Wrapping up the successful 1130 memory substitute project

RESOLUTION OF THE ISSUE

As I covered in my last blog post, the addition of a braided ground wire with many fine strands was sufficient to solve the high frequency impedance of the ground connection. The board is now solid as a rock. 

RERAN CPU DIAGNOSTIC AND MEMORY DIAGNOSTIC SUCCESSFULLY

All diagnostics run clean, thus the memory and indeed the CPU are working properly. I can move back to testing of my Virtual 2315 Cartridge Facility which expands the usefulness of the internal disk drive tremendously. 

DECLARING VICTORY AND FINISHING UP THE MOUNTING INTO THE 1130

Based on this, my 1130 MRAM board appears to be working properly. It replaces the core memory stack and associated logic cards that sat in compartment B-C1 of the 1130 system, since that core stack was unrepairable. Three ribbon cables plug into my board instead of into the backplane in compartment B-C1. I disconnected all the power connectors to that compartment, but left all the components in place. 

My design includes two holes for attachment of the printed circuit board onto mounting brackets to hold the board inside the compartment. I fabricated something and have the board in its permanent home. It was necessary to remove the top row of SLT cards from the compartment to allow the PCB, cable connectors and FPGA daughtercard to fit within the air plenum at the top of compartment B-C1. I ran the braided ground conductor from my board to the ground bus of the 1130 to shunt any high frequency noise around the 16 gauge stranded wire ground connections for +12V and ground.

The 1130 is pretty insensitive to the noise generated but it can cause the ground of the board to shift a bit relative to the ground of the rest of the 1130 due to the impedance of the stranded wire at higher frequencies. The braided conductor bypasses the stranded wire for high frequencies. I dressed all the power lines to the board to make things neat. 

GITHUB FINALIZED

The github repository for the 1130 MRAM substitute project is now up to date with all the files, documents and other information needed by anyone who wants to build a replacement core memory for their 8K 3.6us IBM 1130. 

Failed testing of mechanism to read virtual 2315 cartridges conveniently from a PC

VIRTUAL 2315 CARTRIDGES STORE THE IMAGE ON A MICROSD CARD INSIDE HOLDER

The Virtual 2315 Cartridge Facility (V2315CF) makes use of microSD cards to hold a file with the contents of a 2315 Disk Cartridge for use in the disk drive of an IBM 1130 system. The microSD card is kept in a holder that appears to be a miniature 2315 cartridge, presenting pins on the edge that plug into the main box of the V2315CF to use that image for access on the 1130.

In order to read and change the files on the microSD from a PC, one would normally have to remove the microSD card from inside the holder's socket and place it into a card reader plugged into the PC. It is preferable to have the mini 2315 cartridge assembly remain glued together rather than opening it for access. 

I decided to build a simple component that the mini cartridge could plug into, with the component connected by USB cable to a PC. The microSD card will appear on the PC as a disk drive, thus it can be accessed just as if it were removed and put into a card reader but leaving the mini 2315 cartridge sealed.

The unit is implemented on a Raspberry Pi PICO with just a few resistors and the socket added so that the mini 2315 cartridge can plug into the unit. The PICO was programmed to open the microSD card as a FAT file system and present that on the PC in the same way that a USB memory stick appears to be a disk drive. The first design made use of Carl J Kugler III's library no-OS-FatFS-SD-SPI-RPI-PICO after suggestions from Google Gemini. The code did not open the microSD card successfully. 

Since debugging was going to be a bit awkward since I was using the PICO USB cable to appear as a disk drive to the PC, requiring me to wire up a UART link for debugging messages. I tried blinking the LED on the PICO board to let me know where it went astray, but it was some issue the library found with the microSD card image that I couldn't readily determine. 

I went back to the drawing board, this time accepting advice from Gemini to use an Arduino IDE approach, leveraging the PICO core from Earle Philhower to access the microSD card in a more direct and hopefully more successful way. I built that version and loaded it onto the PICO for testing. 

That failed and failed and failed. Lots of unrecognized USB device errors. Gemini seems to be doing brainless google searches of symptoms and steering me to each fix from those posts, without truly understanding what is happening. It gave me fifteen different attempts before doing a test and blaming a timing race between Windows and the PICO. 

It then had me download CircuitPython onto the PICO and load some scripts. That continued to show errors, which several iterations worked on but ultimately it decided that now we had to switch to MicroPython. About a dozen iterations later, including one where it reported that its previous code had an error crashing the boot, it reached the point where it proudly chimed when the USB cable was connected but showed no drive at all.

Now it is recommending that I go to direct C/C++ code, a precompiled load file for the PICO at a repository link. When I went to the github repository, there are no xxx.uf2 files at all. I pointed that out, got a "you are correct, it is only source code" response and then directed to yet another method. Useless. Completely useless. This is simply regurgitating posts it scrapes from the web. 

I am going back to the Visual Studio C code I originally worked with, but asking MS Copilot for how to accomplish it. Hopefully I will find the deviation from what Gemini offered. It is hard to believe that companies believe they can replace programmers with AI at least based on my experiences. 

Needed to wait for Lattice Semi to send the hobbyist license file

FOUND ONLINE COMMENTS THAT SUGGEST FORMATTING OF MAC IS AN ISSUE

Some internet messages suggested that Lattice expects the MAC address of the network interface to be formatted a specific way, without hyphens or colons as most systems display them. My first request changed the subject line to Renewal from their boilerplate New iCEcube2 License Request wording. I then changed it to what they had, since they may have a simple script grabbing the license requests. 

When I still had radio silence for a long period, I did some searches to see if others were experiencing delays or other problems. That is where I found hints that they expect the MAC to be 12 contiguous hex digits although their boilerplate simply asks "MAC address for license generation: " without any format guidance. I sent off a third request just now, hopefully matching the unspoken rules and allowing me to receive the license file shortly.

RESPONSE RECEIVED - LOG ON AND REQUEST LICENSE FILE

I was given a subscription number as the response to my earlier email requests. That had me log onto the Lattice website and request a license for the subscription. With that number entered plus my MAC address without hyphens or spaces, it told me to wait for an email. 

Great news, however, because the license file arrived almost immediately. I set up the program to point at the license and was able to synthesize and create the bitmap which I have to flash onto the FPGA memory device so that the new logic becomes active. 

SUBSTANTIAL PROGRESS DOCUMENTING BUILD OF V2315CF

It is a complex project that requires building and then modifying George Wiley's RK-05 Emulator, building several custom PCBs, modifying the internal disk drive of the IBM 1130, making wiring changes in the 1130, connecting quite a few units together and then installing them in a custom enclosure or inside the 1130 system. 

There is also the need to create Solid Logic Technology (SLT) compatible male and female connectors since we are intercepting signals that run between the disk drive and the 1130. Mini 2315 cartridge replicas are constructed to hold the contents of the virtual disk cartridges, and software is used to manage theses mini cartridges. 

I have generated many images to help guide the builder in these steps, then written about each step with those pictures in support. I had to cross reference many schematics and design files to be able to clearly identify where wires are connected or removed. 

I estimate that the document is now 75% complete. A few more days work and I should be able to upload it to the github repository. 

More this and that, while waiting

BUILDING BRACKETS AND COATING THE 1130 MRAM BOARD FOR INSTALLATION

The gates in a Solid Logic Technology (SLT) generation mainframe have multiple compartments, each hosting as many as 96 SLT printed circuit cards which plug into a printed circuit board that interconnects those 96 card slots plus some top and bottom signal cables. One side of the compartment has the large board with about 2,500 wire-wrap pins that form the 104 sockets for SLT cards or cable connectors. 

The other side of the compartment is a metal cover behind which the SLT cards are inserted. These cards are oriented so that air flows in the 'aisles' between the cards, from bottom to top, to remove heat. Fans sit on the bottom of the compartment and pull air through filters to blow it up over the SLT cards. The top of the compartment is a grill through which the warmed air exits.

Compartment C1 in gate B housed the original core memory for this IBM 1130. It has a three dimensional core memory stack installed on the big board in place of about half the card slots. The remaining card slots have SLT cards which provide the addressing, driving and sensing circuitry for the core memory. 

Since the core memory stack has irreversible corrosion that is eating internal traces, it is no longer feasible to use it on the 1130. I developed a printed circuit board to replace all of the functionality of that card compartment. The three cables which connect this compartment to the rest of the 1130 circuitry are plugged into my PCB instead of the big board in the compartment. All power connections to that compartment are removed, thus nothing is operating in the compartment; my PCB serves as the core storage for the system. 

My PCB is mounted inside the compartment, just below the top grill where the hot air would escape. The three cables originally plugged into the compartment backplane in the top connector slots T1, T3 and T4. My board has those cables fitted and is suspended at an angle inside the gate just below the grill so that it is cooled by the airflow from the fans below. 

SLT backplane/compartment

mounting method

I cut some brass to form the brackets that will hold the PCB at a diagonal under the grill, permitting the existing SLT cards that are inactive to remain in place. The PCB and its brackets were given conformal coating to keep the electrical components insulated from any contact with the compartment walls or grill. The coating should be fully dry by Wednesday when I intend to bolt the memory PCB in place and close up the 1130 system. 

STILL FIGHTING WITH THE HEAD CLAMPS OF THE DIABLO 31 DRIVE

The Diablo model 31 disk drive mounts two read/write heads on the arm, one each for the upper and lower side of the disk platter that is inside the 2315 disk cartridge. These are held in place by three clamps - one each for the upper and lower head holders and a third that holds both head holders in place.

These had been loosened too much and could not be tightened into their proper position. The upper and lower head holder clamps have a tang at the bottom that nestles into a groove on the drive, keeping the clamp upright so that the bolt simply loosens or tightens it. The bolts had been turned too many times and now the tang was not in place, allowing the clamp to spin around. 

Access to the area where the clamps sit is exceedingly restricted and hard to even see into. I finally pulled out a fiber optic camera on a cable that I could push into the area and try to get enough visibility to work. Below is a view from the camera of one of the two head holder clamps, rotated out of position but at least with the bolt still threaded into the end. 

View through the fiber optic camera - not great

I was able to finally work the lower head holder clamp into position so that it tightened up, held from rotation by the tang. That took quite a bit of fussing and work until I finally got the clamp in place.

I then began working on the upper head holder clamp, but that seems jammed against the lower clamp or perhaps against the third (common) clamp. I need to get this one sorted out before I can move on to the third clamp which should be easier to orient once I slide one of the head holders into place. I ran out of steam; this will be waiting for me when I get back into the shop.

CREATING THE BUILD AND INSTALLATION MANUAL FOR THE V2315CF PROJECT

I am now at a point where I will be finalizing the debugging of the Virtual 2315 Cartridge Facility (V2315CF), an ambitious feature that works with the internal disk drive of the IBM 1130 to allow access to a wide range of cartridge images either archived from real disk cartridges or created on IBM simulators. These can be mounted and accessed as if they were real physical disk cartridges, with the internal drive spinning and the arms moving in and out. 

However, the heads do not actually load down onto the one physical cartridge that is inside the drive, thus eliminating the risk of crashes that could destroy the rare disk heads or the disk cartridges. The data for a virtual 2315 cartridge is held on a microSD card inside a little 2" replica of a cartridge which is plugged into the V2315CF main box. The data that is ready by the 1130 comes from the virtual disk image, rather than the heads in the drive. Any data written or changed by the 1130 will be stored on the virtual cartridge's microSD card. 

Virtual cartridge images can be transferred to and from the IBM 1130 simulators that run on modern computers. As well, the collection of physical 2315 cartridges that I have collected will be archived by the other current project, the Diablo Archiver, so that they can be used on the V2315CF. 

The only issue that was outstanding when I had to walk away from the debugging (due to the core memory of the 1130 failing) was the coordination of seeks (disk arm movement between the 203 cylinders of a 2315 cartridge) between the internal disk drive, IBM 1130 and the V2315CF. I am optimistic that this will shortly be resolved, after which I can finalize the installation of the V2315CF in the IBM 1130 that belongs to the Vintage Computer Federation and which I am restoring. 

This is a complicated system that involves modifications to the internal disk drive, several printed circuit boards, a complex power system with battery backup, and the main box of the V2315CF. The main box is an extensively modified derivative of George Wiley's RK-05 Emulator which he built to emulate the DEC disk drive which is a derivative of the internal disk drive from the IBM 1130. There are also the virtual cartridges, software to transfer the disk images and changes to the RK-05 Emulator kit. Finally, a plexiglass case mounts the main box and some of the other components inside the top cover of the IBM 1130, right atop the internal disk drive. 

I began writing a manual which details all the modifications, construction details and other tips necessary for someone to build and install a V2315CF for use with their own IBM 1130. The project is shared on Github along with PCB design files, Verilog and C code and other essential files, but the manual covers the essentials for putting it all together. This manual will be at least 50 pages long and may grow substantially beyond that as I validate that a reader will have all the information they need to successfully implement the project.

WAITING TO PROCEED ON OTHER TASKS

I have no response yet from Lattice about the license file I need to synthesize the FPGA logic for the V2315CF - those changes are what I must test to finish debugging the seek behavior of the project.  

I am waiting for filter and gasket materials to get the Diablo model 31 disk drive in good working order for the Diablo Archiver project to begin reading and saving the contents of the 2315 cartridges from my collection. 

I will also be tied up all day Wednesday providing a tour of Cape Canaveral Space Force Station and its historical facilities to 200 undergrad and graduate college interns, a Brigadier General and other brass in support of the Air Force Civilian Services organization. It is likely that my progress is mostly stalled until Thursday when the awaited items may be on hand and when I can get time to go back into the workshop.

This and that - waiting while moving several projects along

WAITING FOR FILTER FOAM AND MATERIAL TO REPLACE HEPA FILTER ON DIABLO

The Diablo archiver project depends upon the Diablo model 31 disk drive being ready to safely read the pile of 2315 disk cartridges I have with IBM 1130 software and data on them. The heads are not yet mounted but I also have to ensure that the air supply is clean enough to protect the drive from head crashes that dust or other tiny contaminants might cause.

Bits of foam and gasket material have degraded over the years and must be replaced. They have to provide a tight seal for the purified air that comes in through the main filter on the drive. This filter has a HEPA 13/14 level filter to block all the tiny particles, with a foam prefilter to stop bigger junk from reaching the HEPA filter. There are also gaskets where the filter joins the drive body and also where the clean air enters the 2315 disk cartridge - these are degraded and must be replaced.

I have ordered products I can use to replace the gaskets, the prefilter foam and the HEPA filter so that the drive is again able to provide a clean air environment for reading the cartridges.

MUST WAIT FOR NEW LICENSE FROM LATTICE FOR ICECUBE2 TO TEST V2315CF

Having completed the simulation of the improved seek functionality for the Virtual 2315 Cartridge Facility, I started up iCEcube2 to synthesize the Verilog and prepare to program the FPGA. When it started, I was informed that the free hobbyist license had expired. I submitted the email for a renewal/replacement license, but as it is Sunday I expect it to take a day at minimum and probably more. 

WORKED WITH BETTER BRAIDED GROUND WIRE FOR 1130 MRAM

I received this tinned copper mesh ground wire today and began to install it on the 1130 to provide a low impedance ground path from the 1130 MRAM memory substitute board to the 1130 power rails. There is a bit of work to do with the mounting brackets to place the board safely inside gate B compartment C1 which was where the IBM core memory circuitry resided. 

That wire mesh is enormous overkill, but I want the memory to run clean and after fighting mysterious issues due to the ordinary stranded ground wire, I don't want to accept any risk at all of memory problems in the future. 

Returning to testing for the Virtual 2315 Cartridge Facility

1130 SYSTEM NOW SOLID - POWER AND MEMORY ISSUES RESOLVED

When I was last testing the cartridge facility, I began to encounter parity stops due to continued degradation of traces inside the core memory stack of the system. I had previously added wiring to bypass broken traces on several sense lines, but another cropped up. I realized that the memory was going to continue its slide into oblivion due to whatever corrosion was occurring inside the memory stack on a surface to which I had no practical way to gain access. 

I designed a replacement for the core memory, based on a magnetic RAM chip (MRAM) which would preserve memory contents when power is off just as the original IBM core memory does. During testing of the core memory substitute board, I encountered a worsening of a second problem that had been plaguing the machine - a circuit breaker tripping on the +6V power regulator.

This would happen mostly when I had powered down the machine for a short time and then turned it back on. Very occasionally it would turn off while the machine was working. The rate of the breaker trip began to increase, so I wanted to resolve that before I could finish the memory board testing. 

I changed components on the Standard Modular System (SMS) card that performs the regulation inside the regulator module, until the flaky behavior disappeared. With solid power, I wrapped up the memory board testing. The machine was now ready to support my testing of the disk project.

THE VIRTUAL 2315 CARTRIDGE FACILITY BEING TESTED

The Virtual 2315 Cartridge Facility enhances the 1130 system, allowing the user to use the disk drive more flexibly and reliably while preserving the experience of the original disk drive operation. The disk drive in the IBM 1130 uses cartridges that contain a 14" disk platter inside a plastic housing. These slide into the disk drive. The drive spins the platter inside the cartridge and uses a pair of read/write heads, one per side of the platter, to access the 512K words of storage available on a cartridge. 

The disk cartridge is organized into 203 concentric circles on each side of the platter, reached by the drive moving the read/write heads on their arm inward to the hub center or outward to the edge of the platter surface. The movement of the arm to the 203 positions is called a seek. 

When the drive operates with a physical cartridge (IBM 2315), the motor spins it up to a speed of 1500 RPM for use. The arm moves in and out making a grunting sound as it moves. The 1130 system vibrates slightly due to the mass of the spinning platter and shakes a bit more due to each arm movement. The sound of the motor is also audible.

The Virtual 2315 Cartridge Facility modifies the disk drive so that the read/write heads do not actually move down onto the surface of the disk platter. They arm still moves, the platter still rotates, and all the sounds and sensations are the same. However, the data that would have been read from the surface is instead coming from a small plug-in virtual cartridge. Any changed data that is written out by the 1130 is captured and put onto the small plug-in virtual cartridge. 

This eliminates the risk that the heads will crash on the surface of the platter, damaging both themselves and the cartridge. It also allows the user to have as many of the small cartridges as they wish, rather than being restricted to 2315 cartridges which are no longer sold. Finally, the files on the small virtual cartridge can be used with an IBM 1130 simulator running on a PC or Mac. This interchangeability gives access to a much wider range of disk content that is likely to exist when constrained to using only actual 2315 cartridges. 

The virtual cartridge is implemented on a micro SD card that is installed inside a small plastic housing that looks like a small version of a 2315 cartridge. The SD card can be pulled out of the housing and inserted in a reader for use with the simulator, then re-installed to use it with the 1130 system. 

The Virtual 2315 Cartridge Facility involves a small control box that sits under the top lid of the IBM 1130, into which the virtual cartridge is plugged. It is connected to an interface board inside the 1130 that sits between the disk drive and the 1130 logic. 

A small motorcycle battery and related hardware ensures that the Virtual 2315 Cartridge Facility remains operating when power is abruptly removed from the 1130, long enough to ensure the virtual cartridge has preserved all new data written just prior to the power-down. 

BACK TO TESTING THE SEEK FUNCTIONALITY

The disk diagnostic programs from IBM have run against the Virtual 2315 Cartridge Facility, with all the reading and writing of data passing completely successfully. The seek of the drive is the one area that was not fully correct - sometimes the virtual facility would be out of sync with the disk drive arm position. 

The facility is simply observing the movement commands sent to the disk drive and should therefore always match the location of the read/write heads. In cases involving longer movements, it was sometimes off by a few positions, leading to the diagnostic issuing error messages.

The 1130 commands the disk drive to move 1 or 2 cylinders (positions), either forward toward higher cylinder numbers (the center of the platter) or backwards towards the outermost position on the platter which is called the home cylinder (0). Long movements consist of sequences of 2 cylinder movement commands, only followed with a 1 cylinder movement command if the total movement is an odd number of positions. 

It was possible that noise on the connection to the V2315CF was causing it to miss a move or spuriously record a seek that did not occur. Another vulnerability was that the disk drive documentation claimed that the seek was started with a short pulse on -Access Go but the logic of the disk controller inside the 1130 actually asserts -Access Go for a long time, dropping it once the seeking is over. 

I worked on the state machine logic to make it as bulletproof as I could. The main signal that advanced the state machine when I shadowed the actual seek operation between the 1130 and the disk drive was +Access Ready which I debounced. I counted time periods when the signal was high or low, updating a running counter which I allowed to move between 0 and 10. 

A sequence of 9 positive states followed by 9 negative states would never advance the counter to 10. Similarly a sequence of up to 9 negative states followed by a long run of positive states would never drop the counter to 0. Thus I had to have a steady signal to consider +Access Ready to be true or false. 

When we saw the -Access Go arrive, the state machine would next check that +Access Ready was true. If not, this is considered a spurious condition and we go back to idle. If it was true, we then sit and wait for the +Access Ready signal to become false, which occurs about 5 ms into a seek. A safety timer will count off 15 ms and if we are still sitting here waiting, we consider this a spurious seek and go back to idle. If +Access Ready did go false, we update the cylinder location and then wait for +Access Ready to return to true which is the end of our seek. 

The control signal we generate when a seek is requested happens for one cycle when we see a falling edge on -Access Go and the drive is online and ready. This is what moves the state machine out of idle. The previous version was generated continuously as long as -Access Go was asserted low, which is not correct but was driven by the error in the disk drive documentation that shows -Access Go as a single downward pulse. 

SIMULATION TO TEST THE SEEK LOGIC PRIOR TO TESTING ON THE 1130

I ran a simulation of the FPGA logic in a testbench to try out the functionality, including as many cases of noise and intermittent signals as I could think of. Once I was satisfied that the logic worked as I intended, it was time to fire up the 1130 system and test with the real hardware. 

Debugging work on the multiply-divide issue with the 1130 MRAM board - memory fixed and working flawlessly!!!!!

FALSE BIT 13 WHEN READING CERTAIN ADDRESSES WITH UNKNOWN CONDITIONS

The CPU diagnostic runs a test of the multiply and divide hardware which consistently fails after having successfully tested many sets of values. The memory location that holds one of the values - 0x0CFB - will consistently create a parity check when I attempt to access it using the Display mode of the 1130. Bit 13 will be turned on in the Storage Buffer Register (SBR) after the location is read, but the P2 parity bit is set as if that bit is not on, thus generating the parity check. 

It is strange that I can use the Load mode of the 1130 to set the value in the word, dropping bit 13 so that it matches what I believe was intended, but the next Display will again see bit 13 on and suffer a parity check. I should be able to store a value in location 0x0CFB and retrieve it without the phantom bit 13 turning on.

Now, this does NOT happen when I first bring up the 1130 system. It does not happen if I use the Storage Load and Storage Display modes of the 1130. It only happens once the diagnostic has run and we reach the error stop for the multiply-divide test. Something has happened that puts the 1130 or the memory board in a condition that then causes this strange behavior. 

HAPPENED TO ADD A BRAIDED GROUND WIRE IN PARALLEL WITH 18GA STRANDED

I had dual 18 gauge ground wires to the PCB from the IBM 1130, but decided to use a braided ground wire in place of one of the regular stranded wires. The thought was that the braided wire has many more strands, smaller strands, which gives a lower impedance path for high frequency currents to ground that ordinary stranded wire. 

I then ran the CPU Diagnostic to successful completion about ten times, then loaded the core memory diagnostic program and ran it multiple times to successful completion. The problem was indeed ground impedance, as one of my readers had been suspecting. In the DC domain I had extremely low impedance with the multiple heavy ground wires but the issue was the fast switching demands of the chips.

MEMORY SUBSTITUTE BOARD NOW WORKING PERFECTLY

The project is finally working to my satisfaction. I will update the bill of materials and build instructions to cover the very necessary braided ground wire. 

MINOR IMPROVEMENTS TO THE PCB DESIGN

Last night I broadened the ground traces for the MRAM chip on the board and added a second decoupling capacitor under the chip, a 10uF tantalum next to the .1uF ceramic. I also opened the solder mask for the four ground pads that would be used to solder a magnetic shield over the chip on the PCB. Unless I see evidence that the fault is one that these are needed to correct, I won't be building the new PCB but I am sharing the improved version on Github.