LX51: LINKER LEAVES BIG GAPS IN MEMORY WHEN USING _AT_

Information in this article applies to:

• LX51 Version 3.51p

QUESTION

I'm building a project with PK51 V7.02b and extended linker enabled (LX51 V3.51p). This project has 62K of xdata variables, some of those variables were declared using the _at_ keyword, to put them in a specific address like 4B70H and 4FA0H, and I've notice a big gap in xdata before those _at_ variables. The linker is not placing variables before those _at_ variables and a lot of space is wasted. The old C51 V7.01 doesn't show the same behavior. Here's the map file showing the gap under V7.02b:

* * * * * * * * * * *  X D A T A   M E M O R Y  * * * * * * * * * * * * *
003430H   003631H   000202H   BYTE   UNIT     XDATA          ?XD?HELLO
003632H   004B6FH   00153EH   ---    ---      **GAP**
004B70H   004B71H   000002H   BYTE   OFFS..   XDATA          ?XD?HELLO?0
004B72H   004F9FH   00042EH   ---    ---      **GAP**
004FA0H   004FA1H   000002H   BYTE   OFFS..   XDATA          ?XD?HELLO?1
004FA2H   0051A1H   000200H   BYTE   UNIT     XDATA          ?XD?TEST1
0051A2H   0055A1H   000400H   BYTE   UNIT     XDATA          ?XD?TEST2
0055A2H   005FA1H   000A00H   BYTE   UNIT     XDATA          ?XD?TEST3

In the example above, ?XD?TEST1, ?XD?TEST2, ?XD?TEST3 should be placed before ?XD?HELLO?0, but they are not.

The following is the correct behavior when I use C51 V7.01, for example:

* * * * * * * * * * *  X D A T A   M E M O R Y  * * * * * * * * * * * * *
003430H   003631H   000202H   BYTE   UNIT     XDATA          ?XD?HELLO
003632H   003831H   000200H   BYTE   UNIT     XDATA          ?XD?TEST1
003832H   003C31H   000400H   BYTE   UNIT     XDATA          ?XD?TEST2
003C32H   004631H   000A00H   BYTE   UNIT     XDATA          ?XD?TEST3
004632H   004B6FH   00053EH   ---    ---      **GAP**
004B70H   004B71H   000002H   BYTE   OFFS..   XDATA          ?XD?HELLO?0
004B72H   004F9FH   00042EH   ---    ---      **GAP**
004FA0H   004FA1H   000002H   BYTE   OFFS..   XDATA          ?XD?HELLO?1

Is it a problem with the tools or am I missing something?

ANSWER

This was a problem with the LX51 Linker that has been corrected. You may download the latest updates from the Keil Website.

Last Reviewed: Friday, July 15, 2005