Data read method and memory storage device using the same

1. A data read method adapted for a memory controller of a memory storage device, comprising:

receiving a first read command from a host system for reading first data;

calculating an error bit number of the first data;

comparing the error bit number of the first data to a predetermined number;

performing a correction of the first data using a n-bit error-correction code (ECC) and returning the corrected first data to the host system during a period provided by a pre-defined clock if the error bit number is not greater than the predetermined number; and

receiving a second read command from the host system for reading the first data, performing the correction of the first data using a m-bit ECC and returning the corrected first data to the host system after the period provided by the pre-defined clock if the error bit number is greater than the predetermined number, wherein n and m are integers, and n is smaller than m,

wherein if the error bit number is greater than the predetermined number, the corrected first data is returned to the host system during a period provided by:

a subsequent first system clock of a second frequency, wherein the second frequency is lower than the first frequency, and the subsequent first system clock is subsequent to the pre-defined system clock;

at least two subsequent second system clocks of the first frequency, wherein the subsequent second system clock is subsequent to the pre-define system clock; or

the subsequent second system clock of the first frequency and at least one dummy clock of the first frequency after the pre-defined system clock.

2. The data read method as claimed in claim 1 , wherein the pre-defined clock is a pre-defined system clock, wherein a system frequency at the pre-define system clock is a first frequency.

3. The data read method as claimed in claim 1 , wherein step of calculating the error bit number of the first data comprises:

retrieving the first data by using a first sensing reference according to the first read command; and

calculating the error bit number of the first data under a multiple bits ECC scheme.

4. A data read method adapted for a memory controller of a memory storage device, comprising:

receiving a first read command from a host system for reading first data;

calculating an error bit number of the first data, wherein step of calculating the error bit number of the first data comprises:

retrieving the first data by using a first sensing reference according to the first read command; and

calculating the error bit number of the first data under a multiple bits ECC scheme;

comparing the error bit number of the first data to a predetermined number;

performing a correction of the first data using a n-bit error-correction code (ECC) and returning the corrected first data to the host system during a period provided by a pre-defined clock if the error bit number is not greater than the predetermined number; and

performing the correction of the first data using a m-bit ECC and returning the corrected first data to the host system after the period provided by the pre-defined clock if the error bit number is greater than the predetermined number, wherein n and m are integers, and n is smaller than m,

wherein if the error bit number is greater than the predetermined number, the data read method further comprises:

receiving a second read command from the host system for reading the first data; and

retrieving the first data by using a second sensing reference according to the second read command, wherein the second sensing reference is different from the first sensing reference.

5. The data read method as claimed in claim 1 , further comprising:

sending an error flag to the host system before the period provided by the pre-defined clock, wherein the error flag indicates the error bit number of the first data, wherein the host system receives the error flag and receives the first data after the period provided by the pre-defined clock according to the received error flag.

6. The data read method as claimed in claim 1 , further comprising:

sending an error flag to the host system during the period provided by the pre-defined clock, wherein the error flag indicates the error bit number of the first data, wherein the host system receives the error flag and receives the first data after the period provided by the pre-defined clock according to the received error flag.

7. The data read method as claimed in claim 1 , wherein the predetermined number is preset according to at least one correction cost for correcting data read from the memory storage device.

8. A memory storage device, comprising:

a host interface configured to couple to a host system;

a memory array; and

a memory controller coupled to the host interface and the memory array, wherein the memory controller receives a first read command from the host system for reading first data, calculates an error bit number of the first data, and compares the error bit number of the first data to a predetermined number,

the memory controller performs a correction of the first data using a n-bit error-correction code (ECC) and returns the corrected first data to the host system during a period provided by a pre-defined clock if the error bit number is not greater than the predetermined number, and

the memory controller performs the correction of the first data using a m-bit ECC and returns the corrected first data to the host system after the period provided by the pre-defined clock if the error bit number is greater than the predetermined number, wherein n and m are integers, and n is smaller than m,

wherein when the memory controller calculates the error bit number of the first data, the memory controller retrieves the first data by using a first sensing reference from the memory array according to the first read command, and calculates the error bit number of the first data under a multiple bits ECC scheme,

wherein if the error bit number is greater than the predetermined number, the memory controller receives a second read command from the host system for reading the first data, and further retrieves the first data by using a second sensing reference according to the second read command, wherein the second sensing reference is different from the first sensing reference.

9. The memory storage device as claimed in claim 8 , wherein the pre-defined clock is a pre-defined system clock, wherein a system frequency at the pre-define system clock is a first frequency.

10. The memory storage device as claimed in claim 9 , wherein if the error bit number is greater than the predetermined number,

the memory controller returns the corrected first data at a subsequent first system clock of a second frequency, wherein the second frequency is lower than the first frequency, and the subsequent first system clock is subsequent to the pre-defined system clock.

11. The memory storage device as claimed in claim 9 , wherein if the error bit number is greater than the predetermined number,

the memory controller returns the corrected first data at at least two subsequent second system clocks of the first frequency, wherein the subsequent second system clock is subsequent to the pre-define system clock.

12. The memory storage device as claimed in claim 9 , wherein if the error bit number is greater than the predetermined number,

the memory controller returns the corrected first data at a subsequent second system clock of the first frequency and at least one dummy clock of the first frequency after the pre-defined system clock.

13. The memory storage device as claimed in claim 8 , wherein the memory controller further generates an error flag indicating the error bit number of the first data, and sends the error flag to the host system before the period provided by the pre-defined clock, wherein the host system receives the error flag and receives the first data after the period provided by the pre-defined clock according to the received error flag.

14. The memory storage device as claimed in claim 8 , wherein the memory controller further generates an error flag indicating the error bit number of the first data, and sends the error flag to the host system during the period provided by the pre-defined clock, wherein the host system receives the error flag and receives the first data after the period provided by the pre-defined clock according to the received error flag.

15. The memory storage device as claimed in claim 8 , the predetermined number is preset according to at least one correction cost for correcting data read from the memory storage device.