NAME

hsa − HVME SCSI Adaptor

DESCRIPTION

The HVME SCSI Adaptor (HSA) provides disk device functionality similar to that provided by the HVME Disk Controller (HDC) but for SCSI disks instead of SMD disks.  It does so by providing essentially the same board level interface to the system as the HDC, with only minor deviations to support noticeable differences between SCSI and SMD interface disks.  Additionally, the HSA can operate as a traditional VME to SCSI bus adaptor supporting tape drives and perhaps other type of SCSI devices.  In this mode, arbitrary SCSI commands are "passed through" the HSA and directly to the SCSI target devices.  The HSA manages all the details of the SCSI interface including device selection, command transmission, data transmission, message transmission, and disconnection and reconnection of target devices on the SCSI bus.  The CPU is only notified via interrupts when commands are accepted and when they are completed.  The HSA also efficiently handles data chaining to host memory (scatter-gather), command queueing, and SCSI bus scheduling.  SCSI Devices

The HSA firmware and software have been designed to work with SCSI devices that support a set of common extensions to the level 1 SCSI standard.  These extensions known as the Common Command Set (CCS) extensions.  Most SCSI device vendors now supply embedded SCSI controllers that support the CCS extensions.  The CCS extensions have also been incorporated into the more recent SCSI-2 standard, implying those devices which support the SCSI-2 standard may work with the HSA as well. However, drives not supporting the SCSI-1 standard plus the CCS extensions are not likely to operate correctly with the HSA without some customization of system software. 

While the HSA software has been tested with a wide variety of devices, it has only been extensively tested with the standard devices available directly from Harris.  Because the compatibility testing done with third party SCSI devices is not nearly as complete as the testing that occurs with standard Harris products, Harris does not guarantee that any third party SCSI device will function correctly when connected to an HSA.  Harris can provide some limited technical assistance to integrators experiencing difficulties with non-Harris devices, however, the variations in third party SCSI hardware are too great to guarantee that all devices will function properly with the HSA hardware and software.  Hardware Configuration

HSA controllers are supported on the Harris Enhanced VME bus (HVME).  A system may be configured with as many HSAs as it has available HVME slots.  The SCSI standard allows for 8 devices address on the SCSI bus called SCSI bus IDs.  An HSA can support any combination of up to 7 SCSI target devices since it must reserve a bus ID for itself.  By convention, SCSI bus ID 7 is reserved for the HSA’s use and should not be used by any target device.  Also by convention, disk devices are generally assigned first from SCSI bus ID 0 up to SCSI bus ID 6.  Tape devices are generally assigned SCSI bus IDs 5 down to SCSI bus ID 0.  SCSI bus ID 6 is only assigned if all other IDs are already assigned.  The /etc/master system configuration file identifies which bus IDs correspond to which disk/tape units.  An excerpt from a configuration file is included below.  Additional limits of 32 disk units of all types and 16 tape units of all types are imposed by the CX/UX system software. 
Software Configuration

Disk and tape drives connected to an HSA are configured as any other disk or tape drive.  The following excerpt from a config(1M) file devices section illustrates a sample configuration of two HSAs, each with four disk drives, and a 1/4" cartridge tape unit. 

 ...
 ...
controllerhs0at vba0 csr 0x03vector hsintr
controllerhs0at vba0 csr 0x04vector hsintr
 diskdsk0at hs0 drive 0
diskdsk1at hs0 drive 1
diskdsk2 at hs0 drive 2
diskdsk3 at hs0 drive 3
diskdsk4 at hs1 drive 0
diskdsk5 at hs1 drive 1
diskdsk6 at hs1 drive 2
diskdsk7 at hs1 drive 3
 tapemt0at hs0 drive 5
tape            mt1     at hs1 drive 5
 ...
 ...

CX/UX Device Drivers

Like all disks on a CX/UX system, disks configured on an HSA will be accessed via the Generic Disk driver (gd(7)).  The advantage of this approach is that programs that could interact with potentially many disk device drivers will instead interact with a single common device driver.  This results in a high degree of compatibility for both user and system level software.  The use of a common driver also insures consistency in device naming and numbering conventions, and facilitates almost identical system administration procedures such as formatting, partitioning, etc.  Refer to gd(7) for more information about the generic disk driver, and its facilities. 

Similarly, all tapes (with the exception of Pertec interface tapes configured on a Xylogics tape controller) will use the Generic Tape driver (gt(7)).  Again, user and system level software see a single common driver interface that insures application portability among different tape drives as well as common administration procedures.  Refer to gt(7) for more information about the generic tape driver, and its facilities.  Performance

The HSA can support both synchronous and asynchronous transfers on the SCSI bus.  In either case, the HSA can transfer data at up 3.3 Mbytes/sec on the SCSI bus.  However, in practice, the achievable transfer rates are generally limited to the transfer rates of the SCSI target devices with which the HSA communicates. 

FILES

/hsawcs - HSA downloadable microcode/control store

SEE ALSO

config(1M), master(4), format(1M), hdc(7), ise(7), gd(7), gt(7)

CX/UX Administrator’s Reference