I'm a decent collector of big iron, aka mini computers, mainly DEC and DG.
I'm often facing common problems with storage devices, magnetic discs and tapes 
are a little prone to give headaches after years, and replacement drives/media 
in case of a severe failure are unobtainable.
In some cases, the ability to make a dump of the media, also without a running 
computer is very important.

Whence the idea: realize an universal device, with several input/output 
interfaces, which could be used both as storage emulator, to run a computer 
without real storage, and as controller emulator, to read/write a media without 
a running computer.
To reduce costs as much as possible, and to allow the better compatibility, the 
main board shall host enough electrical interfaces to support a large number of 
disc standard interfaces, ideally by exchanging only a personality adapter for 
each specific interface, i.e. connectors and few components.

There are several orders of problems:
- electrical signals, number and type (most disk employ 5V TTL or 3.3V TTL, 
some interfaces use differential mode for some faster signals?)
- logical implementation: several electrical signals are used for a specific 
interface. These must be handled with correct timings
- software implementation: the universal device shall be able to switch between 
interface modes and be controlled by a remote PC

I suppose the only way to obtain this is to employ an FPGA for logic 
implementation of the interface, and a microprocessor running Linux to handle 
software management, data interchange to external (via Ethernet). This means a 
Xilinx Zynq module for instance.
I know there are several ready devices based on cheaper microcontrollers, but 
I'm sure these can't support fast and tight timing required by hard disk 
interfaces (SMD-E runs at 24MHz).

The main board should include a large enough array of bidirectional 
transceivers, possibly with variable voltage, to support as much interfaces as 
possible, namely at least Shugart floppy, ST506 MFM/RLL, ESDI, SMD, IDE, SCSI1, 
DEC DSSI, DEC RX01/02, DG6030, and so on, to give a starting point.
The common factor determining what kind of disc interface can be support on 
hardware side is obviously the type of transceiver employed, for instance a 
SATA would require a differential serial channel, which could not be available.
But most old electronic is based on TTL/CMOS 5V logic, so a large variety of 
computer generations should be doable.

For the first phase, I would ask you to contribute with a list of interfaces 
which could be interesting to emulate, specially if these are similar to one 
from my list.
I please submitters to send me by email or by web link when possible, detailed 
documentation about the interface they propose, so I can check if it could be 
doable and what kind of electrical signals are needed.
Also detailed information about interfaced I listed is appreciated, as could 
give some detail I'm missing.


Reply via email to