Plan for i5/OS PASE

When you begin to work with i5/OS™ PASE, the points listed in this topic might be helpful to you.

i5/OS PASE provides an AIX^® runtime environment on i5/OS that lets you port your AIX applications to the iSeries™ server with minimal effort. In fact, many AIX programs run in i5/OS PASE with no change. This is because i5/OS PASE supplies many of the same shared libraries that are available on AIX, and it provides a broad subset of AIX utilities that run directly on the iSeries PowerPC^® processor in the same way that they run on the pSeries^® AIX PowerPC processor.

Some points to keep in mind as you begin to work with i5/OS PASE:

• There is a correlation between the target release of an AIX binary and the release of i5/OS PASE where the binary will run.

  If you compile your i5/OS PASE applications on AIX, the application binary created on AIX needs to be compatible with the version of i5/OS PASE that you want the application to run in. The following table shows which AIX binary versions are compatible with different versions of i5/OS PASE. For example, a 32-bit application created for AIX release 5.1 will run on i5/OS PASE V5R4, V5R3, or OS/400^® PASE V5R2, but not on OS/400 PASE V5R1. Similarly, a 64-bit application created for AIX release 4.3 will run on OS/400 PASE V5R1, but not on i5/OS PASE V5R4, V5R3, or OS/400 PASE V5R2.

  AIX release	OS/400 V5R1	OS/400 V5R2	i5/OS V5R3	i5/OS V5R4
  4.3 (32-bit)	X	X	X	X
  4.3 (64-bit)	X	-	-	-
  5.1 (32- or 64-bit)	-	X	X	X
  5.2 (32- or 64-bit)	-	-	X	X
  5.3 (32- or 64-bit)	-	-	-	X

• i5/OS PASE does not provide the AIX kernel on i5/OS.

  Instead, any low-level system functions that are needed by a shared library are routed to the i5/OS kernel or to the integrated i5/OS functions. In this regard, i5/OS PASE bridges the gap across the AIX and i5/OS platforms: your code uses the same syntax for the APIs in the shared libraries as you can find on AIX, but your i5/OS PASE program runs within an i5/OS job and is managed by i5/OS just like any other i5/OS job.

• In most cases, the APIs you call in i5/OS PASE behave in exactly the same manner as they do on AIX.

  Some APIs, however, might behave differently in i5/OS PASE, or might not be supported in i5/OS PASE. Because of this, your plan for preparing i5/OS PASE programs should begin with a thorough code analysis using the API Analysis Tool. This tool gives you a comprehensive summary of the types of program modifications you need to consider in porting your AIX application to i5/OS PASE.

• Consider some of the differences that exist between the AIX and i5/OS platforms:
  • AIX is generally case-sensitive, but certain i5/OS file systems are not.
  • AIX generally uses ASCII for data encoding, but i5/OS generally uses Extended Binary Coded Decimal Interchange Code. This will be a consideration if you want to manage the details of calling ILE code from your i5/OS PASE program. For example, you must explicitly code i5/OS PASE programs to handle character encoding conversions on strings when you make calls from i5/OS PASE to arbitrary ILE procedures. i5/OS PASE runtime support includes the iconv_open(), iconv(), and iconv_close() functions for character encoding conversion.
    Note: i5/OS PASE and ILE have independent implementations of iconv() interfaces, each with its own translation tables. The translations supported by i5/OS PASE iconv() support can be modified and extended by users because they are stored as byte stream files in the integrated file system.
  • AIX applications expect that lines (for example, in files and shell scripts) will end with a line feed (LF), but personal computer (PC) software and i5/OS software typically end lines with a carriage return and line feed (CRLF).
  • Some of the scripts and programs you use on AIX might use hardcoded paths to standard utilities, and you might need to modify the path to reflect the paths you will be using in i5/OS PASE. See Analyze your program's compatibility with i5/OS PASE for more information.

i5/OS PASE automatically handles some of these issues. For example, when you use the i5/OS PASE runtime service that the system provides (including any system call or runtime function in a shared library shipped with i5/OS option 33), i5/OS PASE performs ASCII-to-EBCDIC conversions as needed, although generally no conversions are done for data that is read or written to a file descriptor (byte stream file or socket).

You can use other low-level functions, such as _ILECALL, to extend the functionality of your i5/OS PASE program with calls to ILE functions and APIs, but as mentioned above you might need to handle data conversion. Also, coding these extensions into your program requires the use of additional header and export files.