Disk drive system for dynamically selecting optimum I/O operating system
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent documents or the patent disclosure as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to disk drive systems which have a controller which employs a look ahead operating system for processing a look ahead command set and a tag queuing operating system for processing a tag queuing command set issued by a host processor. 
     2. Description of the Related Art 
     A disk drive system will perform best using a control operating system that has been optimized to the command set that is used by the host processor for communicating with the disk drive system. 
     A first command set used by host processors is the look ahead command set which requires the host processor to await the completion of a command issued to the disk drive system before issuing the next command and for the disk drive system to perform multiple threaded sequential operations. In this case the disk drive system will perform best by using a look ahead operating system that is optimized to perform n-segment look ahead operations that anticipate what the next command from the host computer will be and will pre-fetch data associated with the next anticipated command to avoid latencies. The use of the optimized look ahead operating system in communicating with the host processor will increase the computing system&#39;s performance. 
     A second command set used by host processors is the tag queuing command set where the host computer issuing multiple commands at one time to the disk drive system and the disk drive system receives and store the command for subsequent processing of the commands by the disk drive system. When the tag queuing command set is used, it is no longer necessary for the disk drive system to anticipate what command the host processor will next issue because with more than one command stored in the queue in the disk drive system, the disk drive system will know exactly what the host computer wants to do next. Therefore, the disk drive system will best operate using an optimized tag queue operating system to take advantage in the processing of the multiple outstanding commands so as to boost the performance of the system and to not waste time doing unnecessary look ahead operations. 
     Disk drive system manufacturers may produce an optimized disk drive system for use with host processors employing the look ahead command set and an optimized disk drive system for use with host processors employing the tag queuing command set. This approach has the undesirable effect of requiring that two models of the same disk drive system must be marketed where the only difference is the operating system used in communicating with the host processor. Therefore disk drive system manufacturers have endeavored to provide a disk drive system which is capable of responding to both the look ahead command set and the tag queuing command set. However, in attempting to provide a single operating system so as to make the disk drive system transparent to the command set being used by the host computer, the optimization of the operating system for both of the command sets had to be compromised. This compromise results in the decrease in efficiency of the system from the system efficiency that could have been obtained if the optimum operating systems could have been used for the command sets. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a disk drive system which uses the optimized operating system for the look ahead command set and the tag queuing command set. 
     Briefly, the invention is directed to a disk drive system in which the executable optimize look ahead operating system for the look ahead command set and optimize tag queuing operating system for the tag queuing command set are both stored in reserved cylinder on the media within the disk drive system. The reserve cylinders are not normally accessible to the user except during the write buffer download micro command. The look ahead operating system is optimized for multiple threaded look ahead operation. The tag queuing operating system is optimized for (1) preprocessing received commands and then placing the pre-processed command on hold until the system facilities are available to complete the pre-processed command and (2) for reordering the received commands from the sequence the commands were received into a sequence that minimizes system latencies thereby improving system performance. The disk drive system, at power up, will load the look ahead operating system from the media. The disk drive system will operate with the look ahead operating system as long as no tag queuing commands are received from the host processor. When a tag queuing command is received, that command will be processed as a look ahead command by the look ahead operating system and the disk drive system will load the tag queuing operating system from the media to replace the look ahead operating system such that all further commands received from the host processor will be processed using the tag queuing operating system. 
     It is expected that the host processor will normally only utilize one of the two command sets and therefore the disk drive system will process only one tag queuing command by the look operating system before the optimized tag queuing operating system is loaded and made available for processing the tag queuing command issued by the host processor. 
     An advantage of the present invention is that the latest version of the optimized look ahead operating system and the optimized tag queuing operating system may be loaded into the proper location on the media. In this manner the system may always operate at the latest version the optimized operating system for both command sets, thereby maintaining the expected efficiency from the disk drive system with regard to executing commands received from the host processor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with respect to the particular embodiments thereof and references will be made to the drawings, in which: 
     FIG. 1 is a disk drive system embodying the invention; and 
     FIG. 2 is a flow chart illustrating the operation of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a disk drive system which embodying the invention. The disk drive system comprises microprocessor 12 which operates under program operating systems stored in ROM 13 and RAM 14. Microprocessor 12 controls host interface controller 11 for the receiving and sending of data and commands from and to the host processor. Microprocessor 12 communicates with buffer sequencer 28 which controls the data flow to and from memory buffer 27 and with microprocessor 51 which implements operations associated with control words received from the host processor. Microprocessor 51 operates under programs stored within ROM 37 and instructions received from microprocessor 12. Microprocessor 51 controls actuator control circuity 52 for positioning of the actuator 63, track following and motor spin control and read/write circuity 53 for reading and writing to and from the media 65 by means of transducer 64. The use of microprocessors 12 and 51, allows the system to perform a read and/or write operation under the control of microprocessor 51 while transferring or receiving data to or from the host processor through the host interface controller under control of microprocessor 12. 
     The optimized look ahead operating system and tag queuing operating system are stored in dedicated cylinders on media 65. ROM 13 stores the operating system which includes routine B9, for loading the tag queuing operating system into RAM 14 whenever a tag queuing command has been received by microprocessor 12 for processing. 
     FIG. 2 is a flow chart which illustrates the operation of the invention within the disk drive system of FIG. 1. In step 201, when the disk drive system is powered up, the start up sequence 7 will load the look ahead operating system from media 65 into RAM 14 in anticipation of the host processor issuing a look ahead command. Upon receiving a command from the host processor through the host interface controller 11, microprocessor 12 will process that command by the look ahead operating system stored in RAM 14. In step 203, when the command is complete but before status is sent to the host processor, the look ahead operating system enters into a polling loop in preparation for receiving the next command from the host processor. Instructions in that polling loop test whether or not the instruction, that has just been completed, was a tag queuing command. In step 205, if the command was a look ahead command, then status is sent to the host processor and, in step 207, the next command received by microprocessor 12 will be processed in accordance with the look ahead operating system stored in RAM 14. 
     In step 204, if the command that had been processed was a tag queuing command then the system will branch to routine B9 in ROM 13 for loading the tag queuing operating system into RAM 14. In step 206, once the tag queuing operating system has been successfully loaded into RAM 14 in place of the look ahead operating system, status is sent to the host processor. In step 208, all commands received from the host processor thereinafter will be processed using the tag queuing operating system. 
     Routine A8 is that portion of the polling loop of the look ahead operating system that tests whether or not the command previously processed was a tag queuing command. As can be seen from routine A8 if, in fact, a tag queuing command has been sensed, the look ahead operating system will branch from the look ahead operating system to a routine QTAGPL stored in ROM 13. Routine A8 is set forth below: 
     
         ______________________________________                                    
ROUTINE A8       TEST FOR TAG COMMAND                                     
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POLL.sub.-- 70?:                                                          
 LDAB   &lt;S.sub.-- ERNUM,Y                                                 
                     ;Retrieve error for SETSNS                           
 BNE      POLL.sub.-- 75?                                                 
                     ;Branch if error                                     
 LDAA   V.sub.-- TAGRCV                                                   
                     ;Check tag command received                          
 BEQ      POLL.sub.-- 72?                                                 
                     ;Branch if not                                       
 COMA                ;TAGRCV holds initiator ID                           
 STAA   V.sub.-- ATNFS                                                    
                     ;Set attention initiators                            
 JMP      QTAGPL     ;Jump to change code sets.                           
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     Routine B9 is routine QTAGPL and is set forth below. Routine B9 is invoked whenever a tag queuing command has been sensed by the look ahead operating system which results in the system bus is being held, the tag queuing operating system being loaded into RAM 14 and transfer of operations to the tag queuing operating system. 
     
         ______________________________________                                    
                       LOAD TAG                                           
                       QUEUING                                            
          ROUTINE B9   COMMAND SET                                        
______________________________________                                    
QTAGPL:                    ;ROM entry for                                 
                           change                                         
 LDS        #M.sub.-- STAK ;                                              
 CLRA                      ;                                              
 STAA       V.sub.-- ALGNCE                                               
                           ;Clear allegiance                              
                           flags                                          
 STAA       V.sub.-- UTAGIP                                               
                           ;Global flag                                   
 JSR          QINIT        ;Construct command                             
                           q array                                        
 LDY        #V.sub.-- CQEQF                                               
                           ;Point to first                                
                           CQE entry                                      
 LDD        #0             ;Initialize offset                             
                           entry                                          
 STD        &lt;S.sub.-- CHANOFF,Y                                           
                           ;PROCCMD to                                    
                           channel                                        
 HALT.NITWOT               ;Channel processor                             
                           idle                                           
 LDAA       #5AH           ;                                              
 STAA       V.sub.-- RAMFLAG                                              
                           ;Set flag code                                 
                           loading                                        
 JSR          IPLDOK       ;Load tag queue                                
                           command set                                    
 LDAA       #5AH           ;                                              
 CMPA       V.sub.-- RAMFLAG                                              
                           ;Set flag code                                 
                           loaded                                         
 BNE          TPLERR       ;                                              
 LDX        #V.sub.-- EMPTY                                               
                           ;Point to empty                                
                           queue                                          
 LDY        &lt;S.sub.-- NXT,X                                               
                           ;Point to first                                
                           entry                                          
 STY        V.sub.-- CURCQE                                               
                           ;Store in CQE on                               
                           SCSI bus                                       
 LDD        #0             ;                                              
 STD        &lt;S.sub.-- CHANOFF,Y                                           
                           ;                                              
 LDAA       V.sub.-- TAGRCV                                               
                           ;                                              
 STAA       &lt;S.sub.-- HBIN,Y                                              
                           ;Initiator ID                                  
 STAA       &lt;S.sub.-- CINITBIN,Y                                          
                           ;Also current                                  
                           initiator                                      
 CLRB                      ;                                              
 JSR          SNDSTS       ;Send status                                   
 LDAA       #SWP.sub.-- NPROCESS                                          
                           ;Set flag code                                 
                           changed                                        
 ORAA         V.sub.-- SWAPFLG                                            
                           ;                                              
 STAA         V.sub.-- SWAPFLG                                            
                           ;                                              
 JMP        RAM.sub.-- START                                              
                           :Process with new                              
                           code                                           
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     In routine B9, the first 17 steps are used to initialize the disk drive system for the swapping of the operating systems stored in RAM 14. Instruction HALT.NIWOT is a micro code routine that ensures that processor 51 is in an idle state having finished the processing of the previous instruction. After the steps of storing the tag queuing operating system into RAM 14, instruction B9 JSR SNDSTS will send status to the host processor. After status is sent, flags are set indicating that the operating systems have been interchanged. Finally control is then passed to the tag queuing operating system, now stored in the RAM 14, for the processing of all commands received from the host processor. 
     The invention as described heretofore uses known digital software implementation and the microcode of routines A8 and B9 were assembled using Motorola 68Z11 Assembler, Series 5.0. It is understood that the invention can be executed by other software programs using other software languages and or assemblers. Further the invention may be implemented in hardware for example by employing a state machine to carry out the described procedures as set forth in routines A and B and as described heretofore in this specification. 
     While the invention has been particularly shown and described with references to the preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and detail may be made therein without departing from the spirit and scope of the invention. Given the above disclosure of general concepts and specific embodiments, the scope of the protection sought is defined by the following.