BL51: Data Memory Overlap When Using PRECEDE Directive

Information in this article applies to:

• C51

SYMPTOMS

When I add printf() (or other functions that have local variables) to my project, I get a Memory Overlap Error from the linker for the Data space. Part of my map file looks like the following:

            TYPE    BASE      LENGTH    RELOCATION   SEGMENT NAME
            -----------------------------------------------------

            * * * * * * *   D A T A   M E M O R Y   * * * * * * *
            ...
            DATA    0018H     0024H     UNIT         _DATA_GROUP_
* OVERLAP * DATA    0028H     0002H     UNIT         ?DT?EVL_INIT
            DATA    003CH     0010H     UNIT         ?DT?DEMO1
                    004CH     0024H                  *** GAP ***
            ...

The segment ?DT?EVL_INIT is located at 0028H with the linker DATA directive. The linker PRECEDE directive is used with the _DATA_GROUP_ segment.

PRECEDE(_DATA_GROUP_) DATA(?DT?ELV_INIT(0x28))

CAUSE

When you added the printf() call, the size of the _DATA_GROUP_ segment increased in size to the point where it could not fit into Data memory before the ?DT?EVL_INIT segment. When the linker tried to place the ?DT?EVL_INIT segment into memory, it failed because part of that space was already taken by the Data Group. The reason the _DATA_GROUP_ segment was located before the ?DT_EVL_INIT segment was because the PRECEDE directive is used.

RESOLUTION

Remove _DATA_GROUP_ from the PRECEDE directive so the linker can fit the Data Group into Data memory after locating the ?DT?EVL_INIT segment. This gives the linker the greatest flexibility in locating the segments.

If it is not possible to remove _DATA_GROUP_ from the PRECEDE directive, then the DATA directive must be used to juggle the segments around so they can all fit into Data memory.

MORE INFORMATION

• Refer to DATA in the BL51 User's Guide.
• Refer to PRECEDE in the BL51 User's Guide.
• Refer to Overlay Groups in the BL51 User's Guide.

Last Reviewed: Thursday, February 25, 2021