Testing my new seek logic for the Virtual 2315 Cartridge Facility - part 17

RESEATED CARDS AND CABLE CONNECTORS IN 1130, RESUMING TESTING

I pulled out some of the SLT cards to gain access to gate A compartment C1 of the 1130 where the disk controller logic is housed and where the signal cable from the V2315CF is plugged in. As previously reported a couple of cables had come loose from the compartment, I believe when I was testing my 1627 plotter controller card project. 

ERRATIC INDICATOR LAMP INDICATES SHORT TERM GLITCHES ON A SIGNAL

The RD lamp on the main box of the Virtual 2315 Cartridge Facility (V2315CF) lights when the 1130 asserts the -Read Gate signal asking for the upcoming sector to be read into 1130 main memory. This is triggered by the falling edge of that signal and remains on for two rotations of the disk, about 80 milliseconds so that it is detectable. 

The lamp was flickering on and off, although the V2315CF did not treat this as a valid request for a read otherwise. I realized it was due to very short term glitches on the signal line. My FPGA logic for reading will immediately return the state machine to its idle state if the request has dropped before it is time to send the sync word to the 1130 disk controller followed by the 321 word sector data. It did not extinguish the RD indicator, however.

ADDED DEBOUNCERS FOR BOTH READ AND WRITE SIGNALS

I added in my debouncer module that requires a signal to be steady on or off for 500 nanoseconds before switching the output to that state, monitoring both the -Read Gate and -Write Gate control signals. The time scale of disk input-output operations is much larger than this delay. One word coming from disk requires about 27.8 microseconds to be read, a single bit about 2.78 microseconds, thus if the control signal drops in 0.5 microseconds it is quick enough to stop at the same bit as if it were undelayed. 

Further, operations like read and write are requested by the disk controller activating the control signal but don't actually begin until the sector marker for the next sector arrives, telling the controller that the read/write head is just starting into a sector. I changed the start of the indicator lamp activation until this further point - thus it turns on when a read or write is really in process not just a few milliseconds before as it did in the previous version of the logic. 

I simulated these, introducing various glitches and measuring the timing of the logic that performs the read or write operations. Once satisfied, I prepared a new bitstream to load into the FPGA in the V2315CF. 

SOMETHING WRONG WITH -WRITE GATE CONTROL SIGNAL

I put the oscilloscope on several signals coming from the disk controller logic and watched the correct operation of the -Read Gate as well as some others. However, the -Write Gate signal, which should be logic high and only drop to low as a trigger for a write, was permanently low and not changing. 

When I next get to the shop, I will chase this down to locate the fault and correct it, so that I can test out both read and write operations now that seek seems to be solid.