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Need interface MCU initial boot firmware

jeffd

Please don't give the usual response of 'try the troubleshooting guide' to flash the J-Link or Mbed firmware.  

What I (and probably others) really need is the real initial bootloader firmware for the AT91SAM3U2 that shows up as the BOOTLOADER drive when the IF/BOOTRESET pin is pressed on power on.  It seems that if the J-link operational firmware is corrupted, no amount of BOOTLOADER recovery seems to work to restore the J-Link.  I'm able to restore the Mbed firmware but that just allows the device to show up as a USB drive to program the nRF52x code which is *not* what i need to do.

I've been unable to determine where the actual initial Mbed-enabled boot code is.

What i've done is cut SB31 and applied VDD to the ERASE pin of the interface MCU to get the SAM-BA bootloader interface connected.  Then i've attempted to 'Enable Flash Access', 'Erase All Flash', 'Send File Name' with the .bin file for the J-Link firmware, and then finally 'Boot From Flash (GPNVM1)' before cycling power to the DK board.  There's no detection of the USB link after that.  I've obviously erased the initial Mbed bootloader because it doesn't appear anymore when IF/BOOTRESET is pressed during power on.  

It seems to me there's the initial Mbed-enabled bootloader for the interface MCU which will boot into either the J-Link firmware or the Mbed firmware if they exist, but the J-Link and secondary Mbed firmware don't include the initial boot capability.  I'd rather not have to get the Mbed development software and build my own since Nordic has already done it.

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    ok, for any subscribers of this issue, some further debug and i've gotten the mbed bootloader back installed and showing up as a drive.  i actually found this link: https://devzone.nordicsemi.com/f/nordic-q-a/37759/alternative-way-to-re-flash-interface-mcu-using-tc2050-j3-on-pca10040 which describes exactly what i already figured out by reading the AT91SAM3U2 datasheet and the nRF52 DK schematic.  (forgot to mention, applying VDD to the cut SB31 was simply a wire on one of the nRF current management pins to SB31 1/2 moon closest to the chip for a second while applying power).  

    when i used the 140828_MBED_bootloader.bin from the link above (scroll down to the bottom, file is JLINK Restore.zip) i'm able to get back to the BOOTLOADER drive with the IF/BOOTRESET button. 

    previously, the firmware i was trying to load was called nrf5x_atsam3u2c_if_mbed_V0221_11012017.bin (a 35K file), vs the 140828_MBED_bootloader.bin file which is 19K.  The nrf5x_xxx file is what you get from the nRF52 DK downloads page.

    please note that the above zip file has a guide in it that basically says that it may not work in all cases, so YMMV.    If you have a new board like mine, be aware that the SB31 is shorted to GND, use a razor blade to cut the link.  The MCU has a permanent pulldown already so it should work as normal without it.

    i'm still not able to get the board to show up as a JLINK device though, but after sending the JLINK firmware to it and restarting, LED5 is flashing pretty fast, maybe 10Hz.  windows recognizes *something* based on the sounds, but nothing shows up in device manager.  i'm wondering if the security bit needs to be enabled for the JLINK firmware to boot.  perhaps they are protecting it?  well, just tried that and it didn't make a difference.   continue digging.

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    ok, for any subscribers of this issue, some further debug and i've gotten the mbed bootloader back installed and showing up as a drive.  i actually found this link: https://devzone.nordicsemi.com/f/nordic-q-a/37759/alternative-way-to-re-flash-interface-mcu-using-tc2050-j3-on-pca10040 which describes exactly what i already figured out by reading the AT91SAM3U2 datasheet and the nRF52 DK schematic.  (forgot to mention, applying VDD to the cut SB31 was simply a wire on one of the nRF current management pins to SB31 1/2 moon closest to the chip for a second while applying power).  

    when i used the 140828_MBED_bootloader.bin from the link above (scroll down to the bottom, file is JLINK Restore.zip) i'm able to get back to the BOOTLOADER drive with the IF/BOOTRESET button. 

    previously, the firmware i was trying to load was called nrf5x_atsam3u2c_if_mbed_V0221_11012017.bin (a 35K file), vs the 140828_MBED_bootloader.bin file which is 19K.  The nrf5x_xxx file is what you get from the nRF52 DK downloads page.

    please note that the above zip file has a guide in it that basically says that it may not work in all cases, so YMMV.    If you have a new board like mine, be aware that the SB31 is shorted to GND, use a razor blade to cut the link.  The MCU has a permanent pulldown already so it should work as normal without it.

    i'm still not able to get the board to show up as a JLINK device though, but after sending the JLINK firmware to it and restarting, LED5 is flashing pretty fast, maybe 10Hz.  windows recognizes *something* based on the sounds, but nothing shows up in device manager.  i'm wondering if the security bit needs to be enabled for the JLINK firmware to boot.  perhaps they are protecting it?  well, just tried that and it didn't make a difference.   continue digging.

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