Thomas James Just a geek.

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.net MicroFramework 4.3 BitConverter

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The BitConverter was added to the .net microframework in version 4.3 and provides a way to turn an array of bytes into a meaningful primitive such as a long.

var bytes = new byte[] 
{
    0x01, 0x02,
    0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A,
}
var someValue = BitConverter.ToInt64(bytes, 2);

Using it in my netduino targeting code, I encountered a number of occurrences where the netduino would hard lock and require a reset to become responsive again. I traced this back to some usages of the BitConverter but not others. Essentially the var someValue = ... line in the above code snippet.

In researching this issue I stumbled upon a related bug report in the netmf project, BitConverter startIndex not correct, which suggested that with the way the code was implemented the values being converted needed to be word aligned otherwise it wouldn’t work.

It looks like there are alignment issues. 32 bit pointers must be aligned on arm processors. Adding packed would solve this or use memory copy.

I was able to reproduce the issue on the EMX, G400, and Hydra. The Cerb and G120 perform properly, however they crash on non-zero start indexes for the 64bit conversions. I looked at the native code and it seems fine, it just adds the index to the pointer and casts it. It’s essentially: reinterpret_cast(buffer + start_index).

Giving this a try by padding the long value out was successful, ending the hard lock & reset cycle.

Eg

var bytes = new byte[] 
{
    0x01, 0x02, 0x00, 0x00, 
    0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A,
}
var someValue = BitConverter.ToInt64(bytes, 4);
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