Dr. Reddy's Guide to HP Palmtops

Programming the Palmtop (Part II)

Children's Health Pediatric Resources Fun Sites for Kids HP Palmtops Dr. Reddy's Home Page Feedback Our Real Office

An HP 200 LX HP's Palmtop Home Page

Like programs for other GUI operating systems (Mac, Windows, Palm OS, ...), HP Palmtop System-Manager compliant application programs are event-driven. This means that the System Manager will report each important event to your program. Your program will spend most of its time in a loop waiting for an event; when the event occurs, your program will respond appropriately to it and then go back and wait for the next event. Most of the event are keystrokes, but other events that System Manager will send to your program include

(when another Palmtop application is started up)
(when your app regains control)
(when System Manager is low on memory: the user is given a choice of which open applications should be closed, and your app may be one of those given the axe)
(sent if System Manager wants the screen redrawn)
(this message is sent at regular intervals, mainly to help keep the date-time display in the title bar honest)

Much of the structure of a Palmtop app is also dictated by the Lotus Handheld Application Programming Interface, or LHAPI. Like other GUI operating systems, LHAPI provides many of the basic constructs for Palmtop app user interfaces. The screen in a Palmtop app contains a main window and child windows which appear and disappear as needed by the program. Each window can be configured to perform different functions, and LHAPI has many preconfigured windows to do everything from check boxes and radio buttons to file selection dialogs and multiline text editing. The data structures for LHAPI windows are described in the Developer's Guide, and the disk provided with the Kit contains the C and assembler header files needed to access the routines.

Below is a System-Manager compliant application program. In the Kernighan and Ritchie tradition, all the program does is displays "Hello, world" (and "Goodbye, world") on the screen. The comments are my attempt to explain what is going on in each part of the code.

/*                                                                          */
/*  Hello, world  program for the HP 100/200 LX                             */
/*     Copyright (c) 1996, 2002  Vinay N. Reddy, M.D.                       */
/*     All rights reserved.                                                 */
/*     This program may be used freely for any non-commercial purposes.  It */
/*     may not be reproduced, distributed, or otherwise used commercially   */
/*     without permission from the author.  The author makes NO guarantee   */
/*     that this program is bug-free, or that it may be used safely for any */
/*     purpose; it is presented only as an example of HP Palmtop System     */
/*     Manager application programming.                                     */
/*                                                                          */
/*  This program displays the messages "Hello, world" and "Goodbye, world"  */
/*    under function key and menu control.                                  */
/*                                                                          */
/*  Routines used:                                                          */
/*      main()  More-or-less generic main program for HP 100/200 apps       */
/*      EventDispatcher                                                     */
/*              Command key/event key processor loop                        */
/*      ProcessEvent                                                        */
/*              Actual command dispatcher                                   */
/*      MyCardHandler                                                       */
/*              Main window handler modified to process hot keys            */
/*      DoHello, DoBye                                                      */
/*              Message display routines                                    */
/*      DoBeep  Routine to produce a beep on command                        */
/*      DoBlank Routine to blank out the current message                    */
/*      DoQuit  Routine to set quit flag on command                         */
/*      DoNothing                                                           */
/*              Null action routine (just a null statement)                 */
/*                                                                          */

/******** Include header files **********************************************/
/*                                                                          */
/* These header files are those included with the HP Palmtop Developer's    */
/* Kit. Equivalent file names for NKIT are given in the NKIT documentation. */
/*                                                                          */

#include "cap2.h"        /* Included in all CAP (old name for LHAPI)
                             programs; you may also use "lhapi.h" */

#include "interfac.h"    /* System manager includes (read the #included */
#include "event.h"       /* files for details */
#include "cougraph.h"
#include "lstring.h"
#include "chtype.h"
#include "dosfile.h"
#include "dtn_edit.h"
#include "sysdefs.h"
/*                          CHKTSR contains a C function that checks for
                            the presence of TKERNEL, the desktop version
                            of the System Manager service routines.  While
                            debugging on the desktop, you need to have
                            TKERNEL installed, or your program will crash
                            your desktop quickly and efficiently.  Of course,
                            you don't want to check for TKERNEL on your
                            Palmtop, since System Manager is present in full
                            glory.  The Development Kit makefile allows you
                            to specify whether you are compiling a desktop
                            version (with or without CodeView support) or
                            a "real" (EXM'able) version.
#ifdef TKERNEL
#include "chktsr.c"

/* Defines for text and title bar placement */

#define  TITLE_HEIGHT  10
#define  TEXT_ORIGIN_X 43
#define  TEXT_ORIGIN_Y 56

/* Defines for program status (for redrawing purposes) */

#define  STATUSBLANK    0
#define  STATUSHELLO    1

/* Because of the Palmtop's architecture (see the Developer's Guide, or the */
/* articles in Handheld Systems Magazine, for details), an app's data       */
/* segment can be moved at any time by System Manager,  This usually        */
/* when another app is activated or deactivated, or when your or another    */
/* app asks for more memory or releases part of previously-allocated memory.*/
/* To allow for this movement, string constants and large data items are    */
/* referred to by near pointers to far pointers to the actual data.  The    */
/* far pointers need to be "fixed up" every time the app is reactivated; one*/
/* way to do this is to keep all of the pointers in a table and fix them at */
/* each reactivation.  Thus, all string constants are declared with         */
/* pointers.  We'll see later how the pointers are handled (and fixed).     */

/* Title strings */

char far *msgTestApp    = "Hello, Cougar";
        /* Name of application (used by System Manager) */

char far *msgAppTopLine = "Hello, world, this is the Cougar";
        /* Title of application (displayed in main window title bar */

/* Function key labels */

char far *fkeyHello   = "Hello";
char far *fkeyBeep    = "Beep";
char far *fkeyBlank   = "Blank";
char far *fkeyBye     = "Bye";

/* Menu labels */

char far *menuHello   = "&Hello\tH";
char far *menuGoodbye = "&Goodbye\tG";
char far *menuExit    = "E&xit";
char far *menuHi      = "&Hi";
char far *menuQuit    = "&Quit";

/* Message strings */

char far *msgHello  = "Hello, world  ";
char far *msgGoodbye= "Goodbye, world";
char far *msgEmpty  = "              ";
char far *msgNull   = "";

/* String pointer table  (required to allow pointer fixups on reactivation */

char far **StringTable[] = {


/* Command processors  (prototype function declarations) */

int far MyCardHandler(PWINDOW Wnd, WORD Message, WORD Data, WORD Extra);

void far DoQuit(void);
void far DoHello(void);
void far DoBlank(void);
void far DoNothing(void);
void far DoBeep(void);
void far DoBye(void);

/* Global state data structures */

EVENT    app_event;
CAPBLOCK CapData;      /* CAP was the predecessor to LHAPI; with the HP
                          Development Kit header files, the terms are
                          interchangeable */
BOOL     Done;         /* Program termination flag */
int      progStatus;   /* Program status */

/* Function key definitions                                              */
/*                                                                       */
/* Structure:                                                            */
/*   { <title-string>, <command-processor>, <Fkey number>, 0 }, */
/*   The last Fkey definition should have the const LAST_FKEY OR'ed with */
/*   the Fkey number.                                                    */
/*                                                                       */

FKEY MyFKeys[] = {
 {  &fkeyHello,         DoHello,        2,              0 },
 {  &fkeyBeep,          DoBeep,         3,              0 },
 {  &fkeyBlank,         DoBlank,        9,              0 },
 {  &fkeyBye,           DoBye,          10+LAST_FKEY,   0 }

/*                                 Menu structures                          */
/*                                                                          */
/*  See Developer's Guide, pp 8-312 - 8-313, for complete definitions.      */
/*  Briefly: there are five parts to the definition of each menu item:      */
/*   1.) a pointer to the menu item text string (which should be in the     */
/*       pointer tables and fixed up at each reactivation or memory change) */
/*   2.) the name of the handler routine (unlike function passing in other  */
/*       forms of C, parentheses are _not_ required after the function name)*/
/*     OR                                                                   */
/*       a pointer to the structure that defines the "pull-down" submenu    */
/*   3.) the scan code of the "Hot Key" that the user can press to execute  */
/*       the function without having to use the menu (set to 0 (zero) if no */
/*       hot key is defined for the item)                                   */
/*   4.) style bits (defined in the Developer's Guide and in LHAPI.H) which */
/*       can be OR'ed together to combine styles.  An important example,    */
/*       shown below, is MENU_PULLDOWN, which must be set to signal that a  */
/*       pull-down menu is invoked by the item                              */
/*   5.) the index number used by the Help Engine to ID the help text for   */
/*       this menu item.  Since HP has never made the matching Help Compiler*/
/*       available, this is of no use and should be set to NO_HELP, or just */
/*       omitted. (If you need on-line help in your app, you will likely    */
/*       have to do it with a (probably _large_ collection of text boxes.)  */
/*                                                                          */

MENU HiMenu[] = {
 { &menuHello,   DoHello, 0 ,0, NO_HELP},
 { &menuGoodbye, DoBye,   0 ,0, NO_HELP},
 { &menuExit,    DoQuit,  0, 0, NO_HELP},
 { 0,            0,       0, 0, 0}

MENU TopMenu[] = {
 { &menuHi,      (PFUNC) HiMenu,        0, MENU_PULLDOWN },
 { &menuQuit,    DoQuit,                0  },
 { 0,            0,       0,  0, 0}

/* Main window definition (See Developer's Guide, page 8-307 ff  */

WINDOW MyCard = {
 MyCardHandler, 0, 0, 640, 190,
  NULL, 0,
  0, 0,
  NULL, MyFKeys, TopMenu, NO_HELP};

WINDOW DateTimeArray[] = {0}; /* Filled in by TitleBar handler*/

WINDOW TopBar = {
        TitleBar, 0, 0, 0, 0,
        (PLHRES)&msgAppTopLine, 0, 0, STYLE_NOFOCUS,
        NULL, NO_FKEYS, (PLHRES)&DateTimeArray, NO_HELP

/*          */
/*   Code   */
/*          */

void far DoQuit(void)
/*   Input:       None
     Output:      Sets Done flag TRUE
     Calls:       Nothing
     Description: Sets flag to terminate Event Dispatcher (main) loop */
     Done = TRUE;

void far DoBeep(void)
/*   Input:       None
     Output:      Sounds system beep
     Calls:       System Manager m_beep
     Description: Sounds system beep; no other action */

void far DoHello(void)
/*   Input:       None
     Output:      Displays msgHello
     Calls:       DrawText
     Description: Displays "Hello" message using the LHAPI DrawText
                  function, which draws text on the screen starting at a
                  specified position and with a specified font. */
   progStatus = STATUSHELLO;

void far DoBlank(void)
/*   Input:       None
     Output:      Displays blank line, erasing current text at location
     Calls:       DrawText
     Description: Blanks current message, also using DrawText */
   progStatus = STATUSBLANK;

void far DoNothing(void)
/*   Input:       None
     Output:      None
     Calls:       Nothing
     Description: Null command routine */

void far DoBye(void)
/*   Input:       None
     Output:      Displays msgGoodbye
     Calls:       DrawText
     Description: Displays "Goodbye" message, also using DrawText function */
   progStatus = STATUSGOODBYE;

void FixupFarPtrs(void)
/*   Input:       None
     Output:      Corrects far pointers to entries in string table
     Calls:       countof (macro defined in LHAPI)
     Description: Fixes up far pointers to string table entries after
        app reactivation, and whenever else fixups are required.
        The fixing-up is done by replacing the high-order part of each
        pointer with the current/new data segment (which is obtained by
        reading the DS register -- an operation that must be written in
        assembler.) */
  int i;
  int dataseg;

  _asm {
    mov ax,ds
    mov dataseg,ax

  for (i=0; i<countof(StringTable); i++)
      *(((int *)(StringTable[i]))+1) = dataseg;

void CreateMainView(void)
/*   Input:       None
     Output:      None
     Calls:       SendMsg (to MyCard)
     Description: Creates (initializes) main window display, by sending
                  CREATE messages to both the main window ("MyCard") and
                  the title bar window */
     SendMsg(&MyCard, CREATE, CREATE_FOCUS, 0);
     SendMsg(&TopBar, CREATE, CREATE_NORMAL, 0);

int far MyCardHandler(PWINDOW Wnd, WORD Message, WORD Data, WORD Extra)
/*   Input:       Wnd:     Window data structure/identifier
                  Message: Message type
                  Data:    Message data
                  Extra:   Extra message data (not used here)
     Output:      If message type is KEYSTROKE, appropriate action for key
                  If message type is DRAW, redraw main window
     Calls:       DoHello, DoBye, ClearRect, Rectangle, DrawText, SubclassMsg
     Description: Handles special actions for main window (hotkey processing
                        and window updating  */
  switch (Message) {

    case KEYSTROKE:
     switch (Data) {
      case 'h':
      case 'H':
          return TRUE;
      case 'g':
      case 'G':
          return TRUE;
      } /* end of switch (Data) and of case KEYSTROKE */

    case DRAW:
       if (Data&DRAW_FRAME) {
    } /* end of switch MESSAGE */
    SubclassMsg(Object, Wnd, Message, Data, Extra);

int ProcessEvent(EVENT *app_event)
/*  Input:        *app_event:   pointer to app event structure
    Output:       None
    Calls:        FixupFarPointers, ReactivateCAP, DeactivateCAP,
                        SendMsg, SendFocusMsg
    Description: Process SysMgr event messages */
    switch (app_event->kind) {      /* Branch on SysMgr event */
      case E_REFRESH: /* Redraw screen */
      case E_ACTIV:   /* Reactivate app */
         switch (progStatus) {
          case STATUSHELLO:
          case STATUSGOODBYE:

      case E_DEACT:  /* Deactivate app */

      case E_TERM:   /* Terminate app */
         Done = TRUE;

      case E_NONE:   /* Sent by System Manager every 1/2 second if nothing
                        else is going on */
         SendMsg(GetFocus(), NULLEVENT, app_event->shifts, app_event->scan);

      case E_KEY:    /* Key pressed that app must handle */
         /* (KeyCode converts gray 101-key */
         /*   arrows/movement scan codes into "normal" (PC) scan codes) */
         SendMsg(GetFocus(), KEYSTROKE,
                 app_event->scan);   /* Make sure we send the scan code too */

void EventDispatcher(void)
/*   Input:        None
     Output:       None
     Calls:        m_action, ProcessEvent
      EventDispatcher grabs events from the System Manager and translates
      them into CAP messages.  Every program will have an Event Dispatcher,
      and the structure should follow this one. */
  Done = FALSE;                    /* Set terminate flag to FALSE */

  while (!Done) {                  /* While loop not terminated */
    app_event.do_event = DO_EVENT;

    m_action(&app_event);          /* Grab system manager event */

void main(void)
/* Input:       None
   Output:      None
   Calls:       CheckTSRs (if TKERNEL defined), m_init_app,
                InitializeCAP, SetMenuFont, SetFont, m_reg_app_name,
                CreateMainView, EnableClock, EventDispatcher, m_fini
   Description: Main program.  Initialize SysMgr interface and CAP/LHAPI,
                sets type fonts, initializes main window display and
                enables title bar date/time display, and processes
                events until there ain't no more. */
#ifdef TKERNEL
     m_init_app(SYSTEM_MANAGER_VERSION); /* Register with SysMgr */
     InitializeCAP(&CapData);            /*  and with LHAPI      */
     m_reg_app_name(msgTestApp);         /* sets app name for use in SysMgr */


     progStatus = 0;   /* Should display blank screen at startup */



Visit the HP Palmtop Ring Homepage

This HP Palmtop Ring Site is owned by Vinay N. Reddy, M.D. Visit The Webring.

[ Next | Skip Next | Next 5 | Previous | Previous 2 ]

Search the Office for:


See the Detailed Search page for complete instructions on searching the Office.

Back to Programming, Part I
Back to Dr. Reddy's Guide to HP Palmtops
Back to Dr. Reddy's Pediatric Office on the Web
We welcome your comments and questions.

Copyright © 2002 Vinay N. Reddy, M.D. All rights reserved.
Written 01/12/02; last revised 01/16/02 counter