This is SD-SCSI, a simple adapter to use microSD cards in SCSI hosts.

The materials here are provided "as-is", without warranty of any kind. You may make your own adapters for non-commercial use, commercial use is strictly prohibited.

How to build the SD-SCSI adapter.

Building the SD-SCSI adapter consists of several steps:

• Make the PCB by whatever process you prefer
• Put together most of the PCB, leaving out the SCSI drivers (74F06)
• Flash the firmware and check if it basically works
• Solder the 74F06 in place
• Configure the adapter for your needs

Make the PCB

In this repository, you find gEDA files for the PCB. The schematics and the PCB layout. Using the pcb program, you should be able to generate all files you need, you can also do some copy&paste if you want to make several boards at once. For your convenience, a PDF with PCB layout and schematics is also provided. The layout in the PDF is not mirrored, so you may want to mirror them before printing on film if you work with photosensitive PCBs, as i did.

Besides this, you're on your own on how to make your board. With the schematics, you can also use a QFP-adapter to put everything together on veroboards, if you like :)

The layout is optimized for DIY PCBs, so all the vias are not covered by components, you can use 0.5mm diameter wire to connect them. But you also need to make sure that you solder both sides on the SCSI connector, the termination resistor sockets and the power jumper (maybe using thin wire to connect the sides of the boards here).

Put together the PCB

After making the PCB, it's time to put it together. Using the documents, solder all components in place but leave away the 75F06s. They will be installed after flashing the firmware. The reason for this is GPIO use - all ports are used in this adapter, so there is no JTAG or SWD available during normal operation. The port assignment is designed for simpler PCB layout, not for intelligent use of the ports, so the JTAG/SWD pins are "input" pins on the SCSI side, meaning that they can be tied to GND using the 74F06s. And without a firmware, exactly this will happen, blocking your JTAG and SWD. While there is a workaround for this situation using some pull-downs on the relevant 74F06 pins (i use this on my development adapter), it's easier to first install the firmware and then solder the 74F06s in place (like i did with the 8 other boards).

After putting together the PCB, you have one 1-pin header on the PCB, which is NRST, the other JTAG signals are available on the SCSI connector. Make sure the termination resistors and the 74F06s are not installed and wire your JTAG adapter to the SD-SCSI board the following way (numbers in brackets are 20 pin JTAG connector pins):

• TMS (7) to SCSI pin 42
• TCK (9) to SCSI pin 38
• TDI (5) to SCSI pin 36
• TDO (13) to SCSI pin 18
• NTRST (3) to SCSI pin 14
• NRST (15) to NRST pin on PCB
• GND (4) to SCSI pin 20

You can power the SD-SCSI board using USB.

Flash the firmware, run a first check

The firmware consists of several parts that need to be flashed into the correct locations. Have a look at the provided openocd.cfg to find out what goes where. You can also use this config file to flash your SD-SCSI adapter with a simple "populate" after "reset halt".

• kernel.bin is the main firmware for the SD-SCSI adapter
• dfuboot.bin is a DFU boot loader, so you can update the firmware using USB later
• dfustart.bin is a starter for the DFU boot loader, which always sits 256 bytes before FLASH end
• current.hib is a "hardware information block", which always sits 16 bytes before FLASH end

The whole firmware is based on MiKOS, a realtime operating system project i'm working on since several years and it currently is not planned to open source this project. I hope you understand that i will just provide a binary firmware for this reason.

Besides some other information, the serial number of the adapter resides in the HIB, bytes 4-7, as a 32 bit unsigned integer. I usually use a number with the format YYYYMMDDNN for this, representing the date i made the adapter plus a sequence number starting at 01 in NN. You can do the same, you can take the HIB unmodified, it's up to you. Just don't change the other values in the HIB as this might break the firmware (it's board type, revision, xtal freq, cpu freq).

After flashing everything, you can run the following basic test:

• Connect the adapter without any card installed to USB - the red LED should light up and you should see an USB device in DFU mode. This is how you update the firmware (tool follows, libusb based, you get the source).
• Connect the adapter with a card installed to USB - the adapter should work as a simple card reader now, giving you access to the whole card, enabling you to partition the card and install the configuration file.

If both tests were successful, you can put the remaining components in place.

Configuring the SD-SCSI adapter

The SD-SCSI adapter works the following way on startup:

• Check if an SD card is installed. If not, start DFU boot loader to allow updating the firmware
• If an SD card is installed, check if partition 1 contains a valid FAT12 or FAT16 file system (other file systems not supported!). If yes, check for a file SD-SCSI.cfg and parse it to configure the adapter.
• If there was no suitable file system in partition 1 or no configuration file has been found or an error was found in the configuration file, the default configuration "whole card as USB LUN 0" is created, giving you access to the full card via USB.

So all you need to do:

• Create a partition 1, which may be very small (i often use just 256KB), create a FAT12 or FAT16 file system in it and copy your SD-SCSI.cfg there.
• Create more partitions for every partition you use in SD-SCSI.cfg. 1-4 are primary partitions, 5 upwards are extended partitions, partition 0 is the whole card.