Running IBM disk diagnostic 309 against the Virtual 2315 Cartridge Facility - part 4

SIMULATION USED TO CHECK OUT THE NEW LOGIC FOR SEEKS

I carefully simulated seek behavior with the significantly changed code for the seek function in the Virtual 2315 Cartridge Facility (V2315CF). This runs under the Vivado design suite, although the actual generation of the code for the FPGA is done with the IceCube2 suite. 

It seemed to work well, but then again the prior version of the code seemed to work properly. In the real world, the signals come from the 1130 disk controller to the Virtual 2315 Cartridge Facility (V2315CF) and are passed out to the 2310 disk drive inside the IBM 1130. The controller and the drive appear to be in sync at all times, but the V2315CF which is just trying to shadow or observe the seeks ends up with the wrong cylinder number quite often. 

FIXES APPLIED TO V2315CF

My new version of the FPGA logic was loaded into the V2315CF. Up came the 1130 system and the virtual cartridge in real mode. I used my manual instructions once again to see if it does better in maintaining solid synchronization with the 2310 disk drive. 

Alas, I saw similarly bad behavior this time, in spite of an entirely different approach to shadowing the disk arm movements. For example, I performed a forward seek to cylinder 202, by setting the seek value to xC9 which is 201 decimal. When I did a read of the sector, I did see the proper relative sector number in the first word of the sector. 

However, when I tried to back up by 200, which would put me at cylinder 1, the Home indicator came on. I was either not fully at 202 with the forward seek or moved further than 200 in reverse. I tried some small seek values and saw similar mistracking.

It has been my belief that the physical 2310 and the 1130 disk controller were in sync, but I need to test that directly. If I take the top cover off of the 2310 disk drive, I can see the marked cylinder locations on the side of the disk arm actuator. It will be better if I can be completely certain that the drive and the disk controller are correct before I keep mucking with the logic in the V2315CF. 

Next I need to make the PICO debugging output list the cylinder number, allowing me to quickly see where the V2315CF believes we are and compare that to the arm actuator scale and to the intent of the instructions I execute.