HEAP size of the HiFi 4 DSP on RT685 Audio EVK

[AleP]

Hi,

I'm currently working on the DSP (HiFi 4) of a RT685 Audio EVK. I would like to know the HEAP size on that DSP and how to change that value.

Thank you.

[kerryzhou]

Hi @AleP ,

  Please check the build properties:

elf32xtensa.x,memmap.xmm

path:SDK_2_13_0_EVK-MIMXRT685\devices\MIMXRT685S\xtensa\gdbio\ldscripts

Wish it helps you!

Best Regards,

Kerry

[AleP]

Hi Kerry,

I've found the value, thank you. But could you please explain in detail what that value mean?

I read 0x480000, is that the address at which the HEAP starts? Or is it the HEAP size?

Thank you.

Best regards,

Alessandro

[kerryzhou]

Hi @AleP ,

 It should be the heap size.

Do you meet any issues about it?

Best Regards,

Kerry

[AleP]

Hi,

My device, from the datasheet, has 4.5 MB of RAM, but 0x480000 (the value I've found in my project) is actually 4.5 MB. How is that possible? Where is the stack then if all the memory is HEAP?

This is my configuration (default):

BEGIN dsp_core
0x00200000: sysram : dsp_core : 0x280000 : executable, writable ;
dsp_core : C : 0x00200000 - 0x0047ffff : STACK : HEAP : .rodata .literal .text .data __llvm_prf_names .bss;
END dsp_core

BEGIN dsp_uncached
0x20000000: sysram : dsp_uncached : 0x480000 : uncached, executable, writable ;
dsp_uncached : C : 0x20060000 - 0x2006ffff : NonCacheable.init NonCacheable ;
END dsp_uncached

BEGIN dram0
0x24000000: dataRam : dram0 : 0x10000 : writable ;
dram0_0 : C : 0x24000000 - 0x2400ffff : .dram0.rodata .ResetVector.literal .Level2InterruptVector.literal .Level3InterruptVector.literal .DebugExceptionVector.literal .NMIExceptionVector.literal .KernelExceptionVector.literal .UserExceptionVector.literal .DoubleExceptionVector.literal .iram0.literal .dram0.data .dram0.bss;
END dram0

Best regards,

Alessandro

[kerryzhou]

Hi @AleP ,

   I find the SDK doc Getting Started with Xplorer for EVK-MIMXRT685.pdf already mention the stack and heap situation:

So, the 0x00480000 is the entrypoint, it it the top of the segment, and count top down, so, in fact, the size also from 0x00480000.

Please check the doc on your side.

Wish it helps you!

Best Regards,

Kerry

[AleP]

Hi,

Thank you for your feedback. The board should have 64 MB of RAM:

Board Memory

• 64MB Macronix MX25U51245GXDI00 quad SPI flash
• 64MB AP Memory APS6408L-OBM-BA PSRAM 

Is therefore possible to expand the RAM available to the DSP? 2.5 MB sometimes is not enough.

If it's possible, do I have to change only the 48 0000 value? Do I have to change it in all the files that are visible in your screenshot?

Thank you for your support.

Best regards,

Alessandrp

[kerryzhou]

Hi @AleP ,

  If you expand the RAM side, do you want to use the external RAM chip?

Best Regards,

Kerry

[AleP]

Hi,

Yes, if it's possible it would be very useful. 

Thank you.

Best regards,

Alessandro

[kerryzhou]

Hi @AleP ,

  As I know, the RT685 can expand the RAM with the flexSPI, you can check the SDK code:

SDK_2_13_0_EVK-MIMXRT685\boards\evkmimxrt685\driver_examples\flexspi\psram

 It is using the external PSRAM with the flexSPI interface.

Wish it helps you!

Best Regards,

Kerry

[AleP]

Ok, thank you, I will look at that example!

[kerryzhou]

Hi @AleP ,

   Please keep patient, let me double check it internally, then I will give you the updated information.

Best Regards,

Kerry