Disk drive using loopback to calibrate transmission amplitude

1. A disk drive for connecting to a host, the host comprising loopback circuitry operable to loop a pattern received from the disk drive back to the disk drive, the disk drive comprising:

(a) a disk;

(b) a head actuated over the disk;

(c) interface circuitry for interfacing with the host, the interface circuitry comprising:

a transmitter driver operable to transmit transmission signals at a transmission amplitude; and

a receiver driver operable to receive reception signals; and

(d) control circuitry operable to calibrate the transmission amplitude by:

configuring the transmitter driver to transmit at an initial transmission amplitude;

transmitting a calibration pattern to the host through the transmitter driver;

monitoring the reception signals received by the receiver driver to detect a loopback pattern representing a loopback of the calibration pattern;

processing the loopback pattern to detect an error; and

adjusting the transmission amplitude in response to the error.

2. The disk drive as recited in claim 1 , wherein the interface circuitry comprises a serial communication interface.

3. The disk drive as recited in claim 2 , wherein the interface circuitry comprises a serial advanced technology attachment (SATA) interface.

4. The disk drive as recited in claim 2 , wherein:

(a) the disk drive is operable to receive an out-of-band signal from the host; and

(b) the control circuitry is operable to calibrate the transmission amplitude in response to the disk drive receiving the out-of-band signal from the host.

5. The disk drive as recited in claim 4 , wherein the out-of-band signal comprises a COMWAKE signal.

6. The disk drive as recited in claim 1 , wherein the control circuitry is operable to adjust the transmission amplitude by increasing the transmission amplitude.

7. The disk drive as recited in claim 1 , wherein the control circuitry is operable to adjust the transmission amplitude by decreasing the transmission amplitude.

8. The disk drive as recited in claim 1 , wherein the control circuitry is operable to adjust the transmission amplitude until the error reaches a predetermined threshold.

9. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

set the transmission amplitude to a plurality of different values and detect a plurality of corresponding error values; and

select an operating transmission amplitude in response to the plurality of error values.

10. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to transmit a request to the host to enable the loopback circuitry.

11. The disk drive as recited in claim 10 , wherein the control circuitry is further operable to transmit a built-in self test frame information structure (FIS) to the host to enable the loopback circuitry.

12. The disk drive as recited in claim 1 , wherein the control circuitry is operable to detect the error by comparing the loopback pattern to the calibration pattern.

13. The disk drive as recited in claim 1 , wherein the control circuitry is operable to detect the error by encoding the calibration pattern and detecting invalid data in the loopback pattern.

14. A method of calibrating a transmission amplitude of transmission signals generated by a disk drive connected to a host, the host comprising loopback circuitry operable to loop a pattern received from the disk drive back to the disk drive, the method comprising the steps of:

transmitting a calibration pattern to the host at an initial transmission amplitude;

detecting a loopback pattern representing a loopback of the calibration pattern;

processing the loopback pattern to detect an error; and

adjusting the transmission amplitude in response to the error.

15. The method as recited in claim 14 , wherein the disk drive is a serial attached disk drive.

16. The method as recited in claim 15 , wherein the disk drive is a serial advanced technology attachment (SATA) disk drive.

17. The method as recited in claim 14 , wherein the method is performed during a calibration interval of a communication reset procedure.

18. The method as recited in claim 17 , wherein:

the disk drive is operable to receive an out-of-band signal from the host; and

the calibration interval occurs in response to the disk drive receiving the out-of-band signal from the host.

19. The method as recited in claim 18 , wherein the out-of-band signal comprises a COMWAKE signal.

20. The method as recited in claim 14 , wherein the step of adjusting the transmission amplitude comprises the step of increasing the transmission amplitude.

21. The method as recited in claim 14 , wherein the step of adjusting the transmission amplitude comprises the step of decreasing the transmission amplitude.

22. The method as recited in claim 14 , wherein the step of adjusting the transmission amplitude comprises the step of adjusting the transmission amplitude until the error reaches a predetermined threshold.

23. The method as recited in claim 14 , further comprising the steps of:

setting the transmission amplitude to a plurality of different values;

detecting a plurality of corresponding error values; and

selecting an operating transmission amplitude in response to the plurality of error values.

24. The method as recited in claim 14 , further comprising the step of transmitting a request to the host to enable the loopback circuitry.

25. The method as recited in claim 24 , wherein the step of transmitting the request to the host to enable the loopback circuitry comprises the step of transmitting a built-in self test frame information structure (FIS) to the host.

26. The method as recited in claim 14 , wherein the step of processing the loopback pattern to detect the error comprises the step of comparing the loopback pattern to the calibration pattern.

27. The method as recited in claim 14 , wherein the step of processing the loopback pattern to detect the error comprises the steps of encoding the calibration pattern and detecting invalid data in the loopback pattern.