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DK-TM4C129X enet_s2e Example

SL
Intellectual 410 points

I'm using the enet_s2e example and I'm able to build and run it.  However, when I change the APP_BASE, it stops working.  When debugging it and pausing the execution, the disassembly opens with the message "No source available for "0xfffffffe"".  When the APP_BASE is 0, the application works just fine.  Shouldn't I be able to change the APP_BASE to something else?  I can change other examples APP_BASE without any issue.

Thanks.

  • 0
    TI__Guru 59540 points
    Hi SL, I've forwarded your post a team member that has had a lot of experience with s2e applications. They should get back with you shortly.
  • 0 in reply to Chuck Davenport
    TI__Mastermind 22640 points

    When the value of APP_BASE is changed, the interrupt vector table is moved from the default memory location (that is 0x0) to this new changed location.

    The register VTABLE has to be updated to this location, so that  NVIC can branch to the correct interrupt handlers on an interrupt. Also the SP and PC should be loaded with the values at (APP_BASE) and (APP_BASE + 4) locations respectively. This is typically done by the bootloader, which sits at the default location and updates the SP, PC and VTABLE values to run the application at APP_BASE.

    Some IDEs like CCS automatically load the correct SP and PC values, when run in debug mode. Hence the applications that don't use interrupts might work, but the applications that use interrupts will fault. Most likely this is the issue you are noticing.

    Is there a reason you are changing the APP_BASE without using a bootloader?

    Sai

  • 0 in reply to Sai Reddy
    Intellectual 410 points

    Sai,

    Thanks, that was it.  it was the VTABLE that was missing since the enet_s2e uses interrupt whereas the other examples I tried did not.  We will be using a bootloader but I just wanted to test out the enet_s2e to make sure that it would work at a different location than 0.

    Thanks.

  • 0 in reply to Sai Reddy
    Intellectual 410 points

    Sai,

    I actually have a follow up question and hope you can help with it.  So we're building a custom bootloader.  It's still in the beginning stages but we were testing the jump to the application but it doesn't appear to work.  What we did was program the TM4C129X with one of the example programs at address 0x10000 and we have our customer bootloader at address 0.  When we program an example without interrupts, the jump works perfectly fine.  However, if we program an example with interrutps, the jump doesn't work.  I'm guessing this has something to do with what you mentioned above with regards to the VTABLE.  We tried a couple of ways to setting the VTABLE, one right before we jump to the application and the second where we modified the application to set it right at the beginning.  However, it's not working.  So is there something else that I need to do on the bootloader to in order to successfully jump to the application.

    Here's the inline assembly code we're using to perform the jump to the application code:

    __asm(" movd r0, #65536 \n"

    " ldr r1, [r0] \n"

    " mov sp, r1");

    __asm(" ldr r1, [r0, #4]\n"

    " mov pc, r1");

     

    Thanks.

  • 0 in reply to SL
    TI__Mastermind 22640 points
    TivaWare has a example for the flash-based bootloader in the folder "/examples/boards/dk-tm4c129x/". Did you already refer that? If not, I would recommend using this bootloader as the base for your custom bootloader.

    Did you check other threads on this forum? Bootloader questions are pretty common and the chance that this question is answered is very high.

    One last thing - it is better to start a new thread as the title of this thread does not reflect the content. So the discussion here won't be useful for others.

    Thanks,
    Sai