Redesigned the sector and index pulse generator module - either uses real drive pulses or generates emulated pulses

GOAL OF MODIFICATION

I want a setting for the emulator where it can pass along the pulses from the physical 2310 drive in the IBM 1130, as well as operating without a drive by producing its own pulses. With a physical drive switched on, the disk arm will seek at the same time that the emulator virtually seeks. 

The disk controller logic in the IBM 1130 is wired to the physical 2310 drive, but the emulator is also tapped into the signals. Thus, when the controller tells the real disk arm to move forward one track, the emulator will see that and also advance the virtual track number itself. 

The disk controller sees the sector and index pulses, which it uses to determine when to turn on the read or write electronics of the physical drive. The emulator is passing along the physical drive's pulses so that both are in lock step. Thus when the controller sees it has entered the desired disk sector, it begins to read the clock and data lines from the physical drive (for a read) or controls the write data line when writing to the physical drive.

The heads are mechanically blocked from lowering onto the spinning disk surface of the physical drive. However, the controller is sent a signal that the heads have loaded and the drive becomes ready for access. 

As the write data line is modulated, the head is trying to record on the disk but it is very far above the platter and has no effect. The emulator is tapping this signal, however, capturing the bit pattern to write onto our virtual disk cartridge in the DRAM of the FPGA. 

As the drive enables the heads to sense the clock and data pulses from the spinning platter, no signal is detected since the head is too far above the surface. The emulator injects the signals into the line as if the disk head amplifier had read them, thus giving the 1130 and its disk controller the stream of bits it would have seen if using the physical disk in its traditional way. 

I set up a control signal, real_sectors, that tells this module whether to shadow the physical drive or to produce its own pulses. I might connect this to a switch on the RK-05 emulator or make it a configuration parameter. 

MADE CHANGES AND SIMULATED TO VERIFY OPERATION

The simulation shows perfectly shaped and timed pulses generated in both cases - real drive or emulated. My last remaining design task is to finish the sector write logic, where we capture the data being written from the 1130 to the drive. The emulator logic appears to correctly model the disk drive in all aspects. 

The top level module that ties together all the functional modules must be changed since we have different signals connected to a 2310 than to an RK-05. The various functional modules have changes in their input-output which have to be reflected and meshed together. 

The software in the Raspberry Pi needs updating to reflect our 2310 specific functionality. Too, I want to make use of the disk format files from simH versions of the IBM 1130, which likely differ from the RK-05 format files used by George Wiley's emulator.