Method for controlling the expansion of connections to a SCSI bus

Claim 2

In a peripheral storage subsystem having a bridge controller for expanding to a maximum allowable number of disk drives connected to a SCSI channel, said bridge controller including a microprocessor coupled to a DMA bus, a buffer memory having control inputs coupled to said DMA bus, a first bus controller coupled between said SCSI channel and said buffer memory and a second bus controller coupled between said buffer memory and said disk drives, a method operating in said microprocessor and said bus controllers executing a program for controlling data flow in said bridge controller comprising the steps of: a. receiving a disk drive identifier and a command from said SCSI channel in said first bus controller; b. initializing queue pointers in said microprocessor in response to said disk drive identifier and said command; c. determining type of said command and setting flags and pointers in said microprocessor in response thereto; d. when said command is a write operation, transferring a write block of data from said SCSI channel and storing said write block of data in said buffer memory; e. disconnecting said bridge controller from said SCSI channel after said write block of data has been stored in said buffer memory; f. in said second bus controller, selecting a disk drive derived from said disk drive identifier to receive said write block of data by sending message and command bytes derived from said command to said disk drive; g. in said second bus controller, transferring said write block of data from said buffer memory to said disk drive selected in step f above; h. disconnecting said bridge controller from said disk drive after status and message bytes are received from said disk drive; i. reconnecting said bridge controller to said SCSI channel after transfer of said write block of data has been completed; j. disconnecting from said SCSI channel after sending status and message bytes to said SCSI channel; and, k. clearing queue flags and performing cleanup operations in said bridge controller.

Claim 3

A method as in claim 1 wherein said command is a read data operation and steps d through j are replaced with the following steps: a. in said second bus controller, selecting a disk drive derived from said disk drive identifier and sending message and command bytes derived from said command to said disk drive; b. transferring a read block of data from said disk drive and storing said read block of data in said buffer memory; c. disconnecting said bridge controller from said disk drive after status and message bytes are received; d. reselecting said SCSI channel for receiving said read block of data by sending message bytes to said SCSI channel; e. transferring said read block of data from said buffer memory to said SCSI channel in said first bus controller; and, f. disconnecting from said SCSI channel after sending said status message bytes to said SCSI channel.

Claim 4

In a peripheral storage subsystem having a bridge controller for expanding to a maximum allowable number of disk drives connected to a SCSI channel, said bridge controller including a microprocessor coupled to a DMA bus, a buffer memory having control inputs coupled to said DMA bus, a first bus controller coupled between said SCSI channel and said buffer memory and a second bus controller coupled between said buffer memory and said disk drives, a method operating in said microprocessor and said bus controllers executing a program for controlling data flow in said bridge controller comprising the steps of: a. receiving a disk drive identifier and a command from said SCSI channel in said first bus controller; b. initializing queue pointers in said microprocessor in response to said disk drive identifier and said command; c. determining type of said command and setting flags and pointers in said microprocessor in response thereto; d. when said command is a write operation, transferring a write block of data from said SCSI channel and storing said write block of data in said buffer memory; e. disconnecting said bridge controller from said SCSI channel after said write block of data has been stored in said memory; f. in said second bus controller, selecting a disk drive derived from said disk drive identifier to receive said write block of data by sending message and command bytes derived from said command to said disk drive; g. in said second bus controller, transferring said write block of data from said memory to said disk drive selected in step e above; h. disconnecting said bridge controller from said disk drive after status and message bytes are received from said disk drive; i. reconnecting said bridge controller to said SCSI channel after transfer of said write block of data has been completed; j. disconnecting from said SCSI channel after sending status and message bytes to said SCSI channel; k. clearing queue flags and performing cleanup operations in said bridge controller; l. when said command is a read data operation, in said second bus controller, selecting a disk drive derived from said disk drive identifier and sending message and command bytes derived from said command to said disk drive; m. transferring a read block of data from said disk drive and storing said read block of data in said buffer memory; n. disconnecting said bridge controller from said disk drive after status and message bytes are received; o. re-selecting said SCSI channel for receiving said read block of data by sending message bytes to said SCSI channel; p. transferring said read block of data from said buffer memory to said SCSI channel in said first bus controller; q. disconnecting from said SCSI channel after sending said status message bytes to said SCSI channel; and, r. clearing queue flags and performing cleanup operations in said bridge controller.

Claim 5

In a peripheral storage subsystem having a bridge controller for expanding to a maximum allowable number of disk drives connected to a SCSI channel, said bridge controller including a microprocessor coupled to a DMA bus, a buffer memory having control inputs coupled to said DMA bus, a first bus controller coupled between said SCSI channel and said buffer memory and a second bus controller coupled between said buffer memory and said disk drives, a method operating in said microprocessor and said bus controllers executing a program for controlling data flow in said bridge controller comprising the steps of: a. receiving a disk drive identifier and a command from said SCSI channel in said first bus controller; b. initializing queue pointers in said microprocessor in response to said disk drive identifier and said command; c. determining type of said command and setting flags and pointers in said microprocessor in response thereto; d. when said command is a write operation, transferring a write block of data from said SCSI channel and storing said write block of data in said buffer memory; e. disconnecting said bridge controller from said SCSI channel after said write block of data has been stored in said memory; f. in said second bus controller, selecting a disk drive derived from said disk drive identifier to receive said write block of data by sending message and command bytes derived from said command to said disk drive; g. in said second bus controller, transferring said write block of data from said memory to said disk drive selected in step e above; h. disconnecting said bridge controller from said disk drive after status and message bytes are received from said disk drive; i. reconnecting said bridge controller to said SCSI channel after transfer of said write block of data has been completed; j. disconnecting from said SCSI channel after sending status and message bytes to said SCSI channel; k. clearing queue flags and performing cleanup operations in said bridge controller; l. when said command is a read data operation, in said second bus controller, selecting a disk drive derived from said disk drive identifier and sending message and command bytes derived from said command to said disk drive; m. transferring a read block of data from said disk drive and storing said read block of data in said buffer memory; n. disconnecting said bridge controller from said disk drive after status and message bytes are received; o. re-selecting said SCSI channel for receiving said read block of data by sending message bytes to said SCSI channel; p. transferring said read block of data from said buffer memory to said SCSI channel in said first bus controller; q. disconnecting from said SCSI channel after sending said status message bytes to said SCSI channel; and, r. clearing queue flags and performing cleanup operations in said bridge controller.