Tuesday, August 23, 2016

Substantial progress wiring up board for Diablo driver role, plus some Calcomp investigation


I took another look at the Diablo drive that this cable originally came with, since it would have had to compensate for the lack of a Select Unit line otherwise needed to activate the drive. Nothing was changed in the drive, but I happened to notice a couple of wires on the terminator that was attached to the drive.

The Select Unit 1 line was pulled to ground by a wire on the terminator itself, which is a great idea because it is easily accessible when attaching my tool. The user hooking my driver to a Diablo drive would just jumper across the resistor for pin L (Select Unit 1) that runs to ground, thus pulling the signal permanently on.

In addition to the Select Unit, my terminator also pulled Read Gate to ground, permanently streaming bits from the heads. With no wire in the cable, I will have to logically block this with a virtual read gate inside the fpga.

With this solved, I don't need to hunt for, wait to receive and install extra pins in my cable. I can move right into wiring this up as it sits. My level shifter chips won't arrive until Friday thus I can't have the entire extension board complete today.

I grabbed socket diagrams and IC sockets to begin wiring up the extension board. In addition, I carefully identified each signal wire and labeled it, to make it easy to wire them on when it is time.

By lunchtime I had a bit less than half of the input section wired and am one 16 pin socket short of what I need for the complete board. I hoped to scrounge through my side shed to see if I had even one more socket on hand, but I have to buy more. I can't install the chips.

By dinnertime I had completely wired the input section, other than attaching the actual disk cable, had wired all the power for three of the four chips in the output section (since I don't have the fourth chip socket yet), and have most of the select and enable lines hooked up.

I did buy a plug for use in the emulator role, which should arrive in about a week. It has solder-on terminals and a full set of pins allowing me to implement all the signals I need or want. I went looking for a protective housing which I found on eBay. It has to travel here from Israel, so could be 3-4 weeks until I can properly build the emulator role cable.

After dinner, I went back to my wiring and now have all the lines that will go to the cable hooked to all chips but one, and I am almost done connecting the other sides of those chips to the FPGA connector. When I have a chip socket to put in place and a few more hours, this will be almost complete. The chips themselves go into the socket and a few tantalum power filtering capacitors get added to wrap it up.

I began writing out the various finite state machines (FSMs) in pseudocode to work out the overall flow and process for the driver functionality. Once I have a reasonable idea at this level, I can convert them to FSM diagrams which ensures I think through all the transitions correctly.

I also began plotting out the pseudocode level for FSMs to handle the emulator role, since I may identify sharing opportunities or need to modify a driver role FSM slightly to fit the emulator needs. I have just the grossest levels worked out, but will iterate down through the details in the coming days.


I did some research and satisfied myself that I should be able to shrink the aluminum on the plotter drum in the few places where it is stretched, thus with enough patience and time this drum can be trued up and flat again. The solution is to use a friction wheel, called a shrinking disc, to heat the stretched sections then cool with a spray of water.

If I can make a cylinder the correct size for the inside of the drum and push it inside the aluminum cylinder, it will act as a base to shrink against or stretch any small remaining dents. I need someone with a wood lathe to turn a piece to the size I need.

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