I am switching from using GNU ARM toolchain to using the ARM DS-5 compiler toolchain. The microcontroller I am programming has flash memory starting at 0x08000000, and RAM starting at 0x20000000. My application contains a main() function that just increments a global variable. I set the initial value of the global variable to 0xaa, however it seems that the scatterload function does not copy the initial value to the variable's execution address. When I debug the code the initial value is 0xFFFFFFFF(the default value of the flash memory). I think what is happening is that the scatterload function is accessing where the initial value should have been in flash and copying it to RAM. The problem is that the data was not loaded to the flash. When I print out the map of the elf file, I see the variable in the .data.var section.
Here is what my scatter file looks like:
LOAD_ROM_1 0x08000000 0x100000 { FLASH 0x08000000 { startup_stm32l476xx.o (RESET, +FIRST) * (InRoot$$Sections) .ANY (+RO) } SRAM1 0x20000000 0x18000 { .ANY (+RW, +ZI) } }
I am debugging my code using arm gdb from the GNU toolchain. One think that looks odd to me is when I load the program it displays:
(gdb) load Loading section FLASH, size 0x5a8 lma 0x8000000 Loading section SRAM1, size 0x8 lma 0x20000000 Start address 0x8000188, load size 1456 Transfer rate: 6 KB/sec, 728 bytes/write. (gdb)
It seems like the SRAM region is being loaded directly to the microcontroller RAM. I intended it to be loaded into flash after the read-only memory and then be copied into RAM by the scatterload function.
There seems to be something I don't understand about the scatterloading process. Anyone else see what I am doing wrong?
Thanks
FromELF is Keil's AXF/ELF dumping tool
Normally the statics are unpacked from the load region by the __main function called in the startup.s file.
Thanks for your help,
I am able to step through __main, and it branches to __scatterload_rt2 and then branches to __rt_entry_sh. Eventually __main calls main(), however when I print out the value of my global variable it has not been initialized to the value I set but is instead set to 0xFFFFFFFF.
So my understanding is... Everything in the load region (LOAD_ROM_1 in my case) is loaded at 0x08000000. Then when the program is run, every execution region with a different address from the load address is copied to its execution address. So in my case SRAM1 is copied from where it was loaded in flash to its execution address(0x20000000). Is this understanding correct?
What seems to be actually happening is a little different, it seems that the SRAM1 section is being loaded to (0x20000000).
Here are the first three sections listed fromelf:
** Section #1 'FLASH' (SHT_PROGBITS) [SHF_ALLOC + SHF_EXECINSTR] Size : 1448 bytes (alignment 4) Address: 0x08000000 ** Section #2 'SRAM1' (SHT_PROGBITS) [SHF_ALLOC + SHF_WRITE] Size : 8 bytes (alignment 8) Address: 0x20000000 ** Section #3 'SRAM1' (SHT_NOBITS) [SHF_ALLOC + SHF_WRITE] Size : 1632 bytes (alignment 8) Address: 0x20000008
Also I think I should clarify, I am not using the entire DS-5 development studio, I am only using the ARM Compiler toolchain that it uses(ARMCompiler6.6). Couldn't figure out how to edit my post so the tag is a bit misleading. For now I am just trying to get something simple working using cmake.
Running objdump on the elf file clears things up a little for me..
ubuntu@ubuntu-xenial:~/clang_test/build$ arm-none-eabi-objdump -h HARDWARE_TESTS.elf HARDWARE_TESTS.elf: file format elf32-littlearm Sections: Idx Name Size VMA LMA File off Algn 0 FLASH 000005a8 08000000 08000000 00000038 2**2 CONTENTS, ALLOC, LOAD, READONLY, CODE 1 SRAM1 00000008 20000000 20000000 000005e0 2**3 CONTENTS, ALLOC, LOAD, DATA 2 SRAM1 00000660 20000008 20000008 000005e8 2**3 ALLOC 3 .debug_abbrev 00000151 00000000 00000000 000005e8 2**0 CONTENTS, READONLY, DEBUGGING 4 .debug_frame 000004d4 00000000 00000000 00000739 2**0 CONTENTS, READONLY, DEBUGGING 5 .debug_info 0000055e 00000000 00000000 00000c0d 2**0 CONTENTS, READONLY, DEBUGGING 6 .debug_line 000002cd 00000000 00000000 0000116b 2**0 CONTENTS, READONLY, DEBUGGING 7 .debug_pubnames 000000ba 00000000 00000000 00001438 2**0 CONTENTS, READONLY, DEBUGGING 8 .debug_pubtypes 0000008e 00000000 00000000 000014f2 2**0 CONTENTS, READONLY, DEBUGGING 9 .debug_str 000003a2 00000000 00000000 00001580 2**0 CONTENTS, READONLY, DEBUGGING 10 .debug_ranges 00000030 00000000 00000000 00001922 2**0 CONTENTS, READONLY, DEBUGGING 11 .note 0000001c 00000000 00000000 0000439c 2**2 CONTENTS, READONLY 12 .comment 00000344 00000000 00000000 000043b8 2**0 CONTENTS, READONLY
When my program is linked SRAM1 region is given load address 0x20000000. What I want is VMA to be 0x20000000 and LMA to be 0x08000000+(some offset). Not sure why this is happening though. Are there any other parameters I need to pass to the linker other than --scatter file?