Overview

rx02_emulator is a hardware/software emulation of a DEC RX02 (or RX01) dual 8" floppy disk drive. The software runs on an Arduino Mega2560 processor board with a custom hardware interface shield that maps a dozen or so digital port bits to the custom DEC RX drive interface protocol.

The emulator simulates two RX02/RX01 drives mapped to files on an attached MicroSD card.

This implementation was originally based on the design at: http://www.chdickman.com/rx02/ but has been extensively modified for the Arduino and to provide the functionality necessary to pass the DEC RX02 hardware diagnostics.

Currently this design boots/runs under the PDP-11 XXDP and RT-11 operating systems and the PDP-8 OS/8 operating system.

The MicroSD card in the emulator is a FAT32 formatted filesystem, and it can be inserted (offline) into a WindowsPC to copy files to/from the device. By default, the files 'RX0.DSK' and 'RX1.DSK' are mapped to drive 0 and 1 on initialization.

Detection of single density media (256,256 bytes total) and double density media (512,512 bytes total) is done thru two differrent mechanisms. Files with the extension .RX1 will be forced to be single density, and resized appropriately (zero padded at the end, and truncated to size if required). Similarly files with the extension .RX2 will be forced to double density, and resized if necessary. Files with any other extension (ie, like .DSK) will be detected as single density if they are EXACTLY 256,256 bytes in size; and detected as double density if they are EXACTLY 512,512 bytes in size. Files that are other sizes will NOT be capable of being mounted until they are resized appropriately (the E and F commands can do this).

The emulator interfaces thru a simple ASCII terminal command line via the USB port on the Arduino device. After booting, typing: H<cr> types out the available commands. Below is a sample interaction showing the use of the H, L, S and 0 commands, and the debug level 1 log of what happens when b dy0 is typed on the attached PDP-11/44 console terminal.

Startup configuration is saved in an ASCII text file SETUP.INI that contains user interface commands that are replayed on startup. The SETUP.INI file is written using the W command, and the current 0/1/Y/N/D/M/T options are saved in the file.

The hardware shield has three indicator LEDs:

(RED) ON when INIT is asserted from the host or an error is detected in the emulator. OFF at command start.
(YEL) ON when the emulator is actively accessing the microSD card storage. OFF otherwise.
(GRN) ON when a command is inititated from the host, OFF when the command has completed (DONE set).

Normal operation will see the GRN/YEL LEDs blinking rapidly or mostly ON. For non-storage commands (eg, buffer fill/empty) only GRN will be ON.

Hardware design files (schematics, PCB layout, BOM) are available in the documentation directory. Includes full schematic, PCB layout plots, and all gerbers.

The Arduino controller software has been moved into the source directory.

Example

Sample boot log in the Arduino USB serial monitor window:

RX02 Emulator v2.02 (IDE 1.8.19/gcc 7.3.0) - Nov  3 2023 - 22:16:19
SD: libVersion=2.2.2
SD: cardType=SD3
SD: cardSize=3781MB
SD: volType=FAT32
SD: volBytesPerCluster=4096
SD: volClusterCount=964992
SD: volSizeBytes=3768MB
2016-09-24 18:02:14     512512 RX0.DSK
2016-09-27 15:06:44     512512 RX1.DSK
2020-04-01 00:00:26         50 SETUP.INI
2017-10-31 20:37:04     512512 RT11.RX2
2017-10-31 20:37:14     512512 OS8V3D.RX2
2016-10-24 11:31:02     256256 OS8V3Q.RX1
Valid MicroSD card detected.
RX: waiting for INIT to clear ... t=1154ms
RX: INIT has NOT cleared t=11155ms
RX: INIT rx_xmit_es(0244)

Processing setup file 'SETUP.INI' ...
0 RX0.DSK
Setting file[0]: 'RX0.DSK'
Y 0
Setting file[0] mode: R/W
1 RX1.DSK
Setting file[1]: 'RX1.DSK'
Y 1
Setting file[1] mode: R/W
D 1
Setting debug mode: 1 (Low)
M 2
Setting emulation mode: 2 (RX02+any)
T 0
Setting timing mode: 0 (Fastest)
S
Current file[0]: 'RX0.DSK' (R/W)
Current file[1]: 'RX1.DSK' (R/W)
... setup file processing complete!

Initialization complete.
H

Commands available:

  0 FILENAME    -- set unit 0 file to FILENAME; default RX0.DSK
                   file name 'none' (any case) for no disk present
  1 FILENAME    -- set unit 1 file to FILENAME; default RX1.DSK
                   file name 'none' (any case) for no disk present
  y(es) N       -- set unit N file read-write (default)
  n(o) N        -- set unit N file read-only
  m(ode) N      -- set emulation mode, 0=RX01+RX11, 1=RX01+RX8E, 2=RX02+any; default 2
  d(ebug) N     -- debug level, 0=none, 3=max; default 1
  t(iming) N    -- timing mode, 0=fast, 1=medium, 2=normal; default 0
                   0 as fast as possible; 2 simulates real RX02 drive
  r FILENAME    -- remove file FILENAME
  e FILENAME    -- extend/truncate file FILENAME to single density size
  f FILENAME    -- extend/truncate file FILENAME to double density size
  l(ist)        -- list all files on the SD card
  s(how)        -- show current unit filename assignments
  p(rint)       -- print full emulation state
  i(nit)        -- initialize emulator (like unibus INIT)
  k(ill)        -- kill the emulator (reset and restart, like reset button)
  w(rite)       -- write current configuration into the SETUP.INI file
  z(ap) STAMP   -- set current timestamp for file access
                   format is: YYYY-MM-DD HH:MM:SS or YYYY-MM-DD HH:MM
  h(elp)        -- display this text

Note: chars in () are optional. Case does not matter.

S
Current file[0]: 'RX0.DSK' (R/W)
Current file[1]: 'RX1.DSK' (R/W)
0 XXDP.DSK
Setting file[0]: 'XXDP.DSK'
W
Generating setup file 'SETUP.INI'

RX: waiting for INIT to clear ... t=49342ms
RX: INIT has cleared t=49438ms
RX: INIT rx_xmit_es(0244)

RX: cmd=0007
RX: RDSECT unit=0 den=S
RX: RDSECT sa=001
RX: RDSECT ta=001
RX: RDSECT rx_xmit_es(0060)

RX: waiting for INIT to clear ... t=49462ms
RX: INIT has cleared t=49557ms
RX: INIT rx_xmit_es(0244)

RX: cmd=0407
RX: RDSECT unit=0 den=D
RX: RDSECT sa=001
RX: RDSECT ta=001
RX: RDSECT pos=6656. len=256.
RX: RDSECT rx_xmit_es(0040)

RX: cmd=0403
RX: EMPBUF unit=0 den=D
RX: EMPBUF wc=200
RX: EMPBUF rx_xmit_es(0000)

RX: cmd=0407
RX: RDSECT unit=0 den=D
RX: RDSECT sa=003
RX: RDSECT ta=001
RX: RDSECT pos=7168. len=256.
RX: RDSECT rx_xmit_es(0040)

RX: cmd=0403
RX: EMPBUF unit=0 den=D
RX: EMPBUF wc=200
RX: EMPBUF rx_xmit_es(0000)

...

Notes

(1) This code has been written with the assumption that Xprintf support has been added to the PRINT class in the Arduino development environment.

(2) This code uses the SDfat library available at: https://github.com/greiman/SdFat

(3) This code was written with tap stops set at 4 (versus the default of 2). Manually edit the Arduino preferences.txt file tab size line to be: editor.tabs.size=4 if desired.

ALTERNATIVE to ARDUINO IDE

For those not interested in the source and/or installing the full Arduino IDE environment and tweaking it as necessary, I have now added a precompiled .hex version of the code representing the state of the current source. It is located in the 'binary' folder. There are two versions, without and with the bootloader image present. In most cases you would want to use the version of the .hex without the bootloader as the bootloader is already present (and required to be working) in any purchased ArduinoMEGA2560 board.

There are at least two methods to download a .hex image file to the Arduino (and I am sure there are more):

(1) Using avrdude in command line mode. This is the way the Arduino IDE does it when you install the IDE and use it to download the compiled .hex file. You can use the installed version of avrdude to do the download, or alternatively if you don't want to install the full IDE and compile from source, you can download the avrdude program directly from here: https://github.com/avrdudes/avrdude

On the command line:

  avrdude -D -cwiring -pm2560 -b115200 -PCOM# -Uflash:w:rx02_emulator.ino.hex:i

where COM# is the port that is associated with your mega2560 Arduino board, and other options that you may desire. Refer to the avrdude documentation.

(2) Using a program called xLoader that is available from here: https://github.com/binaryupdates/xLoader . It is a simple Windows standalone application.

The process to download the .hex image using xLoader is documented here: https://www.aranacorp.com/en/generating-and-uploading-hex-files-to-an-arduino/

INSTALLATION

The following sections detail the installation and configuration of the Arduino software environment, getting the rx02_emulator code, compiling it, and downloading it to a target board.

Arduino IDE

If you don't have the Arduino development environment installed on your system, the first step is to download and install it. Go to:

https://www.arduino.cc/

and click on the Software tab to get to the download page.

Scroll down to the Download the Arduino IDELegacy IDE (1.8.X) section and download the installer appropriate for your system. All development and testing to data has been with the legacy 1.X IDE. I have done nothing with the newer 2.X IDE, so if you want to use that you are on your own.

Update: I have installed the IDE 2.2.1 alongside my existing IDE 1.8.19. They live in separate directories so can be simultaneously installed. They share library and board file definitions, so I was able to launch IDE 2.2.1 and recompile and download the existing design done under IDE 1.8.19 with no errors. So the changes below for adding printf support and installing the SDFAT (and optional TIMELIB) libraries should take place following the existing instructions. One anomaly is after the compile the Arduino IDE version reported is IDE 1.6.7, when one might expect it to be IDE 2.2.1. This is a 'bug' reported in github and it appears the Arduino developers don't seem to feel it makes a difference and are reluctant to change it. So just be warned about the somewhat bogus report the program was compiled under IDE 1.6.7 when it appears in the compiled code welcome message.

Run the install.

SD FAT Library

The emulator software requires a third party SD card FAT filesystem access library. Go to:

https://github.com/greiman/SdFat

On the right hand side of the page there is a Clone or download green button; click it and select Download ZIP and save the file. It will likely be named SdFat-master.zip.

Unzip the contents of SdFat-master.zip into a folder. There should be a folder inside the top level folder named SdFat.

Move the folder SdFat into your Arduino local library folder. On Windows, this would be into the folder:

C:\Users\yourname\My Documents\Arduino\libraries

which probably just contains a readme.txt file. The SdFat library is now installed and ready for use.

As of version v1.96 release the code is compatible with either the existing v1 SDfat library (eg, v1.1.4) or the newer v2 SDfat library (eg, v2.2.0) code.

I have tested with the v2.0.6, v2.0.7, v2.1.0, and v2.2.0 SDfat libraries. There were some changes from 2.0.x to 2.1.x and later and these are accounted for in some conditionals.

PRINTF Configuration

The emulator code is written assuming that the printf/sprintf methods have been added to the serial I/O and file access routines. The default Arduino install does not have this support so it needs to be configured.

The following page:

http://playground.arduino.cc/Main/Printf

describes several ways to do this; the preferred method I suggest is described under Adding printf() to Print class.

It is not difficult, but does require editing a standard Arduino system file and adding some code.

On windows, the target file to be modified is:

%ProgramFiles(x86)%\Arduino\hardware\arduino\avr\cores\arduino\Print.h

the following code:

#include <stdarg.h>
#define PRINTF_BUF 80 // define the tmp buffer size (change if desired)
   void printf(const char *format, ...)
   {
   char buf[PRINTF_BUF];
   va_list ap;
        va_start(ap, format);
        vsnprintf(buf, sizeof(buf), format, ap);
        for(char *p = &buf[0]; *p; p++) // emulate cooked mode for newlines
        {
                if(*p == '\n')
                        write('\r');
                write(*p);
        }
        va_end(ap);
   }
#ifdef F // check to see if F() macro is available
   void printf(const __FlashStringHelper *format, ...)
   {
   char buf[PRINTF_BUF];
   va_list ap;
        va_start(ap, format);
#ifdef __AVR__
        vsnprintf_P(buf, sizeof(buf), (const char *)format, ap); // progmem for AVR
#else
        vsnprintf(buf, sizeof(buf), (const char *)format, ap); // for the rest of the world
#endif
        for(char *p = &buf[0]; *p; p++) // emulate cooked mode for newlines
        {
                if(*p == '\n')
                        write('\r');
                write(*p);
        }
        va_end(ap);
   }
#endif

needs to be added near the end of the file, just prior to the second to last non blank line: };

NOTE this change must be made ANY TIME a new version of the Arduino IDE is installed, as the new install will overwrite the change to the Print.h file. In most recent Arduino upddates (since 1.6.X at least) the Print.h file has not changed, so a copy of the updated file can be squirreled away to save some time in the update process. Note that there was a minor change to the base Print.h file as of Arduino IDE 1.8.2 (this change should be integrated in the updated Print.h file as well).

At this point the Arduino IDE should be fully setup for use in compiling the emulator software.

Under the Preferences menu, I find ticking the Show verbose output compilation and upload boxes to be useful.

I also recommend checking the Verify code after upload box in the same dialog.

RX02 Emulator

To download the RX02 emulator Arduino software, go to:

https://github.com/AK6DN/rx02_emulator

and (like in the library download) click the Clone or download green button on the right side of the page, select Download ZIP, and save the file. It will likely be named rx02_emulator-master.zip.

Unzip the contents into a folder, it will likely end up being named rx02_emulator-master. You must rename it to rx02_emulator as the Arduino IDE requires the outer level folder name match the project name (which is rx02_emulator.ino).

Compiling

You should now be able to launch the Arduino IDE by going into the source/rx02_emulator folder and double clicking on the top level design file rx02_emulator.ino.

Before compiling you need to select the board and processor type.

Under the Tools menu select Board: and validate it is: Arduino/Genuino Mega or Mega 2560

Under the Tools menu select Processor: and validate it is: ATmega2560

You should now be able to, under the Sketch menu, select Verify/Compile (or type CTRL-R) to compile.

There should be no errors flagged if the SDfat library was installed correctly, the printf mod was performed, and the board and processor type have been configured correctly.

Uploading

After verifying the compile you are now ready to be able to upload the code to your board.

NOW plug your Arduino Mega2560 board into a USB port on your system and wait for the USB driver to install.

When done, go to the Tools menu (again) and select the Port: entry to correspond to the USB serial port your board has been configured as.

You should now be able to select menu Sketch then Upload (or type CTRL-U) to upload the code to your board.

Running

After a successful upload, your Arduino should start running immediately. To get access to the menu window, select under the Tools menu the Serial Monitor item (or type CTRL-SHIFT-M).

You will need to configure the baud rate / line ending of the monitor window before you can see output and type input.

In the lower right of the window, select the maximum baud rate 250000 baud that the Arduino supports over USB. This minimizes the impact of the debug output window on performance, and the emulator software selects this rate by default. As of emulator code v1.8 and Arduino IDE 1.8.2 or later it is possible to enable higher debug window baud rates (500Kb, 1Mb, or 2Mb) but not all Arduino Mega2560 boards may support these rates 100% reliably. You will have to test your board individually to see if a higher baud rate can be enabled.

In the lower right, select Carriage Return line ending, so when you type in the text box at the top of the window, and then click SEND a CR character will be appended to the end of the string.

At this point you should be seeing debug output in the serial monitor window, and be able to send menu commands to it.

Validation

Testing to date has been performed with a UNIBUS PDP-11/44 with each of an RX211 and an RX11, a UNIBUS PDP-11/34A with each of an RX211 and an RX11, and an OMNIBUS PDP-8m with an RX8E/RX28 so RX01/RX8E and RX02/RX28 configurations can be tested. I do not have access to RXV11 or RXV21 boards for testing (nor do I have an QBUS systems). Users have tested the emulator with QBUS RXV21 and RXV11 and provided positive feedback.

I have personally tested and validated the following confgurations:

PDP-11/44 with M8256 RX211 ... ZRXFB0 RX211/RX02 Functional Test  ........ PASS
                               ZRXDC0 RX211/RX02 Performance Exerciser ... PASS
                               XXDPv25 DY boots and runs ................. PASS
                               RT-11v5.7 DY boots and runs ............... PASS
                               RX02WR and RX02RD home grown diagnostics .. PASS

PDP-11/34A with M8256 RX211 .. ZRXFB0 RX211/RX02 Functional Test  ........ PASS
                               ZRXDC0 RX211/RX02 Performance Exerciser ... PASS
                               XXDPv25 DY boots and runs ................. PASS
                               RT-11v5.7 DY boots and runs ............... PASS
                               RX02WR and RX02RD home grown diagnostics .. PASS

PDP-11/44 with M7846 RX11 .... ZRXBF0 RX11/RX01 Functional Test .......... PASS
                               ZRXAF0 RX11/RX01 Performance Exerciser .... PASS
                               RT-11v5.3 DX boots and runs ............... PASS

PDP-11/34A with M7846 RX11 ... ZRXBF0 RX11/RX01 Functional Test .......... tbd
                               ZRXAF0 RX11/RX01 Performance Exerciser .... tbd
                               RT-11v5.3 DX boots and runs ............... tbd

PDP-8m with M8357 RX8E/RX01 .. OS8v3Q boots and runs ..................... PASS
                               RXTEST home grown diagnostic .............. PASS

PDP-8m with M8357 RX28/RX02 .. OS8v3D boots and runs ..................... PASS
                               RXTEST home grown diagnostic .............. PASS

Other users have supplied the following test results:

PDP-11/34 with M7846 RX11 .... ZRXBF0 RX11/RX01 Functional Test .......... PASS (thunter0512)
                               ZRXAF0 RX11/RX01 Performance Exerciser .... PASS (thunter0512)

Hardware

UPDATED 09-Aug-2021 -- the timing macros for the data transfer to/from the interface board have been modified to allow working with a longer flat cable. As of the v1.95 release the emulator has been tested and worked flawlessly using a DEC BC06R-12 cable (12' long, about 4m) on a PDP-11/44 with an RX211 interface. Performance degradation due to the slightly slower data transfer handshake timing has been measured at about 5% or less, which in practice is not noticeable. Of course it still works flawlessly using a shorter 0.5 to 1.5m cable as well.

DEPRECATED 09-Aug-2021 -- Many original RX01/2 configurations come with an up to 5m controller card to connector cable (a 40p flat cable with 2x20p IDE connectors). It has been noticed that in some configurations using this same cable to connect to the RX02 emulator from the RXnn controller card results in unreliable operation or it does not work at all. The recommendation is to use a shorter 40p flat cable, on the order of 0.5m to 1.5m at most, for reliable operation.

The End

xllrt/rx02_emulator

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