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Interphase V/SCSI-2 4220 (Cougar II)

MTW sc4220


The V/SCSI-2 4220 Cougar II is available as a Fast or Fast and Wide SCSI-2 controller. The Cougar II is capable of controlling any combination of up to 14 SCSI-2 devices, seven on the primary SCSI channel and seven more if the optional secondary SCSI channel is installed. The Cougar II Wide is capable of controlling any combination of up to 15 Fast or Fast and Wide devices per channel.

The system-level interface, referred to as MACSI (Multiple Active Command Software Interface), is implemented in Short I/O. In addition to supporting command queuing, MACSI enables multiple commands to be active simultaneously. The Cougar accepts commands from the host and queues them internally. It then acts on each command as soon as possible within the confines of the SCSI bus. As commands are completed, the board notifies the host of each command's completion as well as the completion status.

The concept of work queues is integral to the way that MACSI allows multiple commands to be active simultaneously. Information in the Command Queue entry determines the work queue into which a particular command is placed. At any time, there is an In Progress command for each work queue that has at least one entry. The Next command waits for the In Progress command from that work queue to complete.

Since the SCSI bus allows many tasks to overlap on multiple devices, the MACSI interface allows for commands from all work queues to be interspersed. Assuming that the SCSI devices support overlapped activity on the SCSI bus (using Disconnect/Reconnect), one In Progress command for each attached SCSI device can be simultaneously active, resulting in overlapped data streams. Since the Cougar can have two fully independent SCSI buses, it can support two truly simultaneous data streams. If some devices do not support overlapped activity, they can be relegated to the optional second channel, allowing fully functioning devices on the primary channel unrestricted operation. Both channels can, of course, support full SCSI functionality.


  • 4220w-001ug.pdf Users Guide for the 4220 and 4220W Cougar II VME SCSI adapters - Oct 1994
  • ugr0105a.pdf ReadMeFirst "Init Controller" - Jul 1997

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Last modification: 29.05.2011 20:36:52