Running IBM disk diagnostic 309 against the Virtual 2315 Cartridge Facility - part 8

TESTING IN REAL MODE

With the V2315CF set to real mode, the 13SD disk drive inside the IBM 1130 runs and participates in the disk activity along with the V2315CF. With a virtual cartridge loaded into the V2315CF and any old physical 2315 cartridge loaded into the 13SD, flip the motor power switch on to spin up the drive. 

Once the disk drive finished its 90 second purge of dust from within the spinning drive, the File Ready lamp on the 1130 main console lit up as well as the RDY light on the V2315CF box. The 13SD drive believes it has lowered the heads onto the surface of the spinning platter, but they remain safely above. This made the disk ready to be accessed by the diagnostic or any other program on the 1130.

INITIAL FAILURE TO RUN TRACKED DOWN TO A BROKEN WIRE

When I began to test, the 1130 never indicated that the drive became ready. The FILE READY lamp should have illuminated, as well as the RDY light on the V2315CF box. I did hear the solenoid on the disk drive click on to load the heads down, which should have sent a signal -File Ready from the drive to the V2315CF and onward from there to the 1130. 

A quick check with a continuity tester identified the wire which carries that signal was broken in the cable. After a bit of work, the connection was restored and the drive ready state would recognized by the 1130. 

TESTING RESTARTED

The diagnostic moves the disk arm around first to verify the behavior of the Home (cylinder 0) detection and correct arm movement. Once it backed up to the home cylinder, it executed a seek to cylinder 199 but based on the data read back from the V2315CF, we believed we were at 196. A second attempt to move to 100, by seeking 3 cylinders forward, retrieved data from cylinder 197, but after that the system did sync up at 199. 

Test routine 2 began, which would perform patterns of seeks such as two cylinders forward, one cylinder back, each time reading a sector to verify the proper location was achieved. At some point during this test, the diagnostic issued a diagnostic complaining that after it issued an XIO instruction, the disk drive device status did not indicate a busy condition, just a not ready status. 

Shortly thereafter the diagnostic reported that a completion interrupt never arrived. This caused the diagnostic to terminate. My analysis of this is that the controller logic set the drive to not ready status, as if it had been switched off manually. The next XIO attempt would produce exactly the symptoms detected by the diagnostic. 

I don't know why the disk went off line like it did, but I will work out a test plan to track down the cause. Further, I have an easy way to point the blame for the initial seek failures, by setting the diagnostic to halt on the first error. Thus when it attempts to seek to cylinder 199 and receives data from cylinder 196, I can compare the disk arm in the physical 13SD drive to both of the reported locations. 

If the disk is at 199, then the failure is in my V2315CF. If the drive is at 196, then the failure is in the IBM 1130 disk controller logic or in the drive itself.