Why is RamFunction located in SRAM_DTC and not SRAM_ITC

[p_shep]

The MCUxpresso generated linker section for SRAM_DTC looks like the following:

/* Main DATA section (SRAM_DTC) */
.data : ALIGN(4)
{
FILL(0xff)
_data = . ;
PROVIDE(__start_data_RAM = .) ;
PROVIDE(__start_data_SRAM_DTC = .) ;
*(vtable)
*(.ramfunc*)
KEEP(*(CodeQuickAccess))
KEEP(*(DataQuickAccess))
*(RamFunction)
*(.data*)
. = ALIGN(4) ;
_edata = . ;
PROVIDE(__end_data_RAM = .) ;
PROVIDE(__end_data_SRAM_DTC = .) ;
} > SRAM_DTC AT>PROGRAM_FLASH

The equivalent SRAM_ITC section does have some ramfunc.*, but not the main *(RamFunction).

Wondering why that is?

ITC is otherwise not used for anything. Seems wasteful.

Thanks,

Paul.

[p_shep]

OK, so I've just tried, and now I know why.... it doesn't work.

Hit this issue:

https://community.nxp.com/t5/i-MX-RT/RT1064-How-to-solve-gcc-linker-error-ARM-exidx-0x0-relocation/t...

Essentially, since ITC is located at 0x00000000, the jump from Flash (0x70000000) is too great and you get a linker failure.

So that 128K of RAM is wasted? 

[jingpan]

Hi,

I don't understand what you mean. But jump from flash to ITCM is no problem. You can have the bootloader to copy code from flash and jump to there, or you can copy and jump by yourself. There isn't any address restriction to ARM CPU.

Regards,

Jing

[p_shep]

OK, so no technological reason for it, just the way the SDK has it set up.

Thanks.

[jingpan · Accepted solution]

Hi p_shep,

The examples in SDK default use flash and DTCM. Because DTCM is data TCM, ITCM is instruction TCM. If you want to put code or data into ITCM you can set in MCUXpresso. Then IDE will update .ld file. 

Click the yellow up arrow to move selected memory up in the table.

Link application to RAM or change Heap and Stack placement.

Regards,

Jing