Flash Size on STM32

Two possibilities come to mind right away:

1) you didn't inform the tools that you only have internal flash, and/or its exact size

2) you underestimate the cleverness of the tools.  The master copy of the RW data may be kept in a (slightly) compressed form, allowing it to use less than those 3304 bytes.

For the full story, you'll have to look deeper into the linker's work output than that summary line, i.e. the actual map file.

Two possibilities come to mind right away:

1) you didn't inform the tools that you only have internal flash, and/or its exact size

2) you underestimate the cleverness of the tools.  The master copy of the RW data may be kept in a (slightly) compressed form, allowing it to use less than those 3304 bytes.

For the full story, you'll have to look deeper into the linker's work output than that summary line, i.e. the actual map file.

I agree with both of the above. You should specify region sizes to ensure you do not overflow.

https://developer.arm.com/documentation/101754/0624/armlink-Reference/Scatter-loading-Features/The-scatter-loading-mechanism/Scatter-loading-images-with-a-simple-memory-map

Assuming you have done this, data compression is almost certainly the reason.

The report from the MDK IDE shows the uncompressed values, for example 2572 bytes below:

Program Size: Code=6284 RO-data=536 RW-data=2572 ZI-data=5204

However if you look at the generated .map file (and assuming Totals Info is enabled in the Target Option > Listing tab), you will see the compressed value:

      Code (inc. data)   RO Data    RW Data    ZI Data      Debug   

      6284        310        536       2572       5204     214117   Grand Totals
      6284        310        536        428       5204     214117   ELF Image Totals (compressed)
      6284        310        536        428          0          0   ROM Totals

==============================================================================

    Total RO  Size (Code + RO Data)                 6820 (   6.66kB)
    Total RW  Size (RW Data + ZI Data)              7776 (   7.59kB)
    Total ROM Size (Code + RO Data + RW Data)       7248 (   7.08kB)

==============================================================================

In this example the "Total ROM Size" uses the compressed data size (428 bytes), but the RW size uses the uncompressed size.

See also:

https://developer.arm.com/documentation/101754/0624/armlink-Reference/armlink-Command-line-Options/--datacompressor-opt

https://developer.arm.com/documentation/100748/0624/Getting-Image-Details/Example-of-using-the---info-linker-option