Difference between revisions of "NXP LPC2xxx valid user code"
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== Example Calculation == |
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Revision as of 13:51, 9 September 2019
Some MCUs (e.g. LPC2xxx family) designed by NXP Semiconductors expect a checksum of the interrupt vectors to validate the user code. If the checksum matches the user code will be executed as expected, otherwise the code will not be executed.
Calculation
The interrupt vector at 0x0000_0014 should contain the Two's complement of the sum of the interrupt vectors before.
Example Calculation
Example content of interrupt vectors:
Address | Value |
---|---|
0x0000_0000 | 0xEA000006 |
0x0000_0004 | 0xEAFFFFFE |
0x0000_0008 | 0xEAFFFFFE |
0x0000_000C | 0xEAFFFFFE |
0x0000_0010 | 0xEAFFFFFE |
0x0000_0018 | 0xEAFFFFFE |
0x0000_001C | 0xEAFFFFFE |
Sum of all interrupt vectors (despite 0x0000_0014):
Sum = 0x6BFFFFFA
Checksum at 0x0000_0014 (two's complement of sum):
Checksum = ~(Sum) + 1 = 0x94000006
Troubleshooting
J-Flash will display a pop-up if the checksum is not valid and will offer to calculate the correct checksum for the user code:
If you do not want that the pop-up will show up, make sure that the checksum is correctly calculated in your data-file (see Calculation).