Disk drive adjusting command execution in response to control circuitry die temperature

[0001] Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo controller to control the velocity of the actuator arm as it seeks from track to track.

[0002] Because the disk is rotated at a constant angular velocity, the data rate is typically increased toward the outer diameter tracks (where the surface of the disk is spinning faster) in order to achieve a more constant linear bit density across the radius of the disk. To simplify design considerations, the data tracks are typically banded together into a number of physical zones, wherein the data rate is constant across a zone, and increased from the inner diameter zones to the outer diameter zones. This is illustrated in FIG. 1, which shows a prior art disk format 2 comprising a number of tracks 4, wherein the tracks are banded together in this example to form three physical zones from the inner diameter of the disk (ZONE 1) to the outer diameter of the disk (ZONE 3). The prior art disk format of FIG. 1 also comprises a number of servo sectors 6₀-6_N recorded around the circumference of each track. Each servo sector 6, comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a track address, used to position the head over a target track during a seek operation. Each servo sector 6, further comprises groups of servo bursts 14 (e.g., A, B, C and D bursts), which comprise a number of consecutive transitions recorded at precise intervals and offsets with respect to a track centerline. The groups of servo bursts 14 provide fine head position information used for centerline tracking while accessing a track during write/read operations.

[0015] FIG. 2A shows a disk drive according to an embodiment of the present invention comprising a disk 16 having a plurality of tracks 18, wherein each track comprises a plurality of data sectors. The disk drive further comprises a head 20 actuated over the disk 16, and control circuitry 22 fabricated on a die. The control circuitry 22 executes the flow diagram of FIG. 2B wherein a plurality of disk access commands are received from a host and stored in a command queue (step 24), wherein each disk access command identifies at least one data sector. A temperature of the die is determined (step 26), and a first disk access command is selected from the command queue in response to the die temperature (step 28). The selected command is then executed (step 30).

[0016] In the embodiment of FIG. 2A, the tracks 18 are defined by a plurality of servo sectors 32₀-32_N. The control circuitry 22 processes a read signal 34 to demodulate the servo sectors 32₀-32_N into a position error signal (PES). The PES is filtered with a suitable compensation filter to generate a control signal 36 applied to a voice coil motor (VCM) 38 which rotates an actuator arm 40 about a pivot in order to position the head 20 radially over the disk 16 in a direction that reduces the PES. The servo sectors 32₀-32_N may comprise any suitable position information, such as a track address for coarse positioning and servo bursts for fine positioning. Also in the embodiment of FIG. 2A, the tracks 18 are banded together to form a plurality of physical zones, wherein the data rate of the data sectors within each zone is constant across a zone, and increases from the inner diameter zones toward the outer diameter zones.

[0017] FIG. 3A is a flow diagram according to an embodiment of the present invention wherein when the die temperature does not exceed a threshold (step 42), a next disk access command is selected from the command queue based on a rotational position optimization (RPO) algorithm (step 44). However, when the die temperature exceeds the threshold (step 42), a next disk access command is selected from the command queue based on the data rate of the corresponding zone (step 46). FIG. 3B shows an example of this embodiment wherein a first disk access command identifying data sectors 48A may be selected using the RPO algorithm when the die temperature does not exceed the threshold, whereas a second disk access command identifying data sectors 48B having a lower data rate may be selected when the die temperature exceeds the threshold. Executing a disk access command having lower data rate data sectors allows the die to cool since the clocking frequency of the control circuitry is lower. In one embodiment, the higher the die temperature, the lower the acceptable data rate. In the embodiment of FIG. 3B, a first die temperature may allow disk access commands to be selected from physical zones 1 or 2, whereas a second (higher) die temperature may allow disk access commands to be selected only from physical zone 1.

[0018] In one embodiment, the RPO algorithm may be used to select the next disk access command after restricting the allowed disk access commands based on the die temperature. For example, if the die temperature restricts the selection to physical zone 1, the RPO algorithm may be executed to select the disk access command out of those that correspond to physical zone 1.

[0019] FIG. 4A is a flow diagram according to an embodiment of the present invention wherein when the die temperature exceeds the threshold (step 42), a next disk access command is selected from the command queue based on the number of data sectors identified by each disk access command (step 50). FIG. 4B shows an example of this embodiment wherein a first disk access command identifying data sectors 52A may be selected using the RPO algorithm when the die temperature does not exceed the threshold, whereas a second disk access command identifying fewer data sectors 52B may be selected when the die temperature exceeds the threshold. Executing a disk access command having fewer data sectors allows the die to cool between execution of the disk access commands. In one embodiment described in greater detail below, the higher the die temperature, the fewer the number of allowed data sectors per disk access command.

[0020] FIG. 5A is a flow diagram according to an embodiment of the present invention wherein when the die temperature exceeds the threshold (step 42), a next disk access command is selected from the command queue using the RPO algorithm (step 54). FIG. 5B shows an example of this embodiment wherein the RPO algorithm may identify a first disk access command 56A when the die temperature does not exceed the threshold, and identify a second (next best) disk access command 56B when the die temperature exceeds the threshold. The second disk access command 56B has a higher access latency (seek and rotational latency) which allows the die to cool between execution of the disk access commands. In one embodiment, the RPO algorithm may continue to select the next best disk access command until the access latency ensures the die temperature will cool sufficiently.

[0021] FIG. 6 is a flow diagram according to an embodiment of the present invention wherein when the die temperature exceeds the threshold (step 42), a write command is selected from the command queue (step 58). In this embodiment, a write command may require less power to execute since the components of the read channel for processing a read command would be idle or shut off. In one embodiment, the write commands in the command queue are selected for processing over read commands until the die temperature falls below the threshold (step 42).

[0022] FIG. 7 is a flow diagram according to an embodiment of the present invention wherein when the die temperature exceeds the threshold (step 42), the control circuitry slips a revolution of the disk (step 60) before executing the next disk access command. Slipping a revolution of the disk allows the die to cool down before executing the disk access command. In one embodiment, the die temperature is determined just prior to executing the disk access command after performing the seek operation and settling on the target track.

[0023] FIG. 8 is a flow diagram according to an embodiment of the present invention wherein after selecting a disk access command from the command queue using the RPO algorithm (step 62), a delta temperature is determined for the selected command (step 64). The delta temperature represents the corresponding rise in the die temperature if the disk access command is actually executed. In one embodiment, the delta temperature is determined based on the number of data sectors identified by the disk access command. If the current die temperature plus the delta temperature exceeds a threshold (step 66), a next best disk access command is selected from the command queue and a corresponding delta temperature determined.

[0024] FIG. 9 shows an embodiment of the present invention wherein the relationship between the number of data sectors and the corresponding delta temperature is a linear relationship. Also in the embodiment of FIG. 9, the slope of the line for read commands is steeper than the slope of the line for write commands since read commands may require more power to execute as described above.

[0025] FIG. 10 is a flow diagram according to an embodiment of the present invention wherein the control circuitry determines the die temperature (step 70) after executing the selected disk access command, and then updates the corresponding delta temperature for the number of data sectors just processed (step 72). In other words, the relationship between the delta temperature versus the number of data sectors (e.g., as shown in FIG. 9) is continuously updated since it may change over the life of the disk drive, and/or over varying environmental conditions. In one embodiment, the relationship over the entire range of data sectors is updated, for example, by adjusting the slope of the line shown in FIG. 9 after executing a single disk access command identifying a particular number of data sectors. In yet another embodiment, a number of data points may be determined and then the relationship updated by curve fitting through the data points.

[0026] FIG. 11 is a flow diagram according to an embodiment of the present invention wherein after determining the die temperature (step 26) a maximum number of accessible data sectors is determined that will prevent the die temperature from exceeding a threshold (step 74). The next disk access command is then selected from the command queue using the RPO algorithm (step 62). If the number of data sectors identified by the selected disk access command exceeds the maximum accessible (step 76), then the next best disk access command is selected from the command queue. This process repeats until the selected disk access command identifies a number of data sectors that is less than the maximum accessible. In one embodiment, a different maximum number of accessible data sectors is determined for read commands and write commands, and the corresponding maximum at step 76 differs depending on whether the selected disk access command is a read command or write command.

[0027] Any suitable control circuitry may be employed to implement the flow diagrams in the embodiments of the present invention, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain steps described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into an SOC.

[0028] In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the steps of the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.