Serial port communication for storage device using single bidirectional serial data line

1. A method to provide communication between a controller and a preamplifier in a storage device, comprising:

implementing a serial port that is configured to transmit digital signals between the controller and the preamplifier over a single bidirectional serial data line; and

controlling the serial port to selectively transmit digital signals over the bidirectional serial data line in either a first direction from the controller to the preamplifier or a second direction from the preamplifier to the controller.

2. The method of claim 1 , wherein controlling the serial port comprises:

transmitting a serial bit stream over the bidirectional serial data line from the controller to the preamplifier;

generating a clock signal in the preamplifier using a phase-locked loop circuit, wherein the clock signal is generated based on a bit rate of the serial bit stream received by the preamplifier; and

using the clock signal to receive and deserialize the serial bit stream received by the preamplifier.

3. The method of claim 2 , wherein controlling the serial port further comprises:

transmitting a direction switch control signal over the bidirectional serial data line to the preamplifier; and

following detection of the direction switch control signal by the preamplifier,

generating a control signal to suspend phase and frequency adjustments of the phase-locked loop circuit of the preamplifier and maintain a static clock signal output from the phase-locked loop circuit of the preamplifier;

assuming control of the bidirectional serial data line by the preamplifier; and

using the static clock signal to serialize and transmit data from the preamplifier to the controller over the bidirectional serial data line.

4. The method of claim 3 , wherein transmitting a direction switch control signal to the preamplifier comprises:

detecting an asserted flag bit that is associated with a digital signal to be transmitted from the controller to the preamplifier;

generating and transmitting the direction switch control signal to the preamplifier over the bidirectional serial data line in response to the asserted flag bit; and

wherein controlling the serial port further comprises transmitting the associated digital signal over the bidirectional serial data line following transmission of the direction switch control signal.

5. The method of claim 3 , wherein the digital signals transmitted between the controller and the preamplifier are encoded and decoded using an 8B/1 OB coding protocol, and wherein the direction switch control signal is generated as an 8B/1 OB control character.

6. The method of claim 3 , wherein controlling the serial port further comprises generating a clock signal in the controller using a phase-locked loop circuit in the controller based on a reference signal that is input to the phase-locked loop circuit, wherein generating the clock signal in the controller comprises:

using a port bit rate clock signal as the reference signal to generate a clock signal that is used for encoding and serializing digital signals to be transmitted over the bidirectional serial data line from the controller to the preamplifier; and

using a serial bit stream transmitted from the preamplifier as the reference signal to generate a clock signal that is used for deserializing and decoding the serial bit stream transmitted from the preamplifier over the bidirectional serial data line.

7. The method of claim 1 , further comprising forcing a reset of the preamplifier, wherein forcing a reset comprises:

forcing a run-length violation by maintaining a logic level on the bidirectional serial data line for a predetermined period of time; and

the preamplifier detecting the run-length violation and initiating a reset operation.

8. The method of claim 1 , further comprising forcing a reset of the preamplifier, wherein forcing a reset comprises:

forcing an increases or decrease of a common-mode voltage on the bidirectional serial data line; and

the preamplifier detecting the forced increase or decrease of the common-mode voltage on the bidirectional serial data line and initiating a reset operation.

9. The method of claim 1 , wherein the bidirectional serial data line is a signal line of an analog bus which is used by the preamplifier and a recording channel to perform a data access operation, and wherein controlling the serial port comprises:

controlling the serial port to selectively transmit digital signals over the signal line of the analog bus in either a first direction from the controller or a second direction from the preamplifier to the controller, during periods in which the signal line is not being utilized by the preamplifier and the recording channel to perform a data access operation; and

controlling the serial port to cease transmitting digital signals over the signal line of the analog bus during periods in which the signal line is being utilized by the preamplifier and the recording channel to perform a data access operation.

10. A storage device comprising:

a storage medium;

a read/write head configured to read data from and write data to the storage medium, a preamplifier configured to process data that is written to and read from the storage medium;

a controller configured to control the preamplifier; and

serial port circuitry configured to transmit digital signals between the controller and the preamplifier over a single bidirectional serial data line, wherein the serial port circuitry is configured to selectively transmit digital signals over the bidirectional serial data line in either a first direction from the controller to the preamplifier or a second direction from the preamplifier to the controller.

11. The storage device of claim 10 , wherein the serial port circuitry comprises:

master serial port control circuitry that is implemented by the controller; and

slave serial port control circuitry that is implemented by the preamplifier, wherein the master serial port control circuitry is configured to transmit a serial bit stream over the bidirectional serial data line to the preamplifier, wherein the slave serial port control circuitry comprises a phase-locked loop circuitry that is configured to generate a clock signal based on a bit rate of the serial bit stream received by the preamplifier, wherein the slave serial port control circuitry is configured to use the clock signal to receive and deserialize the serial bit stream received by the preamplifier, wherein the master serial port control circuitry is configured to generate and transmit a direction switch control signal over the bidirectional serial data line from the controller to the preamplifier; and

wherein the slave serial port control circuitry is configured to detect the direction switch control signal, and in response to detecting the direction switch control signal, the slave serial port control circuitry is configured to (i) suspend phase and frequency adjustments of the phase-locked loop circuit of the slave serial port control circuitry and output a static clock signal from the phase-locked loop circuit of the preamplifier, (ii) assume control of the bidirectional serial data line, and to (iii) use the static clock signal to serialize and transmit data from the preamplifier to the controller over the bidirectional serial data line.

12. The storage device of claim 10 , wherein the bidirectional serial data line is implemented using a signal line of an analog bus, wherein the signal line is used by the preamplifier and recording channel circuitry to perform a data access operation with the storage medium, wherein the storage device comprises multiplexing circuitry configured to enable sharing of the signal line by the serial port circuitry during periods of time in which the signal line is not being utilized to perform a data access operation with the storage medium.

13. The storage device of claim 12 , wherein the signal line of the analog bus is a read signal line on which read data is transmitted from the preamplifier to the recording channel circuitry during a read operation, wherein during a during a write operation, the multiplexing circuitry is configured to connect the serial port circuitry to the read signal line; and

wherein during the read operation, the multiplexing circuitry is configured to disconnect the serial port circuitry from the read signal line.

14. The storage device of claim 13 , wherein the read operation, the multiplexing circuit is further configured to connect the serial port control circuitry to a write signal line of the analog bus on which write data is transmitted from the recording channel circuitry to the preamplifier during a write operation, and wherein during the write operation, the multiplexing circuitry is configured to disconnect the serial port control circuitry from the write signal line.

15. A virtual storage system comprising the storage device of claim 10 .