Use different memory bank

Antoine Zen-Ruffinen


I have trouble getting full usage of the RAM on my SoC using zephyr and I might need a little help as I have not found the needed information in the doc. Here's the situation:

I'm using Zephyr on the iMXRT1062 platform which is an Cortex-M7 with 3 separate non-contigus memory banks, from the datasheet (I's a little more complicated than that, but here I simplify):

ITCM (Instruction Tight Coupled Memory) @ 0x0000'0000, size 128K

DTCM (Data Tight Coupled Memory) @ 0x2000'0000, size 128K

OCRAM (General RAM, slower) @ 0x2020'0000, size 768 K

This setup is clearly defined in the .dts and the linker script in `zephyr/soc/arm/nxp_imx/rt/linker.ld`. When compiling an image, I get this same setup printed form the build system too (OCRAM is renamed SRAM by the build system, don't know why):


[7/12] Linking C executable zephyr/zephyr_prebuilt.elf
Memory region         Used Size  Region Size  %age Used
            DTCM:          0 GB       128 KB      0.00%
            ITCM:          0 GB       128 KB      0.00%
           FLASH:      276524 B        16 MB      1.65%
            SRAM:      114196 B       768 KB     14.52%
        IDT_LIST:         344 B         2 KB     16.80%
[12/12] Linking C executable zephyr/zephyr.elf

As you can see all is placed in SRAM section. I can change and have everything linked to DTCM using KConfig option "CONFIG_DATA_DTCM", but then it's EVERTHING there . I've discovered that there is a macro `__dtcm_data_section` defined in `zephyr/include/linker/section_tags.h` that I thought it will place the variable in DTCM, but if I use it, I got the following error from the linker:

/home/antoine/tools/SDKs/zephyr-sdk-0.11.1/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/9.2.0/../../../../arm-zephyr-eabi/bin/ld: warning: orphan section `.dtcm_data' from `app/libapp.a(com_uart.c.obj)' being placed in section `.dtcm_data'

My questions: 

 - How to use different non-contigus  memory region with Zephyr ?

 - How can I specify what data should be placed on witch RAM bank ?

 - How to specify that code should be relocated to ITCM while using CODE_DATA_RELOCATION ? I have tried "zephyr_code_relocate(ram_func.c ITCM)" but with no success.

 - Can I place, for instance, all kernel code into ITCM with similar mechanism as "zephyr_code_relocate()" (ITCM  is faster than flash as the flash is external on this SoC)? 

Antoine Zen-Ruffinen

Riedo Networks Ltd
Route de la Fonderie 6, 1700 Fribourg, Switzerland
Tel: +41 26 505 50 03, Fax: +41 26 505 50 01

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