Small Form Factor Pcs
Contents
1. null respawn usr bin rfcomm to sign dev rfcomm4 dev ttyS2 null respawn usr bin rfcomm to sign dev rfcomm5 dev ttyS2 As usual execute init q to have init start these processes without rebooting Note that rfcomm to sign uses syslogd for most errors and debugging Check var log messages for errors and notifications the first few times you run the program Also keep in mind that var log messages is on a memory filesystem and is lost each time you reboot If you have problems run the program from a shell window and see what happens when you send a message to the Figure 9 12 Mounting the gumstix to sign through Bluetooth the back of the Pro Lite sign Small Form Factor PCs Buy the full book online makezine com sff 22 Chapter 9 Bluetooth LED Sign Mounting the gumstix on the Sign Most likely you ll want to put the sign up on display for others to see If so you can take a few minutes and attach the gumstix to the back of the sign as shown in Figure 9 12 With a few sticky pads and cable ties you can hide everything including the serial cable You ll probably want to leave the Bluetooth antenna sticking up or down a little bit for better reception Sending Messages to the Sign Finally we have everything in place to send a message to the sign from a Bluetooth enabled device This section describes a few ways to do just that From PalmOS If you have a Palm PDA or a phone that runs PalmOS you can in2. both of these with one command W aoun fost a G A desktop stty echo cread lt dev bluetooth rfcomm 1 Bar bar bar PEFS 5 Sign Page 2 Sign Page 3 Sign Page 4 Fortunately the stty settings are sticky so you should only need to set them once before using an RFCOMM device F Now if you want to interactively write messages to the sign simply run Feme 7 Faes 08 Tota 0 Folders desktop cat gt dev bluetooth rfcomm 3 Figure 9 18 Browsing Bluetooth services Small Form Factor PCs Buy the full book online makezine com sff 24 Chapter 9 Bluetooth LED Sign Then type your messages one line at a time The RFCOMM connection stays up as long as cat stays running You can type y gt Hp 8 like b a h 8 7P Bluetooth Serial Chat as many messages as you ike but with our one page per connected to 00 80 37 1C 3A FF on channel 4 RFCOMM device design each additional message overwrites the ready gt previous one Generating messages using echo from a shell script is a little trickier The problem is that the RFCOMM device must stay open long enough for the gumstix to open the RFCOMM device on its side and then read from it This command for example probably won t work Please bring me a pizza desktop echo this does not work gt dev bluetooth rfcomm 2 I Figure 9 19 KDE Bluetooth chat The reason is that the device gets closed right after the
3. 809898 bytes loaded to 0xa2000000 Booting image at a2000000 Image Name uImage 4 Image Type ARM Linux Kernel Image gzip compressed Figure 9 7 The Bluetooth antenna Data Size 809834 Bytes 790 9 kB installed Load Address a0008000 Entry Point a0008000 Verifying Checksum OK Uncompressing Kernel Image OK Starting kernel Small Form Factor PCs Buy the full book online makezine com sff 5 Chapter 9 Bluetooth LED Sign Then you ll see a more or less typical Linux kernel boot sequence At the end is a login prompt Welcome to the Gumstix Linux Distribution gumstix login Enter root at the login prompt and gumstix for the password Then you should have a no frills shell prompt from which you can run commands such as ps ls and df Note that most of these commands are a part of the BusyBox collection which we also talked about in Chapter 6 Take some time to explore the system and find out what s there and what s not For example the gumstix has vi but not less It has an SSH server Dropbear and an HTTP server Boa It has ifconfig ping and other networking utilities but no true Ethernet interfaces Be sure to take a moment to marvel at how much functionality the gumstix has on its tiny 4MB filesystem df h Filesystem Size Used Available Use Mounted on dev mtdblock2 3 8M 3 4M 388 0k 90 Customizing the System Admittedly there is not much to customize but you might want to e Chan
4. as a vCard If you plan to use this technique to get messages to the LED sign you ll need to write some code to strip out the vCard tags and other formatting Small Form Factor PCs Buy the full book online makezine com sff 31 Chapter 9 Bluetooth LED Sign If you re having a hard time getting OBEX to work kill the opd daemon process and run it from the command line You should see output like this during a successful transfer obex_event 1 6 EV_UNKNOWN O CMD CONNECT 0 Unknown event 6 obex_event 1 1 EV_REQHINT O CMD_CONNECT 0 obex_event 1 2 EV_REQ O CMD CONNECT 0 opd 338 OBEX connect from 00 07 E0 00 1F F8 obex_event 1 3 EV_REQDONE O CMD_CONNECT 0 obex_event 1 1 EV_REQHINT 2 CMD PUT 0 obex_event 1 O EV_PROGRESS 2 CMD PUT 0 obex_event 1 O EV_PROGRESS 2 CMD PUT 0 obex_event 1 2 EV_REQ 2 CMD PUT 0 HEADER_LENGTH 15 Handle OBEX_CMD_PUT Skipped header 05 HEADER _TYPE text plain 11 00 74 65 78 74 2f 70 6c 61 69 6e 00 text plain Handle OBEX_CMD_ PUT Skipped header c0 Filename tmp obex memo via txt Wrote tmp obex memo via txt 15 bytes obex_event 1 3 EV_REQDONE 2 CMD PUT 0 obex_event 1 1 EV_REQHINT 1 CMD DISCONNECT 0 obex_event 1 2 EV_REQ 1 CMD DISCONNECT 0 opd 338 OBEX disconnect from 00 07 E0 00 1F F8 obex_event 1 3 EV_REQDONE 1 CMD DISCONNECT 0 obex_event 1 4 EV_LINKERR O CMD CONNECT 0 opd 338 lost link to 00 07 E0 00 1F F8 O
5. s gt s lt FZ gt lt s gt page buf nextpage write sign str fd newbuf free newbuf return 0 void validate_page char page if strlen page gt 1 page lt A page gt Z errx 1 Page should be a single character A Z int main int argc char argv int rfcomm char buf NULL char rfcomm_dev NULL char sign_ dev NULL char page NULL char nextpage NULL if argc 5 fprintf stderr usage rfcomm to sign rfcommdev signdev page nextpage n exit 1 openlog rfcomm to sign 0 LOG DAEMON rfcomm_dev argv 1 sign_dev argv 2 page argv 3 nextpage argv 4 validate_page page validate_page nextpage rfcomm open_rfcomm rfcomm_dev for 33 int len int lock int sign write rfcomm ready gt r n 7 if len read_rfcomm rfcomm amp buf lt 0 break lock get_sign_lock sign open_sign sign dev Small Form Factor PCs Buy the full book online makezine com sff 21 Chapter 9 Bluetooth LED Sign write_message sign buf len page nextpage close sign close lock return 0 Here s how rfcomm to sign works It takes four command line arguments an RFCOMM device pathname the serial port pathname for the sign and two sign page names A Z The first page refers to where the message will be stored while the second will be the name of the page to display after this one The program begins
6. the antenna Either we ordered the wrong one or they only offered it after we bought ours Since the case is made of plastic it is easy to cut out a notch We marked the top of the case with two lines on each side of the antenna and used a small coping saw to cut out the notch as shown in Figure 9 6 The result is shown in Figure 9 7 Figure 9 5 We need to cut a notch in the Explori n g the gu m sti X waysmall case for the Bluetooth antenna To start playing with the gumstix connect the serial port cable between the gumstix and your PC and use a terminal program such as kermit screen or HyperTerminal to set up a serial console and then apply power In Figure 9 8 you see a pair of round mini din connectors which are serial ports The one that is closest to the center is ttyS0 or the console port The other one is ttyS2 The gumstix serial port is configured for 115 200 bps and 8N1 The power connector is located on the side of the case As soon as you apply power you should see the following output on the console U Boot 1 1 1 Oct 3 2004 18 38 12 Figure 9 6 Cutting the case with a Welcome to Gumstix coping saw U Boot code A3F00000 gt A3F1B01C BSS gt A3F4CB54 RAM Configuration Bank 0 a0000000 64 MB erase_region_count 32 erase_region size 131072 Flash 4 MB Hit any key to stop autoboot 0 JFFS2 loading boot uImage to 0xa2000000 Scanning JFFS2 FS done JFFS2 load complete
7. the gumstix flash Although that procedure is overkill if you have just one or two files to copy we ll describe it anyway in case you want to upgrade all of the gumstix software later These instructions for installing a new filesystem image come from the gumstix org web site Be sure to check there occasionally for more recent instructions Small Form Factor PCs Buy the full book online makezine com sff Chapter 9 Bluetooth LED Sign The gumstix boot monitor called u boot supports uploading new file system images with the Kermit transfer protocol We ll use the Kermit terminal emulation program on Linux to do this kermit C Kermit 8 0 209 17 Mar 2003 for Linux Copyright C 1985 2003 Trustees of Columbia University in the City of New York Type or HELP for help C Kermit gt set port dev tts 0 C Kermit gt set speed 115200 dev tts 0 115200 bps C Kermit gt set carrier watch off C Kermit gt connect Connecting to dev tts 0 speed 115200 Power up your gumstix and interrupt the boot procedure by pressing any key within three seconds U Boot 1 1 1 Oct 3 2004 18 38 12 Welcome to Gumstix U Boot code A3F00000 gt A3F1B01C BSS gt A3F4CB54 RAM Configuration Bank 0 a0000000 64 MB erase region count 32 erase region size 131072 Flash 4 MB Hit any key to stop autoboot 0 GUM gt From here issue the following command to tell the gumstix you are uploading a file GUM gt loadb a200
8. the prompt from rfcomm to sign writes the message and then waits for the next prompt We also added the necessary stty settings for good measure Here s how you would use it desktop date ledsign sh 4 One drawback to the second version is that it might get stuck on one of the read prompt calls Since there is no timeout the script will block until interrupted If you are sending messages to the sign automatically versus interactively you may want to use the sleep approach instead Pro Lite Control Protocol As we mentioned earlier you can use different colors fonts and effects with the Pro Lite sign by inserting special codes in your message For example to display a message in red you could send lt CB gt 50 Off Today Only The following tables show the control codes for the sign s colors fonts effects and a few miscellaneous things Colors Table 9 1 lists the 26 color codes supported by the Pro Lite sign Note that the sign really only has five colors red orange yellow lime and green The yellow and lime colors are almost the same One of the colors called Rainbow uses all five colors at once In addition to the five colors the sign also has three different brightness levels Some of the color codes use shadows and different background colors as well Some of these look okay and some look hideous You should try them out for yourself to see which ones you like Table 9 1 The Pro Lite s color
9. until we explicitly add them The syntax is gumstix usr bin sdptool add channel 2 SP Note that SP refers to Bluetooth s Serial Port profile It is essentially a virtual serial port running over the Bluetooth connection You may have noticed that the gumstix advertises an SP on RFCOMM channel 1 by default This channel is used by getty so we can log in to the gumstix over Bluetooth We think it is a good idea to leave getty running but you probably don t want it announced by SDP because as we ll see later certain Bluetooth applications will try connecting to the first SP channel they find They should connect to the LED sign process rather than getty So we need to delete this channel from the SDP configuration We recommend adding the following lines to etc init d S31bluetooth delete the entry for channel 1 which connects to our getty assume its id is always 0x10000 usr bin sdptool del 0x10000 usr bin sdptool add channel 2 SP usr bin sdptool add channel 3 SP usr bin sdptool add channel 4 SP usr bin sdptool add channel 5 SP usr bin sdptool add channel 6 SP If you want to get really fancy you can also use sdptool to add descriptions for each SP channel usr bin sdptool setattr 0x010001 0x100 LED Sign Chan 1 usr bin sdptool setattr 0x010002 0x100 LED Sign Chan 2 usr bin sdptool setattr 0x010003 0x100 LED Sign Chan 3 usr bin sdptool setattr 0x010004 0x100 LED Sign Chan 4 usr bin sdptool s
10. 0000 Then escape back to the Kermit prompt by typing Control C or whatever it told you the escape sequence is At the Kermit prompt issue the following commands to send the file C Kermit gt robust C Kermit gt send tmp root_fs_arm_nofpu Kermit displays the upload progress which should take a few minutes When it s done you ll see the C Kermit prompt again Connect back to the serial port and you ll see a status message from the gumstix about the upload C Kermit gt connect Connecting to dev tts 0 speed 115200 Escape character Ctrl ASCII 28 FS enabled Type the escape character followed by C to get back or followed by to see other options Total Size 0x003b2da4 3878308 Bytes Start Addr 0xA2000000 Small Form Factor PCs Buy the full book online makezine com sff Chapter 9 Bluetooth LED Sign Then issue the following commands to install the new filesystem image on the gumstix flash Note if you have a 16 MB xm model use era 1 2 127 instead GUM gt echo filesize 3B2DA4 GUM gt era 1 2 31 Erase Flash Sectors 2 31 in Bank 1 oae E a EEE sea done GUM gt cp b a2000000 40000 filesize Copy to Flash done GUM gt When it s done reboot the gumstix GUM gt reset resetting U Boot 1 1 1 Oct 3 2004 18 38 12 Welcome to Gumstix U Boot code A3F00000 gt A3F1B01C BSS gt A3F4CB54 RAM Configuration Bank 0 a0000000 64 MB erase region count 32
11. Bluetooth uses a Universal Asynchronous Receiver Transmitter UART which is essentially a serial port hciattach is the program that attaches the Bluetooth device to the UART HCIATTACH SPEED is the speed at which these two devices should communicate The default setting of 921600 is too high especially for our 200 MHz model gumstix By lowering this setting all of our Bluetooth communications problems disappeared These speed problems may have been fixed in the recent gumstix software releases However since this application does not require high speed communication we still recommend the 230400 setting The hcid daemon manages local Bluetooth devices and responds to certain Bluetooth queries It has a configuration file named etc bluetooth hcid conf This configuration file is where you ll set the security policy and other param eters such as the device name Here is our hcid conf HCId options options autoinit yes security none pairing none Default settings for HCI devices device name LED sign class 0x820116 iscan enable pscan enable lm master accept lp rswitch hold sniff park Small Form Factor PCs Buy the full book online makezine com sff 11 Chapter 9 Bluetooth LED Sign The security none line means that other Bluetooth devices can connect without establishing a trust relationship first If you set it to auto instead you ll need to place a numeric password in etc bluetooth pin and give
12. Color Il RJ11 plug RJ11 plug crimper PC running Linux with GCC installed Bluetooth enabled PC phone or PDA Chapter 9 Bluetooth LED Sign If you just want to control the sign from a computer you don t really need the gumstix All you need is a serial port and some code However using Bluetooth opens up more possibilities such as sending messages from PDAs and mobiles phones and easily allowing more than one person or computer to display a message The inspiration for this project goes back to a Linux Journal article pub lished in 1999 in Issue 62 http www linuxjournal com article 2823 The author of that article Walt Stoneburner also maintains a number of web pages about various LED signs http wls wwco com ledsigns Walt s origi nal work was done with the Pro Lite PL M2014R sign with which he seems to have a love hate relationship He also mentions BetaBrite signs as another inexpensive alternative In fact both Pro Lite and BetaBrite appear to use the same communication protocol We decided to use a Pro Lite sign also largely because someone has written a Perl module that implements the control protocol We purchased a Pro Lite sign through eBay not really knowing if it would work with this module In fact it works very well It turned out to be a PL M2014RV6 which is printed only on the back of the sign Neither the user manual nor box gives any hint as to the model number of the sign This leads us to be
13. PROJECTS SMALL FORM FACTOR BUILD A COMPUTER THAT FITS INSIDE ANYTHING Matthew Weaver Duane Wessels O REILLY Time 3 4 days Difficulty difficult In this chapter we ll show you how to use a gumstix waysmall computer to control an LED moving sign These are the signs that you see displaying scrolling messages in bars restaurants airports and so on The sign we re using has a serial port and a relatively open control protocol The waysmall computer has two serial ports and a Bluetooth interface It receives messages for the sign via Bluetooth and then issues appropriate formatting and control commands over a serial port to the sign If you re having a hard time seeing why we think this is a cool project here are some ideas e Use it ina NOC environment to know when critical systems or services go down e Build your own news or stock ticker e Display text messages received from IM or IRC e Allow people to entertain themselves by posting messages from their mobile phones Display the artist and title of a song being played on your digital jukebox e Remind you when the next bus or train is coming Buy the full book online makezine com sff Gumstix basix platform board with Bluetooth Gumstix waysmall STUART expansion board Multi Media Card optional 2 Mini DIN 8 to DB9 null modem serial cables Scrolling LED sign with serial port such as Pro Lite Tru
14. TARGETS bluez utils openobex If you changed the Makefile build a new root filesystem and upload it to the gumstix flash memory Recall that by updating the flash memory any files that you have added or edited will be lost If you have an MMC or SD card you may want to make a copy of these files before updating the flash memory etc default bluetooth etc bluetooth hosts etc bluetooth hcid conf etclinit d S60ttyS2 etc inittab etc init d S31bluetooth Small Form Factor PCs Buy the full book online makezine com sff OBEX Versus SP If you have the option to use either OBEX or SP you may prefer to use OBEX for long or repeated messages You can save a long message as a note or memo and then send it many times SP mode on the other hand is better for usage that resembles a con versation Once the serial port session has been established you can quickly send multiple messages 30 Chapter 9 Bluetooth LED Sign You ll need to make an important change to etc bluetooth hcid conf One of the settings there is the device class Bit 20 0x100000 hex in the class value should be turned on to indicate OBEX support The default value is 0x820116 so you can change it to 0x920116 Local device class class 0x920116 Reboot or restart the Bluetooth daemons after editing hcid conf Then after verifying that opd is installed add these lines to etc init d S31bluetooth test d tmp obex mkdir tmp obex usr sb
15. by opening the RFCOMM device The open call will fail until another device establishes a connection on the correspond ing channel so the program loops until the open call succeeds Then it reads characters from the RFCOMM device When it reads an end of line character it writes the message to the sign Since the sign serial port may be shared by numerous processes i e other RFCOMM channels the program uses file locking to make sure that it has exclusive access to the serial port while writing Note that you can t compile source code on the gumstix itself You ll need to cross compile it on another Linux box using buildroot tools described in Building Software for the gumstix earlier in this chapter Assuming the source code file is named rfcomm to sign c you can compile it like this adjusting the pathnames as necessary desktop XGCC some where gumstix buildroot build_arm_nofpu staging_ dir bin arm 1linux uclibc gcc desktop XGCC Wall o rfcomm to sign rfcomm to sign c Copy the binary to the gumstix using Zmodem Kermit or with the MMC card You need to run the program for every RFCOMM channel that you want to use Assuming you ve saved the binary as usr bin rfcomm to sign add these lines to etc inittab null respawn usr bin rfcomm to sign dev rfcomm1 dev ttyS2 A B null respawn usr bin rfcomm to sign dev rfcomm2 dev ttyS2 B C null respawn usr bin rfcomm to sign dev rfcomm3 dev ttyS2 C D DE EA
16. codes Code Color lt CA gt Dim red lt CB gt Red lt CC gt Bright red lt CD gt Orange lt CE gt Bright orange lt CF gt Light yellow lt CG gt Yellow lt CH gt Bright yellow lt CI gt Lime lt CJ gt Dim lime lt CK gt Bright lime Small Form Factor PCs Buy the full book online makezine com sff 26 Chapter 9 Bluetooth LED Sign Code Color lt CL gt Bright green lt CM gt Green lt CN gt Dim green lt CO gt Yellow green red lt CP gt Rainbow lt CQ gt Red green 3 D lt CR gt Red yellow 3 D lt CS gt Green red 3 D lt CT gt Green yellow 3 D lt CU gt Green on red lt CV gt Red on green lt CW gt Orange on green lt CX gt Lime on red lt CY gt Green on red 3 D lt CZ gt Red on green 3 D Fonts Table 9 2 lists the Pro Lite s font codes Note that these all start with the letter S probably because the Pro Lite documentation also refers to these as size codes The font choices are pretty simple normal bold italic and bold plus italic Any of those can be made to flash as well for a total of 8 font codes The bold font looks okay but italic is a little too hard to read The bold plus italic font displays about half as many characters on the sign as the normal font Table 9 2 The Pro Lite s font codes Code Font lt SA gt Normal lt SB gt Bold lt SC gt Italic lt SD gt Bold italic lt SE gt Flashing normal lt SF gt Flashi
17. cr cat T gt dev null amp date lt T Y m d u H M S0 gt gt T kill 1 Small Form Factor PCs Buy the full book online makezine com sff 29 Chapter 9 Bluetooth LED Sign Extra Credit If you ve followed all the steps in this chapter you have a pretty neat Bluetooth enabled Linux powered LED sign Here are some ideas for mak ing the project even better Using OBEX Transfers We ve shown you how to transfer data from a handheld device to the gum stix using Bluetooth s serial port emulation While this seems to work okay it is not the only option If your phone PDA doesn t have an application that supports the Bluetooth serial port SP profile you can use the Object Exchange OBEX protocol instead OBEX is essentially a file transfer protocol Bluetooth devices use OBEX to send images vCards i e address book entries calendar data and other types of files OBEX was originally developed for use with infrared IrDA interfaces but has been adopted by Bluetooth as well Your gumstix should already have everything you need to accept files via OBEX In particular make sure that the OBEX Push Daemon usr sbin opd is present If not you ll need to go to the gumstix buildroot environment as described in Building Software for the gumstix earlier in this chapter and build a new filesystem Make sure that openobex has been added to the TARGETS variable in the top level Makefile For Bluetooth
18. ct Miscellaneous Table 9 4 lists a few miscellaneous protocol commands We use the first one lt Px gt in rfcomm to sign c to program each page The second one lt RPx gt instructs the sign to run or display the specified page immediately Table 9 4 Miscellaneous protocol commands Code Description lt Px gt Program page x lt RPx gt Run display page x lt TYYYYMMDDWhhmms sX gt Set the time The code for setting the time is a little bit different than the others Most of the commands must be preceded by a sign identifier such as lt ID01 gt The time setting command however must not That means that you can t use rfcomm to sign to set the time since the program inserts the ID string before each command In the command string given in Table 9 4 the T represents an actual T for time All other letters must be replaced by numbers YYYYMMDD represents the year month and day W represents the day of the week 1 7 hhmmss represents the hour minute and seconds X is either 0 for AM PM mode or 1 for 24 hour mode Make sure that the gumstix clock is set correctly before using the following commands to set the sign s clock We ve noticed that the gumstix clock is reset when it reboots Since you can t use rfcomm to sign to set the clock you can use this trick instead T dev ttyS2 stty F T speed 9600 cs8 parenb cstopb cread clocal crtscts ignpar echo nl1 cr3 opost ocrnl onl
19. devices at once However each device can use multiple RRCOMM channels and some devices may be The drawback is that each page requires two processes running from etc disconnected when idle inittab the rfcomm listen process and rfcomm to sign At some point this may become a significant burden for the lil gumstix Our design has a one to one mapping of RFCOMM channels to sign pages Although our examples use only five channels and pages you could easily extend this to all 26 of the Pro Lite s pages One way to reduce the number of processes is by modifying rfcomm to sign so that a single process manages all channels and pages This makes the program more complicated since it will need to use nonblocking I O and select On the upside however a single process makes certain sign related tasks easier For example you can chain pages together based on the number of active messages or change the order in which they are displayed Small Form Factor PCs Buy the full book online makezine com sff 34 Chapter 9 Bluetooth LED Sign With a single rfcomm to sign process you can also do away with the one channel per page limitation Instead messages might be displayed in the order they are received regardless of who sends them You can in theory have up to 60 RFCOMM channels However since each channel requires a separate rfcomm listen process this may not be realistic If you really need that many you ll probably want have a
20. en you can use the infrared remote control However for our purposes we ll need to use the sign s serial port to send instructions from the gumstix The Serial Port The Pro Lite sign should come with a serial cable It has a DB9 connector on one end and an RJ11 plug on the other The gumstix uses a round 8 pin Mini DIN connector so this cable won t work You might be able to find a DB9 to Mini DIN 8 adapter but we Receive Ground Transmit Rw nN gt think it s not too difficult to make a custom cable One easy way Mini DIN 8 plug RT plug is to buy a pre made cable with the Mini DIN connector then cut off the other end and crimp an RJ11 plug in its place Figure 9 11 Diagram of the serial cable between gumstix and the sign The serial cable needs only three wires receive data transmit data and signal ground On the mini din connector these are pins 3 Transmit 4 Ground and 5 Receive These should be connected to pins 1 2 and 3 of the RJ11 plug as shown in Figure 9 11 Note that we re assuming the RJ11 plug has 4 pins such that 2 and 3 are in the center but some might actually have 6 If you have a 6 pin plug then add one to the RJ11 pin assignments The PL M2014R s serial port defaults to 9 600 bps which is the highest speed that it supports Using the gumstix s second serial port on the waysmall STUART board requires a little bit of
21. erase region size 131072 Flash 4 MB Hit any key to stop autoboot 0 JFFS2 loading boot uImage to 0xa2000000 Scanning JFFS2 FS done JFFS2 load complete 710820 bytes loaded to 0xa2000000 Booting image at a2000000 Image Name ulmage Image Type ARM Linux Kernel Image uncompressed Data Size 710756 Bytes 694 1 kB Load Address a0008000 Entry Point a0008000 Verifying Checksum OK Learning About Bluetooth One of the most exciting things about the gumstix is its built in Bluetooth interface Bluetooth is sometimes called Personal Area Networking which is to say that it has a range of about 10 feet One of the most common uses for Bluetooth today is for mobile phone headsets and synchronizing PDAs Bluetooth devices support a number of profiles designed to facilitate interoperation For example there s a headset profile a fax profile a serial port profile a file transfer profile and many more We ll be using the Serial Port SP profile which creates a virtual serial port over a Bluetooth connection Small Form Factor PCs Buy the full book online makezine com sff Chapter 9 Bluetooth LED Sign The gumstix boots with Bluetooth enabled so we don t need to worry about configuring the kernel or drivers For example you should see something like this when the kernel boots Bluetooth Core ver 2 7 NET Registered protocol family 31 Bluetooth HCI device and connection manager i
22. etattr 0x010005 0x100 LED Sign Chan 5 Small Form Factor PCs Buy the full book online makezine com sff 18 Chapter 9 Bluetooth LED Sign Getting Messages from Bluetooth to the Sign The next step in our little project is to write some code that reads messages from the RFCOMM devices adds some formatting instructions and then writes them to the Pro Lite sign Example 9 1 shows one way to accomplish this in C We call this program rfcomm to sign Example 9 1 The rfcommm to sign c program include lt stdio h gt include lt unistd h gt include lt stdlib h gt include lt string h gt include lt fcntl h gt include lt err h gt include lt assert h gt include lt termios h gt include lt syslog h gt include lt errno h gt include lt sys file h gt define INPUT BUF_LEN 1024 define LOCK_PATH tmp sign 1ck int get_sign_lock void int fd open LOCK PATH 0 RDONLY O CREAT if fd lt 0 err 1 LOCK_PATH if flock fd LOCK EX lt 0 err 1 LOCK_PATH return fd int open_sign char dev struct termios T int fd open dev O_RDWR if fd lt 0 err 1 dev syslog LOG DEBUG sign opened if tcgetattr fd amp T lt 0 err 1 tcgetattr cfsetspeed amp T B9600 T c_cflag CS8 CREAD CLOCAL T c_iflag 0 T c_oflag 0 T c_lflag 0 T c_cc VMIN 0 T c_cc VTIME 0 if tcsetattr fd TCSANOW amp T lt 0 err 1 tcgetattr
23. ge the root password e Add a non root user Change the hostname via etc hostname Change the time zone via etc TZ In the next section we ll show you how to add software packages to the gumstix Building Software for the gumstix The gumstix folks provide a nifty buildroot environment This is a direc tory structure that you can copy to an existing Linux box It provides a cross compiler so you can build new binaries for the gumstix You ll need the cross compiler later when we write some code for sending messages to the sign Small Form Factor PCs Buy the full book online makezine com sff Figure 9 8 Connecting the waysmall computer to a laptop You can get Ethernet on other gumstix expansion boards just not on the one we are using waysmall STUART Chapter 9 Bluetooth LED Sign The buildroot environment is available through a Subversion source code control server To get it you first need to install a Subversion client on your other Linux box For example to install the Subversion client on Gentoo try this USE berkdb emerge av subversion With Subversion installed use this command to check out the gumstix buildroot environment svn co http svn gumstix com gumstix buildroot trunk gumstix buildroot You may notice that the checked out repository is not very big about 15 MB That s because it doesn t actually contain all the files that you need to create the environment It mostly c
24. help installing the KDE Bluetooth software visit http kde bluetooth sourceforge net On Gentoo Linux we installed net wireless kdebluetooth from Portage Small Form Factor PCs Buy the full book online makezine com sff Btserial Pro ee ee eee Source code available Figure 9 13 Launching BtSerial BtSerial Pro ear Source code available Looking for devices __ Found 2 devices LICR CILED sign Concel Connect Figure 9 14 Device names shown by BtSerial Btserial Pro Sena eae Figure 9 15 BtSerial s diagnostic messages 23 Chapter 9 Bluetooth LED Sign Clicking on the KDE Bluetooth icon brings up Konqueror the KDE web file browser with bluetooth in the location box Figure 9 17 The main BtSerial Pro window shows two icons one for the LED sign and another for the local Bluetooth device The icons are chosen based on the class reported by each device DECOM e nnn Co i Click on the LED sign icon and you ll see something like the window shown in Figure 9 18 Now you are browsing the services available on the gumstix Although you can click on the Public Browse Group Root and SDP Server icons they don t really lead to anywhere interesting since KDE doesn t know how to display the data it receives The useful icons are the ones that look like serial port cables They show up as Sign Page 1 etc for us because we added those descri
25. in opd mode OBEX channel 10 path tmp obex sdp daemon Files sent to the gumstix will appear in the tmp obex directory The sdp option instructs opd to automatically advertise the OBEX service via the Service Discovery Protocol You may want to run opd manually a few times before running it from 31bluetooth Use the same command line but with out the daemon option When opd is running make sure that OBEX appears in the list of Bluetooth services sdptool browse ff ff ff 00 00 00 Service Name OBEX Object Push Service RecHandle 0x10006 Service Class ID List OBEX Object Push 0x1105 Protocol Descriptor List L2CAP 0x0100 RFCOMM 0x0003 Channel 10 OBEX 0x0008 Profile Descriptor List OBEX Object Push 0x1105 Version 0x0100 Now you are ready to attempt a file transfer from your phone or PDA If you have a PDA running PalmOS go to the Memo Pad and create a new memo While still viewing the memo press the Menu button You should see a Send Memo option Select it and then find your gumstix in the device list Click on OK If everything works you should have a new file in the tmp obex directory Bluetooth enabled mobile phone users may have to work a little harder to use OBEX transfer If your phone has a way to store notes or memos it probably also has an option to send them via Bluetooth Otherwise you can try sending an address book entry to the gumstix It should show up on the other side
26. k offset 0x2269 class 0x820116 If you don t get any output the first time run the command again Note that the Bluetooth address 00 80 37 1C 3A FF here should match what you see in the hciconfig output on the gumstix If not then either you are running the command from the wrong computer or you have other Bluetooth devices nearby At this point you can try using l2ping to test low level Bluetooth connectivity desktop 12ping 00 80 37 1C 3A FF Ping 00 80 37 1C 3A FF from 00 E0 98 CC A3 B4 data size 20 20 bytes from 00 80 37 1C 3A FF id 200 time 37 74ms 20 bytes from 00 80 37 1C 3A FF id 201 time 31 09ms 20 bytes from 00 80 37 1C 3A FF id 202 time 35 18ms 20 bytes from 00 80 37 1C 3A FF id 203 time 28 39ms 20 bytes from 00 80 37 1C 3A FF id 204 time 30 48ms 20 bytes from 00 80 37 1C 3A FF id 205 time 36 68ms 20 bytes from 00 80 37 1C 3A FF id 206 time 42 81ms qgqQqqqaqaaqa W Small Form Factor PCs uy the full book online makezine com sff 12 Chapter 9 Bluetooth LED Sign The next step is to try to establish a serial port connection over Bluetooth This uses a Bluetooth protocol called Radio Frequency Communications RFCOMM To begin you must bind a remote Bluetooth address to a local pseudo tty device Here is the command that binds the first RFCOMM tty to the gumstix Bluetooth address desktop rfcomm bind 0 00 80 37 1C 3A FF To print the current bindings run rfcomm with no arguments des
27. ktop rfcomm rfcomm0 00 80 37 1C 3A FF channel 1 clean Next configure a serial port communications program such as minicom to open the rfcomm device It might be either dev bluetooth rfcomm 0 or dev rfcomm0 depending on your particular Linux distribution and version The port speed settings are unimportant for Bluetooth After starting the communications program press Enter a few times and you should see a login prompt Welcome to the Gumstix Linux Distribution gumstix login Now you can log into the gumstix over Bluetooth If you are brave you can even do away with the serial cable connected to ttyS0 and just use Bluetooth instead We don t recommend it however Here are some other commands that may help you debug Bluetooth problems When the Bluetooth connection is established rfcomm shows some slightly different output desktop rfcomm rfcomm0 00 80 37 1C 3A FF channel 1 connected tty attached You can also see some connection information with hcitool desktop hcitool con Connections lt ACL 00 80 37 1C 3A FF handle 41 state 1 lm MASTER Small Form Factor PCs Buy the full book online makezine com sff 13 Chapter 9 Bluetooth LED Sign The Pro Lite LED Sign For this project we need a LED messaging sign that we can control through a serial port Unfortunately the market for these signs is not very hacking friendly That is the sign makers perceive their customers as people who are not smar
28. lieve that Pro Lite probably does not make any other similar signs that are not compatible with the same control protocol Introducing the gumstix The gumstix is an extremely small general purpose computer system by today s standards It is based on Intel s XScale proces sor which is really an ARM CPU The gumstix is similar to the kind of hardware that you d find inside a cell phone PDA or GPS Not surprisingly the gumstix is about the same size and shape as a stick of gum as shown in Figures 9 1 and 9 2 The gumstix comes in either 200 or 400 MHz models The origi ria ee nal boards have 4 MB flash memory and 64 MB RAM Newer xm models feature 16 MB flash memory A version of Linux currently kernel 2 6 11 and the BusyBox suite of applications are pre installed The gumstix comes with a number of daughterboard options Technically gumstix refers only to the CPU board itself When paired with a daughter board and a case the gumstix becomes a waysmall computer We ll use the terms interchangeably in this book Small Form Factor PCs Buy the full book online makezine com sff Figure 9 1 Front side of the gumstix board i TETE Figure 9 2 Back side of the gumstix board showing Bluetooth and MMC connectors 3 Chapter 9 Bluetooth LED Sign For this project we ve chosen the waysmall STUART daughter board which includes two serial ports and a USB device i
29. local interface hcitool dev hcid 00 80 37 1C 3A FF You may want to add this address to your etc bluetooth hosts file echo 00 80 37 1C 3A FF gumstix gt etc bluetooth hosts Also run hciconfig which should remind you of ifconfig hciconfig hci0 up hciconfig a hci0 Type UART BD Address 00 80 37 1C 3A FF ACL MTU 672 8 SCO MTU 64 0 Small Form Factor PCs Buy the full book online makezine com sff 10 Chapter 9 Bluetooth LED Sign UP RUNNING PSCAN ISCAN INQUIRY RX bytes 900 acl 0 sco 0 events 99 errors 0 TX bytes 838 acl 0 sco 0 commands 48 errors 0 Features Oxff Oxfb 0x01 0x00 0x00 0x00 0x00 0x00 Packet type DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 Link policy RSWITCH HOLD SNIFF PARK Link mode SLAVE ACCEPT Name Gumstix 0 Class 0x820116 Service Classes Networking Information Device Class Computer Palm HCI Ver 1 1 0x1 HCI Rev 0x8105 LMP Ver 1 1 0x1 LMP Subver 0x8d40 Manufacturer Ericsson Technology Licensing 0 We initially had a lot of difficulty with Bluetooth on the gumstix It was not communicating very well with other Bluetooth devices At first we suspected interference from our nearby 802 11 network But eventually we found some good suggestions in the gumstix users mailing list archive The trick was to change the setting for HCIATTACH_SPEED in etc default bluetooth HCIATTACH_SPEED 230400 Most Bluetooth interfaces for PCs have a USB interface On the gumstix however
30. look at the rfcomm source code and see if you can write a new program that manages multiple listeners or perhaps build it directly into a program like rfcomm to sign Small Form Factor PCs Buy the full book online makezine com sff 35
31. message is written The RFCOMM connection does not stay up long enough for our rfcomm to sign program to return from its short sleep and successfully open the device An easy way to solve this problem is to add a sleep call after the echo and run both commands from a subshell like this desktop echo this works better sleep 5 gt dev bluetooth rfcomm 2 Our rfcomm to sign program uses a three second sleep between attempts to open the RFCOMM device so five seconds here should be sufficient You may want to write a little shell script that hides some of the ugliness For example bin sh set e RNUM 1 shift stty echo exec gt dev bluetooth rfcomm RNUM cat sleep 5 Then you can use it like this desktop echo this works better ledsign sh 1 Another way is to use a slightly more complicated shell script that also reads from the RFCOMM device If we can make it read the ready gt prompt before writing the message we can be sure that the message is actually received by rfcomm to sign Here is one way to do it bin sh set e RNUM 1 shift read MSG exec lt dev bluetooth rfcomm RNUM exec gt dev bluetooth rfcomm RNUM stty echo cread read prompt echo MSG read prompt Small Form Factor PCs Buy the full book online makezine com sff 25 Chapter 9 Bluetooth LED Sign The script first reads the message from stdin Then it reassigns stdin and stdout to the RFCOMM device It reads
32. mm r listen null respawn usr sbin rfcomm r listen null respawn usr sbin rfcomm r listen null respawn usr sbin rfcomm r listen WOPWNPR AuRWN Reboot or type init q to have init re read its configuration file and start these processes Small Form Factor PCs Buy the full book online makezine com sff 17 Chapter 9 Bluetooth LED Sign By default the gumstix only has four RFCOMM device entries in dev The preceding example goes up to rfcomm5 so we ll need to add at least two more One way to do it is by editing sources device_table txt in the gumstix buildroot source tree Then of course build and install a new filesystem image as described in Building Software for the gumstix earlier in this chapter An easier way is to execute a few mknod commands manually Even though dev is a memory filesystem the device entries should persist between reboots To add four new RFCOMM devices run bin mknod dev rfcomm4 c 216 4 bin mknod dev rfcomm5 c 216 5 bin mknod dev rfcomm6 c 216 6 bin mknod dev rfcomm7 c 216 7 Next we need to talk about Bluetooth s Service Discovery Protocol SDP This protocol allows one Bluetooth device to ask another about the services it pro vides For example to see the services offered by your gumstix you can type gumstix sdptool browse ff ff ff 00 00 00 Services are not automatically advertised Even though we have some rfcomm listeners they won t be announced via SDP
33. nce OBEX is working to the point where files appear in the tmp obex directory you ll need to write some scripts that send the message to the sign The following shell script should help get you started bin sh scan obex sh periodically scan the OBEX dropoff directory and send incoming messages to the sign cd tmp obex test d tmp trash mkdir tmp trash while true do sleep 1 for k in do test k amp amp continue echo found file k msg cat k tr r tr nt S msg echo msg echo sending message msg usr local bin to sign sh A msg mv k tmp trash sleep 30 done done Small Form Factor PCs Buy the full book online makezine com sff 32 Chapter 9 Bluetooth LED Sign Note that the to obex sh script assumes that files might contain whitespace characters It also changes newlines and carriage returns in the message to spaces It calls another script named to sign sh to actually send the mes sage to the sign bin sh to sign sh write a message to the LED sign tty T dev ttyS2 PAGE 1 shift MSG stty F T speed 9600 cs8 parenb cstopb cread clocal crtscts ignpar echo nl1 cr3 stty F T opost ocrnl onlcr cat T gt dev null amp echo lt IDO1 gt gt T echo lt IDO1 gt lt P PAGE gt MSG lt FP gt gt T echo lt IDO1 gt lt RP PAGE gt gt T Remove Special Characters from Received Messages Most of the Pro Lite control codes do u
34. neat things about Bluetooth is you can run a number of different services on the same interface using channels We ll actually run a number of virtual serial ports over the Bluetooth connection This allows multiple PDAs phones computers to be connected at the same time It also means that we can reserve one channel for logging into the gumstix and the other channels for talking to the sign By default the gumstix runs getty on chan nel 1 We need to set up the other channels using rfcomm Earlier we showed you how to use rfcomm bind on another computer to bind a local RFCOMM device to a remote Bluetooth address But on the gum stix we don t know the addresses of the devices that will connect We want to accept RFCOMM connections from anyone In this case we use rfcomm listen instead It waits for an RFCOMM connection on a given channel and then sets up the necessary binding Our getty process uses rfcomm0 and channel 1 Use this command to accept incoming connections on rfcomm1 and channel 2 gumstix usr sbin rfcomm r listen 1 2 rfcomm listen waits for a remote connection stays running as long as the other side is connected and then exits when the connection is closed Therefore we need a way to start another rfcomm listen for the next incoming connection You can use a while loop in a shell script or even better do so by adding these lines to etc inittab null respawn usr sbin rfcomm r listen null respawn usr sbin rfco
35. ng bold lt SG gt Flashing italic lt SH gt Flashing bold italic Effects Table 9 3 lists the 26 different effects As you use the sign more and more youll probably want to take advantage of these effects to break up the monotony of a simple scrolling display Small Form Factor PCs Buy the full book online makezine com sff 27 Chapter 9 Bluetooth LED Sign Table 9 3 The Pro Lite s effect codes Code Effect lt FA gt AUTO L lt FB gt OPEN L lt FC gt COVER L lt FD gt DATE lt FE gt CYCLING L EES CLOSE LEFT T lt FG gt CLOSE RIGHT T lt FH gt CLOSE CENTER T lt FI gt SCROLL UP L lt FJ gt SCROLL DOWN L lt FK gt OVERLAP L lt FL gt STACKING L lt FM gt COMIC 1 L lt FN gt COMIC 2 L lt FO gt BEEP lt FP gt PAUSE T lt FQ gt APPEAR L lt FR gt RANDOM L lt FS gt SHIFT L lt FT gt TIME lt FU gt MAGIC L lt FV gt THANK YOU lt FW gt WELCOME lt FX gt SLOW SPEED lt FY gt NORMAL SPEED lt FZ gt lt x gt CHAIN to page x T Some of these effects are meant to be used at the beginning of a message They affect the way that the message appears on the display Such effects are marked with L in the table For example the OPEN effect erases the display and then causes the message to appear one column at a time from both ends leading toward the center The COVER effect is similar except that the dis play is not erased firs
36. nitialized Bluetooth HCI socket layer initialized Bluetooth HCI UART driver ver 2 1 Bluetooth HCI H4 protocol initialized Bluetooth L2CAP ver 2 6 Bluetooth L2CAP socket layer initialized Bluetooth BNEP Ethernet Emulation ver 1 2 Bluetooth BNEP filters protocol multicast Bluetooth RFCOMM ver 1 3 Bluetooth RFCOMM socket layer initialized Bluetooth RFCOMM TTY layer initialized Those messages indicate Bluetooth support in the kernel One of the system rc scripts etc init d S30bluetooth is responsible for configuring devices and starting various daemon processes It is executed automatically each time the system boots You can also run it manually to start and stop the Bluetooth related daemons etc init d S30bluetooth stop Stopping Bluetooth subsystem pand dund rfcomm hidd sdpd hcid dev ttyS3 To start them again run etc init d S30bluetooth start Set GPIO out clear via proc gpio GPI07 Set GPIO out set via proc gpio GP107 Starting Bluetooth subsystem dev ttyS3 hcid sdpd rfcomm pand pand is the Personal Area Network daemon It provides TCP IP over Bluetooth As cool as it sounds you won t need it for this project You can disable pand by editing etc default bluetooth Find the PAND ENABLE variable and set it to false HCI stands for Host Controller Interface hcitool and hciconfig are tools that you ll use to configure Bluetooth on the gumstix Use this command to see the address of the
37. nterface it also allows you to use Bluetooth in addition to the two serial ports earlier offerings were wired up in such a way that the second serial port and the Bluetooth port used the same UART Figure 9 3 shows the two boards side by side Note that the waysmall original board also has two serial ports but you cannot use the second port and the Bluetooth interface at the same time The waysmall STUART board allows us to use them together A number of other daughter boards are available from the manufacturer including some with audio Compact Flash and even Ethernet The gumstix board also includes a Multi Media Card MMC slot Figure 9 3 The gumstix and waysmall daughter board Here you can add more storage if the on board flash memory 4 or 16 MB is not enough You might want to get an MMC card for the gumstix if only because it is a convenient way to transfer files Note that even though Secure Digital SD memory cards look exactly like MMC cards they are not quite the same thing see http en wikipedia org wiki Secure_Digital Both MMC and SD seem to work well from Linux However if you want to access the card from the gumstix boot monitor perhaps to copy a new software image you d better stick with MMC Assembling the System When you receive your gumstix kit you ll need to assemble the following pieces e The gumstix processor board e The waysmall STUART daughter board part
38. number BRD00003 e The waysmall case e The Bluetooth antenna included with the processor board Snapping the two boards together is simple Align the boards on top of each other so that the white rectangular connectors are together Press the boards together until you hear a snap Figure 9 4 shows how they look when connected and with an MMC card inserted into the slot At this point you can actually start tinkering with the gumstix if you like But you might as well take the time to fit it into its little case Small Form Factor PCs Buy the full book online makezine com sff Figure 9 4 The gumstix and waysmall boards connected with SD memory card inserted What s a STUART The gumstix s PXA proces sor has four different UARTs or Universal Asynchronous Receiver Transmitters They are named FFUART STUART BTUART and HWUART The first serial port is connected to FFUART The waysmall STUART board connects the STUART to the second serial port That means that you cannot use both Bluetooth and the second serial port with the original waysmall board See http www gumstix org tikiwiki tiki view_faq php faqld 13 Chapter 9 Bluetooth LED Sign The two boards should fit snugly inside the white plastic waysmall case Figure 9 5 shows our case which unfortunately didn t come with a cutout for the Bluetooth antenna so we made our own It looks like the gumstix site does sell a version of the case with a hole for
39. ontains scripts Makefiles and empty directories These scripts and Makefiles download various source files such as a C library C C compiler and the Linux kernel from various other locations To finish the installation cd gumstix buildroot make Unless something is seriously wrong make should run to completion without errors The end result is a J2FFS filesystem image which will be named root_fs_arm_nofpu The buildroot environment includes some extra software packages that are not built by default For example we were frustrated with the BusyBox bin sh and wanted to use bash instead Getting bash compiled for the gumstix is as easy as adding this line to the top level Makefile TARGETS bash Then run make again You can search the Makefile for other commented out TARGETS lines to see what other software is available You can also list the mk files in the make directory After you ve built new software how should you copy it to the gumstix If you have a program like minicom you can use the Zmodem file transfer protocol to upload it Another option is to use a MMC card if you have one Unfortunately you cannot or should not remove the MMC card while the system is running A third option is to connect the gumstix s USB port to another computer and use usbnet see http www gumstix org tikiwiki tiki index php page tutorial to copy the files over Finally another way is to install the new J2FFS filesystem image on
40. peating in the same order each time The PL M2014R boasts 26 different colors In fact it has five different colors red orange yellow lime green 3 brightness levels dim normal bright and a number of color combinations rainbow green on red etc See Table 9 1 page 257 for the list of available colors The sign also has 8 different fonts or character sizes In addition to the normal font it has bold italic and flashing These can be combined to create fonts such as flashing bold italic See Table 9 2 page 258 for the full list The sign also has 26 different effects Most of these determine how messages appear or disappear For example you can have messages enter from the left top or bottom or just appear all at once Also included among Small Form Factor PCs Buy the full book online makezine com sff 14 Chapter 9 Bluetooth LED Sign the possible effects are commands to pause the scrolling display and to show the date and time See Table 9 3 page 259 for the full list of effects The Pro Lite has a trivia mode and comes with a number of pre loaded questions and answers In trivia mode it displays a normal page then ques tion then another normal page and finally the answer You can delete all the trivia data to have more memory for your own messages You can also program your own trivia questions and answers If you just need the sign to display messages that don t change very oft
41. ptions to our etc init d S31bluetooth file Click on one of the serial port icons to establish an RFCOMM connection KDE should then bring up the Bluetooth Serial Chat H bluetooth Konqueror teox Location Edn View Go Bookmarks Toot Setings Window Help window as shown in Figure 9 19 Here you ll see the ready gt Y QW Oo i seen Lc prompt from rfcomm to sign Type some text into the bottom box amp taesten sassom i and click on Send In our example we re hoping that someone e X receives our request for a pizza LEO eran RA From a Linux Shell me Sending messages to the sign from the Linux shell is almost as easy as just echoing or cating text to the RFCOMM device file However it depends on how you do it But before we get to that we have to talk a little about stty aenooia BT The stty command controls certain terminal device characteris tics such as data rate flow control end of line processing and more Before using shell commands to read from and write to RFCOMM devices you should make sure they have reasonable Figure 9 17 Browsing Bluetooth in KDE stty settings In particular echo must be disabled Otherwise a Y 9 i y ASis pi gt characters read from the gumstix side of the connection will be amp sp son ag echoed back to the gumstix creating an endless loop You should S a also ensure that the read characteristic is enabled You can set gt jo woe GIESE ai
42. return fd Small Form Factor PCs Buy the full book online makezine com sff 19 Chapter 9 Bluetooth LED Sign int open_rfcomm char dev int fd for 53 4 if fd open dev O_RDWR gt 0 break if ENODEV errno err 1 dev sleep 3 syslog LOG DEBUG s opened dev return fd int read_rfcomm int fd char line static char inbuf INPUT BUF_LEN char c int 1 0 while read fd amp c 1 gt 0 amp amp 1 lt INPUT BUF_LEN if c Oxd c Oxa c 0x0 if 1 break else continue inbuf 1 c inbuf 1 0 syslog LOG DEBUG read s inbuf line amp inbuf 0 return 1 int write _sign int fd char buf int len int i char junk 10 for i 0 i lt len i if write fd buf i 1 lt 0 syslog LOG_ERR write sign s strerror errno break read fd junk 10 usleep 5000 return i int write sign str int fd char buf int len 0 syslog LOG_NOTICE writing s to FD d buf fd Small Form Factor PCs Buy the full book online makezine com sff 20 Chapter 9 Bluetooth LED Sign len write sign fd buf strlen buf len write sign fd r n 2 return len int write _message int fd char buf int len char page char nextpage int nblen len 50 char newbuf malloc nblen write sign str fd lt ID01 gt snprintf newbuf nblen lt IDO1 gt lt P
43. seful things like change colors and add special effects However it probably won t take a really curious person very long to find a number of ways to hack the sign For example a simple command can delete all pages from memory To protect against this you may have to block certain Pro Lite commands You could just block all commands by disallowing the lt and gt characters for example But that seems like overkill since many of the commands are useful Filtering Offensive Messages If you plan to use the sign in a public setting where anyone can post a mes sage you can be sure that someone will write an offensive message just to see if they can You may be forced to add some filtering to the code For example a simple method for detecting profanity is to compare words in messages with those in a bad words file One Less Power Supply It would be nice to have only one power cord running from the wall to the sign The Pro Lite uses a 9V power supply while the gumstix uses 5V With a handful of parts and a little soldering you should be able to build a gizmo that takes 9V from the sign s supply and provides 5V to the gumstix It might be as simple as an LM7805 voltage regulator plus a heat sink Small Form Factor PCs Buy the full book online makezine com sff 33 Chapter 9 Bluetooth LED Sign Prepending the Device Name to Messages If you use the sign in a public setting it may be nice to automatically insert
44. stall the free BtSerial Pro application from http www whizoo com apps btserial php As the name implies it is a Bluetooth serial port communication program After launching BtSerialPro you ll see the screen shown in Figure 9 13 Click on Open to locate nearby Bluetooth devices BtSerialPro opens up another little window and displays a list of device names as shown in Figure 9 14 We gave our gumstix the name LED sign in etc bluetooth hcid conf Click on Connect to establish the Bluetooth connection When BtSerialPro establishes a Bluetooth connection you should see the diagnostic messages shown in Figure 9 15 It will say RFCOMM connection up and tell you about the maximum packet size The ready gt prompt comes from our rfcomm to sign program and provides further evidence that the communication is working properly Now you can enter some text to send to the sign Either use the Grafitti area or bring up the keyboard and enter a message Figure 9 16 shows where we typed go cougs on the Send line After clicking on the Send button BtSerialPro writes the message over the RFCOMM channel to the sign Then our program sends another ready gt prompt indicating it is ready for another message From KDE KDE the K Desktop Environment has pretty good support for Bluetooth If you ve installed the KDE Bluetooth utilities you ll see a little blue K similar to the Bluetooth B in your KDE panel If you need
45. t The AUTO effect introduces the message with a ran domly chosen effect and color each time The RANDOM effect on the other hand introduces the message by turning on one pixel at a time in a random order MAGIC is similar to AUTO except that it only affects the color The effects marked with T are meant to be used at the end of a message They affect the way that the message disappears For example CLOSE LEFT erases the message one row at a time from right to left You may find Small Form Factor PCs Buy the full book online makezine com sff 28 Chapter 9 Bluetooth LED Sign the PAUSE effect to be very useful It freezes the display for one second The Pro Lite documentation says that this is a trailing effect but you can use it in the middle of a message too Two effects are named DATE and TIME These display the date and time based on the sign s internal clock Apparently these effects use hardcoded colors that you cannot change See the next section for the command that sets the sign s clock The CHAIN effect is somewhat special because it must be followed by another code representing the next page to display For example lt FZ gt lt C gt tells the sign to display page C next Note that some of the codes have different effects in older versions of the Pro Lite protocol For example Walt Stoneburner s site describes an earlier version of the sign software where DATE and TIME were together in a single effe
46. t enough to write their own software for controlling the sign Sign manufacturers do not openly publish the protocols used to control their signs The LED Figure 9 9 The Pro Lite PL M2014R signs are often expensive and sold as a part of a kit that includes LED sign Windows based software or even a dedicated computer Figure 9 9 shows what the PL M2014R looks like It s slightly more than two feet wide and four inches high The power and serial port connectors are on the left side It also comes with a remote control not pictured Figure 9 10 is a close up of the sign Here you can see the individual pixels LEDs The display is 7 LEDs high and 80 wide The sign is wide enough to display about 13 characters in the normal font Purchasing a Pro Lite sign can be a little tricky Only a few online retailers offer it and you may have to call a salesperson to place an order We used Ebay where a small number of Pro Lite signs were selling for between 50 and 175 Figure 9 10 Close up of the Pro Lite sign showing individual pixels Pro Lite Sign Features The PL M2014R has 26 pages named with the letters A to Z Each page is limited to about 1 000 characters Pages can either be displayed individually or chained together When displayed individually the message in a given page is displayed over and over until the sign is instructed to do otherwise In chained mode pages are displayed one after the other re
47. that number to Bluetooth users who are allowed to connect One of the most important hcid conf settings is the link mode 1m which we set to master accept In a Bluetooth connection one side is the master and the other side is the slave The device that initiates a connection assumes the role of master This means that the gumstix becomes the slave for incoming connections However when the gumstix is the slave it becomes undis coverable by other devices Fortunately Bluetooth allows devices to switch roles after connecting The link mode setting controls how the device treats incoming connections When set to master accept this device accepts incom ing connections in slave mode but then requests to switch roles and become the master Testing the Bluetooth Connection Eventually our goal is to be able to send messages to the sign from a phone or PDA But if you are new to Bluetooth you ll probably have an easier time if you start playing with another Bluetooth enabled Linux computer To demonstrate how to get Bluetooth up and running we ll show you how to log into the gumstix from another computer On your other computer make sure that Bluetooth is up and running If you ve never done this before you may want to refer to Chapter 7 of Linux Unwired O Reilly When you have the Bluetooth interface up and the gum stix nearby run this command on the other computer desktop hcitool ing Inquiring 00 80 37 1C 3A FF cloc
48. the Bluetooth device name into every message This adds some accountability and makes the message display similar to a chat room Each time rfcomm to sign gets a new RFCOMM connection it can run rfcomm show to get the address of the device connected on its channel Then it can run hcitool name x x x x x x to get the connected device s name If prepending device names is too awkward you may want to at least consider giving each page a different color At the very least this allows viewers to tell when one message ends and another begins Of course if messages include color codes such as lt CB gt the sender can override the default color for a page anyway Aging Messages from the Sign Depending on your particular use of the sign it may make sense to put a time limit on how long a particular message will be displayed The sign doesn t have any built in features to support this so you ll need to implement it in software on the gumstix One approach is to modify rfcomm to sign so that it keeps track of how long it has been trying to open the RFCOMM device After some amount of time say 10 minutes it can send a message to the sign to erase the cor responding page If you are using the page chaining technique you don t want to actually erase the page but instead send an empty message followed by an instruction to jump to the appropriate page Scaling the Software A Bluetooth device cannot be con nected to more than seven other
49. the token lt ID01 gt This is the identifier for sign 1 in case you have multiple signs chained together The first command that we send is empty and is there just to wake up the sign in case we haven t talked to it for a while The second command sends some text to the sign lt PA gt refers to page A of the sign s memory The third command lt RPA gt means run page A Here s another neat little trick You can use the following command to display the current date and time date lt IDO1 gt lt PA gt c gt T As you continue playing with the sign you ll probably discover some of its annoying quirks In particular updates to the currently displayed page take effect immediately In other words a long message gets cut off as soon as you send a new one Normally this won t be a problem But it does become difficult to use the sign as a frequently updated display To see what we mean try this while true do date lt IDO1 gt lt PA gt c gt T sleep 1 done Small Form Factor PCs Buy the full book online makezine com sff 16 Chapter 9 Bluetooth LED Sign Putting It All Together By now you should have Bluetooth working That is you can log in to the gumstix over Bluetooth from another computer or perhaps a PDA You should also be able to send messages to the LED sign over the serial port In this section we ll explain how to glue these two together Bluetooth Configuration One of the
50. voodoo We have to tell the gumstix processor to connect the second serial port to the PXA s STUART Put the following lines into etc init d S60ttyS2 and make the file executable bin sh Configure dev ttyS2 if test 1 start then echo Configuring dev ttyS2 modprobe proc_gpio echo AF2 in gt proc gpio GP1046 echo AF1 out gt proc gpio GP1047 fi Small Form Factor PCs Buy the full book online makezine com sff 15 Chapter 9 Bluetooth LED Sign Then either reboot or run the script manually etc init d S60ttyS2 start Configuring dev ttyS2 Set AF2 in set via proc gpio GP1046 Set AF1 out set via proc gpio GP1047 Testing the Sign s Serial Port After building the cable you should test it out to make sure that everything is connected and working properly Here s how you can send some simple test messages to the sign from the shell T dev ttyS2 stty F T speed 9600 cs8 parenb cstopb cread clocal crtscts ignpar echo nli cr3 stty F T opost ocrnl onlcr cat T gt dev null amp echo lt IDO1 gt gt T echo lt ID01 gt lt PA gt testing 123 gt T echo lt IDO1 gt lt RPA gt gt T The stty commands configure certain serial port parameters such as the speed flow control and other settings The cat command is necessary to read characters coming back from the sign The echo commands send data to the sign Each sign command begins with
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