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EMULATOR HIGH LEVEL LANGUAGE API (EHLLAPI) IN IBM PERSONAL COMMUNICATIONS

  
For an introduction to API’s and emulator programming in IBM Personal Communications, refer to the link below:-

https://community.ibm.com/community/user/ibmz-and-linuxone/blogs/mahua-chanda/2021/08/31/personal-communications-session-api-pcsapi-in-ibm

In this blog we will explore more about EHLLAPI APIs.

PCOMM provides functions to access emulator "presentation space" data (such as characters on the host screen), sending keystrokes to the host, intercepting user-entered keystrokes, querying the status of the host session, uploading and downloading files, etc. The different EHLLAPI programming interfaces are listed below:
  • IBM Standard HLLAPI Support (HLLAPI): This is a standard programming interface which allows programmatic access to a host emulator session.
  • IBM Enhanced HLLAPI Support (EHLLAPI): This interface is based on the IBM Standard HLLAPI interface. It provides all the existing functionality but uses modified data structures.
  • Windows High Level Language API (WinHLLAPI): This interface provides much of the same functionality of IBM Standard EHLLAPI and adds some extensions that take advantage of the Windows environment.

​The figure below showcases different EHLLAPI layers.


Languages

Any programming language which can invoke an entry point in a DLL with the "Pascal" calling convention can be used to execute EHLLAPI functions. However, the Personal Communications EHLLAPI toolkit provides header files and function prototypes only for the C++ languages. These are present under the ‘\Samples’ Directory. A clear understanding of data structure layout and calling conventions is required to use any other language. The EHLLAPI toolkit supports the following C/C++ compilers:
          •       C/C++
          •       Visual Basic for Automation
          •       Visual Basic Scripting
 
EHLLAPI C/C++ applications must include the Personal Communications EHLLAPI header file (HAPI_C.H).

EHLLAPI Call Format

The EHLLAPI entry point is always called with the following four parameters:
Function Name (EHLLAPI Function Number, Data Buffer, Buffer Length, Position/Return Code);
EHLLAPI Function Number ​Input
Data Buffer Input/Output
​Buffer Length Input/Output
Position/Return Code Input/Output


Compiling and linking
Applications using EHLLAPI functions must include the appropriate header file to obtain the proper function prototypes, constants, and data structure definitions. These header files may be used with any of the supported C/C++ compilers.

Note: If a different compiler or language is used, then you must provide your own equivalent definitions and structures. There are two possible ways to link the application program, depending on how the entry point is to be resolved.

​The following table shows which header files to use for which flavour of EHLLAPI.


Function Calling convention
PCOMM Session APIs follow a simple prototype for all functions to keep the programming straightforward. As mentioned above these API’s can be accessed and programmed using multiple programming languages (VBA, C/C++, C#, etc).

Function Type Function Name (Arguments);
Where:
Function Type The return type of the API
Function Name The function to be called
Arguments ​Input argument to be passed to the function and can vary from 1 to 3
EHLLAPI Functions and their opcodes:

​Below figure shows different EHLLAPI functions and their Opcodes. Details about these functions, Operations, Data type, Length and Return values can be found here.


A Simple EHLLAPI ‘C’ Sample Program
The following sample windows application enters the character string "Hello World!" in the first input field of host session 'A'.

A.      Includes
 
 
//Include standard library functions
#include <stdlib.h>
#include <stdio.h>
#include <windows.h>
//EHLLAPI header file
#include "hapi_c32.h"
 
B.      Main Function body and reset connection (if any)
 
 
int main(char **argv, int argc)
{
int HFunc, HLen, HRc;
char HBuff[1];
struct HLDConnectPS ConnBuff;
// Send Key string for HOME+string+ENTER:
char SendString[] = "@0Hello World!@E";
//Reset the automation system
HFunc = HA_RESET_SYSTEM;
HLen = 0;
HRc = 0;
hllapi(&HFunc, HBuff, &HLen, &HRc); //standard EHLLAPI Calling format
if (HRc != HARC_SUCCESS)
{
printf("Unable to access EHLLAPI.\n");
return 1;
}
 
C.  Establish connection between program and emulator (Step A must be performed before any other steps)

 
//Initialize the automation Engine by establishing connection
HFunc = HA_CONNECT_PS;
HLen = sizeof(ConnBuff);
HRc = 0;
memset(&ConnBuff, 0x00, sizeof(ConnBuff));
 
ConnBuff.stps_shortname = 'A';
hllapi(&HFunc, (char *)&ConnBuff, &HLen, &HRc);
switch (HRc) {
case HARC_SUCCESS:
case HARC_BUSY:
case HARC_LOCKED:
//If here, we are good with connection
break;
case HARC_INVALID_PS:
printf("Host session A does not exist.\n");
return 1;
case HARC_UNAVAILABLE:
printf("Host session A is in use by another EHLLAPI application.\n");
return 1;
case HARC_SYSTEM_ERROR:
printf("System error connecting to session A.\n");
return 1;
default:
printf("Error connecting to session A.\n");
return 1;
}
 
D. Write “HelloWorld” on the Emulator Screen
 
 
//Send the Keystroke as recorded in SendString Buffer
HFunc = HA_SENDKEY;
HLen = strlen(SendString);
HRc = 0;
hllapi(&HFunc, SendString, &HLen, &HRc);
switch (HRc) {
case HARC_SUCCESS:
break;
case HARC_BUSY:
case HARC_LOCKED:
printf("Send failed, host session locked or busy.\n");
break;
default:
printf("Send failed.\n");
break;
}

E.    Disconnect from the PCOMM Engine (Clean disconnect)
//All operations done. Now disconnect
HFunc = HA_DISCONNECT_PS;
HLen = 0;
HRc = 0;
hllapi(&HFunc, HBuff, &HLen, &HRc);
printf("EHLLAPI program ended.\n");

return 0;

Download the Sample code:
ehllapi_sample.zip

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Avinash Sable
Lead - Lab Services, IBM HACP & HATS