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MDE Massbus Disk Emulator on-line!
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Posted 4/15/2009 6:20 PM
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We have put our disk emulator, designed to replace the RP06 and RP07 drives with modern technology, into temporary service on the 2065 in order to see how well it stands up.

If you have an account, you should check it out.

If you don't have an account, why not???


Rich Alderson
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Posted 7/9/2010 3:40 PM
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Quote: We have put our disk emulator, designed to replace the RP06 and RP07 drives with modern technology, into temporary service on the 2065 in order to see how well it stands up.If you have an account, you...

This is great news!

We are very interested in such a thing for our DEC 2020 project!

If there is any more information about your emulator, please share it with us!

/ragge

(our project: http://wiki1.csc.kth.se/nadja)

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Posted 7/9/2010 3:45 PM
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We currently have our prototype MDE working with our running 2065, presenting itself as 4 RP06 drives to the system. Our experience with the prototype has led to a number of changes in the design of the next revision, which is still some months away from turning out a new board. Some of the design changes are necessitated by discontinued parts, some by improved understanding of the issues.

We haven't yet tried attaching our prototype to a 2020, for the simple reason that we are not confident that it will work well on a Unibus. (This is our experience with the PDP-11/40 front end on the 2065.)

Our ultimate plan is to release the board design and microprocessor code, but we want to wait until the next revision before we consider doing that.
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Posted 7/9/2010 4:50 PM
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In private mail, Ragge asked about my statement regarding problems between the MDE and the PDP-11/40 front end, specifically whether the MDE is a Unibus card.

The MDE consists of a circuit board containing driver/receiver chips, 4 processors (a Rabbit Z80 architecture SBC with Ethernet and 3 PIC architecture chips handling control signals, data lines, and RP drive status registers respectively), and a Massbus connector. This board connects to a Massbus interface such as an RH20 or RH11 via a standard Massbus cable, and to an FTP server via a 100baseT Ethernet (in our case, a Slackware Linux system with a large disk array). It responds to host-side disk transfer requests by reading and writing files on the FTP server, representing each disk as a directory of files each containing 1 track of data.

The RH20 interface on the KL-10 processor is a typical PDP-10 device, responding to I/O instructions from the CPU to send or request data from one of up to 8 devices attached to the Massbus. The MDE is fully able to keep up with it at its highest demand rate.

The RH11 interface on the 11/40 (an integral part of the system, like the 8080 in a 2020) is a typical PDP-11 memory-mapped I/O device. Device status is tested in tight 2-instruction loops which drive the prototype MDE so hard that the Ethernet runs near the theoretical max rate of 100Mbps. The revised design uses a faster processor (Rabbit finally produced one faster than 50MHz with sufficient I/O pins) as well as larger dual-ported memories for data transfer to allow it to keep up with the RH11. Until that work is done, the system requires an RP06 to boot.
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Posted 3/9/2011 1:27 PM
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Last week, as an experiment, I connected the prototype MDE to a 2020, with the intention
of building an ITS system on an emulated RP06 drive. The 2020 uses a Unibus and RH11,
like a PDP-11, rather than the internal bus of the KL-10 processor in the 2065.

Upon starting the file system creation routine booted from 9 track tape, I immediately got
a large number of Unibus error reports. Shut down, re-cabled the MDE to the 2065, rebooted
the 2020 from an RM03 (real hardware), and moved on.

Just keeping things up to date on the MDE.
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