off-the-shelf embedded-network connectivity
Contents
1. cause my deployed device would proba bly use an ISP I thought I might develop my design under real world conditions OTHER CONSIDERATIONS It s easy to focus primarily on the software side of evaluation After all most product development is software related so the quality of the software tools significantly impacts your product cycle You may find yourself shifting from the conventional view that software can compensate for hardware and be willing to force the hardware team to use its third choice part because of the development envi ronment Also given that part of the appeal of many of these chips is that they have room for your application leave yourself some time to look beyond the connectivity libraries to evaluate the application tools as well Look into how the stack interacts with inter rupts A stack that uses interrupts could increase the latency of other real time inter rupts in your application A stack that operates as a thread or separate task however can become resource starved if you too infre quently yield control resulting in lost packets Be aware of equipment that is optional For example although a few LEDs on the board could give you limited debugging feedback for example the green LED means you got to a certain part of the code having an LCD screen means you can display more meaning ful debugging messages to yourself On some boards an LCD screen is standard On others you can get an LCD scr2. gle evaluation board when you have to clear your desk to work on another project Working with multiple boards allowed me to see just how portable my code was among boards Ideally should have been able to use the same Web pages and Java applets and sup port C code but each board worked slightly differently with the stack Abstracting the stack function calls and creating my own API application program ming interface made it easier to port all types of code www edn com showing pictures Others assume that you know what you are doing a classic example is a manual that fails to mention that you need an Ether net crossover cable If you ve never con figured a network even a small one you could run into a lot of trouble I learned only a few years ago what a subnet is all devices on a subnet share the first three numbers of an IP address and have a dis tinct fourth number when my home router disappeared from the network for two weeks and brought down the DSL line You might consider inviting some hands onproject 2bedded network connectivity one from IT to share your weekly dough nuts just as backup lest you find your self banging your head on the desk over a networking problem CRUNCHING CODE Some demos offer challenging stum bling blocks For example to test an e mail transmission I needed access to a mail server I balked at the idea of setting up a mail server on my computer Be
3. Web pages is inconsequential worry ing about compressing Web pages doesn t yield any real gains The same situation holds true if you need to serve up only a few pages Given that a nonengineer someone not worried about memory usage may design a product s final Web pages it s probably best to focus on ways to process and compress fin ished Web pages rather than on building compressed Web pages For example instead of removing white space by hand you could build a utility that automatically removes it during the build process Many Web designers use sloppy specialized editors that add many extrane ous comments Some comments are useful for developing pages but you can remove them from the posted version because source code doesn t have to be human readable Cropping images or reducing quality can yield easy yet significant reduc tions You can also make good compression gains by replacing commonly used letter combina tions with control codes and then decompressing the codes before serving up the page Again compressing pages may have limited value to you if you re serving up only a few pages Currently compression tools aren t readily available from vendors so you ll have to roll your own if you need to conserve memory However because it makes more sense for embedded devices to supply more information about and control themselves you ll see more vendors add compression to their spec sheets
4. full blown ap plications rather they need to illustrate key aspects of a function To the vendors who argue that it would take only a few hours to develop the code to implement a function such as FTP I ask Then why don t you have one of your engineers do it Thus one key differentiation among systems is the available application li brary If the demos are insufficient for building your application you need to work the cost of learning the API and building your application from scratch both in dollars and time to market into your final decision If you re still a few months out on your project the lack of sufficient demos will probably become yo The RCM3000 evaluation kit from Rabbit Semiconductor comes with an evaluation board a connectivity module a power sup ply a compiler and other application tools a manual board specs and schematics less of a differentiating factor as slacking vendors begin to fill out their offerings Still out on the horizon even for ven dors with a fairly complete demo base is further abstracting connectivity func tions into a parameterized library for mat Templates are great but even when you tear them apart youre still working at a fairly low level Further reducing complexity to a few canned and config urable functions makes network connec tivity even more accessible Second to the breadth of the applica tion library is how well the code is doc umented and organi
5. space for USB All other things being equal if you re considering two chips and one board has a USB port available today and the other has a serial port but USB is coming choose the one with the USB port Spend the hours you ll save over the course of a project with your family instead of at your workbench For the same reason when you develop your own hardware prototype consider adding a higher speed port One problem encountered when using a board with a paral lel port stemmed from the fact that also have a printer directly connected to my computer Fortunately had a parallel port switchbox lying around so did n t have to keep unplugging cables whenever wanted to print something For those of you using network printers you ll run into a different but no less annoying issue To make the evaluation board visible over Ethernet the Getting Started manual advises you to put your computer on the subnet to which the evaluation board defaults Unfortunately doing so makes the corporate network invisible to your computer blocking your access to the net work printer as well as network services such as e mail Then again being free from e mail for a few hours might not be such a bad thing One remedy is to put a router between you and the corporate network giving the router your IP Internet Protocol identity Another is to figure out how to get the board to use DHCP Dynamic Host Con f
6. By Nicholas Cravotta Technical Editor REACHING OUT off the shelf embedded network connectivity Illustration by Federico Jorden www edn com IS IT REALLY AS EASY TO NETWORK ENABLE EMBEDDED DEVICES AS MANY VENDORS CLAIM OR YEARS you ve heard fan F tastic stories about network enabled refrigerators and toast ers stories that from my per spective have only reduced the credibility of embedding con nectivity However as the cost of connectivity continues to drop an increasing number of embed ded applications can make seri ous enough use of such technology to justify the extra expense Reference 1 For this hands on project I wanted to see for myself just how ready embedded TCP IP Transmission Control Proto col Internet Protocol is for mass de ployment Given that myriad companies offer networking chips and TCP IP stacks I chose to work with several kits to give myself multiple data points I chose kits from Connect One Cyan using a stack from CMX Rabbit Ubicom and Zilog My goal was to determine whether embedded TCP IP is truly affordable in both dollars and development time what I could expect from vendors and which processor software combination promis es to best meet the constraints of an application Quickly getting the evaluation boards up and running was critical Foremost I didn t want to spend a lot of time learn ing a system just to evaluate it Some of the te
7. as TCP IP is that any browser can query your device using a pro prietary security scheme instead of a stan dard such as IPSec Secure Internet Protocol or SSL Secure Sockets Layer defeats this capability Just remember to keep your overall goal for connectivity in mind Note that security does not come free Encryption functions can have a small foot print and low performance cost but encryp tion is not security IPSec and SSL which manage keys and sessions require a lot of code which makes them less suitable for 8 and 16 bit processors If security is important to your application you may need to consid er a 32 bit processor even if you don t need high throughput Several times was tempted to figure out how to solve a problem such as how to cre ate dynamic Web pages through some workaround of my own invention For exam ple thought of creating static pages with placeholders for dynamic information could filter for the placeholders before transmitted information and replace them with the actual data don t recommend this www edn com The eCog evaluation board from Cyan offers an LCD for easier debugging an Ethernet port requiring crossover cable code downloading over a parallel port and a prototyping area for adding your own hardware connections type of experimentation however Doing things the proper way usually pays higher dividends invariably created new problems with my clever an
8. ause I forgot which context I was working in TWO KITS ARE BETTER THAN ONE I assumed that every developer s kit had everything I was going to get noth ing else was coming to ease my job If I had problems with simple issues such as setup I got nervous about the rest of the kit However the problem was some times me I just didn t understand certain concepts the first time through If you work with only one evaluation kit you ll learn whether you like it but you won t have any idea of whether you should ex pect more Thus I strongly recommend that you look at several kits Kits cost rel atively little and the cost is effectively zero when you spread it across a high volume device You can donate the kits you don t use to a local university for a write off or sell or give them to a col league looking to expand his or her en gineering skills Using different kits worked for me in several ways For example looking at dif NOVEMBER 14 2002 EDN 55 ferent kits showed me which aspects of designing connected devices are constant across processors and which are factors of the individual ven dors For example once I understood how to post data to a Web page from the Web server with one kit doing it with the next kit was a matter of figuring out which system call to make Also the va riety of support tools and the approach TESTING THROUGHPUT One goal of your evaluation may be to veri fy a vendor s t
9. ch as how many resends the system made during your test Finally if you do find yourself closing in on the acceptable threshold of performance for your application make sure that your computer or development environment such as Windows for exam ple isn t imposing the bottleneck Run your tests from another slower or faster computer and compare results they should be equal Of course if the device serves up only 1 kbyte Web pages connection speed doesn t matter Or does it If many devices are present in a network the connection rate could matter because connection speed determines the total time it takes to connect to a device and could affect the total number of devices you can connect to in a certain time period The situation is analogous to watering a lawn You might water each zone for only 15 minutes but if you ve got 10 acres of lawn it s going to take you four days to water it all As the number of devices you have to manage scales up you must make a trade off between sending less information and checking in less often www edn com es to performing certain types of tasks are varied One of the most valuable benefits I discovered was that an issue that confused me when working with one kit became clear to me when working with another kit In this light I worked with several kits concur rently see sidebar Evaluating in tan dem and shortened my learning curve Switching among kits also enabled
10. chnical manuals that come with these kits are daunting you shouldn t have to read 300 pages just to blink an LED or serve up a Hello World page I also wanted to be able to evaluate sever al kits to increase the number of proces sors from which I could make my final se lection I wanted to take a tour of each platform quickly loading a demo appli cation making changes that would bet ter reflect the conditions of my applica tion verifying performance and getting an idea of the usefulness of the available tools As I worked with the kits I realized that the price of the processor and soft ware although important probably wasn t going to be the most important consideration in my final selection In general the vendors seemed fairly com petitive on price in the ballpark of 10 for the processor in volume quantities including the cost of the stack and de velopment tools Next I looked at per formance and code footprint which the vendors often tout as the primary con siderations for selecting a processor and stack However if you re sending limit NOVEMBER 14 2002 EDN 47 At a glance Delving into the stack 48 Paying your time tax 50 Evaluating in tandem 52 Other considerations 54 Testing throughput 56 For more information 58 Go to our Web site at wwwedn com to find additional material related to this article ed data maximum throughput is l
11. d adequate sample demo applications you should be able to strip down these applications to their basic com ponents to determine the stack calls you have to make to send or receive packets FTP File Transfer Protocol files POST and GET data and so on with out understanding what any of those calls really do Are there reasons to delve into the stack I ve heard the most popular use of stack source code is to learn TCP IP fundamentals If you don t have this burning desire then you don t necessarily need access to source code More rare rea sons Include optimizing the source code to squeeze more performance from the chip either to increase the transmis sion rate or to free up head room for application code adding protocols that the stack doesn t support implementing proprietary data schemes and integrating third party code such as security and encryption functions In some cases you can use a stub function an empty function called by the stack for example before it sends or packetizes data to implement such functions with out understanding or breaking into the stack An additional benefit of not breaking into the stack is that you need not recertify the stack code www edn com garage hobbyists so that they can t overwhelm tech support If you re a serious customer and have enough leverage there s a strong chance that the vendor will dramatically drop the price After all too many play
12. d only after complaining to vendors I discovered that code for a function was available but buried in some nondescript directory or documented only through an obscure reference I appreciate it when vendors write doc umentation assuming that the user un derstands neither the API nor the details of TCP IP Some Getting Started manu als reveal explicitly how to set up the computer and the evaluation board even Working with several kits at one time has its drawbacks Some times confused the function names Also because each ven dor uses a different directory scheme for managing the various types of files HTML Hyper Text Markup Language Java C com piled code headers and so on l sometimes forgot where should put files This lapse led to various compilation problems such as 52 EDN NOVEMBER 14 2002 using the old incorrect version of code instead of my new code Another difficulty was that each evaluation board used a different subnet requiring my computer to use a different IP Internet Protocol address If wanted to try an idea between two boards would have to change the IP address and reboot my comput er To keep my sanity created a profile for each board describing the equipment including cable type and the setting to use on the switch box if required and each IP address it used A profile serves as a checklist to ensure that you always correctly set up the board It also works for a sin
13. d untested and unneces sary workarounds If you re thinking of serving up a hefty user s manual from your device consider some of these alternatives to save on memo ry You could serve up a zip file which moves decompression from your device to the faster machine hosting the browser It also saves on bandwidth which is especially important across constrained connections such as phone lines If the computer com municating with the device has Web access you could instead send a URL to another server This option saves device memory and avoids many of the version control issues inherent in shipping the manual in flash memory If you develop a useful utility such as compressing Web pages you might consider selling it back to the vendor Vendors have limited resources for expanding and improv ing their product lines especially in today s economy yet every utility and sample appli cation gives their products a competitive edge Becoming a supplier of this nature can also give you leverage in directing the ven dor s course through its product develop ment road map Most vendors have some mechanism for accepting suggestions However instead of focusing on how useful a new feature would be for you explain to the vendor how the feature would benefit their entire customer base If you can convince the vendor that your suggestion will help a broad cross sec tion of its customer base or open new mar kets you ll stand a b
14. een as part of an optional board Some boards offer more than just an Ethernet interface including 802 11 and Bluetooth interfaces In general the TCP IP Transmission Control Protocol Internet Protocol stack should operate over any of these physical media Such operation depends on whether the vendor has written a driver for the protocol Additionally each physical layer needs drivers for the physical layer in use even the Ethernet PHYs If you 54 EDN NOVEMBER 14 2002 want to use an Ethernet PHY other than the one on the evaluation board you may have to write your own drivers or entice the vendor to do so Setting a device s IP address in the field can seem like a chicken or the egg problem How do you connect to the device to set its IP address if you don t have an IP address with which to connect to the device Devices con nected through a LAN can use DHCP Dynamic Host Configuration Protocol to obtain an IP address Remote dial in devices don t need an IP address per se but could call a toll free number to obtain a local ISP Internet service provider number and a log in ID to reduce costs For devices connected to a network without a DHCP server such as a home network you can use an elegant technique sometimes called ping gleaning Because each Ethernet MAC media access controller has a unique address you can create a utility to run ona PC that asks the user for a device s serial number the device s un
15. eferencing it with a macro the macro takes care of the rest of the work Again this differ ence isn t major but it can tell you which ven dors take ease of use seriously The cost of software can be a tricky subject Vendors consider some functions optional and give them an additional price Some pric ing includes source code Some models require upfront fees and royalties or the soft ware is free meaning that the vendor has worked it into the price of the processor Be sure to understand what your true costs will be based on your projected volumes across a product family and through a range of dis tinct product lines Support is an important part of both the evaluation and development cycles and can come in many forms For example attended one training seminar and found that could have covered the material on my own in half the time however it did give me direct access to someone who could answer my questions about embedded networks In this light recommend attending a seminar or a tutorial in which you work directly with a kit at the onset of your evaluation before you invest a lot of time learning the fundamentals the hard way Online forums dedicated to proces sors also exist It s worth checking out whether a site is user or vendor run to deter mine its agenda and whether it s a hodge podge of postings or well organized with managed FAQs Security should be on your radar screen if your device will be access
16. embedded TCP IP market has indeed reached a point at which TCP IP is an off the shelf product gt Your evaluation is based on what you see not what s actually there gt One key differentiation among current systems is the available application library gt If you work with only one evaluation kit you ll learn whether you like it but you won t have any idea whether you should expect more Connect One s iChip Internet controller TCP IP chip mediates the connection between a host device s processor and the Internet evaluation board over a serial port so I could test a PPP Point to Point Proto col connection through the phone line to an ISP Internet service provider I DELVING INTO THE STACK hands onproject Embedded network connectivity found one at a local store for the sur prising cost of 100 If you have more time to secure a modem you can prob ably find one in your garage or over the Internet for less Several companies offer a variety of boards with names such as evaluation and developer or standard and ad vanced In some cases the difference lies in software alone The evaluation kit for example might provide only binaries and a subset of the development tools Some differences lie in hardware RAM based boards unlike flash based boards lose their code image when you crash and have to power down The develop er s kit may also include an emulator for s
17. ers with solid products in this market are willing to almost give their kits away to get your business Software vendors on the oth er hand have less flexibility with evalu ations because it s not difficult to steal code and never pay royalties for it once you ve got a copy Then again if they won t let you use the code and tools you can t properly evaluate the overall devel opment environment GETTING STARTED The key to a successful and efficient evaluation is proper documentation Your evaluation is based on what you see not what s actually there More than one technical manual was actually an alpha betical catalog of function calls with no clear description of their relationship to each other After a bit of searching I usu ally found a readme doc or Getting Started manual that provided a descrip tion of how to bring the board up A Get ting Started manual is especially impor tant for evaluation boards running third party software and should be writ ten specifically for the board or chip youre evaluating The Getting Started manuals don t teach much They are enough only to get you going on the board within an hour showing you how to start the develop ment environment and build and down load a demo system My next step was to explore on my own I began by printing the demo source files in an attempt to fig ure out what the demo actually did From this foundation I was able to strip down the dem
18. ess important see sidebar Testing throughput Also if your appli cation isn t complex footprint isn t crit ical because you don t need a lot of headroom Thus my primary concern became which development environ ment could most efficiently help me de velop my application see sidebar Oth er considerations EQUIPMENT CHECKLIST As a strong believer in a positive out of the box experience when I finally made time to look at an evaluation board I wanted to begin the evalua tion not discover that I was expected to supply a critical piece of equipment that I didn t have handy For example some kits come with an Ethernet cable some don t If you re going to directly connect the evaluation board to your computer however you need a crossover cable If you connect through a hub or router you need a standard cable Using the wrong cable can set you back for a while until you figure out what you ve done One way to improve your out of the box experience is to check the kit when it arrives don t wait until the day you want to use it One advantage of evalu ating several kits is that one kit usually includes the missing part from anoth er Before you start mixing kits how ever tag each component with a stick er so that you remember which cable came from which kit One difficult to locate piece of equipment was an exter nal modem that could connect to the AT A GLANCE gt The
19. etter chance of your suggestion s making it to the top of the com pany s to do list defaulting to the last one you down loaded Granted the step was neither a major problem nor a major convenience but my guess is that if the product devel opers actually used the product they cer tainly would have coded such short cuts Another aspect that takes getting used to is the use of various languages Learn ing the difference between source files index htm and generated files index c takes some careful reading HTML and JavaScript which is not at all like Java are necessary to create Web pages for the Web server see sidebar Web page com pression on the Web version of this ar ticle at www edn com Java is necessary to create classes for passing information between the Web server and the remote monitoring browser I also needed to run C on the embedded networking proces sor to interface the hardware and the ap plication software to the Java applets And I needed a separate Java develop ment environment otherwise I d have to build and download my application and then serve up pages just to test simple changes see sidebar Paying your time tax Because these languages closely re semble each other I had to carefully change my frame of mind when I changed languages remembering the various subtleties and differences be tween them Unfortunately I still ended up stumped by the occasional frustrating error bec
20. etting breakpoints and capturing code traces In some cases the difference in price is small between the standard and the ad vanced kits In general developing code for a standard board might take some what longer than it would for an ad vanced kit given limited tools and lack of debugging hooks It might be worth the extra bucks to be able to see the entire tool suite because the tools usefulness will almost surely be a major factor in your final selection Some features such as PPP SNMP Simple Network Man agement Protocol or a real time oper ating system may be optional and re quire a separate purchase You ll also often get better tech support with an ad vanced kit Most evaluation kits cost less than 500 Some kits however come in at several thousand dollars In many cases the vendor raises the price to filter out In previous years network enabling a device required inti mate knowledge of the TCP IP Transmission Control Pro tocol Internet Protocol stack and direct system calls to manipulate and manage tt Today TCP IP is pretty much an off the shelf technology mean ing that you can link to the library make a few calls and have connectivity Unless you stumble across some weird cor ner case of TCP IP or stress the stack in an unanticipated way 48 EDN NOVEMBER 14 2002 you probably won t have to actually know anything about TCP IP to get results Additionally if the vendor has provide
21. heoretical maximum through put claims In general the board itself shouldn t impose bottlenecks on your throughput tests you might need to worry about this situation with higher speed con nections but if you re evaluating an 8 or a 56 EDN NOVEMBER 14 2002 hands onproject Embedded network connectivity 16 bit embedded networking processor what you see is what you get You need to be thorough however For example the vendor may have preconfigured the board to run at a reduced clock rate to conserve power When verifying throughput it s impor tant to profile the throughput based on the type of traffic you expect to see under real world operation Also sending a stream of small packets will give you an idea of the aggregate overhead associated with each packet A stream of long packets will minimize overhead giving you a bet ter idea of the true maximum data rate you can achieve Try tearing down the connection between each packet to determine how long it takes to open and close a session an important factor for devices that will manage many other connected devices Also be sure to test FTP File Transfer Protocol function to see how the stack handles large file transfers this figure is useful for profiling large data dumps in either direction Sending set or pseudoran dom patterns allows you to verify the accuracy of the connection You may also want to determine how to access performance statistics su
22. ible across the Internet or a public network Though you may not require security this year your customers may require it of you when they panic after a www edn com ple from the development environments Thad to run batch files in a DOS window manage my files outside the environ ment or run utilities either from a DOS window or a build batch file of my cre ation Vendors could have made some of these steps more transparent allowing the tools to launch a utility from the en vironment or to automatically create and manage build files It was also difficult or annoying to complete certain simple and regular tasks For example one environ ment expects you to select the file you want to download every time instead of high profile embedded hack At worst you should understand your various options for implementing security If the vendor doesn t have a straightforward demo or template you may want to spend time determining just how complex it will be to later add secu rity to properly implement security you ll more than likely need to break open the TCP IP stack One option is to create your own security scheme which is probably suffi cient if you re talking about a consumer device such as a camera which isn t worth hacking But creating your own scheme has questionable value for an application such as a utility meter whose security is worth com promising for financial reasons One reason to use a standard such
23. idea In the end I was able to make a better final evaluation of each processor I not only had more ex perience with what I could expect from a processor but also more options to choose from REFERENCE 1 Cravotta Nicholas Managing In ternet enabled devices EDN Sept 20 2001 pg 48 ACKNOWLEDGMENT Many people at each of the companies mentioned in this article too many to name here offered their assistance with this article I thank them warmly AUTHOR S BIOGRAPHY Technical Editor Nicholas Cravotta hopes to connect an entire house for his next hands on project You can reach him at 1 530 346 8556 fax 1 530 346 9777 or nick edn com www edn com WEB PAGE COMPRESSION A common characteristic of embedded applications is scarci ty of memory It may not seem obvious but because a Web server does not display pages it does not need to support a JVM Java Virtual Machine or the 1 Mbyte of memory that a JVM requires Depending upon how much information you want to be able to serve you might have an extensive user s manual stored on the device memory can get tight Because you need to store static pages In non volatile memory whether you have to worry about compres sion is a function of how close you come to overflowing the available memory before you have to go to the next size However the application itself may require enough memory that the relative size of
24. iguration Protocol to obtain a dynamic IP address from your router The most efficient method found was to change the board s fixed IP address to one that matched my computer s IP sub net In some cases a macro or a constant was clearly labeled in the demo program In many demos however the fixed IP address was buried and little documentation was available to help me find it For my money setting the fixed IP address of an evaluation board to one of my preference should be a standard part of the getting started process www edn com hands onproject complete range of sample ap plications were easier to learn and use and offered a more competitive edge From this perspective the em bedded TCP IP market has in deed reached a point at which TCP IP is off the shelf meaning that you can buy everything nec essary to embed connectivity into a device Given the maturity and low cost of stacks you no longer need to develop your own stack You can use a well defined API to access it However the market is now racing to also bring the de velopment tools and environ ments up to off the shelf stan dards moving from requiring you to learn a complex API to letting you work with templates that il lustrate how the API works A proper collection of applications enabled me to create templates to learn how to use functions and to use as foundations that I could drop into my own applica tion Demos needn t be
25. ique MAC address and then pings that MAC address with an IP address The device can then use that IP address as its own Ping gleaning is an exam ple of a function that a vendor may support directly through its API application program ming interface but hasn t necessarily docu mented if you don t know to ask about it you might never discover its usefulness Minor differences among vendor products can make development that much easier For example most platforms first convert HTML files to C files With this method each time you add a page to your device you must manually add the file name to the build file insert it into your project and add external references in your application code With so many steps you re bound to make a mistake The challenge became finding out the IP address because you can t use the mail isp net format that desktops employ You could call your ISP although it s probably easier to send an e mail to your self and use a packet sniffer to track the message Additionally if you work in a corporate office getting a live phone line that you can use as a modem can be chal lenging the system tied to your current phone line may not support modems Some development tools are difficult to use because they mix Windows and command line environments For exam every now and then and lose time trying to figure out what you missed At least one plat form allows you to add a Web page just by r
26. me to continue my evaluation on other boards while I waited for tech support to solve a problem that had brought evaluation on one board to a standstill A key facet of evaluation is that it takes much less time to work on the third and fourth kits than it does on the first two While evaluating the first two kits I 58 EDN NOVEMBER 14 2002 hands onproject Embedded network connectivity FOR MORE INFORMATION For more information on products such as those discussed in this article go to www edn com info and enter the reader service number When you contact any of the following manufacturers direct ly please let them know you read about their products in EDN CMX Systems Inc Rabbit 1 904 880 1840 Semiconductor Wwww cmx com 1 530 757 8400 Enter No 344 www rabbit semiconductor com Connect One Enter No 347 1 408 986 9602 www connectone com Ubicom Enter No 345 1 650 210 1500 www ubicom com Cyan Technology Enter No 348 Ltd 1 781 246 4646 Zilog www cyantechnology 1 408 558 8500 com www zilog com Enter No 346 Enter No 349 SUPER INFO NUMBER For more information on the products available from all of the vendors listed in this box enter no 350 at www edn com info struggled with learning how to use cer tain aspects of TCP IP my learning curve with subsequent kits was significantly shorter My questions evolved from How do I do this to How does this vendor implement this
27. o code to bare bones creating a template for developing my own appli cation and understanding how to per form basic connectivity tasks For me the most important part of documentation was the sample applica tions Again I didn t want to have to learn the entire API for the TCP IP stack just to serve up a test page see sidebar Delv ing into the stack I learn better when I m tearing apart a working example than when I m mulling over an explanation in a manual Some demos are excellent One shows the status of DIP switches on the board It provides a simple example without a lot of confusing bells and whistles of how to send a few bits of data dynamically to PAYING YOUR TIME TAX hands onproject Embedded network connectivity a Java applet I ran into trouble howev er when I tried to send a different data type from the one in the demo Because had not yet learned the specifics of Java I had to take a detour to the library and the Web to find a Java primer Then I dis covered that knowing Java doesn t tell you everything you have to use CGI Common Gateway Interface pro grams in other words C code to ex change information with the Java ap plets Unraveling this interconnected scheme took me longer than I wanted it to A second and third demo that sent dif ferent types of information or even one page that sent three data types would have been helpful so I could learn the differences in the func
28. tions Unfortunately the range of demos that each kit includes varies and some lack completeness For example in one kit I could find neither a demo of FTP File Transfer Protocol which is a fair ly fundamental network operation nor a demo of sending e mail Kits com monly demonstrated how to send static pages but failed to show how to create or send dynamic pages Without a demo application I had to resort to the 300 pg manual to continue my evaluation Thus I found that the kits with the more It may seem like a minor Issue but your choice of interface from your PC to the evaluation board plays a significant role in deter mining your productivity during development This port transfers your program and Web pages to the evaluation board The most commonly used port is serial Robust dependable and ubiqui tous the serial port is also the slowest of interfaces As project complexity increases downloads take longer There s not much you can do in the two minutes it takes to download code except per haps read a few paragraphs of an EDN article The situation starts to feel like a Vegas poker game in which the dealer shucks away a few dollars with every deal every time you download you lose another two minutes and those minutes quickly add up 50 EDN NOVEMBER 14 2002 Preferred interfaces are paral lel or USB connections which reduce your downloading time At least one board evaluated had an unpopulated
29. zed Even within a single demo the documentation often lacks consistency Often an editor such as Microsoft Front Page generates the HTML Hyper Text Markup Language documents resulting in code without sufficient comments that is not format ted to read when you print it Despite the EVALUATING IN TANDEM fact that Java and C are similar the Java class code and C code of ten used different commenting conventions Some code has a full page of comments describing what it is doing the variables it uses and the methods into and out of the function The other code within the same demo has comments that seem like an af terthought and offer little guid ance to understanding how the code works Some vendors cram all the rel evant demo files into a single di rectory Other vendors scatter the code throughout several directo ries making it more difficult to locate files or even understand which files are in use for a demo A proper project manager lists all sources files and their dependen cies with one click access to each In sev eral cases I had to break open build files to locate code modules Connectivity ap plications are written in several lan guages and if the flow of code isn t doc umented it s not always clear which role a function plays and thus which lan guage it should be written in One fea ture I missed in too many instances was a simple list and description of sample code More than once an
Download Pdf Manuals
Related Search