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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def trace_start(self):
 """Starts collecting trace data. Args: self (JLink):
 the ``JLink`` instance. Returns: ``None`` """

        cmd = enums.JLinkTraceCommand.START
        res = self._dll.JLINKARM_TRACE_Control(cmd, 0)
        if (res == 1):
            raise errors.JLinkException('Failed to start trace.')
        return None