Need help in Keil 5 locating code for RAM execution

Thank you for this reply.  I tried many different variations of the .sct file, and looked at the .mp file generated.  Some attempts did not compile because it appears that the order of the sections in the .sct file makes a difference.  With the FLASH_EXEC section first, it works, but with it placed later in the file, I get these errors:

RxModule\RxModule.axf: Error: L6788E: Scatter-loading of execution region FLASH_EXEC to execution address [0x08000000,0x0805aac4) will cause the contents of execution region FLASH_EXEC at load-address [0x08001fdc,0x0805caa0) to be corrupted at run-time.
RxModule\RxModule.axf: Error: L6202E: __main.o(!!!main) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: __scatter.o(!!!scatter) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: __scatter_copy.o(!!handler_copy) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: __scatter_zi.o(!!handler_zi) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: anon$$obj.o(Region$$Table) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6203E: Entry point (0x080001ad) lies within non-root region FLASH_EXEC.

This is the .sct file that worked for me:

FLASH    0x08000000    0x000C0000
{
    ;It appears this must be first to make it the root region
    FLASH_EXEC    0x08000000    0x000C0000
    {
        *.o (RESET, +First)
        * (+RO)
    }

    ;This code will be loaded into RAM from flash by library c_w.l
    NORMAL_RAM        0x20000000    0x00030000
    {
        main.o (+RO)
        Boot.o (+RO)
        Flash.o (+RO)
        AddPrintf.o (+RO)
        stm32f4xx_hal_msp.o (+RO)
        * (+RW +ZI)
    }

    ARM_LIB_STACKHEAP    0x10000000    EMPTY    0x00010000
    {
    }
}

Note that I am reserving flash after 0x000C0000 for other purposes.

I still have a few of questions:

1. In my .sct file, I have *.o and explicit lines line main.o.  It looks like main.o will be assigned before *.o, but I am not sure.  It would be a pain if I had to list every .o file explicitly.  Is there a syntax for *.o except main.o, ... ?

2. If I include main.o, for example, in NORMAL_RAM and main calls printf, will the compiler include the C library code for printf in RAM as well?

3. When I added the linker switch "--datacompressor=off", the resulting flash size was slightly smaller.  I would have expected it to be larger without compression.  Any idea why?

4. It looks like all the work of moving code from flash to RAM, including decompression if needed, is performed by c_w.l.  Is the source code for this library available anywhere?  Or, is there documentation for this library indicating the format of the data in flash that it references, including the compression method?

My goal is a very detailed understanding of how the startup code works.

Thank you again to everyone who replied.

Thank you for this reply.  I tried many different variations of the .sct file, and looked at the .mp file generated.  Some attempts did not compile because it appears that the order of the sections in the .sct file makes a difference.  With the FLASH_EXEC section first, it works, but with it placed later in the file, I get these errors:

RxModule\RxModule.axf: Error: L6788E: Scatter-loading of execution region FLASH_EXEC to execution address [0x08000000,0x0805aac4) will cause the contents of execution region FLASH_EXEC at load-address [0x08001fdc,0x0805caa0) to be corrupted at run-time.
RxModule\RxModule.axf: Error: L6202E: __main.o(!!!main) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: __scatter.o(!!!scatter) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: __scatter_copy.o(!!handler_copy) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: __scatter_zi.o(!!handler_zi) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6202E: anon$$obj.o(Region$$Table) cannot be assigned to non-root region 'FLASH_EXEC'
RxModule\RxModule.axf: Error: L6203E: Entry point (0x080001ad) lies within non-root region FLASH_EXEC.

This is the .sct file that worked for me:

FLASH    0x08000000    0x000C0000
{
    ;It appears this must be first to make it the root region
    FLASH_EXEC    0x08000000    0x000C0000
    {
        *.o (RESET, +First)
        * (+RO)
    }

    ;This code will be loaded into RAM from flash by library c_w.l
    NORMAL_RAM        0x20000000    0x00030000
    {
        main.o (+RO)
        Boot.o (+RO)
        Flash.o (+RO)
        AddPrintf.o (+RO)
        stm32f4xx_hal_msp.o (+RO)
        * (+RW +ZI)
    }

    ARM_LIB_STACKHEAP    0x10000000    EMPTY    0x00010000
    {
    }
}

Note that I am reserving flash after 0x000C0000 for other purposes.

I still have a few of questions:

1. In my .sct file, I have *.o and explicit lines line main.o.  It looks like main.o will be assigned before *.o, but I am not sure.  It would be a pain if I had to list every .o file explicitly.  Is there a syntax for *.o except main.o, ... ?

2. If I include main.o, for example, in NORMAL_RAM and main calls printf, will the compiler include the C library code for printf in RAM as well?

3. When I added the linker switch "--datacompressor=off", the resulting flash size was slightly smaller.  I would have expected it to be larger without compression.  Any idea why?

4. It looks like all the work of moving code from flash to RAM, including decompression if needed, is performed by c_w.l.  Is the source code for this library available anywhere?  Or, is there documentation for this library indicating the format of the data in flash that it references, including the compression method?

My goal is a very detailed understanding of how the startup code works.

Thank you again to everyone who replied.

0) The errors make sense - the scatter loading code must itself execute from a non-moved address (known as a ROOT region). In the above, FLASH_EXEC is a ROOT region, as load address (from the outer braces FLASH) and execution address are the same.

There are ordering rules within regions that go beyond the order listed in the scatter file, hence the +FIRST qualifier to force the vector table to be exactly the first thing in that region.

Also, regarding the size of FLASH_EXEC, don't forget that FLASH (load region) also needs space to store the code (and data) that will be relocated to NORMAL_RAM.

1) The * (+RO) will catch all code from objects that are not explicitly referenced elsewhere in the scatter file. You can also use .ANY if you wish to share them in multiple regions.

2) No. It will be amongst "* (+RO)" unless explicitly placed therein.

3) Compare code size - if no data compression, then no need for the code to decompress. I suspect you are referring to just a few bytes.

4) Source is not available. The init sequence is described here:

https://developer.arm.com/documentation/100748/0623/Embedded-Software-Development/Application-startup

Also, some docs on the compression below:

https://developer.arm.com/documentation/101754/0623/armlink-Reference/Linker-Optimization-Features/Optimization-with-RW-data-compression/How-compression-is-applied

Regards, Ronan