Disc sequencer supporting pipelined and non-pipelined read

Details Disc sequencer supporting pipelined and non-pipelined read Disc sequencer supporting pipelined and non-pipelined read

2001-06-01

2004-02-17

Faber, Alan T (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Data clocking

Reexamination Certificate

active

06693753

ABSTRACT:

FIELD OF THE INVENTION
This application relates generally to a disc drive and more particularly to a disc sequencer in a disc drive.
BACKGROUND OF THE INVENTION
In a disc drive, data are stored on one or more discs coated with a magnetizable medium. Data are written to the discs by an array of transducers, typically referred to as read/write heads, mounted to a radial actuator for movement of the heads relative to the discs. The information is stored on a plurality of concentric circular tracks on the discs until such time that the data are read from the discs by the read/write heads. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The heads are used to transfer data between a desired track and an external environment, which includes, among many components, a host computer. During a read operation the read/write head senses the data previously written on the disc track and transfers the information to the external environment. During a write operation, data are written onto the disc track. Once the data are written to the disc, each sector holds a block of data, which is the absolute smallest quantity that can be written to the disc during a single write operation.
Typically, the read/write heads are positioned with respect to the disc surfaces by an actuator assembly driven by a voice coil motor. The voice coil motor is responsible for pivoting the actuator body about a pivot shaft, thus moving the heads across the disc surfaces. The actuator thus allows the heads to move back and forth in an accurate fashion between an inner radius and an outer radius of a disc. The actuator arm is driven by a control signal fed to the voice coil motor at the rear end of the actuator arm. A servo control system is used to sense the position of the actuator and control the movement of the read/write head above the disc using servo signals read from a disc surface in the disc drive. The servo control system relies on servo information stored on the disc. The signals from this information generally indicate the present position of the read/write head with respect to the disc, i.e., the current track position. The servo control system uses the sensed information to maintain head position or determine how to optimally move the read/write head to a new position centered above a desired track. The servo control system then delivers a control signal to the voice coil motor to position the read/write head over a desired new track or to maintain the position over the desired current track.
The transfer of files between the host computer and the disc is controlled in a multi-level setting characterized by a bi-level transfer scheme. At a macroscopic level, track sectors are selected to contain the data sectors of which the file is divided. More specifically, and in a microscopic sense, cells along a track are magnetized to correspond to the bit structure of the file for the purposes of subsequent reading. A disc drive typically includes a buffer to implement this bi-level transfer scheme. The purpose of the buffer is to accept the sectors of data during its transfer between the host computer and the disc and then transfer the data to the proper component—either the host computer or the disc.
Typically, the system microprocessor contains programming designed to locate the sectors on the track where the data are to be read from or written to. The microprocessor is also programmed to control the transfer of the file at the sector, or macroscopic, level. The transfer of data to and from the buffer is accomplished at a microscopic level in character-by-character fashion. The conventional method of accomplishing a transfer at the microscopic level is through the use of a buffer controller, a host interface controller, or a disc interface controller.
The transfer of a file from a disc to a host is carried out under the overall control of the system microprocessor and a more precise control of a disc interface controller. With respect to overall control, when a file is to be read from a disc, the host computer prompts the system microprocessor with generalized information pertaining to the file and the microprocessor selects a buffer segment to temporarily store the data as it is read from the disc. The microprocessor then sets up the transfer by issuing commands to the servo system to bring the read/write heads into radial alignment with the track that contains the sectors at which the file is stored. The microprocessor issues commands and control parameters to the disc interface controller to transfer one or more sectors from the disc to the buffer segment. Once stored in the buffer segment, the microprocessor issues commands to a host interface controller to initiate the transfer of the sectors of data from the buffer segment to the host.
With respect to more specific control, the disc interface controller controls the transfer of the blocks of data from the appropriate sectors on a disc to the buffer segment pursuant to commands issued by the system microprocessor once the read/write heads are positioned over the track that is to receive the file. The data are read from the disc by a read/write head and transmitted to a disc sequencer of the disc interface controller via a read/write channel, which decodes the data before it reaches the disc sequencer. Data decoded by the read/write channel and received by the disc sequencer are typically referred to as NRZ, or channel, data. The disc sequencer, which is the interface between the disc interface controller and the read/write channel, is also responsible for transmitting control signals through the channel to control accessing of the disc by the read/write head.
Conventional read/write channels combine trellis-coded partial response equalization with maximum-likelihood sequence detection based upon a Viterbi algorithm. A dramatic and constant increase in the bits per inch (BPI) and the tracks per inch (TPI) of a disc surface yields a proportional increase in the bit error rate (BER) of a disc drive. In order to handle the increasingly high BER, a Viterbi detector is used to perform the maximum-likelihood sequence detection. A post-processor is used to eliminate some of the dominant error events in electronic and media noise at the output of the Viterbi detector. The combination of the post processor and the Viterbi detector provides a net Signal Noise Ratio (SNR) performance relative to partial response maximum-likelihood (PRML) or enhanced partial response maximum-likelihood (EPRML) channels over the range of linear densities. A problem occurs in that the post-processor causes the overall read latency to potentially increase from 10 bytes to 30 or more bytes.
A pipelined read mode can be used in order to alleviate potential format efficiency hits caused by an increase in read latency. The key aspect associated with the typical pipelined read mode is the relatively small size of the gap (typically, 6-8 bytes) between sectors on the disc media. In contrast, a relatively large gap (typically, 25-50 bytes) between sectors on the disc media that is associated with a non-pipelined read mode actually adds to the inefficient characteristics of drives having the increasing read latency. Although current read/write channels support both non-pipelined and pipelined read modes, conventional disc sequencers cannot operate in the pipelined read mode thereby hindering current disc drive efficiency.
SUMMARY OF THE INVENTION
Against this backdrop the present invention has been developed. The present invention is a disc sequencer incorporating parallel state machines to support both pipelined and non-pipelined read modes. A read command, which may be associated with either the pipelined read mode or the non-pipelined read mode, is communicated to the disc sequencer from a system microprocessor through a microprocessor interface of the disc sequencer. The read command initializes the disc sequencer to control the transfer of a file stored on a recordable media through a read/write channel. The file, which contains s

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