UNINIT section gets initialized

Hi Ron,

Thanks for your reply.
I already read those articles and tried to solve this issue using them, but it does not change anything.

Here is my full scatter file :

LR_IROM1 0x00000000 0x00080000  {    ; load region size_region

        ER_BOOTLOADER 0x00000000 0x00001000 {
                *.o (BLRESET, +First)
                *.o (.bl_start)
                *.o (Bootloader)
        }

        RO_PARAMETERS0 0x00001000 FIXED 0x00001000 {
                *.o (ModuleParameters0, +First)
        }

        RO_PARAMETERS1 0x00002000 FIXED 0x00001000 {
                *.o (ModuleParameters1, +First)
        }

        ER_BOOT 0x00003000 FIXED 0x00000100 {
                *.o (MAINSTART, +First)
        }

        ; Following section needed to align vector table to a multiple of 256
        ER_ACTUAL 0x00003100 FIXED 0x0003CF00 {
                *.o (IRQVECT, +First)
                *(InRoot$$Sections)
                .ANY (+RO)
        }

        RW_BOOTLOADER 0x10000020 UNINIT 0x0000FFE0  {   ; Overlap RW_ACTUAL. Must be defined before RW_ACTUAL.
                *.o (Bootram)                                                           ; Use --diag_warning=L6221E linker cmd line option
                *.o (Bootstack)
        }

        RW_ACTUAL 0x10000020 0x0000FFE0  {
                .ANY (+RW, +ZI)
                file_config.o (+RW, +ZI)
        }

        RW_SUP_1 0x20000000 0x00004000  {
                .ANY (+RW, +ZI)
        }

        RW_SUP_2 0x20004000 0x00004000  {
                mci_*.o
                emac_*.o (+RW, +ZI)
                .ANY (+RW, +ZI)
        }
}

Please note that it is intended that RW_ACTUAL overlap RW_BOOTLOADER. That's the reason why I need that RW_BOOTLOADER region not to be initialized.

Thanks by advance.
Antoine

Hi Kevin,

Thanks for your answer. Unfortunately, it is exactly what I already tried.

In fact, as explained in article, --bss_threshold=0 is intended to force compiler to place "small global ZI data items in ZI data sections". My area is not small at all.
Additionally, my area is specified in an assembly file and not in C file. So compiler is not used.

In the first article, as you wrote, it is explained that NOINIT keyword in AREA tell "NOINIT Indicates that the data section is uninitialized, or initialized to zero... You can decide at link time whether an area is uninitialized or zero-initialized.".

But, HOW can I tell the linker to not init this space to zero ? As I understand, the UNINIT keyword in scatter file should do the job. Am I wrong ?

Thanks again by advance.
Antoine

        RW_BOOTLOADER 0x10000020 UNINIT 0x0000FFE0  {   ; Overlap RW_ACTUAL. Must be defined before RW_ACTUAL.
                *.o (Bootram)                                                           ; Use --diag_warning=L6221E linker cmd line option
                *.o (Bootstack)
        }

        RW_ACTUAL 0x10000020 0x0000FFE0  {
                .ANY (+RW, +ZI)
                file_config.o (+RW, +ZI)
        }

There is something I am not understanding here. Here is what I would expect to happen before main

1) Bootram would be initialized to appropriate values

2) Bootstack would not be initialized to zero

3) RW_ACTUAL .ANY would be initialized (to zero or values) It seems to me that it is highly likely that variables in RW_ACTUAL are at the same location as variables from RW_BOOTLOADER. (You would see this in the map file and see if this is the case.

4) file_config.o would have already matched the .ANY section and would have been located and initialized based the .ANY rules.

Are you expecting something different and if so, what is it that you are expecting.

I think the Error L6221E was there for a reason and would require some work to make sure everything in the overlapping regions worked correctly when you changed it to a warning.

Hi Robert,

Your understanding is nearly correct. Bootram and bootstack are used in a pre-main code et are no more used in main code. It is why the two regions can overlap and so, yes I now what I do when I turn error L6221E to a warning.

But since the initialization is done by the call to __main function of Keil lib, the bootram and bootstack are not initialized at startup because I use them before that call.

It is so why I do not want them to be initialized by the lib, since they are no more useful at that time.

So, in your points :
1) Yes, but it is done by my code and not by the lib.
2) Yes, it is correct before main code. But it is initialized later when calling __main and it is what I try to avoid.
3) Yes and overlap is under control.
4) It is not relevant for my problem, but to be clear, since their is 3 regions with .ANY, this force the linker to put file_config object in this one (due to limitations of NXP LPC RAM architecture).

I hope that I am clear.

Thanks.
Antoine

That helps some.

1) Yes, but it is done by my code and not by the lib.

OK, you initialize Bootram yourself, but when __scatter is called (as part of calling __main) it seems like it will will be initialized again.

2) Yes, it is correct before main code. But it is initialized later when calling __main and it is what I try to avoid.

It appears as if you are doing it correct such that Bootstack will not be zero initialized and Bootram will be re-initialized when __main is called. Please just verify that BootRam is being initialized and that even though I think Bootstack should not be initialized to 0, it is being initialized to zero. (obviously if you are still using that stack, having it set back to zero is an issue)

Only ZI data in UNINIT sections remain un-initialized, however any RW data in the UNINIT section does get initialized.

Everything posted so far addresses how to make a Zero Init section to not initialize. It explains why if your Zero Init data gets optimized into a RW region that even though you said it should not be initialized, it will still be initialized.