Testing a write after conditioning the Sector Marker signal for the Virtual 2315 Cartridge Facility

FIXES MADE BEFORE DIAGNOSTIC TESTING RESUMED

The new Signal Conditioner board is in place and ensuring that glitches on the -Sector Marker signal receive by the IBM 1130 logic won't lead to incorrect results. Since that signals looked really good now, I expected everything to work properly now. 

LOGIC ANALYZER SHOWS THAT THE SECTOR MARKER ISSUES ARE GONE!

I recorded the same signals that showed me that doubled edges were caused by the ringing of the signal and led to a spurious termination of the write after only half a sector - 5 milliseconds instead of 10. This time, everything was perfect and the write continued for the full 10 ms. 

The flipflop logic that blocks every other 5ms raw sector marker pulse (+Alt pulse and -Alt pulse) are alternating just as they should, thus the -Sector Marker signal at 5ms is blocked and only the second one is passed through as -4 Sector Pulses and that terminates the write. The probe lead had fallen off the raw sector marker signal, which would have been signal 5 (green) in the trace, but we know the pulse comes at the 5ms point in the write operation. 

ALMOST PERFECT TEST OF WRITE IN VIRTUAL MODE ACHIEVED

This time I did achieve a good capture of the data I wrote to the virtual 2315 cartridge, including the entire sector. I set up a known pattern in a memory buffer in the 1130 and issued an XIO instruction to write to a given sector of the disk (cylinder 0, head 0 and sector 1). I issued an XIO to read in the same sector to a different buffer, confirming that the contents matched what I had written. An offline view of the mini 2315 cartridge using the Showsector.exe program I provided confirmed the content of the sector as well. 

It was not flawless, however, as there was a single bit shift in the data for the last 48 words of the 321 in the sector. If you look at the data from the sector as it was extracted with Showsector.exe, you will see starting at word 0x111 the data was recorded as 0x0224 when it should be 0x0112. Every word from that point forward is the same as the data I tried to write out except for the one bit shift, ending with 0x0282 which was intended to be 0x0141. 

The data that I wrote out was almost the same as in my previous tests, however, words 2 and 3 were changed to 0x2600 in the buffer where they had been 0x0002 and 0x0003 in my original test. Thus I wrote what we see above, at least up to word x111 where things went slightly astray.

I had previously identified that the signal -Write Clock Phase B which comes from the V2315CF into the 1130 might cause this kind of issue. The signal will advance the shift register after each clock. A spurious double edge would cause the register to shift the data by one bit. I had finessed the signal termination to really ameliorate signal issues but they were not ideal. It does appear that we had this one error in about 6,500 clock intervals during the write. That is quite good but not good enough.

The solution is the sledgehammer! One board has five channels of signals that it can process. The -Write Clock Phase B signal is definitely worth slamming into shape, so it is going to be processed. On my next visit to the shop I will be wiring the other four signals I identified so that they pass through the Signal Conditioner board. I don't anticipate any errors after I sledgehammer the signal into shape.