Do not read or write feature flags from an ISR

[sergeuz]

Problem

Device panic (assertion failure) occurs when DFU mode is triggered via baud rate change.

Solution

Do not read or write feature flags, which are stored in DCT, from an ISR. Users are still allowed to call such methods as System.reset() and System.dfu() from an ISR to preserve backwards compatibility.

Steps to Test

• Try to enable DFU mode via baud rate change.
• Check what happens with System.resetReason(), characterize the behavior.

Example App

N/A

References

N/A

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[technobly]

Any reason we don't use the same error checking pattern here?

int result = dct_read_app_data_copy(DCT_RADIO_FLAGS_OFFSET, &current, sizeof(current));
if (result != 0) {
    return result;
}
//...
result = dct_write_app_data(&current, DCT_RADIO_FLAGS_OFFSET, 1);
if (result != 0) {
    return result;
}