Roland Quick Disk Emulation

Overview The Quick Disk drive in the early Roland samplers is prone to failure and long since obsolete. One of my background projects is to create an micro processor emulator, as I have 3 of these samplers. This post details progress to this goal.

How the data is stored Each side of a QD contains one bank of 64k bytes of data which contains sample data, wave parameters and the performance parameters and split points. When a QD disk is loaded it moves the sample data as 12-bits into DRAM wave memory and replaces the current 8-bit wave and performance parameter values in the SRAM chip with the new ones. However you can choose to just load the sample and wave data and not the 26 performance parameters, if you want to keep the original settings. You can also preview the name of the sample before loading the disk.

Variations The S-220 introduced the capability to store more parameters as it introduced new capabilities beyond the S-10 and MKS100. The S-220 OS recognizes three types of sample disk:

• Type I – S-220 Basic Information (F2 pushed during save)
• Type II – S-220 All Information
• Type III – S-10 or MKS-100

The different amount of parameter data does not affect how the QD works or is emulated.

Sample Memory The wave memory is built from six HM50464P 64kx4 bit DRAM chips, which provides 128k of 12-bit sample storage in total. Because this data is stored in 8 bit bytes on the QD the 12-bit sample data is stored as 2 complements in 2x 8 bit words onto the disk. A disk side therefore contains 48k bytes of sample data and up to 16k bytes of wave and performance data. The 29 items of wave data control how the sample is played back; loop points, envelope settings, auto bend etc.

The limitations of the QD storage size means Roland had to split the sample memory into 4 banks, with each bank requiring a single side of a QD. So a full memory load means 2 disks and 4 load operations.

The samples are replayed via a 16-bit DAC at 15 or 30 kHz, which provides 2.18 seconds or 1.09 seconds of sample time per bank. This is remarkable short compared with today’s software sampling but it is the same wave memory size the Emulator 1 used in 1981 at a cost of $10k.

The sample bank can have a name which is 9 alphabetical characters which is stored as two hex characters.

Use Cases The QD in the Roland S-10, MKS-100 and S-220 has only a few use cases;

• There is no formatting of the disk, as it has no sectors.
• Full Read – reads the complete sample bank of 64kb
• Monitor Read – reads just the sample bank name and structure
• Full Write – writes the complete sample bank of 64kb
• Verified Write – checks whether there is sample data or its an empty disk then writes the complete sample bank

Essentially the QD needs to do only 3 things; partial read, full read or full write. Partial read is controlled by the OS and is not a QD function.

QD Interface The interface to the QD consists of 10 lines:

1. /WRITE PROTECT – indicates whether the disk is write protected or not
2. /WRITE DATA – data is written here when WRITE GATE is high
3. WRITE GATE – enables recording
4. /MOTOR ON – Low sets the disk motor running
5. READ DATA – read data stream
6. /READY – reading or writing can take place
7. /MEDIA SW – indicates disk is inserted or not
8. /RESET set low for reset period after POWER ON RESET
9. +5V
10. GND

The read and write hand shaking is very basic and described in the Roland services notes. The QD uses standard MFM encoding (its a DD disk!) and has a clock rate of 101 kHz much lower than the DS/DD floppy drive clock of 250 kHz.

QD Read & Write Timing

Gotek Flash Floppy Solution Originally I was going to make my own ARM chip based emulation, but after seeing how the Gotek floppy emulator can be loaded with a completely new and flexible code set, I ditched my plans. There are three challenges:

• The clock rate is lower and not an integer, however the FF code can be configured to run at different clock speeds.
• The QD has no software sectors or notion of indexes and steps across tracks. Its just one track. This can be configured as simple 64kb FTE.
• The hand shaking and I/O pins are a bit different to a floppy. Once again this can be configurable in the code and mapped in cabling.

I/O Mapping Lets take a look of how the 10-pin QD connector maps to a standard Shugart floppy 34 pin connector.

A Solution Kief Fraser is the developer behind Flash Floppy and the wiki is here. In mid August a version of the code was announced that supports Quick Disk and I have tested this out on a Roland S-220. The Gotek drive casing is 2 mm wider than the QD drive and 2 mm smaller in height. I took 1 mm off each side of the drive using a craft knife and then designed a PCB that attaches to the base of the drive and to the QD metal mounting bracket, so the drive is at exactly the right place. The PCB is 150 x 120 mm and contain a JST 10 pin connector for the cable to the Roland main board, a 34-pin IDC connector to attach the drive to, along with 4-pin power.

The original 10 pin connector on the QD is an unusual JST like format but it is not the same and I have not found a modern equivalent. I have replaced this connector (at the end of the Roland cable) with a new 10-pin JST one, which mates with the JST socket on the PCB.