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Signature Creator for NXP Cortex-M Devices

The command-line utility, ElfDwT, computes and writes a signature into the application image file. The signature is a checksum required for NXP devices based on Cortex-M processors and must be used with Flash loaders that do not implement this computation automatically. The ULINK Family of Debug and Trace Adapters do compute the signature automatically when used as a Flash loader.

The executable file, ElfDwT.exe, is located in the folder ..\ARM\BIN. Use the application image file as an argument. The result is written back into the image file. If no BASEADDRESS is specified, then the base address 0x00 is assumed. For example:

ElfDwT blinky.axf
ElfDwT blinky.axf BASEADDRESS(0x1B000000)

Algorithm for creating the checksum
The reserved Cortex-M exception vector location 7 (offset 0x 001C in the vector table) should contain the 2’s complement of the checksum of table entries 0 through 6. This causes the checksum of the first 8 table entries to be 0. The boot loader code checksums the first 8 locations in sector 0 of the flash. If the result is 0, then execution control is transferred to the user code.

Note

  • Use the Signature Creator utility in Options for Target - User - Run User Programs after Build/Rebuild to compute the checksum automatically after a build process.
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