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Bypass ATSAMD21 Cortex M0 Bootloader with J-Link Commander

Here’s a simple and interesting hack from Alexander Sparkowsky at roamingthings.de for using ‘J-Link to change the boot loader protection of a SAM D21.’

BOOTPROT defines the size of the boot loader in bytes. The defined boot loader section is write protected. So to (over)write the bootloader or write a programme without using a bootloader, this value has to be set to 0x7 which leads to a bootloader size of 0 bytes.

On the Feather M0 basic proto boards I used the BOOTPROT value has been set to 0x2 which results in the first 8k of the flash memory to be writeprotected.

The possible values are described in the SAMD21 datasheet in chapter 22.6.5. NVM User Configuration

Read more.


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