SCSI2SD

The SCSI Hard Drive Emulator for retro computing.

(prototype version shown)

News

3 Oct 2013:
Source code and PCB files uploaded.

10 Sep 2013:
It works! I have a working prototype that works well. There are a few minor errors in the PCB layout that will be fixed in the next revision.

Overview

Traditional hard drives last 5 years^*. Maybe, if you're luckly, you'll get 10 years of service from a particular drive. The lubricants wear out, the spindles rust. SCSI2SD is a modern replacement for failed drives. It allows the use of vintage computer hardware long after their mechanical drives fail. The use of SD memory cards solves the problem of transferring data between the vintage computer and a modern PC (who still has access to a working floppy drive ?)

^*All statistics are made up.

Features

1. In-built active terminator.
2. Can optional supply terminator power back to the SCSI bus
3. Emulates a non-removable hard drive for maximum compatibility.
4. Firmware updatable over USB (TODO software not yet implemented)
5. Highly configurable over USB (TODO software not yet implemented)
   • Selectable SCSI ID
   • Selectable parity support
   • Enable/disable Unit Attention Condition
   • Artificial limits on the SCSI disk size (eg. limit size to 4G to avoid OS bugs)

Technical Specifications

SCSI Interface	SCSI-2 Narrow 8-bit 50-pin connector. Supports asynchronous transfers only.
SD Card Interface	Standard SDSC (1GB maximum size) SDHC (32GB maximum size) SDXC cards are untested. Donations welcome. Communication is via the SPI protocol at 25MHz.
Power	5V via standard molex drive connector.
Dimensions	10cm x 10cm x 1.5cm A 3D-printable bracket is in testing to suit a standard 3.5" hard disk bay.

Performance

As currently implemented:

Sequential read: 250kb/sec Sequential write: 240kb/sec

Tested with a 16GB class 10 SD card, via the commands:

# WRITE TEST
sudo dd bs=8192 count=100 if=/dev/zero of=/dev/sdX oflag=dsync

# READ TEST
sudo dd bs=8192 count=100 if=/dev/sdX of=/dev/null

I am working on updating the slow polling SD card communication to use DMA. I expect the performance to reach 1Mb/sec.

Compatibility

Tested with Linux (current), Apple Macintosh System 7.5.3 on LC-III, and LC-475 hardware.

Files

The schematics, pcb layout, and source code is managed under the git version control system. A copy of all sources can be obtained via the command:

git clone git://www.codesrc.com/git/SCSI2SD

Alternatively, the git sources can be viewed using your web browser by clicking here.

The schematics and PCB layout files can be viewed/edited with the free gEDA tools. For those without access to gEDA, I've exported the content as PDF:

• schematic.pdf
• layout.pdf

The software is built using the Cypress PSoC Creator IDE.

Howto

• FormatWithBasiliskII Format an SD card for use with Apple Macintosh hardware using the Basilisk II emulator

Old

For historical project information see SCSI2SD old