Write to memory address in target

        Note: mask option is not supported by stub loaders, use update_reg() function.

def write_reg(self, addr, value, mask=0xFFFFFFFF, delay_us=0):
        """ Write to memory address in target

        Note: mask option is not supported by stub loaders, use update_reg() function.
        """
        return self.check_command("write target memory", self.ESP_WRITE_REG,
                                  struct.pack('<IIII', addr, value, mask, delay_us))