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iMX28 Bare Metal Code and Boot ROM

Question asked by markwilliams on Jan 24, 2020
Latest reply on Jan 27, 2020 by igorpadykov

Hi, I have created a bare metal memory test to run in the OCRAM of the iMX28. It is based on various OBDS and memtest applications in posts on these forums. I have used IAR for ARM to build the project and modified the elftosb bd file to suit.


Like others I have found that when I download using the usb loader I get an error but the code runs, albeit for a few seconds then stops. I know this because in my DDR test loop I output every 1MB tested and the count stops. However I find that if I re-run the USB downloader, although it doesn't do anything the test code resumes operation from the current MB count and runs forever more. Its like the first error leads to a hang and needs another kick from the downloader to recover and continue.


The error for the downloader is:


C:\D_Drive\Dev2\iMX28MemTest>sb_loader.exe /f
Downloading to device.
CStHidDevice::Download() Error(-13) during Write cbw.
Error(-13) during download.

Press any key to continue . . .


My test code will hang after a few seconds. If I re-run the downloader batch file it hangs in the command window but allows the code to run.

I also found that when the code is running from OCRAM if I unplug the USB cable used to download the image it immediately stops running. Why would the code executing in OCRAM stop when USB is disconnected?


I looked in the reference manual and found a few interesting points. It would seem that the boot ROM actually uses a portion of OCRAM so when using the downloader am I right in that you only have the lower 57K for applications? If so the bd file I have puts IVT at 0x1FF00 which would overlap onto boot ROM ram space:


IVT_ADDR = 0x1FF00;

section (0)
load image;
load ivt (entry = image:__iar_program_start) > IVT_ADDR;
hab call IVT_ADDR;



Also the above uses hab call. If I am jumping to OCRAM to run my code should I use hab jump instead of hab call? I have no intention of returning to boot ROM.


Finally when you jump from boot ROM using USB downloader into your own app I presume the USB peripheral is left configured still. Should custom code gracefully shut that down if it is not being used? Is this why my program crashes when USB is unplugged? Is the USB left configured by boot ROM and not being serviced by my app? Should I immediately disable the USB peripheral in my OCRAM app code?


Sorry lots of questions above - I have searched forums and read ref manuals to try and get the answers but just found lots of others who had similar problems with OCRAM test apps crashing or not running with no resolutions.


Thanks, Mark