Monday, September 28, 2015

Spring 99999, me 0 but continued building out SAC Interface Box functionality


I put in two hours with the fiber optic camera, rotating the typewriter every which way and attempting to find two paths:

  1. a path for the camera head that would let me see the interposer tang and the unattached spring end beyond it
  2. a path for tools to reach in, snag the end of the spring, pull it over the tang and release it there
I was not successful. I made a try again in the early evening when work was done. What I was trying to avoid is the need to disassemble everything once again (remove operational magnets, remove mainspring, unhook linkages for various functions like space and return) which would effectively set me back many weeks. 

I did manage to find a path with both visibility and tool access. It is up from directly under the typewriter, as long as I rotate one mechanism out of the way. Manipulating the spring to fit through the interposer hole was still a very fiddly and business, but after about thirty minutes, it popped off the spring hook and rotated somehow inside so I can't see it, find it or move it.

I rotated the typewriter once to move the spring back where I can see it, but as I barely touched it, the spring fell back into the Stygian depths. After a bit more time, I set the task aside AGAIN.


I cleaned up some logic in the fpga for the virtual card reader/punch, which should allow me to begin testing it after I disable the built in 1442 adapter in the 1131 and I get the typewriter back in operation.


Besides testing the virtual, real and mirror device adapters I already have coded, there is more I can do to complete this circuitry. I have the switch over to the I2C breakout boards, replacing the medium speed SPI links, but also several additional device adapters need to be developed:

  1. real adapters to connect to a pair of IBM 9 track tape drives, requiring a SCSI interface to speak to those two drives. They will appear as 2415 tape drives.
  2. a virtual 2415 tape drive, allowing the PC to act as a tape drive with files acting as tape reels.
  3. real adapters to connect three DEC RK-05 disk drives, emulating 2310 disk drives
  4. a virtual 2310 disk drive allowing an IBM Simulator format disk file to be accessed from the PC. 
  5. a real adapter for my Dura IO Selectric to act like a 2741 terminal for use with APL/1130
  6. a virtual 2250 graphics terminal

Four of the six device adapters are going to be harder than the prior set, partly due to the more complex device management involved, but the virtual 2310 disk drive and real 2741 terminal support won't be that complex. The 2741 will look almost the same as the 1053 adapter logic, which is well documented in the ALDs of the 1130.

The only way that the virtual 2310 drive can work is to drop the goal of matching the real disk drive performance. Since the drive uses cycle steal to move the words being read or written, I can stretch out the IO to work over the USB link transactional system. I already have the scheme for the PC side worked out.

By the end of the evening, I had all four 2310 drives set up in the SAC box fpga - the first three are stubs that simply return a Disk Not Ready status DSW when addressed. The fourth is all the logic needed on the fpga side for the virtual 2310 disk drive.

Knowing the format of the IBM 1130 Simulator disk files, I could begin writing the code in Python for the PC side application. That process will take a day or two.

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