Constant density recording method and system for headless format in hard disc driver

A method of and a system for efficiently using split information stored in an unnecessary data sector, thereby reducing unnecessary data. The system includes first registers respectively adapted to store MCDR values in response to a write control signal generated from a central processing unit; second registers respectively coupled to the first registers, each second register down-loading the MCDR value from the corresponding first register in response to a servo sector interrupt application signal inverted by an inverter, thereby generating signals indicative of an internal flag, an internal CDR value and a split sector number; a multiplexer adapted to multiplex the internal flag signals from the second registers, thereby generating a flag signal; a counter adapted to count the servo sector interrupt application signal, thereby generating a current sector number signal indicative of the number of a sector being currently accessed; a synthesizer adapted to generate a CDR signal based on the split sector number signal from each second register; and a comparator for comparing the split sector number signal from each second register with the current sector number signal from the counter, thereby generating a sector good signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a constant density recording (CDR) method 
used in hard disc drivers, and more particularly to a method of and a 
system for producing information for a CDR upon formatting a hard disc 
drive in a headerless manner by modifying ID fields and data fields. 
2. Description of the Related Art 
For hard disk drivers (HDD's), a headerless formatting method is known. The 
headless formatting method is a data recording method wherein data is 
recorded on an HDD using only data fields. In other words, no ID field is 
used in accordance with the headerless formatting method. In the case of 
HDD's utilizing a headerless format, CDR values should be used for a CDR. 
An example of such a headless formatting method is disclosed in Korean 
Patent Application No. 94-35785. In a conventinoal method, an ID field is 
used along with every data field upon reading and writing data. Positional 
information about data to be read or written is generated from each ID 
field. Such an ID field is used as an overhead for storing the positional 
information. They are not used as information for storing actual 
information for user data. This format is a headerless format. ID field 
signals are generated from a control unit other than that included in the 
HDD. For example, information such as cylinder numbers, head numbers and 
sector numbers are generated from the gray code unit for servo fields. 
It is most efficient to obtain an increase in capacity of the disk of an 
HDD by having the disk store only data. In this case, however, it is 
additionally necessary to load positional information and CDR values. In 
order to satisfy such a requirement, a method is mainly used wherein a 
desired portion of an external buffer RAM is allocated in such a manner 
that a CDR value for every track is stored, as shown in FIG. 1. In 
accordance with this method, CDR values are stored in the buffer RAM. 
Subsequently, the CDR values and positional information are automatically 
loaded on corresponding sectors, respectively. 
Loading of CDR values using the buffer RAM have been simply achieved using 
a method in which CDR values (for respective sectors of every track) 
loaded on a previous ID field are positionally shifted to the buffer RAM, 
thereby achieving an automatic loading thereof. In accordance with 
conventional methods, however, a split is generated in each servo-sector. 
Although data sectors, such as "CDRn" in FIG. 1, involving no split are 
inscribed with actual bytes of data, a data sector, such as "CDRn+2" in 
FIG. 1, involving a split can not be inscribed with actual bytes of data, 
as indicated by the shaded portions in FIG. 1. As a result, there is a 
waste of memory areas. 
On the other hand, loading of CDR values from the buffer RAM is 
automatically carried out. There are five kinds of sources for accessing 
the buffer, namely, those for refresh, error correction, disk, host and 
main processor unit (MPU). In order to load all the CDR values, an 
additional buffer RAM should be used. Furthermore, the loading of CDR 
values should be carried out with a priority over the processing of other 
data values. This results in a burden to the buffer managing unit. 
Meanwhile, the HDD performs an error correction. As the error correction 
ability of the HDD increases, the quantity of data to be accessed per one 
sector increases correspondingly. As a result, the burden of the buffer 
managing unit increases even more. 
SUMMARY OF THE INVENTION 
Therefore, an object of the invention is to provide a method of and a 
system for efficiently using split information stored in an unnecessary 
data sector, thereby reducing unnecessary data. 
In accordance with the present invention, to achieve the above object, a 
servo routine is executed in response to an interrupt from a current servo 
sector. Thereafter, a CDR producing value is down-loaded for the next 
servo sector. Using this value, a CDR value for each desired data sector 
of the next servo sector is loaded. Accordingly, it is possible to load 
CDR values for a headerless format without interfering with the buffer 
management. 
The present invention also provides a circuit for generating CDR (constant 
density recording) values for a headerless format in a hard disk driver 
equipped with a central processing unit comprising: first registers 
respectively adapted to store MCDR values in response to a write control 
signal generated from a central processing unit and received at a write 
control signal stage; second registers respectively coupled to the first 
registers, each second register down-loading the MCDR value from the 
corresponding first register in response to a servo sector interrupt 
application signal which is applied to a servo control stage and inverted 
by an inverter, thereby generating signals indicative of an internal flag, 
an internal CDR value and a split sector number; a multiplexer adapted to 
multiplex the internal flag signals from the second registers, thereby 
generating a flag signal; a counter adapted to count the servo sector 
interrupt application signal applied to the servo control stage, thereby 
generating a current sector number signal indicative of the number of a 
sector being currently accessed; a synthesizer adapted to generate a CDR 
signal based on the split sector number signal from each second register; 
and sector good signal generating means for comparing the split sector 
number signal from each second register with the current sector number 
signal from the counter, thereby generating a sector good signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 is a diagram illustrating a data format for the generation of CDR 
values for one servo sector in a HDD in accordance with the present 
invention. 
The HDD has servo sectors each provided with a maximum of 8 flags. The HDD 
also has split sectors each bearing an intrinsic number. Each split sector 
is defied by a desired number of bytes. 
Referring to FIG. 3, a circuit for generating CDR information to be used 
for a headerless format according to the present invention is illustrated. 
As shown in FIG. 3, the circuit includes first registers 301 which serve to 
store MCDR values, which may be data MCDR CONTROL-1, 2 and 3 in FIG. 2, in 
response to a write control signal generated from a central processing 
unit (not shown) and received at a write control signal stage CDR-WR. 
Second registers 303 are coupled to the first registers 301, respectively. 
Each second register 303 down-loads an output from the corresponding first 
register 301, namely, an MCDR value, in response to a servo sector 
interrupt application signal which is applied to a servo control stage 
SERVO and inverted by an inverter N1. In other words, the MCDR value 
output from each first register 301 is down-loaded in the corresponding 
second register 303 at a negative edge of the servo sector interrupt 
application signal from the servo control stage SERVO because the signal 
from the servo control stage SERVO is inverted by the inverter N1. 
The second registers 303 have a double buffering function so that the 
central processing unit can control them freely. The down-load time of the 
central processing unit is determined so that writing of data can be 
carried out after the receiving of the current servo interrupt, but before 
the generation of a negative edge of the next servo interrupt. After 
shifting the received data in accordance with the output from the inverter 
N1, each second register 303 outputs an internal flag IFLAG (7:0), a split 
sector number SPLIT-SECTOR-NO (2:0), and an internal CDR value ICDR 
(11:0). The internal flag IFLAG (7:0) is applied to a multiplexer 305 
whereas the split sector number SPLIT-SECTOR-NO (2:0) is applied to a 
comparator 309. The comparator 309 includes exclusive NOR gates NOX1 to 
NOX3. On the other hand, the internal CDR value ICDR (11:0) is applied to 
a synthesizer 307. The synthesizer 307 is coupled to the output of the 
comparator via an AND gate AN1 and an inverter N2. The synthesizer 307 
includes OR gates OR1 to OR3. 
Meanwhile, a counter 311 is also coupled to the inverter N1. The counter 
311 is an asynchronous counter which is preset when the signal received at 
the servo stage SERVO is at a high level, namely, when the output from the 
inverter N1 is at a low level. After being preset, the counter 311 counts 
a signal received at a sector terminal thereof. The counted value of the 
counter 311 is changed from "00" in response to a positive edge of the 
signal received at the sector terminal of the counter 311. As a result, 
the counter 311 generates a current sector number CUR-SEC-NO (2:0) which 
is, in turn, applied as a select control signal to the multiplexer 305 and 
as a reference value to the comparator 309. In response to the output from 
the counter 311, the multiplexer 305 generates a flag signal for a 
selected sector based on the internal flag IFLAG (7:0) received from each 
second register 303. On the other hand, the comparator 309 compares the 
split sector number SPLIT-SECTOR-NO (2:0) received from the second 
register 303 with the output from the counter 311. When the split sector 
number SPLIT-SECTOR-NO (2:0) is identical to the output from the counter 
311, the comparator 309 generates a signal having a level of "1". This 
state means that the input at the sector stage SECTOR is identical to the 
input at the split sector number stage SPLIT-SECTOR-NO. In this state, the 
AND gate AN1 outputs a signal having a high level. That is, the AND gate 
AN1 generates a sector good signal GOOD-SEC. This signal is inverted to a 
low level while passing through the inverter N2. The inverted signal is 
then applied to the OR gates OR1 to OR3 of the synthesizer 307 which also 
receive the internal CDR value ICDR (11:0). 
The OR gates OR1 to OR3 of the synthesizer 307 generate CDR values based on 
the received signals, respectively. That is, a flag and a CDR value 
associated with the current sector are generated based on the sector good 
signal GOOD-SEC and the internal CDR value ICDR (11:0). Using these 
values, a CDR is processed. 
Since a central processor unit directly down-loads CDR values, it is 
possible to reduce the management load of buffers. Accordingly, it is 
possible to reduce the number of buffers to be accessed for one sector 
even though the error correction ability increases continuously. 
Therefore, the efficiency of using buffers is improved. It is also 
possible to simplify the data format associated with the flag and CDR 
value for every data sector. This results in a reduction in memory area. 
In accordance with an increase in HDD capacity, existing HDD's can process 
3 or 4 data sectors for one servo sector. In accordance with the present 
invention, however, it is possible to process up to 8 data sectors. 
Accordingly, the above-mentioned effect can be greatly improved. For 
example, in conventional cases, the number of CDR bytes needed for 8 data 
sectors is 16 bytes (2 bytes*8=16 bytes), while in the present invention 
the number of CDR bytes needed for 8 data sectors is 3. 
Although the preferred embodiments of the invention have been disclosed for 
illustrative purposes, those skilled in the art will appreciate that 
various modifications, additions and substitutions are possible, without 
departing from the scope and spirit of the invention as disclosed in the 
accompanying claims.