SCSI2SD old

From code/src wiki
Revision as of 06:04, 30 September 2011 by Michael (talk | contribs)
Jump to navigationJump to search

A device that presents a USB Mass Storage device as a Direct Access device to a SCSI controller.


Why ?

Because there are many vintage computers out there that require a 50-pin SCSI drive to boot from. Such disks are only available second-hand, and it's getting harder and harder to find a working disk.

Alternatives

  • The price of commercial SCSI converters can be much higher than the vintage computers they are used in. However, these devices are still readily available.
  • 50pin to 68pin or 80pin SCSI converters allow the use of newer drives. Availability of new SCSI SCA (80 pin) drives is limited to prohibitively expensive 15K RPM "enterprise" drives.

Requirements

  • The device shall act as the boot device for an Apple LCIII. See Apple LCIII Restoration.
    • NCR AM85C80 controller.
    • SCSI-2
    • Provides a 25-pin external connector, which implies single-ended support only.
    • asynchronous support only to 1.5MB/sec. I think this is specified based on the longest possible external cable, and higher data-rates would be possible with short internal cables.
  • The device shall support a sustained 4MB/s sequential transfer rate.
  • The device shall optionally provide active termination, enabled and disabled via a jumper.
  • The device shall optionally provide termination power, enabled and disabled via a jumper.
    • Some Macs don't provide termination power. See [1]
  • The device shall optionally check parity, enabled and disabled via a jumper.
    • Some Amiga SCSI controllers don't provide parity.
  • The device shall provide jumpers to set the SCSI ID
  • The entirety of the device shall physically fit within a 3 1/2" drive bay, including the storage device.

Design Choices

Storage

- SD card.

Microcontroller

100MIPS, 3.3->3.6v - parity calcs. - DMA - 50MHz SPI - 5v safe IO

SCSI PHY

- direct connection. - No consideration of Low-voltage differential (LVD) mode. RS-485 compatible. Either LVD SCSI transceivers or RS-485 transceivers would be used - not possible for a direct connection. Note that LVD devices must be able to fallback to SE mode, so they can be mixed on the same SCSI chain.

  • TTL logic levels.
  • Active low.
  • Active Terminator voltage regulator brings lines to 2.85V.
  • Passive terminator voltage divider to 3.33V.
Asserted (true) Released (false) LPCXXXX High
Output 0V to 0.5V

up to 48mA sinking current.

2.5V to 5.25V TODO
Input 0V to 0.8V 2V to 5.25V TODO

Parts Required

  • SCSI Terminator. TI UC5601DWPG4
  • AT90USB1286
    • USB Host functionality
    • Sources/Sinks 40 mA per I/O pin (Specs require 48mA, but this includes a very large safety margin).
    • TTL (5V) I/O output
    • Up to 48 tri-state GPIO pins (need minimum of 18 for SCSI data + control signals)
  • 50 pin IDC header
  • USB socket (for programming ? Extra expense!
  • 5V supply via Molex drive connector


Links

Projects

References