2.x
	v2 Prototype (2015)	v2 Prototype (2016)	v2.0 (2016)	v2.1 (2016)	v2.1.1 (2016)
1.x
	v1 Prototype (2012)	v1.0 (2012)	v1.2 (2013)

Features

• ATMega 1284P running at 18.4320MHz
• Data storage on
  • SD-Card
  • SDHC-Card
  • PATA (IDE) hard disk
• compact dimensions
  • fits in a 5.25" Slot in the P8000 Compact
  • can be mounted easily in a 5.25" case for the P8000
• standard power connector (5.25" Molex plug)

Hardware Downloads

Software Downloads

Performance

This are the transfer rates I measured in WEGA. So the times are: P8000 16Bit accesses the Harddisk attached to the original WDC or the Emulator. I executed 10 or more runs of each method. The methods where:

• dd reading /dev/z with a blocksize of 4K and 3840 blocks (RAM-Disk only 768 blocks)
• dd reading /dev/rz with a blocksize of 4K and 3840 blocks (RAM-Disk only 768 blocks)
• dd reading a file in /z with a blocksize of 4K and 3840 blocks (RAM-Disk only 512 blocks)
• Bonnie which was compiled with the unsegmented WEGA system compiler cc with -O optimisation switch working with a 15MiB file (RAM-Disk only 2MiB file)

The following transfer rates are direct accesses from the ATMega without any P8000 communication. The rates strongly depend on the PATA drive and more important on the SD-Card used! With some SD-Cards I experienced less then half of the transfer rates. While the Emulator runs at 18.432MHz for propper baud rate generation, I also tested the speed at 20 MHz.

Story

In May 2012 I finally decided to build a replacement for the old P8000 WDC Controller. The P8000 WDC Controller is a Z80 system interfacing with up to three ST506 hard disks. The WDC Controller communicates with the P8000 Computer via a Z80-PIO which is located on the 16Bit-Board of the P8000 Computer. This PIO is dedicated to the communication with the WDC Controller. As usual, the Z80-PIO is divided into two parts - the PIO-A and the PIO-B each one being able to serve 8 Bits of data.

In this implementation here, PIO-A serves as the data-input/output interface transporting the data blocks from the hard disk as well as the so called "command codes". The PIO-A is programmed in mode 0 (output) and mode 1 (input) and is set to each mode during run-time by the firmware of the Z8001. The PIO-B is used in mode 3 (control) and serves as a status information monitor.

Communication between Computer and Controller in detail

The signals

Initialisation
Before any operation starts, the Z8001 will set the /Reset Signal to high which literally wakes up the WDC. As long as /Reset remains high, the WDC will listen on the Z80-PIO Port A for receiving Command Codes telling the WDC what to do next.

The Command Code
Every communication from the Z8001 to our WDC starts with a Command Code. Such a Command Code is a string length of nine bytes. The first byte always indicates the action the WDC has to do. The following five bytes contain data that has to be interpreted depending on the command code. Such data could be a block number to write on, a head/cylinder/sector to format or even a RAM address to store or read data from. The seventh and eighth byte may also contain valid data for some commands. If they are used, they contain the length of the data to receive from or transmit to the Z8001 after the Command Code arrival. The last, ninth byte is always 0xFF.

Receiving a Command Code
The transfer of the Command Code is only initiated by the Z8001. But the Z8001 will only send a command code when the WDC sets the correct status from its 3 status lines (0x01 = get command). Every transfer will be then set up by the Z8001 by setting the /TE signal to High. Basically, after /Reset went to High, the Emulator sets status 0x01 and then sits there and waits until /TE goes High. When /TE goes high, this tells the Emulator that data will now arrive. After /TE has gone high, the Emulator then waits until the /ARDY signal goes high as well.
Attention! The /ARDY signal of the WDC is the inverted ARDY signal of the Z80-PIO. So - when the /ARDY signal is high on the WDC, it is low (not active) at the Z80-PIO.
After the /ARDY signal is high at the WDC (=Now data is written into the Z80-PIO by the Z8001) a loop is entered. The loop now waits until the /ARDY signal goes to low (high at Z80-PIO) which indicates that data can now be read from the Z80-PIO. At the same moment, the Emulator sets the /ASTB signal to low (=active) telling the Z80-PIO, that now the data transmission happens. As soon as the data has been read by the WDC, the /ASTB signal is set to high to indicate the Z80-PIO, that the data transfer has been finished. Now the WDC waits until /ARDY goes to high again which indicates, that the Z80-PIO realised, that the data was transferred. The loop will now continue with waiting until /ARDY gets low again and so on. This happens nine times to receive all nine bytes of the Command code.

Analysing of the Command Code
TODO description

Receiving Data
TODO description

Sending Data
TODO description

List of all Command Codes

All known codes are listed. Only the Command Codes used by any available Software where implemented. Some commands have a "Drive" parameter. It is checked, by the emulator that the specified "Drive" by the host does not exceed the number of attached drives. Since only 1 drive is attachable, the "Drive" number must always be 0.

Command Code Usage:

Open topics

• Check if BTT handling could or should be implemented. Right now, the BTT is ignored by all accesses
• Check how the error report in sa.format (key "t" at the last question) looks with the original WDC and how it looks with the emulator

  Original WDC - formating CHS 81/0/0 - 81/8/17

  Total Errors since RESET: 42106---> 55330 * 'A'/30076 * 'B'/13175 * 'C'/48051 * '10'/41851 * '11'/50231 * '12'

  Emulator - formatting CHS 145/0/0 - 145/4/16

  Total Errors since RESET: 14202---> 32968 * 'A'/23583 * 'B'/6972 * 'C'/64069 * '10'/16400 * '11'/1282 * '12'

• Check how the output of the timing constants behaves in sa.format

  Original WDC

  PAR --- z40: 203  z41: 209  zmin40: 251  zmax40: 253  zmin41: 241  zmax41: 243

  Emulator

  PAR --- z40: 0  z41: 0  zmin40: 0  zmax40: 0  zmin41: 0  zmax41: 0

Other Stuff

• GitHub Page
• Gallery
• Another WDC Emulator Project