |
I
also hard-coded the PC destination address in the CMX-MicroNet
example code with the following statement:
byte
my_dest_addr[IP_ADDR_LEN] = {192,168,0,2};
In
addition to bouncing UDP packets off the Internet test
panel, I was also able to ping the Easy Ethernet W/PIC18-CMX-MicroNet
pair from the PC using the Easy Ethernet W/PIC18’s hard-coded
IP address of 192.168.0.150.
The
next logical step was to turn on TCP in Server mode
and try to get to the Easy Ethernet W/PIC18 using a
Telnet session and the CMX-MicroNet TCP example code.
A look at Figure 2b shows that I was getting close to
filling up that tube of bologna. There’s nothing exciting
about looking at a drab Telnet window. So, I’ll just
say that the Telnet session worked. The characters were
echoed to the PC’s Telnet window from the Easy Ethernet
W/PIC18-CMX-MicroNet combination as designed.
Now
that I had the Easy Ethernet W/PIC18 jumping through
hoops, I added some fire in the form of DHCP. There
went that loser buzzer again. Check this out:
Error[000]
//Can’t find 0x2C words (0x2C with total) for psect
bss in segment RAM
Error[000]
//Can’t find 0x18 words (0x18 with total) for psect
bss in segment RAM
It
looked like I was out of gas in the PIC’s RAM area.
I turned off TCP to see if I could regain some ground.
However, even with TCP turned off, the RAM utilization
was just above 97%. That means you can run a TCP-based
or UDP-based Easy Ethernet W/PIC18 with DHCP, but you
wouldn’t have much trunk space. So, if you’re going
to soar with the Internet eagles, it’s time to switch
your LAN locomotion.
