Magnetic disk device and method of controlling the same

A magnetic disk device comprising:

• a first decoding circuit that calculates likelihood information by executing Viterbi decoding using a parameter for normalizing a branch metric on a signal sequence read from a magnetic disk;
• a second decoding circuit that generates a first bit data sequence by iterative decoding using the likelihood information, and executes a check using a parity check matrix on the first bit data sequence;
• a control circuit that causes the first decoding circuit and the second decoding circuit to repeatedly execute decoding, and performs updating of the parameter in accordance with a result of the check obtained every time the decoding by the first decoding circuit and the second decoding circuit is executed;
• a storage circuit;
• a determination circuit that determines whether the number of times of executions of the decoding by the first decoding circuit and the second decoding circuit is equal to a first value;
• and
• an acquisition circuit that acquires numerical information corresponding to the number of bit errors included in a second bit data sequence that is the first bit data sequence obtained when the number of times is equal to the first value, and stores the acquired numerical information in the storage circuit.