IBM System/7 Functional Characteristics - All about the IBM 1130 ...

The recommended recovery procedure is as follows:1. Read the residual address. The command to do this is an immediate read commandwith a modifier of hex F (1111). The command may be used by the program todetermine the contents of the data address register which is held and updated bythe disk storage module subchannel. If an overrun occurs, the data addressregister will contain the address of the word where the data service failed tooccur. (See "Read Residual Address" command in this chapter.)2. Determine the sector where the overrun occurred.3. Compute the count, data address, and sector address.4. Reinitialize the device control block.5. Issue the read/write cycle steal command.DPC FILE OPERATIONSI/O operations for the disk storage module are performed by read, write, and seek commands.Each I/O command specifies a register that contains data or control information.(The contents of the specified register are described later under the I/O command descriptions.)Error and status conditions of the disk storage module are indicated by statuswords that can be read at any time. (See "Error and Status Conditions," later in thischapter.)Read DataTwo separate commands must be used to read data from a selected disk. First, a read initializecommand is used to find the sector from which data is to be read. When that sectoris found, the disk storage module begins reading the data from the sector into a fourwordbuffer in the disk storage module. When the buffer is full, the disk storage modulepresents a data-service interruption request to the processor module. At this time, onlyread data commands are required to complete the read data operation.Four read data commands must transfer the buffer contents to processor storage within40 microseconds. The disk storage module again loads the buffer and interrupts theprocessor, and the program again transfers the buffer contents to processor storage. Thissequence continues until 128 words have been read from the disk sector and their checkcharacter is verified. (The disk storage module automatically verifies the check charactersused in reading the sector ID and the data field from the disk.)If fewer than 128 words are to be transferred to processor storage, a terminate commandmust be used instead of a read data command. The terminate command prevents the diskstorage module from requesting any more data-service interruption requests. However, thedisk storage module continues to read data from the disk sector in order to verify the checkcharacter for the entire 128-word data field.Write DataTwo separate commands must be used to write data on a selected disk. First, a writeinitialize command is used to find the desired sector on which data is to be written. Whenthat sector is found, the disk storage module presents a data-service interruption requestto the processor module. At this time, only write data commands are required to completethe write data operation.Four write data commands must transfer data to fill the four-word buffer in the diskstorage module within 40 microseconds so that the module circuits can write the data onthe disk. When the four words are written on the disk, the disk storage module again interruptsthe processor and the program again fills the four-word buffer. The disk storagemodule continues this sequence until 128 words have been written on the disk sector.Then, the disk storage module circuits write the check character that was automaticallygenerated during the writing of the 128 data words.IBM 5022 Disk Storage Module 15-7