SST SST-RE-VME Logical sequence card

The logical block defines the unit of information for disk devices. A disk is viewed by 187Bug as a storage area divided into logical blocks. By default, the logical block size is set to 256 bytes for every block device in the system. The block size can be changed on a per device basis with the IOT command. The sector defines the unit of information for the media itself, as viewed by the controller. The sector size varies for different controllers, and the value for a specific device can be displayed and changed with the IOT command. When a disk transfer is requested, the start and size of the transfer is specified in blocks. 187Bug translates this into an equivalent sector specification, which is then passed on to the controller to initiate the transfer. If the conversion from blocks to sectors yields a fractional sector count, an error is returned and no data is transferred.

Device Probe Function 

A device probe with entry into the device descriptor table is done whenever a specified device is accessed; i.e., when system calls .DSKRD, .DSKWR, .DSKCFIG, .DSKFMT, and .DSKCTRL, and debugger commands BH, BO, IOC, IOP, IOT, MAR, and MAW are used. The device probe mechanism utilizes the SCSI commands "Inquiry" and "Mode Sense". If the specified controller is non-SCSI, the probe simply returns a status of "device present and unknown". The device probe makes an entry into the device descriptor table with the pertinent data. After an entry has been made, the next time a probe is done it simply returns with "device present" status (pointer to the device descriptor).

Disk I/O via 187Bug Commands 

These following 187Bug commands are provided for disk I/O. Detailed instructions for their use are found in the Debugging Package for Motorola 88K RISC CPUs User's Manual. When a command is issued to a particular controller LUN and device LUN, these LUNs are remembered by 187Bug so that the next disk command defaults to use the same controller and device. IOI (Input/Output Inquiry) This command is used to probe the system for all possible CLUN/DLUN combinations and display inquiry data for devices which support it. The device descriptor table only has space for 16 device descriptors; with the IOI command, you can view the table and clear it if necessary

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