Palm Pilot Development Tools

The PalmOS keeps a queue of events being handled by the system. These events are sent to the current application in order to execute the code to handle each event. An event is triggered when a UI button is pressed, the Palm pen touches the screen (penDownEvent) or when other operations occur. An application should transfer any events it doesn't handle to the system. When the event is handled, the PalmOS takes the next event in the queue and passes it on to the application. The application can also put events in the queue. Many PalmPilot functions cause all sorts of events to be placed in the event queue. A list of all events and what they do is in the official documentation for the Palm Pilot.

The main procedure of a program is called PilotMain. When the PalmOS calls PilotMain, it transfers a command to it. The PilotMain procedure should find out what the command says. The command can say, for example, that this is a normal launch of the application (sysAppLaunchCmdNormalLaunch) or that this is a command to find a string (sysAppLaunchCmdfind). PilotMain should ignore or respond to these commands in its code. An example of an application that responds to the sysAppLaunchCmdfind is the address book. Whenever we press the find button, the PalmOS sends this command to all the applications. One application that will accept this command is the address book—it starts searching for the string we entered in its database.

To handle all events, we should use an event loop. An event loop simply takes an event, handles it, then takes the next event in the queue. If we do not want to handle a certain event, we can send it to the PalmOS event handlers so it will be handled for us.

To take advantage of all the functionality of the PalmOS, there is well-documented API for your use. You should read the API manual to see which kinds of events, functions and types of objects exist in the PalmOS. Listing 2 is simple code that writes “Hello World” on the Palm Pilot.

Listing 2

The first step toward running an application on the Palm is to build the resources. As mentioned earlier, we can build the resources using the command pilrc.

pilrc hw.rcp

To add the bitmap with ID 10 to the main form, I used a tool that converts ppm files to Tbmpxxx.bin resources. I used xv to convert the format of peng.gif (found at http://www.linux.org.il/) to black-and-white ppm format. Then I used ppmtoTbmp on the peng.ppm file, and named the result Tbmp000a.bin. The 000a in the file name is the 32-bit hexadecimal value for 10. I needed to specify this value because this is the bitmap ID I wrote in the pilrc resource file for the main form. This tool was written by Ian Goldberg, and it can be found at http://www.pilotgear.com/.

The next step is to compile the C code. To do this, we use the gcc m68-palmos-coff cross compiler, with the same flags as for the normal Linux gcc:

m68k-palmos-gcc -O2 -o hello hello.c

The result of this command is an m68k COFF object file named hello. The m68k COFF object file should be combined with the resources just created using the pilrc program. To complete this mission, we first use the obj-res utility that splits the COFF file into the code and data resources, and then use the build-prc utility to combine resources.

m68k-palmos-obj-res hello

build-prc hello.prc "hello" hwld *.grc *.bin

Testing the application on your Palm Pilot is not such a good idea. A bug might require us to reset the machine, and programs can't be debugged with the normal tools. The best way to test our just-created “Hello World” application is with a program that will emulate the Palm Pilot from within our desktop. POSE, available from http://www.palm.com/ with source code included, is a very good emulator. It can use a special debug ROM, also available from that site. With the debug ROM, we can get more debugging information on our application, which makes finding errors much easier, and we can hook gdb to it in order to debug with this well-known debugging tool. To install POSE, you will need the FLTK X toolkit. All instructions come with the POSE tar file.

There is one more emulator for X, called xcopilot. In order to use your own machine RAM or ROM, you can use the pilot-link package. The pilot-link package gives you the ability to communicate with the Palm Pilot from the serial port. There are some good utilities in this package, available from ftp://ryeham.ee.ryerson.ca/pub/PalmOS/. Using the pilot-link utilities, we can also transfer databases from our desktop to the Palm Pilot and from the Palm Pilot to the desktop.

Figure 1

Figure 1 is how POSE looks with our hello world application for the Palm.

Resources

All listings referred to in this article are available by anonymous download in the file ftp.linuxjournal.com/pub/lj/listings/issue73/3782.tgz.