Electronic communication device, magnetic disk device and serial communication method

A magnetic disk device comprising:

• a disk;
• a head which writes data to the disk and reads data from the disk;
• a memory;
• and
• a controller which controls, according to a number of bit data in which an error has occurred of packet data transferred in serial communication, whether to execute logging of information of the error of the packet data to the memory or stop logging of information of the error of the packet data to the memory,
• wherein
• when the number of times invalid packet data which are not correctable by error correction is transferred consecutively is greater than or equal to a first threshold, the controller stops logging from first information about an error of first packet data transferred after first invalid packet data which is last invalid packet data of the consecutive invalid packet data to the memory, and
• when the number of times valid packet data which are correctable by error correction is transmitted consecutively after the first invalid packet data is greater than or equal to a second threshold, the controller starts logging from second information of an error of second packet data transmitted after first valid packet data which is last valid packet data of the consecutive valid packet data to the memory.